Europ. J.clin. Pharmacol. 9, 423-428 (1976) © by Springer-Verlag 1976
Some Aspects of the Intestinal Absorption of Zinc in Man K.-E. Andersson, L. Bratt, H. Dencker and E. Lanner Departments of Clinical Lund, Sweden
Received: accepted:
Pharmacology
and Surgery,
September I, 1975, and in revised October 16, 1975
form:
University Hospital,
October
15,
1975,
Serum zinc concentrations in peripheral venous blood were determined in 8 healthy volunteers at various times after oral administration of 50 mg Zn ++. The same dose was given to 6 patients surgically treated for obesity by j e j u n o - i l e o s t o m y In the healthy volunteers the mean serum zinc concentration before dosing was 0.89 ~g/ml and a mean peak concentration of 2.39 ~g/ml was found after 3 h. In the patients the starting level was lower, 0.67 ~g/ml, and a mean peak concentration of 1.31 ~g/ml was found 90 min after treatment. In the patients the areas under the serum concentration-time curve was approximately I/3 of that in the healthy subjects. Zn ++ 50 mg was also given to 3 patients undergoing transumbi!ical catheterization of the portal vein for diagnostic purposes and serum zinc concentrations were measured in portal and peripheral venous blood sampled simultaneously. No significant differences were found between the concentration of zinc in portal and peripheral venous blood during absorption, which suggests slow passage of zinc across the intestinal wall. Summary.
Key words: Serum zinc concentration,
catheterization,
intestinal
absorption,
portal vein,
transumbilical
man.
Increasing awareness of the biological role of zinc and of its possible therapeutic effect in various diseases (Prasad et al., 1963; Prasad, 1969; Halsted and Smith, 1970; Chvapil, 1973) has also focused interest on its absorption, metabolism, and elimination. Little information is available at present on the intestinal absorption of zinc in man, mainly because of methodological difficulties (Becker and Hoekstra, 1971). Our knowledge of the site, m e c h a n i s m and extent of its absorption is incomplete. The present study was undertaken to obtain further information about the intestinal absorption of zinc in man. Changes in the concentration of zinc in peripheral venous blood after a single oral dose were measured in healthy volunteers and compared w i t h those found in patients surgically treated for obesity by jejuno-ileostomy. The concentration of zinc in portal and
peripheral venous blood of patients undergoing portal catheterization for diagnostic purposes was also measured after a single oral dose of zinc sulphate.
MATERIAL AND METHODS Subjects
Eight healthy males, aged 24 to 45 years (mean 28 years), weighing 65 to 86 kg (mean 69 kg), volunteered for the first part of the study, which was performed in order to define changes in the serum zinc concentration after administration of a single oral dose of zinc sulphate. Six patients, 3 male and 3 female, surgically treated by jejuno-ileostomy for obesity, took part in the second part of the study. They had undergone operation I - 2 years before the in-
424
v e s t i g a t i o n and w e r e in good p h y s i c a l condition. T h e y w e r e aged 26 to 47 years (mean 34 years); their w e i g h t before the o p e r a t i o n ranged from 116 to 190 kg (mean 154 kg), and at the time of the study from 66 to 130 kg (mean 113 kg). Three p a t i e n t s had b e e n given oral zinc t h e r a p y i n t e r m i t t e n t l y , but none had b e e n t r e a t e d for at least 4 weeks prior to the study. In the third part of the study, the changes in zinc c o n c e n t r a t i o n in p o r t a l and p e r i p h e r a l venous blood after adm i n i s t r a t i o n of a single oral dose of zinc sulphate to 3 p a t i e n t s were measured. The p a t i e n t s w e r e ambulant, in good p h y s i c a l c o n d i t i o n and had app a r e n t l y normal bowel habits. They were I female and 2 males, aged 54, 59, and 64 years, and w e i g h i n g 61, 76, and 85 kg, respectively. All had been o p e r a t e d for c a r c i n o m a of the large i n t e s t i n e 5 - 8 years previously. No m e t a s t a s e s w e r e found at the operation. As a p a r t of a r o u t i n e search for h e p a t i c m e t a s tases the portal v e i n was c a t h e t e r i z e d to p e r m i t i n j e c t i o n of c o n t r a s t medium. In none w e r e m e t a s t a s e s d e m o n s t r a t e d by the p o r t o v e n o g r a p h y or on s c i n t i g r a p h y . N o n e had r e c e i v e d zinc p r e p a r a t i o n s therapeutically. Before the investigation, the purpose of the study and the p r o c e d u r e inv o l v e d were fully e x p l a i n e d and v e r b a l consent obtained.
operation Technique
Five of the obese p a t i e n t s had undergone j e j u n o - i l e o s t o m y a c c o r d i n g to the m e t h o d d e s c r i b e d by Salmon (1971). T h i r t y - s e v e n cm of p r o x i m a l j e j u n u m m e a s u r e d from the ligament of Treitz had been a n a s t o m o s e d end to end to the distal 12 cm of ileum. The p r o x i m a l part of the ileum had been a n a s t o m o s e d end to side to the colon. In the rem a i n i n g p a t i e n t (No. I, Table 2), the p r o x i m a l jejunum (37 cm from the ligam e n t of Treitz) had been a n a s t o m o s e d end to side to the ileum (12 cm from V a l v u l a Bauhini). In all cases the f u n c t i o n a l part of the small i n t e s t i n e was a p p r o x i m a t e l y 50 cm long. Catheterization of the Portal Vein
The u m b i l i c a l cord was r e - o p e n e d w i t h a probe under local or g e n e r a l anaesthesia, and a catheter p l a c e d in the m a i n portal vein under f l u o r o s c o p i c control. The i n v e s t i g a t i o n s were p e r f o r m e d 2 days after i n t r o d u c t i o n of the catheter, w h i c h had been kept p a t e n t by constant i n f u s i o n of h e p a r i n i z e d saline.
