European Journal of Pharmacology, 45 (1977) 261--265
261
© Elsevier/North-Holland Biomedical Press
E F F E C T S O F H I S T A M I N E O N T H E H U M A N PENIS M U S C L E IN V I T R O P.G. ADAIKAN and S.M.M. KARIM Department of Obstetrics and Gynaecology, University of Singapore, Kandang Kerbau Hospital, Singapore 8
Received 15 March 1977, revised MS received 14 June 1977, accepted 20 June 1977
P.G. ADAIKAN and S.M.M. Karim, Effects of histamine on the human penis muscle in vitro, European J. Pharmacol. 45 (1977) 261--265. Histamine produced three types of effects on corpus cavernosa muscle of the human penis: contraction, relaxation or a contraction followed by a relaxation. 2-Methylhistamine, which acts mainly on histamine Hi-receptors, stimulated all the penile strips tested. 4-Methylhistamine, which acts predominantly on H2-receptors produced relaxation in two-thirds of the strips and contraction in the rest. Contractions produced by histamine, 2-methylhistamine and 4-methylhistamine were selectively abolished by mepyramine. Burimamide antagonised the relaxant effect of histamine and of 4-methylhistamine. Corpus cavernosa muscle of the human penis has both histamine Hi-and H2-receptors. Histamine receptors
4-Methylhistamine
Human penis
1. I n t r o d u c t i o n H i s t a m i n e c o n t r a c t s t h e r e t r a c t o r penis muscle o f t h e d o g ( B o t t a z i , 1 9 1 6 ; L u d u e n a and Grigas, 1 9 6 6 ) , bull (Klinge, 1 9 7 0 ) and o x ( A m b a c h e e t al., 1 9 7 5 ) . T h e p r e s e n c e o f hista m i n e in t h e m a m m a l i a n penis has also b e e n r e p o r t e d . T h e r a b b i t erectile penile tissue contains m o r e h i s t a m i n e t h a n adrenaline, noradrenaline, a c e t y l c h o l i n e or 5 - h y d r o x y t r y p t amine (Penttil~i a n d Vartiainen, 1964). W h e t h e r h i s t a m i n e is p r e s e n t in the h u m a n penis and w h e t h e r it has any a c t i o n o n t h e s m o o t h muscle o f t h e h u m a n penis is n o t k n o w n . T h e p r e s e n t s t u d y was u n d e r t a k e n t o s t u d y some p h a r m a c o l o g i c a l actions o f histamine o n s m o o t h muscle o f t h e h u m a n penis.
2. Materials and m e t h o d s Fresh, m a c r o s c o p i c a l l y n o r m a l , h u m a n penes were o b t a i n e d f r o m transsexual p a t i e n t s u n d e r g o i n g sex change o p e r a t i o n . T h e e n t i r e penis was r e m o v e d and i m m e d i a t e l y transf e r r e d t o t h e l a b o r a t o r y in K r e b s - - H e n s e l e i t
Histamine
Corpus cavernosa
2-Methylhistamine
solution. L o n g i t u d i n a l muscles o f the c o r p u s c a v e m o s a (c.c.) were dissected into strips 2--3 m m wide and 3 cm long. T h e y were m o u n t e d in 20 ml organ baths c o n t a i n i n g K r e b s - - H e n seleit s o l u t i o n o f the following c o m p o s i t i o n (g/l) : s o d i u m chloride 6.74; potassium chloride 0.35; calcium chloride ( 2 H 2 0 ) 0.26; potassium d i h y d r o g e n o r t h o p h o s p h a t e 0.16; m a g n e s i u m sulphate ( 7 H 2 0 ) 0 . 2 8 7 ; glucose 1.54; s o d i u m b i c a r b o n a t e 1.86; d i s o d i u m E D T A 0.01. T h e s o l u t i o n was m a i n t a i n e d at 37°C and aerated with 5% c a r b o n d i o x i d e in o x y g e n (pH = 7.4). T e n s i o n (2 g) was applied t o the muscle strips and 1 h equilibration p e r i o d was t h e n allowed. During this t i m e the tension decreased and stabilised at 1--1.5 g. C o n t r a c t i o n and r e l a x a t i o n were r e c o r d e d isometrically using a f o r c e d i s p l a c e m e n t transd u c e r c o n n e c t e d t o a r e c o r d e r . A drug cont a c t t i m e o f 5--10 min and a cycle t i m e o f 20 min were used f o r histamine, 2 - m e t h y l h i s t amine, 4 - m e t h y l h i s t a m i n e and prostagiandin F2~. Adrenaline, n o r a d r e n a l i n e and isoprenaline r e q u i r e d a c o n t a c t t i m e o f 3.5 min and a cycle time o f 10 min. Whenever the antago-
262
P.G. ADAIKAN, S.M.M. KARIM
nists were used they were added to the tissue bath 1 min before addition of the agonists. The following drugs were used: histamine dihydrochloride (Merck); 2-methylhistamine dihydrochloride (SKF); 4-methylhistamine dihydrochloride (SKF); adrenaline bitartrate (Sigma); noradrenaline bitartrate (Sigma); prostaglandin F2~ (Up john); burimamide (SKF); propranolol (I.C.I.); phentolamine (Ciba AG); polyphloretin phosphate (AB Leo). All drugs were prepared in 0.9% sodium chloride solution.