Experimental Procedure
A f t e r an o v e r n i g h t fast, both the h e a l t h y v o l u n t e e r s and patients were given 50 mg Zn ++ orally, as a solution of zinc sulphate c o n t a i n i n g 0.5 mg Zn ++ per ml. The beaker c o n t a i n i n g the zinc sulphate s o l u t i o n was r i n s e d w i t h 50 ml d i s t i l l e d water w h i c h was also swallowed. In the h e a l t h y v o l u n t e e r s and in the obese patients, blood samples were taken from a f o r e a r m vein before, and 30, 60, 90, 120, 240, 360 and 480 min after a d m i n i s t r a t i o n of the zinc. No food or d r i n k were a l l o w e d until the 480 m i n sample had b e e n taken. The same s a m p l i n g schedule was e m p l o y e d in the 3 patients from w h o m b l o o d samples were taken s i m u l t a n e o u s l y from the portal vein and a f o r e a r m vein. These patients r e c e i v e d a light meal after the 240 min sample had been taken. Samples w e r e not c o l l e c t e d from one of the p a t i e n t s after 240 m i n b e c a u s e p e r i p h e r a l venous blood could not be obtained. zinc Analysis
All m a t e r i a l s used for b l o o d sampling w e r e c h e c k e d to avoid c o n t a m i n a t i o n . The serum samples were stored frozen until their zinc content was d e t e r m i n e d by atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y (Helwig et al., 1966) using a V a r i a n 1100 atomic a b s o r p t i o n s p e c t r o p h o t o meter. The samples w e r e a s p i r a t e d into an a i r - a c e t y l e n e flame after t e n f o l d d i l u t i o n w i t h water. The a b s o r p t i o n signal at 213.9 nm was m e a s u r e d and i n t e g r a t e d for 10 sec. S t a n d a r d s added to p o o l e d human serum were used to c o m p e n s a t e for m a t r i x effects and a linear s t a n d a r d curve was obtained. Non-specific background absorption (average v a l u e of 10 sera) was subt r a c t e d before c a l c u l a t i o n of the zinc c o n c e n t r a t i o n in each sample.
Area under the Serum Concentration-Time Curve
The area under the serum c o n c e n t r a t i o n time curve d e t e r m i n e d by the t r a p e z o i d a l rule was taken as the increase in serum zinc c o n c e n t r a t i o n above the starting level from time O to 480 min after dosing.
RESULTS Before the intake of zinc, the m e a n serum zinc value in the h e a l t h y subjects was 0.98 ~g/ml (range 0.83 - 1.23 ~g/ml). A f t e r the intake of 50 mg Zn ++ there was a steady increase in the serum
425
c o n c e n t r a t i o n , and a m e a n m a x i m u m of 2.39 #g/ml was a t t a i n e d a f t e r 180 min. The i n c r e a s e in s e r u m c o n c e n t r a t i o n per unit time r e a c h e d a m a x i m u m d u r i n g the i n i t i a l 90 m i n (O.0153 p g / m l / m i n ) . A t the last sample, 480 m i n a f t e r t r e a t m e n t , the m e a n s e r u m zinc had f a l l e n to 1.13 #g/ml. The m e a n v a l u e s at the d i f f e r e n t times a f t e r a d m i n i s t r a t i o n are i l l u s t r a t e d in Fig. I, and the i n d i v i d u a l v a l u e s are g i v e n in T a b l e I. In the 6 p a t i e n t s w i t h a j e j u n o ileostomy, the m e a n s e r u m zinc c o n c e n t r a t i o n p r i o r to t r e a t m e n t was 0.67 #g/ ml (range O.51 - 0.87 pg/ml). A f t e r adm i n i s t r a t i o n of 50 m g Zn ++ the s e r u m zinc i n c r e a s e d to a m e a n m a x i m u m of 1.31 pg/ml a f t e r 90 min. The m a x i m u m i n c r e a s e in s e r u m c o n c e n t r a t i o n per u n i t time was l o w e r t h a n in the h e a l t h y s u b j e c t s (O.O113 # g / m l / m i n ) . The a r e a u n d e r the s e r u m c o n c e n t r a t i o n - t i m e curve was app r o x i m a t e l y 34 per cent of that in the h e a l t h y subjects. The m e a n s e r u m zinc v a l u e s at the times of s a m p l i n g are g i v e n in Fig. I, and d a t a for i n d i v i d uals in T a b l e 2. In three p a t i e n t s s u b j e c t e d to c a t h e t e r i z a t i o n of the p o r t a l vein, the s e r u m zinc c o n c e n t r a t i o n s in p e r i p h e r a l b l o o d b e f o r e the a d m i n i s t r a t i o n of zinc w e r e 0.70, 0.68, and 0 . 7 0 #g/ml, res p e c t i v e l y . The c o n c e n t r a t i o n s in p o r t a l b l o o d w e r e i n s i g n i f i c a n t l y lower, 0.65, 0.68, and 0.62 #g/ml, r e s p e c t i v e l y . A f t e r t a k i n g the zinc, the c o n c e n t r a tions in p o r t a l and p e r i p h e r a l b l o o d w e r e v e r y similar, b o t h r e a c h i n g a m e a n p e a k v a l u e of 1.58 and 1.54 #g/ml, r e s p e c t i v e l y , at 90 min. The i n c r e a s e in s e r u m c o n c e n t r a t i o n per u n i t time was m a x i m a l d u r i n g the i n i t i a l 60 m i n and of the same m a g n i t u d e (O.0147 ~g/ ml/min) as in the h e a l t h y subjects. The m e a n s e r u m zinc c o n c e n t r a t i o n had r e t u r n e d to the s t a r t i n g level in the last sample, 480 m i n a f t e r t a k i n g the zinc. The m e a n s e r u m zinc v a l u e s in p o r t a l and p e r i p h e r a l v e n o u s b l o o d are s h o w n in Fig. 2 a n d the i n d i v i d u a l d a t a in T a b l e 3. Some of the h e a l t h y s u b j e c t s and some of the p a t i e n t s r e p o r t e d s l i g h t g a s t r o i n t e s t i n a l d i s c o m f o r t w i t h i n 30 60 m i n a f t e r s w a l l o w i n g the zinc sulphate. No o t h e r side e f f e c t s w e r e observed.
DISCUSSION S e v e r a l m e t h o d s are a v a i l a b l e for s t u d y of the g a s t r o i n t e s t i n a l a b s o r p t i o n of zinc in e x p e r i m e n t a l a n i m a l s (for review, see B e c k e t and H o e k s t r a , 1971). R a d i o i s o t o p e t r a c e r t e c h n i q u e s have b e e n c o m m o n l y u s e d in these s t u d i e s
3.0-
Zn-concentration,
pg/ml
2.0
1.0 ¸
T i m e , rnin 0.0
;
6'0
40
240
'" 3o0
"3"6 0
' ....... 48o ' 42o
Fig. I. Serum zinc concentration (mean ± SEM) in 8 healthy subjects ( --- ), and in 6 obese patients (e :) with a jejuno-ileostomy following oral administration of 50 mg Zn ++ as a solution of zinc sulphate
2.0
Zn-concentration, pg/ml
t.0
Time, min 0.0-
i
0
6 -0
i 120
~.......... i 180 240
i 300
i 360
~
420
480
Fig. 2. Mean serum zinc concentrations (n = 3) in portal ( --- ) and peripheral (e) venous blood following oral administration of 50 mg Zn++ as a solution of zinc sulphate
426
Table I. Serum zinc concentrations (zg/ml) in peripheral venous blood from 8 healthy subjects at various times after oral administration of 50 mg Zn ++ Time after administration, min Subject
0
30
60
90
120
180
240
360
480
i
0.86
1.52
2.02
2.01
1.90
1.95
1.70
1.09
0.76
2
0.93
1.04
1.35
1.97
1.97
2.38
1.98
1.29
1.O8
3
1.O2
1.73
2.49
2.70
2.73
2.66
2.33
1.66
1.32
4
0.94
1.54
1.99
2.62
2.78
2.42
2.28
1.27
O.91
5
1.22
1.35
1.97
2.41
2.72
3.14
3.23
2.57
1.88
6
0.95
I.OO
1.13
1.53
1.82
2.05
1.92
1.49
1.18
7
0.83
0.99
1.32
1.61
1.97
2.00
2.10
1.52
0.95
8
i.iO
1.55
2.13
2.44
2.69
2.52
2.09
1.25
0.95
Mean
0.98
1.34
1.80
2.16
2.32
2.39
2.20
1.52
1.13
± SEM
0.05
O. iO
O.17
0.16
O.16
0.14
0.16
0.16
O.12
Table 2. Serum zinc concentrations (zg/ml) in peripheral venous blood from 6 obese patients with a jejuno-ileostomy at various times after oral administration of 50 mg Zn ++ Time after administration, min Patient
O
30
60
90
120
180
240
360
480
i
O.51
0.85
0.92
0.84
0.78
O.71
0.58
0.44
0.44
2
0.69
0.92
1.63
1.76
1.98
1.91
1.56
0.94
0.72
3
0.80
1.13
1.29
1.41
1.37
1.22
1.O3
0.90
0.87
4
0.56
0.80
1.09
1.20
1.13
1.O3
0.83
0.67
0.61
5
0.59
0.94
1.04
1.02
0.93
0.80
0.68
0.58
0.59
6
0.87
1.39
1.51
1.60
1.45
1.26
1.O8
0.76
0.76
Mean
0.67
1.O1
1.25
1.31
1.27
1.16
0.96
0.72
0.67
± SEM
O.O5
0.09
O.11
O.14
O.18
O.18
O.14
0.07
0.O6
and also for investigations in m a n ( S p e n c e r et al., 1965a, b). H o w e v e r , the isotope 65Zn has the disadvantage of a b i o l o g i c a l h a l f - l i f e of m o r e t h a n 3 0 0 d a y s ( S p e n c e r et al., 1 9 6 5 a ) , w h i c h l i m i t s its u s e in h u m a n s . In t h e present study the increase in serum zinc concentration after an oral dose of z i n c s u l p h a t e w a s u s e d to e x a m i n e the site of absorption and passage a c r o s s t h e i n t e s t i n a l w a l l o f t h e ion. T h e m a i n s i t e of z i n c a b s o r p t i o n in t h e i n t e s t i n e is n o t k n o w n . D a t a f r o m some animal studies indicate that abs o r p t i o n is g r e a t e r f r o m t h e d u o d e n u m t h a n f r o m m o r e d i s t a l p a r t s of t h e intestine, and that absorption from the s t o m a c h a n d t h e c o l o n is m i n i m a l (Van
C a m p e n a n d M i t c h e l l , 1965; M e t h f e s s e l a n d S p e n c e r , 1973). H o w e v e r , o t h e r a n i m a l s t u d i e s a p p e a r to s u g g e s t m o r e d i s t a l p a r t s of t h e i n t e s t i n e as t h e m a i n s i t e of a b s o r p t i o n ( P e a r s o n et al., 1966; S a h a g i a n et al., 1966; K o w a r s k i et al., 1 9 7 4 ) . The present study shows that, after oral administration of 50 m g Zn + + in solution to healthy subjects, the zinc concentration i n p e r i p h e r a l b l o o d increased from a mean starting value of 0 . 9 8 ~ g / m l t o a m a x i m u m of 2 . 3 9 ~ g / m l . The increase in serum concentration per u n i t t i m e w a s m a x i m a l w i t h i n 90 m i n , a n d the peak concentration was attained after 180 min. Both the starting and peak concentrations were consistent with
427
Table 3. Serum zinc concentrations (pg/ml) in simultaneous samples of portal and peripheral venous blood from 3 patients at various times after oral administration of 50 mg Zn ++ Peripheral venous blood Time after administration, Patient
min
O
30
60
90
120
180
240
360
480
I
0.70
0.95
1.50
1.65
1.52
1.58
1.16
0.74
0.58
II
0.68
1.23
1.68
1.72
1.78
1.76
1.30
III
0.70
0.76
1.O7
1.26
1.32
1.28
1.18
0.80
0.64
Mean
0.69
0.98
1.42
1.54
1.54
1.54
1.21
0.77
O.61
........
Portal venous blood Time after administration, Patient
I
min
0
30
60
90
120
180
240
360
480
0.65
1.15
1.58
1.67
1.46
1.52
i.ii
0.68
0.58
Ii
0.68
1.19
1.63
1.72
1.63
1.71
1.17
III
0.62
0.94
1.32
1.36
1.42
1.28
1.25
0.85
0.67
Mean
0.65
1.O9
1.51
1.58
1.50
1.50
1.18
0.77
0.63
zinc levels f o u n d by o t h e r i n v e s t i g a t o r s in h e a l t h y s u b j e c t s g i v e n a s i m i l a r d o s e of zinc (Halsted and Smith, 1970; Hetland and B r u b a k k , 1973; P ~ c a u d et al., 1975), but the i n c r e a s e in s e r u m conc e n t r a t i o n per u n i t time was lower t h a n that r e p o r t e d by G e i s l e r et al. (1970) in a series of p a t i e n t s . The o b e s e p a t i e n t s w i t h a j e j u n o i l e o s t o m y h a d o n l y a p p r o x i m a t e l y 50 cm of f u n c t i o n i n g p r o x i m a l small intestine. In these p a t i e n t s the s t a r t i n g zinc level (0.67 ~g/ml) was lower than in h e a l t h y s u b j e c t s (0.98 pg/ml). E v e n if this w e r e t a k e n into account, the m e a n m a x i m u m c o n c e n t r a t i o n attained, 1.31 ~g/ ml, was c o n s i d e r a b l y lower in the o b e s e p a t i e n t s , and the a r e a u n d e r the s e r u m c o n c e n t r a t i o n - t i m e curve in t h e m was only a b o u t I/3 of that in the h e a l t h y subjects. A s s u m i n g that the areas in the two g r o u p s w o u l d h a v e b e e n of the same m a g n i t u d e if the o b e s e p a t i e n t s had h a d an i n t a c t small bowel, these d a t a s u g g e s t that the p r o x i m a l 50 cm of the small i n t e s t i n e a b s o r b s a p p r o x i m a t e l y I/3 of the t o t a l a m o u n t of zinc t a k e n up by the bowel. However, it c a n n o t be e x c l u d e d that d i f f e r e n c e s e x i s t b e t w e e n the a b s o r p t i v e c a p a c i t y of the small i n t e s t i n e in the o b e s e pa-