3. Results
The effect of 2-methylhistamine was studied in 9 corpus cavernosa strips from 6 penes. All responded by contractions. Out of total of 15 strips from 6 penes, 4-methylhistamine produced contractions in 5, relaxation in 9 and a contraction followed by relaxation in 1 (table 1).
3.2. Threshold doses The threshold doses of histamine and its two m e t h y l analogues for contracting or relaxing the corpus cavernosa muscle are shown in table 1.
3.3. Effect of histamine Hi-receptor antagonist
A total of 77 strips from 27 penes were studied. Reproducible responses to drugs could be obtained with the penile tissue for more than 12 h.
3.1. Types o f responses to histamine, 2-methylhistamine and 4-methylhistamine The effect of histamine was studied in a total of 53 muscle strips of corpus cavernosa from 15 penes. Histamine produced three types of effect: contraction, relaxation or a contraction followed by a relaxation (fig. 1). Strips from the same penis usually produced the same type of response. Out of the 53 strips form 15 penes, histamine produced relaxation in 15 (28.3%), contractions in 33 (62.3%) and contraction followed by relaxation in 5 (9.4%).
The contractions of the corpus cavernosa produced by histamine and 2-methylhistamine were selectively abolished by mepyramine at a concentration of 4--8 ng/ml. Mepyramine in a concentration of up to 400 ng/ ml did not modify the contractions produced by prostaglandin F2~ or adrenaline. In the presence of high concentrations of mepyramine (400 ng/ml) the effect of histamine was reversed, i.e. doses that previously produced contractions of the tissue, now had a relaxant effect (fig. 2). No such reversal was observed with 2-methylhistamine. The effect of mepyramine was also studied in four strips in which histamine produced a relaxation. At concentrations of 4--400 ng/ ml mepyramine did not modify the relaxant effect of histamine.
3.4. Effect of histamine H2 receptor antagonist
Hist
•
Fig. 1. T y p i c a l r e s p o n s e s o f t h e h u m a n nosa muscle strips to histamine.
corpus caver-
The effect of burimamide, a histamine H2receptor antagonist was studied in five strips of corpus cavernosa muscle in which histamine and 4-methylhistamine produced contractions and on another five strips which were relaxed by histamine and 4-methylhistamine. Burimamide (0.2--0.8 pg/ml) potentiated
H I S T A M I N E R E C E P T O R S IN H U M A N P E N I S
263
TABLE 1 Percentage distribution of types of responses and threshold concentration of histamine and methylhistamines on c o r p u s c a v e r n o s a muscle o f h u m a n penis. Drug
No. o f penes
Histamine
15
Total No. o f strips
Contraction
53
33
62.3
No.
%
Relaxation
Biphasic
Threshold dose (ng/ml)
No.
%
Threshold dose (ng/ml)
No.
%
Threshold dose (ng/ml)
1 1 2 +_ 24 1
15
28.3
7 1 6 +- 3 3 0
5
9.4
4 0 0 -+ 87
.
6.7
2
2-Me h i s t a m i n e
6
9
9
100.0
2 5 0 +- 58
4-Me h i s t a m i n e
6
15
5
33.3
9 1 2 +- 5 7 0
. 9
60.0
.
. 6 3 4 _+ 2 1 0
.