t i e n t s and the n o r m a l subjects. T h e r e are some i n d i c a t i o n s t h a t the i n t e s t i n a l m u c o s a of the o p e r a t e d p a t i e n t s u n d e r goes c h a n g e s s u g g e s t i v e of an i n c r e a s e in its a b s o r p t i v e s u r f a c e (Andersson, D e n c k e r and G~thlin, u n p u b l i s h e d ) . If this w e r e so, the a b s o r p t i o n of zinc m i g h t be r e l a t i v e l y g r e a t e r in the o b e s e p a t i e n t s than in n o r m a l subjects. However, the f i n d i n g t h a t the i n c r e a s e in s e r u m c o n c e n t r a t i o n p e r u n i t time was lower in the o b e s e p a t i e n t s does not f a v o u r this view. D e s p i t e e x t e n s i v e study, the m e c h a nisms i n v o l v e d in the g a s t r o i n t e s t i n a l a b s o r p t i o n of zinc r e m a i n unknown, and it has not b e e n d e f i n i t e l y e s t a b l i s h e d w h e t h e r a c t i v e t r a n s p o r t is i n v o l v e d (Becket and H o e k s t r a , 1971). As p o i n t e d out by Evans (1974), the l i k e l i h o o d of s i m p l e d i f f u s i o n seems r e m o t e in v i e w of the m o r p h o l o g i c a l b a r r i e r s conf r o n t i n g the zinc ion d u r i n g its c o u r s e f r o m lumen to blood. R e c e n t d a t a p r e s e n t e d by K o w a r s k i et al. (1974) a l s o f a v o u r the v i e w of a c t i v e t r a n s p o r t . S i m u l t a n e o u s s a m p l i n g of p o r t a l and p e r i p h e r a l v e n o u s blood, as u s e d in the p r e s e n t study, o f f e r s a m e a n s of studying the rate of p a s s a g e of v a r i o u s m a t e r i a l s a c r o s s the i n t e s t i n a l w a l l
428
( A n d e r s s o n et al., 1975). A s t h e c o n c e n trations of zinc in portal blood after treatment were found to be close to t h o s e i n p e r i p h e r a l b l o o d , it a p p e a r s that the passage of zinc across the i n t e s t i n a l w a l l is a s l o w p r o c e s s . I t h a s b e e n s h o w n ( G e i s l e r et al., 1971) t h a t t h e i n c r e a s e in s e r u m z i n c concentration p e r u n i t t i m e is d e p e n d e n t on the dose and also on the initial s e r u m z i n c l e v e l , b e i n g g r e a t e r in subjects with low starting levels. Both in the obese patients and in those s u b j e c t e d to p o r t a l c a t h e t e r i z a t i o n the initial serum zinc levels were lower t h a n in t h e h e a l t h y s u b j e c t s , b u t t h e increase in serum concentration per unit time was not greater. Whether this means that the present patients had a decreased ability to absorb zinc, or that the serum zinc level was not the main r e g u l a t o r of t h e r a t e a t w h i c h z i n c appeared in the circulation, cannot be determined at present. REFERENCES Andersson, K.-E., Nyberg, L., Dencker, H., G6thlin, J.: Absorption of digoxin in man after oral and intrasigmoid administration studied by portal vein catheterization. Europ. J. clin. Pharmacol. 9, 39-47 (1975) Becket, W.M., Hoekstra, W.G.: The intestinal absorption of zinc. In: Intestinal absorption of metal ions, trace elements and radionuclides (Ed. S.C. Skoryna, D. WaldronEdward), pp. 229-256. New York: Pergamon Press 1971 Chvapil, M.: New aspects in the biological role of zinc: A stabilizer of macromolecules and biological membranes. Life Sci. 13, 10411049 (1973) Evans, G.W.: Zinc absorption and transport. Symposium on trace elements and human disease. Wayne State University, School of Medicine, Detroit, Michigan: July 1974 Geisler, Ch., Stacher, A., Stuckl, W., Weiser, M.: Ver~nderungen des Serumzinkgehaltes nach peroralen Zinkgaben und verschiedenen Therapieformen. Wien. klin. Wschr. 84, 275179 (1972) Halsted, J.H., Smith, J.C.: Plasma-zinc in health and disease. Lancet 1970 I, 322-324 Helwig, H.L., Hoffer, E.M., Thielen, W.C., Alcocer, A.E., Hotelling, D.R., Rogers, W.H., Lench, J.: Urinary and serum zinc levels in
chronic alcoholism. Amer. Jo clin. Path. 45, 156-159 (1966) Hetland, 0., Brubakk, E.: Diurnal variation in serum zinc concentration. Scand. J. clin. Lab. Invest. 32, 225-226 (1973) Kowarski, S., Blair-Stanek, C.S., Schachter, D.: Active transport of zinc and identification of zinc-binding protein in rat jejunal mucosa. Amer. J. Physiol. 226, 401-407 (1974) Methfessel, A.H., Spencer, H.: Zinc metabolism in the rat. I. Intestinal absorption of zinc. J. appl. Physiol. 34, 58-62 (1973) Pearson, W.N., Schwink, T., Reich, M.: In vitro studies of zinc absorption in the rat. In: Zinc metabolism, pp. 239-256 (ed. A.S.Prasad) Springfield, Illinois: Charles C. Thomas 1966 P~caud, A., Donzel, P., Schelling, J.L.: Effect of foodstuffs on the absorption of zinc sulphate. Clin. Pharmacol. Ther. 17, 469-474 (1975) Prasad, A.S.: A century of research on the metabolic role of zinc. Amer. J. clin. Nutr. 22, 1215-1221 (1969) Prasad, A.S. Miale, Jr. A., Farid, Z., Sandstead, H.H., Schulert, A.R.: Zinc metabolism in patients with the syndrome of iron deficiency anemia, hepatosplenomegaly, dwarfism, and hypogonadism. J. Lab. clin. Med. 61, 537-549 (1963) Sahagian, B.M., Harding-Barlow, I., Perry, Jr. H.M.: Uptakes of zinc, manganese, cadmium and mercury by intact strips of rat intestine. J. Nutr. 90, 259-263 (1966) Salmon, P.A.: The results of small intestine by pass operations for the treatment of obesity. Surgery 132, 965-979 (1971) Spencer, H., Rosoff, B., Feldstein, A., Cohn, S.H., Gusmano, E.: Metabolism of Zinc-65 in man. Rad. Res. 24, 432-445 (1965a) Spencer, H., Vankinscott, V., Lewin, I., Samachson, J.: Zinc-65 metabolism during low and high calcium intake in man. J. Nutr. 86, 169-177 (1965b) Van Campen, D.R., Mitchell, E.A.: Absorption of Cu 64, Zn65, Mo99 and Fe59 from ligated segments of the rat gastrointestinal tract. J. Nutr. 86, 120-124 (1965)
Dr. K.-E. Andersson Dept. of Clinic~l Pharmacology Univ. Hospital S-221 85 Lund Sweden
Some Aspects of the Intestinal Absorption of Zinc in Man K.-E. Andersson, L. Bratt, H. Dencker and E. Lanner Departments of Clinical Lund, Sweden
Received: accepted:
Pharmacology
and Surgery,
September I, 1975, and in revised October 16, 1975
form:
University Hospital,
October
15,
1975,
Serum zinc concentrations in peripheral venous blood were determined in 8 healthy volunteers at various times after oral administration of 50 mg Zn ++. The same dose was given to 6 patients surgically treated for obesity by j e j u n o - i l e o s t o m y In the healthy volunteers the mean serum zinc concentration before dosing was 0.89 ~g/ml and a mean peak concentration of 2.39 ~g/ml was found after 3 h. In the patients the starting level was lower, 0.67 ~g/ml, and a mean peak concentration of 1.31 ~g/ml was found 90 min after treatment. In the patients the areas under the serum concentration-time curve was approximately I/3 of that in the healthy subjects. Zn ++ 50 mg was also given to 3 patients undergoing transumbi!ical catheterization of the portal vein for diagnostic purposes and serum zinc concentrations were measured in portal and peripheral venous blood sampled simultaneously. No significant differences were found between the concentration of zinc in portal and peripheral venous blood during absorption, which suggests slow passage of zinc across the intestinal wall. Summary.