. 1
1 +S.E.M. 2 20 n g / m l c o n t r a c t e d ; 1 0 0 n g / m l relaxed.
the contractions of the corpus cavernosa produced by histamine and 4-methylhistamine. This effect of burimamide could be reversed by changing the bathing fluid (fig. 3). The relaxant effect of histamine and 4methylhistamine was blocked by burimamide (0.8--3.2 pg/ml). In the presence of a higher concentration of burimamide (6.4pg/ml), doses of histamine and 4-methylhistamine which had previously relaxed the muscle now produced contractions. This reversed (contractile) effect of histamine was blocked by mepyramine (40 ng/ml) (fig. 4).
4ng/ml Tension ~
•
Nepyrclmlne - -
3.5. Other antagonists Phentolamine (0.4 pg/ml) selectively antagonised the contractions of the corpus cavernosa which were produced by adrenaline (40 ng/ml) and polyphloretin phosphate (40 pg/ ml) antagonised those produced by prostaglandin F2~ (100ng/ml). Contractions produced by histamine and 2-methylhistamine were not affected by these antagonists. Isoprenaline (70 ng/ml) relaxed the strips of corpus cavernosa muscle. This effect of isoprenaline was blocked by propranolol (0.4
~
5rain
,~.
•
o
•
o
~-
o Adr
• Hist
• Hist
/,OOng/ml
t,,lepyromine -
o Adr
-
I
• Hist
o Adr
• H~st
Fig. 2. E f f e c t of m e p y r a m i n e (4 n g / m l a n d 4 0 0 n g / m l - - d i f f e r e n t strips) o n h i s t a m i n e (o Hist, 4 0 0 n g / m l ) a n d a d r e n a l i n e (© Adr, 16 n g / m l ) i n d u c e d c o n t r a c t i o n s o f c o r p u s c a v e r n o s a m u s c l e strips o f h u m a n penis.
264
P.G. A D A I K A N , S.M.M. K A R I M
I
c ,mr~o "
5 ml,, ~ m
/
recover} "
I
10
m~n
35-
15
•
• /
/ o~/
/
•
o~,
I
•
•
•
•
o~
Bur~rnamlde ~/ug/m~ }
Fig. 3. P o t e n t i a t i o n b y b u r i m a m i d e o f r e p e a t e d doses o f h i s t a m i n e i n d u c e d (o Hist, 4 0 0 n g / m l ) c o n t r a c t i o n s of c o r p u s c a v e r n o s a muscle of h u m a n penis.
pg/ml). Doses of up to 3.2 pg/ml propranolol did n o t have any effect on the relaxant effects of histamine or 4-methylhistamine.
4. Discussion To our knowledge, studies on pharmacological effects of drugs on the h u m a n penis have so far not been reported, possibly because of the difficulty in obtaining the material. Such studies could prove useful in studying the physiology of h u m a n penile erection and ejaculation, and in evaluating the possible roles of naturally occurring substances in these processes. Material obtained from sex change operations in transsexual subjects provides an ideal opportunity to investigate the effect of drugs on the human penis. In this first investigation, we have studied the effects of histamine on the corpus cavernosa muscle of the h u m a n penis. The presence of histamine in high amounts in the rabbit penis (Penttil~i and Vartainen, 1964) and the contractile effect reported for this c o m p o u n d on the isolated retractor penis muscle of the dog (Bottazi, 1916; L u d u e n a and Grigas, 1966), bull (Klinge, 1970) and ox (Ambache et al., 1975) make this study of particular interest. Histamine caused contraction, relaxation or a biphasic effect (contraction followed by relaxation) in the corpus cavernosa muscle of the human penis. The stimulant action of histamine was selectively antagonized by mepyramine, a histamine H~-receptor antagonist but not by other drugs e.g. polyphloretin
Burlmcmlde 0 8,ucJ/ml
Burimomide 3 2 ug/ml
Burimamide
i'~epy ro m i n e
Fig. 4. E f f e c t o f b u r i m a m i d e o n t h e r e l a x a n t e f f e c t o f h i s t a m i n e o n c o r p u s c a v e r n o s a m u s c l e o f h u m a n penis ( e Hist, 4 0 0 ng/ml).
phosphate (a prostaglandin antagonist) or phentolamine (an a-adrenoreceptor blocker). The corpus cavernosa was also contracted by 2-methylhistamine which is known to stimulate mainly Hi-receptors (Black et al., 1972) and this effect was also selectively antagonised by mepyramine. The relaxant action of histamine was selectively blocked by burimamide, a selective H2-receptor antagonist, but not affected by propranolol (a ~-adrenoreceptor blocker). The results thus show that the corpus cavernosa muscle of the human penis contains both histamine H1- and H~-receptors. Although muscle strips from different penes usually respond to histamine by a contraction or a relaxation, it is likely that all penes possess both H1- and H2-receptors, and that the responses depend upon the relative proportion of these receptors. On a penis muscle which responded by a contraction (Hi-receptors), burimamide potentiated the contractile effect of histamine, presumably by blocking the relaxing action on H~-receptors which may have been limiting the stimulating action of histamine. Similar potentiation of stimulant action of histamine with burimamide has been reported to occur with the isolated guinea pig ileum and d u o d e n u m (Bareicha and Rocha e Silva, 1975). Blocking the H~-receptors of the penile muscle (which responds to histamine by a contraction) with mepyramine produces a reversal of effect i.e. a relaxation. This relaxant effect can be blocked by the H2receptor antagonist, burimamide.
HISTAMINE RECEPTORS IN HUMAN PENIS C o n v e r s e l y , tissues t h a t r e s p o n d t o hista m i n e b y a r e l a x a t i o n , are capable o f cont r a c t i n g with t h e same dose o f h i s t a m i n e w h e n the r e l a x a n t H2-receptors are b l o c k e d with b u r i m a m i d e . T h e ensuing c o n t r a c t i o n s can be b l o c k e d with t h e H i - r e c e p t o r b l o c k e r , mepyramine. Whether the effect of histamine on t h e penis is o f physiological i m p o r t a n c e is not known. T h e r e t r a c t o r penis muscle o f d o g and bull possesses post-ganglionic i n h i b i t o r y nerves ( L a n g l e y a n d A n d e r s o n , 1 8 9 5 ) with atropineresistance transmission. L u d u e n a and Grigas (1966, 1972) showed that the stimulation of sacral p a r a s y m p a t h e t i c fibres w h i c h p r o d u c e s r e l a x a t i o n o f the r e t r a c t o r penis muscle o f d o g , is n o t cholinergic or purinergic. R e c e n t l y A m b a c h e et al. ( 1 9 7 5 ) have r e p o r t e d t h a t t h e r e l a x a t i o n o f t r a n s m u r a l l y s t i m u l a t e d isolated steer r e t r a c t o r penis was n o t a f f e c t e d b y mep y r a m i n e o r b u r i m a m i d e . H o w e v e r , it is n o t e w o r t h y that histamine produces only c o n t r a c t i o n in the r e t r a c t o r penis muscle o f d o g , steer and bull (Bottazi, 1 9 1 6 ; L u d u e n a and Grigas, 1 9 6 6 , 1 9 7 2 ; Klinge, 1 9 7 0 and A m b a c h e et al., 1 9 7 5 ) . C o r p u s c a v e r n o s a and c o r p u s s p o n g i o s a muscles o f h u m a n penis possess b o t h i n h i b i t o r y and e x c i t a t o r y hista m i n e r e c e p t o r s . T h e possibility o f h i s t a m i n e i n v o l v e m e n t in p o s t g a n g l i o n i c i n h i b i t o r y nerve transmission t o h u m a n penile muscle c a n n o t t h e r e f o r e be ruled o u t . This possibility is n o w u n d e r investigation.