Key words: Serum zinc concentration,
catheterization,
intestinal
absorption,
portal vein,
transumbilical
man.
Increasing awareness of the biological role of zinc and of its possible therapeutic effect in various diseases (Prasad et al., 1963; Prasad, 1969; Halsted and Smith, 1970; Chvapil, 1973) has also focused interest on its absorption, metabolism, and elimination. Little information is available at present on the intestinal absorption of zinc in man, mainly because of methodological difficulties (Becker and Hoekstra, 1971). Our knowledge of the site, m e c h a n i s m and extent of its absorption is incomplete. The present study was undertaken to obtain further information about the intestinal absorption of zinc in man. Changes in the concentration of zinc in peripheral venous blood after a single oral dose were measured in healthy volunteers and compared w i t h those found in patients surgically treated for obesity by jejuno-ileostomy. The concentration of zinc in portal and
peripheral venous blood of patients undergoing portal catheterization for diagnostic purposes was also measured after a single oral dose of zinc sulphate.
MATERIAL AND METHODS Subjects
Eight healthy males, aged 24 to 45 years (mean 28 years), weighing 65 to 86 kg (mean 69 kg), volunteered for the first part of the study, which was performed in order to define changes in the serum zinc concentration after administration of a single oral dose of zinc sulphate. Six patients, 3 male and 3 female, surgically treated by jejuno-ileostomy for obesity, took part in the second part of the study. They had undergone operation I - 2 years before the in-
424
v e s t i g a t i o n and w e r e in good p h y s i c a l condition. T h e y w e r e aged 26 to 47 years (mean 34 years); their w e i g h t before the o p e r a t i o n ranged from 116 to 190 kg (mean 154 kg), and at the time of the study from 66 to 130 kg (mean 113 kg). Three p a t i e n t s had b e e n given oral zinc t h e r a p y i n t e r m i t t e n t l y , but none had b e e n t r e a t e d for at least 4 weeks prior to the study. In the third part of the study, the changes in zinc c o n c e n t r a t i o n in p o r t a l and p e r i p h e r a l venous blood after adm i n i s t r a t i o n of a single oral dose of zinc sulphate to 3 p a t i e n t s were measured. The p a t i e n t s w e r e ambulant, in good p h y s i c a l c o n d i t i o n and had app a r e n t l y normal bowel habits. They were I female and 2 males, aged 54, 59, and 64 years, and w e i g h i n g 61, 76, and 85 kg, respectively. All had been o p e r a t e d for c a r c i n o m a of the large i n t e s t i n e 5 - 8 years previously. No m e t a s t a s e s w e r e found at the operation. As a p a r t of a r o u t i n e search for h e p a t i c m e t a s tases the portal v e i n was c a t h e t e r i z e d to p e r m i t i n j e c t i o n of c o n t r a s t medium. In none w e r e m e t a s t a s e s d e m o n s t r a t e d by the p o r t o v e n o g r a p h y or on s c i n t i g r a p h y . N o n e had r e c e i v e d zinc p r e p a r a t i o n s therapeutically. Before the investigation, the purpose of the study and the p r o c e d u r e inv o l v e d were fully e x p l a i n e d and v e r b a l consent obtained.
operation Technique
Five of the obese p a t i e n t s had undergone j e j u n o - i l e o s t o m y a c c o r d i n g to the m e t h o d d e s c r i b e d by Salmon (1971). T h i r t y - s e v e n cm of p r o x i m a l j e j u n u m m e a s u r e d from the ligament of Treitz had been a n a s t o m o s e d end to end to the distal 12 cm of ileum. The p r o x i m a l part of the ileum had been a n a s t o m o s e d end to side to the colon. In the rem a i n i n g p a t i e n t (No. I, Table 2), the p r o x i m a l jejunum (37 cm from the ligam e n t of Treitz) had been a n a s t o m o s e d end to side to the ileum (12 cm from V a l v u l a Bauhini). In all cases the f u n c t i o n a l part of the small i n t e s t i n e was a p p r o x i m a t e l y 50 cm long. Catheterization of the Portal Vein
The u m b i l i c a l cord was r e - o p e n e d w i t h a probe under local or g e n e r a l anaesthesia, and a catheter p l a c e d in the m a i n portal vein under f l u o r o s c o p i c control. The i n v e s t i g a t i o n s were p e r f o r m e d 2 days after i n t r o d u c t i o n of the catheter, w h i c h had been kept p a t e n t by constant i n f u s i o n of h e p a r i n i z e d saline.