265 Acknowledgements We are grateful to Professor S.S. Ratnam for providing the surgical materials and to Miss Lo Pia Yong and Miss Tai Mei Yoon for technical assistance. The work was carried out under research grants from The Lee Foundation, Singapore and the Singapore Turf Club. References Ambache, N., S.W. Killick and M. Aboo Zar, 1975, Extraction from ox retractor penis of an inhibitory substance which mimics its atropine-resistant neurogenic relaxation, Brit. J. Pharmacol. 54,409. Bareicha, I. and M. Rocha e Silva, 1975, Occurrence of H2-receptors for histamine in the guinea pig intestine, Biochem. Pharmacol. 24, 1215. Black, J.W., W.A.M. Duncan, C.J. Gurant, C.R. Canellin and E.M. Parsons, 1972, Definition and antagonism of histamine H2-receptors, Nature (London) 236,395. Bottazi, F., 1916, Recherches sur Le 'M. retractor penis' et sur d'autres preparations musculaires lisses, Arch. Ital. Biol. 65,265. Klinge, E., 1970, The effect of some substances on the isolated bull retractor penis muscle, Acta. Physiol. Scand. 78,280. Langley, J.N. and H.K. Anderson, 1895, The innervation of the pelvic and adjoining viscera. Pt. III. The external generative organs, J. Physiol., 19, 85. Luduena, F.P. and E.O. Grigas, 1966, Pharmacological study of autonomic innervation of dog retractor penis, Amer. J. Physiol. 210,435. Luduena, F.P. and E.O. Grigas, 1972, Effect of some biological substances on the dog retractor penis in vitro, Arch. Intern. Pharmacodyn. 196,269. Penttil~, O. and A. Vartiainen, 1964, Acetylcholine, histamine, 5-hydroxytryptamime and catecholamine contents of mammalian penile erectile and urethral tissue, Acta Pharmacol. (Khb). 21, 145.
261
© Elsevier/North-Holland Biomedical Press
E F F E C T S O F H I S T A M I N E O N T H E H U M A N PENIS M U S C L E IN V I T R O P.G. ADAIKAN and S.M.M. KARIM Department of Obstetrics and Gynaecology, University of Singapore, Kandang Kerbau Hospital, Singapore 8
Received 15 March 1977, revised MS received 14 June 1977, accepted 20 June 1977
P.G. ADAIKAN and S.M.M. Karim, Effects of histamine on the human penis muscle in vitro, European J. Pharmacol. 45 (1977) 261--265. Histamine produced three types of effects on corpus cavernosa muscle of the human penis: contraction, relaxation or a contraction followed by a relaxation. 2-Methylhistamine, which acts mainly on histamine Hi-receptors, stimulated all the penile strips tested. 4-Methylhistamine, which acts predominantly on H2-receptors produced relaxation in two-thirds of the strips and contraction in the rest. Contractions produced by histamine, 2-methylhistamine and 4-methylhistamine were selectively abolished by mepyramine. Burimamide antagonised the relaxant effect of histamine and of 4-methylhistamine. Corpus cavernosa muscle of the human penis has both histamine Hi-and H2-receptors. Histamine receptors
4-Methylhistamine
Human penis
1. I n t r o d u c t i o n H i s t a m i n e c o n t r a c t s t h e r e t r a c t o r penis muscle o f t h e d o g ( B o t t a z i , 1 9 1 6 ; L u d u e n a and Grigas, 1 9 6 6 ) , bull (Klinge, 1 9 7 0 ) and o x ( A m b a c h e e t al., 1 9 7 5 ) . T h e p r e s e n c e o f hista m i n e in t h e m a m m a l i a n penis has also b e e n r e p o r t e d . T h e r a b b i t erectile penile tissue contains m o r e h i s t a m i n e t h a n adrenaline, noradrenaline, a c e t y l c h o l i n e or 5 - h y d r o x y t r y p t amine (Penttil~i a n d Vartiainen, 1964). W h e t h e r h i s t a m i n e is p r e s e n t in the h u m a n penis and w h e t h e r it has any a c t i o n o n t h e s m o o t h muscle o f t h e h u m a n penis is n o t k n o w n . T h e p r e s e n t s t u d y was u n d e r t a k e n t o s t u d y some p h a r m a c o l o g i c a l actions o f histamine o n s m o o t h muscle o f t h e h u m a n penis.