Experimental Procedure
A f t e r an o v e r n i g h t fast, both the h e a l t h y v o l u n t e e r s and patients were given 50 mg Zn ++ orally, as a solution of zinc sulphate c o n t a i n i n g 0.5 mg Zn ++ per ml. The beaker c o n t a i n i n g the zinc sulphate s o l u t i o n was r i n s e d w i t h 50 ml d i s t i l l e d water w h i c h was also swallowed. In the h e a l t h y v o l u n t e e r s and in the obese patients, blood samples were taken from a f o r e a r m vein before, and 30, 60, 90, 120, 240, 360 and 480 min after a d m i n i s t r a t i o n of the zinc. No food or d r i n k were a l l o w e d until the 480 m i n sample had b e e n taken. The same s a m p l i n g schedule was e m p l o y e d in the 3 patients from w h o m b l o o d samples were taken s i m u l t a n e o u s l y from the portal vein and a f o r e a r m vein. These patients r e c e i v e d a light meal after the 240 min sample had been taken. Samples w e r e not c o l l e c t e d from one of the p a t i e n t s after 240 m i n b e c a u s e p e r i p h e r a l venous blood could not be obtained. zinc Analysis
All m a t e r i a l s used for b l o o d sampling w e r e c h e c k e d to avoid c o n t a m i n a t i o n . The serum samples were stored frozen until their zinc content was d e t e r m i n e d by atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y (Helwig et al., 1966) using a V a r i a n 1100 atomic a b s o r p t i o n s p e c t r o p h o t o meter. The samples w e r e a s p i r a t e d into an a i r - a c e t y l e n e flame after t e n f o l d d i l u t i o n w i t h water. The a b s o r p t i o n signal at 213.9 nm was m e a s u r e d and i n t e g r a t e d for 10 sec. S t a n d a r d s added to p o o l e d human serum were used to c o m p e n s a t e for m a t r i x effects and a linear s t a n d a r d curve was obtained. Non-specific background absorption (average v a l u e of 10 sera) was subt r a c t e d before c a l c u l a t i o n of the zinc c o n c e n t r a t i o n in each sample.
Area under the Serum Concentration-Time Curve
The area under the serum c o n c e n t r a t i o n time curve d e t e r m i n e d by the t r a p e z o i d a l rule was taken as the increase in serum zinc c o n c e n t r a t i o n above the starting level from time O to 480 min after dosing.
RESULTS Before the intake of zinc, the m e a n serum zinc value in the h e a l t h y subjects was 0.98 ~g/ml (range 0.83 - 1.23 ~g/ml). A f t e r the intake of 50 mg Zn ++ there was a steady increase in the serum
425
c o n c e n t r a t i o n , and a m e a n m a x i m u m of 2.39 #g/ml was a t t a i n e d a f t e r 180 min. The i n c r e a s e in s e r u m c o n c e n t r a t i o n per unit time r e a c h e d a m a x i m u m d u r i n g the i n i t i a l 90 m i n (O.0153 p g / m l / m i n ) . A t the last sample, 480 m i n a f t e r t r e a t m e n t , the m e a n s e r u m zinc had f a l l e n to 1.13 #g/ml. The m e a n v a l u e s at the d i f f e r e n t times a f t e r a d m i n i s t r a t i o n are i l l u s t r a t e d in Fig. I, and the i n d i v i d u a l v a l u e s are g i v e n in T a b l e I. In the 6 p a t i e n t s w i t h a j e j u n o ileostomy, the m e a n s e r u m zinc c o n c e n t r a t i o n p r i o r to t r e a t m e n t was 0.67 #g/ ml (range O.51 - 0.87 pg/ml). A f t e r adm i n i s t r a t i o n of 50 m g Zn ++ the s e r u m zinc i n c r e a s e d to a m e a n m a x i m u m of 1.31 pg/ml a f t e r 90 min. The m a x i m u m i n c r e a s e in s e r u m c o n c e n t r a t i o n per u n i t time was l o w e r t h a n in the h e a l t h y s u b j e c t s (O.O113 # g / m l / m i n ) . The a r e a u n d e r the s e r u m c o n c e n t r a t i o n - t i m e curve was app r o x i m a t e l y 34 per cent of that in the h e a l t h y subjects. The m e a n s e r u m zinc v a l u e s at the times of s a m p l i n g are g i v e n in Fig. I, and d a t a for i n d i v i d uals in T a b l e 2. In three p a t i e n t s s u b j e c t e d to c a t h e t e r i z a t i o n of the p o r t a l vein, the s e r u m zinc c o n c e n t r a t i o n s in p e r i p h e r a l b l o o d b e f o r e the a d m i n i s t r a t i o n of zinc w e r e 0.70, 0.68, and 0 . 7 0 #g/ml, res p e c t i v e l y . The c o n c e n t r a t i o n s in p o r t a l b l o o d w e r e i n s i g n i f i c a n t l y lower, 0.65, 0.68, and 0.62 #g/ml, r e s p e c t i v e l y . A f t e r t a k i n g the zinc, the c o n c e n t r a tions in p o r t a l and p e r i p h e r a l b l o o d w e r e v e r y similar, b o t h r e a c h i n g a m e a n p e a k v a l u e of 1.58 and 1.54 #g/ml, r e s p e c t i v e l y , at 90 min. The i n c r e a s e in s e r u m c o n c e n t r a t i o n per u n i t time was m a x i m a l d u r i n g the i n i t i a l 60 m i n and of the same m a g n i t u d e (O.0147 ~g/ ml/min) as in the h e a l t h y subjects. The m e a n s e r u m zinc c o n c e n t r a t i o n had r e t u r n e d to the s t a r t i n g level in the last sample, 480 m i n a f t e r t a k i n g the zinc. The m e a n s e r u m zinc v a l u e s in p o r t a l and p e r i p h e r a l v e n o u s b l o o d are s h o w n in Fig. 2 a n d the i n d i v i d u a l d a t a in T a b l e 3. Some of the h e a l t h y s u b j e c t s and some of the p a t i e n t s r e p o r t e d s l i g h t g a s t r o i n t e s t i n a l d i s c o m f o r t w i t h i n 30 60 m i n a f t e r s w a l l o w i n g the zinc sulphate. No o t h e r side e f f e c t s w e r e observed.
DISCUSSION S e v e r a l m e t h o d s are a v a i l a b l e for s t u d y of the g a s t r o i n t e s t i n a l a b s o r p t i o n of zinc in e x p e r i m e n t a l a n i m a l s (for review, see B e c k e t and H o e k s t r a , 1971). R a d i o i s o t o p e t r a c e r t e c h n i q u e s have b e e n c o m m o n l y u s e d in these s t u d i e s
3.0-
Zn-concentration,
pg/ml
2.0
1.0 ¸
T i m e , rnin 0.0
;
6'0
40
240
'" 3o0
"3"6 0
' ....... 48o ' 42o
Fig. I. Serum zinc concentration (mean ± SEM) in 8 healthy subjects ( --- ), and in 6 obese patients (e :) with a jejuno-ileostomy following oral administration of 50 mg Zn ++ as a solution of zinc sulphate
2.0
Zn-concentration, pg/ml
t.0
Time, min 0.0-
i
0
6 -0
i 120
~.......... i 180 240
i 300
i 360
~
420
480
Fig. 2. Mean serum zinc concentrations (n = 3) in portal ( --- ) and peripheral (e) venous blood following oral administration of 50 mg Zn++ as a solution of zinc sulphate
426
Table I. Serum zinc concentrations (zg/ml) in peripheral venous blood from 8 healthy subjects at various times after oral administration of 50 mg Zn ++ Time after administration, min Subject
0
30
60
90
120
180
240
360
480
i
0.86
1.52
2.02
2.01
1.90
1.95
1.70
1.09
0.76
2
0.93
1.04
1.35
1.97
1.97
2.38
1.98
1.29
1.O8
3
1.O2
1.73
2.49
2.70
2.73
2.66
2.33
1.66
1.32
4
0.94
1.54
1.99
2.62
2.78
2.42
2.28
1.27
O.91
5
1.22
1.35
1.97
2.41
2.72
3.14
3.23
2.57
1.88
6
0.95
I.OO
1.13
1.53
1.82
2.05
1.92
1.49
1.18
7
0.83
0.99
1.32
1.61
1.97
2.00
2.10
1.52
0.95
8
i.iO
1.55
2.13
2.44
2.69
2.52
2.09
1.25
0.95
Mean
0.98
1.34
1.80
2.16
2.32
2.39
2.20
1.52
1.13
± SEM
0.05
O. iO
O.17
0.16
O.16
0.14
0.16
0.16
O.12
Table 2. Serum zinc concentrations (zg/ml) in peripheral venous blood from 6 obese patients with a jejuno-ileostomy at various times after oral administration of 50 mg Zn ++ Time after administration, min Patient
O
30
60
90
120
180
240
360
480
i
O.51
0.85
0.92
0.84
0.78
O.71
0.58
0.44
0.44
2
0.69
0.92
1.63
1.76
1.98
1.91
1.56
0.94
0.72
3
0.80
1.13
1.29
1.41
1.37
1.22
1.O3
0.90
0.87
4
0.56
0.80
1.09
1.20
1.13
1.O3
0.83
0.67
0.61
5
0.59
0.94
1.04
1.02
0.93
0.80
0.68
0.58
0.59
6
0.87
1.39
1.51
1.60
1.45
1.26
1.O8
0.76
0.76
Mean
0.67
1.O1
1.25
1.31
1.27
1.16
0.96
0.72
0.67
± SEM
O.O5
0.09
O.11
O.14
O.18
O.18
O.14
0.07
0.O6
and also for investigations in m a n ( S p e n c e r et al., 1965a, b). H o w e v e r , the isotope 65Zn has the disadvantage of a b i o l o g i c a l h a l f - l i f e of m o r e t h a n 3 0 0 d a y s ( S p e n c e r et al., 1 9 6 5 a ) , w h i c h l i m i t s its u s e in h u m a n s . In t h e present study the increase in serum zinc concentration after an oral dose of z i n c s u l p h a t e w a s u s e d to e x a m i n e the site of absorption and passage a c r o s s t h e i n t e s t i n a l w a l l o f t h e ion. T h e m a i n s i t e of z i n c a b s o r p t i o n in t h e i n t e s t i n e is n o t k n o w n . D a t a f r o m some animal studies indicate that abs o r p t i o n is g r e a t e r f r o m t h e d u o d e n u m t h a n f r o m m o r e d i s t a l p a r t s of t h e intestine, and that absorption from the s t o m a c h a n d t h e c o l o n is m i n i m a l (Van
C a m p e n a n d M i t c h e l l , 1965; M e t h f e s s e l a n d S p e n c e r , 1973). H o w e v e r , o t h e r a n i m a l s t u d i e s a p p e a r to s u g g e s t m o r e d i s t a l p a r t s of t h e i n t e s t i n e as t h e m a i n s i t e of a b s o r p t i o n ( P e a r s o n et al., 1966; S a h a g i a n et al., 1966; K o w a r s k i et al., 1 9 7 4 ) . The present study shows that, after oral administration of 50 m g Zn + + in solution to healthy subjects, the zinc concentration i n p e r i p h e r a l b l o o d increased from a mean starting value of 0 . 9 8 ~ g / m l t o a m a x i m u m of 2 . 3 9 ~ g / m l . The increase in serum concentration per u n i t t i m e w a s m a x i m a l w i t h i n 90 m i n , a n d the peak concentration was attained after 180 min. Both the starting and peak concentrations were consistent with
427
Table 3. Serum zinc concentrations (pg/ml) in simultaneous samples of portal and peripheral venous blood from 3 patients at various times after oral administration of 50 mg Zn ++ Peripheral venous blood Time after administration, Patient
min
O
30
60
90
120
180
240
360
480
I
0.70
0.95
1.50
1.65
1.52
1.58
1.16
0.74
0.58
II
0.68
1.23
1.68
1.72
1.78
1.76
1.30
III
0.70
0.76
1.O7
1.26
1.32
1.28
1.18
0.80
0.64
Mean
0.69
0.98
1.42
1.54
1.54
1.54
1.21
0.77
O.61
........
Portal venous blood Time after administration, Patient
I
min
0
30
60
90
120
180
240
360
480
0.65
1.15
1.58
1.67
1.46
1.52
i.ii
0.68
0.58
Ii
0.68
1.19
1.63
1.72
1.63
1.71
1.17
III
0.62
0.94
1.32
1.36
1.42
1.28
1.25
0.85
0.67
Mean
0.65
1.O9
1.51
1.58
1.50
1.50
1.18
0.77
0.63
zinc levels f o u n d by o t h e r i n v e s t i g a t o r s in h e a l t h y s u b j e c t s g i v e n a s i m i l a r d o s e of zinc (Halsted and Smith, 1970; Hetland and B r u b a k k , 1973; P ~ c a u d et al., 1975), but the i n c r e a s e in s e r u m conc e n t r a t i o n per u n i t time was lower t h a n that r e p o r t e d by G e i s l e r et al. (1970) in a series of p a t i e n t s . The o b e s e p a t i e n t s w i t h a j e j u n o i l e o s t o m y h a d o n l y a p p r o x i m a t e l y 50 cm of f u n c t i o n i n g p r o x i m a l small intestine. In these p a t i e n t s the s t a r t i n g zinc level (0.67 ~g/ml) was lower than in h e a l t h y s u b j e c t s (0.98 pg/ml). E v e n if this w e r e t a k e n into account, the m e a n m a x i m u m c o n c e n t r a t i o n attained, 1.31 ~g/ ml, was c o n s i d e r a b l y lower in the o b e s e p a t i e n t s , and the a r e a u n d e r the s e r u m c o n c e n t r a t i o n - t i m e curve in t h e m was only a b o u t I/3 of that in the h e a l t h y subjects. A s s u m i n g that the areas in the two g r o u p s w o u l d h a v e b e e n of the same m a g n i t u d e if the o b e s e p a t i e n t s had h a d an i n t a c t small bowel, these d a t a s u g g e s t that the p r o x i m a l 50 cm of the small i n t e s t i n e a b s o r b s a p p r o x i m a t e l y I/3 of the t o t a l a m o u n t of zinc t a k e n up by the bowel. However, it c a n n o t be e x c l u d e d that d i f f e r e n c e s e x i s t b e t w e e n the a b s o r p t i v e c a p a c i t y of the small i n t e s t i n e in the o b e s e pa-
t i e n t s and the n o r m a l subjects. T h e r e are some i n d i c a t i o n s t h a t the i n t e s t i n a l m u c o s a of the o p e r a t e d p a t i e n t s u n d e r goes c h a n g e s s u g g e s t i v e of an i n c r e a s e in its a b s o r p t i v e s u r f a c e (Andersson, D e n c k e r and G~thlin, u n p u b l i s h e d ) . If this w e r e so, the a b s o r p t i o n of zinc m i g h t be r e l a t i v e l y g r e a t e r in the o b e s e p a t i e n t s than in n o r m a l subjects. However, the f i n d i n g t h a t the i n c r e a s e in s e r u m c o n c e n t r a t i o n p e r u n i t time was lower in the o b e s e p a t i e n t s does not f a v o u r this view. D e s p i t e e x t e n s i v e study, the m e c h a nisms i n v o l v e d in the g a s t r o i n t e s t i n a l a b s o r p t i o n of zinc r e m a i n unknown, and it has not b e e n d e f i n i t e l y e s t a b l i s h e d w h e t h e r a c t i v e t r a n s p o r t is i n v o l v e d (Becket and H o e k s t r a , 1971). As p o i n t e d out by Evans (1974), the l i k e l i h o o d of s i m p l e d i f f u s i o n seems r e m o t e in v i e w of the m o r p h o l o g i c a l b a r r i e r s conf r o n t i n g the zinc ion d u r i n g its c o u r s e f r o m lumen to blood. R e c e n t d a t a p r e s e n t e d by K o w a r s k i et al. (1974) a l s o f a v o u r the v i e w of a c t i v e t r a n s p o r t . S i m u l t a n e o u s s a m p l i n g of p o r t a l and p e r i p h e r a l v e n o u s blood, as u s e d in the p r e s e n t study, o f f e r s a m e a n s of studying the rate of p a s s a g e of v a r i o u s m a t e r i a l s a c r o s s the i n t e s t i n a l w a l l
428
( A n d e r s s o n et al., 1975). A s t h e c o n c e n trations of zinc in portal blood after treatment were found to be close to t h o s e i n p e r i p h e r a l b l o o d , it a p p e a r s that the passage of zinc across the i n t e s t i n a l w a l l is a s l o w p r o c e s s . I t h a s b e e n s h o w n ( G e i s l e r et al., 1971) t h a t t h e i n c r e a s e in s e r u m z i n c concentration p e r u n i t t i m e is d e p e n d e n t on the dose and also on the initial s e r u m z i n c l e v e l , b e i n g g r e a t e r in subjects with low starting levels. Both in the obese patients and in those s u b j e c t e d to p o r t a l c a t h e t e r i z a t i o n the initial serum zinc levels were lower t h a n in t h e h e a l t h y s u b j e c t s , b u t t h e increase in serum concentration per unit time was not greater. Whether this means that the present patients had a decreased ability to absorb zinc, or that the serum zinc level was not the main r e g u l a t o r of t h e r a t e a t w h i c h z i n c appeared in the circulation, cannot be determined at present. REFERENCES Andersson, K.-E., Nyberg, L., Dencker, H., G6thlin, J.: Absorption of digoxin in man after oral and intrasigmoid administration studied by portal vein catheterization. Europ. J. clin. Pharmacol. 9, 39-47 (1975) Becket, W.M., Hoekstra, W.G.: The intestinal absorption of zinc. In: Intestinal absorption of metal ions, trace elements and radionuclides (Ed. S.C. Skoryna, D. WaldronEdward), pp. 229-256. New York: Pergamon Press 1971 Chvapil, M.: New aspects in the biological role of zinc: A stabilizer of macromolecules and biological membranes. Life Sci. 13, 10411049 (1973) Evans, G.W.: Zinc absorption and transport. Symposium on trace elements and human disease. Wayne State University, School of Medicine, Detroit, Michigan: July 1974 Geisler, Ch., Stacher, A., Stuckl, W., Weiser, M.: Ver~nderungen des Serumzinkgehaltes nach peroralen Zinkgaben und verschiedenen Therapieformen. Wien. klin. Wschr. 84, 275179 (1972) Halsted, J.H., Smith, J.C.: Plasma-zinc in health and disease. Lancet 1970 I, 322-324 Helwig, H.L., Hoffer, E.M., Thielen, W.C., Alcocer, A.E., Hotelling, D.R., Rogers, W.H., Lench, J.: Urinary and serum zinc levels in
chronic alcoholism. Amer. Jo clin. Path. 45, 156-159 (1966) Hetland, 0., Brubakk, E.: Diurnal variation in serum zinc concentration. Scand. J. clin. Lab. Invest. 32, 225-226 (1973) Kowarski, S., Blair-Stanek, C.S., Schachter, D.: Active transport of zinc and identification of zinc-binding protein in rat jejunal mucosa. Amer. J. Physiol. 226, 401-407 (1974) Methfessel, A.H., Spencer, H.: Zinc metabolism in the rat. I. Intestinal absorption of zinc. J. appl. Physiol. 34, 58-62 (1973) Pearson, W.N., Schwink, T., Reich, M.: In vitro studies of zinc absorption in the rat. In: Zinc metabolism, pp. 239-256 (ed. A.S.Prasad) Springfield, Illinois: Charles C. Thomas 1966 P~caud, A., Donzel, P., Schelling, J.L.: Effect of foodstuffs on the absorption of zinc sulphate. Clin. Pharmacol. Ther. 17, 469-474 (1975) Prasad, A.S.: A century of research on the metabolic role of zinc. Amer. J. clin. Nutr. 22, 1215-1221 (1969) Prasad, A.S. Miale, Jr. A., Farid, Z., Sandstead, H.H., Schulert, A.R.: Zinc metabolism in patients with the syndrome of iron deficiency anemia, hepatosplenomegaly, dwarfism, and hypogonadism. J. Lab. clin. Med. 61, 537-549 (1963) Sahagian, B.M., Harding-Barlow, I., Perry, Jr. H.M.: Uptakes of zinc, manganese, cadmium and mercury by intact strips of rat intestine. J. Nutr. 90, 259-263 (1966) Salmon, P.A.: The results of small intestine by pass operations for the treatment of obesity. Surgery 132, 965-979 (1971) Spencer, H., Rosoff, B., Feldstein, A., Cohn, S.H., Gusmano, E.: Metabolism of Zinc-65 in man. Rad. Res. 24, 432-445 (1965a) Spencer, H., Vankinscott, V., Lewin, I., Samachson, J.: Zinc-65 metabolism during low and high calcium intake in man. J. Nutr. 86, 169-177 (1965b) Van Campen, D.R., Mitchell, E.A.: Absorption of Cu 64, Zn65, Mo99 and Fe59 from ligated segments of the rat gastrointestinal tract. J. Nutr. 86, 120-124 (1965)
Dr. K.-E. Andersson Dept. of Clinic~l Pharmacology Univ. Hospital S-221 85 Lund Sweden