2. Materials and m e t h o d s Fresh, m a c r o s c o p i c a l l y n o r m a l , h u m a n penes were o b t a i n e d f r o m transsexual p a t i e n t s u n d e r g o i n g sex change o p e r a t i o n . T h e e n t i r e penis was r e m o v e d and i m m e d i a t e l y transf e r r e d t o t h e l a b o r a t o r y in K r e b s - - H e n s e l e i t
Histamine
Corpus cavernosa
2-Methylhistamine
solution. L o n g i t u d i n a l muscles o f the c o r p u s c a v e m o s a (c.c.) were dissected into strips 2--3 m m wide and 3 cm long. T h e y were m o u n t e d in 20 ml organ baths c o n t a i n i n g K r e b s - - H e n seleit s o l u t i o n o f the following c o m p o s i t i o n (g/l) : s o d i u m chloride 6.74; potassium chloride 0.35; calcium chloride ( 2 H 2 0 ) 0.26; potassium d i h y d r o g e n o r t h o p h o s p h a t e 0.16; m a g n e s i u m sulphate ( 7 H 2 0 ) 0 . 2 8 7 ; glucose 1.54; s o d i u m b i c a r b o n a t e 1.86; d i s o d i u m E D T A 0.01. T h e s o l u t i o n was m a i n t a i n e d at 37°C and aerated with 5% c a r b o n d i o x i d e in o x y g e n (pH = 7.4). T e n s i o n (2 g) was applied t o the muscle strips and 1 h equilibration p e r i o d was t h e n allowed. During this t i m e the tension decreased and stabilised at 1--1.5 g. C o n t r a c t i o n and r e l a x a t i o n were r e c o r d e d isometrically using a f o r c e d i s p l a c e m e n t transd u c e r c o n n e c t e d t o a r e c o r d e r . A drug cont a c t t i m e o f 5--10 min and a cycle t i m e o f 20 min were used f o r histamine, 2 - m e t h y l h i s t amine, 4 - m e t h y l h i s t a m i n e and prostagiandin F2~. Adrenaline, n o r a d r e n a l i n e and isoprenaline r e q u i r e d a c o n t a c t t i m e o f 3.5 min and a cycle time o f 10 min. Whenever the antago-
262
P.G. ADAIKAN, S.M.M. KARIM
nists were used they were added to the tissue bath 1 min before addition of the agonists. The following drugs were used: histamine dihydrochloride (Merck); 2-methylhistamine dihydrochloride (SKF); 4-methylhistamine dihydrochloride (SKF); adrenaline bitartrate (Sigma); noradrenaline bitartrate (Sigma); prostaglandin F2~ (Up john); burimamide (SKF); propranolol (I.C.I.); phentolamine (Ciba AG); polyphloretin phosphate (AB Leo). All drugs were prepared in 0.9% sodium chloride solution.
3. Results
The effect of 2-methylhistamine was studied in 9 corpus cavernosa strips from 6 penes. All responded by contractions. Out of total of 15 strips from 6 penes, 4-methylhistamine produced contractions in 5, relaxation in 9 and a contraction followed by relaxation in 1 (table 1).
3.2. Threshold doses The threshold doses of histamine and its two m e t h y l analogues for contracting or relaxing the corpus cavernosa muscle are shown in table 1.
3.3. Effect of histamine Hi-receptor antagonist
A total of 77 strips from 27 penes were studied. Reproducible responses to drugs could be obtained with the penile tissue for more than 12 h.
3.1. Types o f responses to histamine, 2-methylhistamine and 4-methylhistamine The effect of histamine was studied in a total of 53 muscle strips of corpus cavernosa from 15 penes. Histamine produced three types of effect: contraction, relaxation or a contraction followed by a relaxation (fig. 1). Strips from the same penis usually produced the same type of response. Out of the 53 strips form 15 penes, histamine produced relaxation in 15 (28.3%), contractions in 33 (62.3%) and contraction followed by relaxation in 5 (9.4%).
The contractions of the corpus cavernosa produced by histamine and 2-methylhistamine were selectively abolished by mepyramine at a concentration of 4--8 ng/ml. Mepyramine in a concentration of up to 400 ng/ ml did not modify the contractions produced by prostaglandin F2~ or adrenaline. In the presence of high concentrations of mepyramine (400 ng/ml) the effect of histamine was reversed, i.e. doses that previously produced contractions of the tissue, now had a relaxant effect (fig. 2). No such reversal was observed with 2-methylhistamine. The effect of mepyramine was also studied in four strips in which histamine produced a relaxation. At concentrations of 4--400 ng/ ml mepyramine did not modify the relaxant effect of histamine.
3.4. Effect of histamine H2 receptor antagonist
Hist
•
Fig. 1. T y p i c a l r e s p o n s e s o f t h e h u m a n nosa muscle strips to histamine.
corpus caver-
The effect of burimamide, a histamine H2receptor antagonist was studied in five strips of corpus cavernosa muscle in which histamine and 4-methylhistamine produced contractions and on another five strips which were relaxed by histamine and 4-methylhistamine. Burimamide (0.2--0.8 pg/ml) potentiated
H I S T A M I N E R E C E P T O R S IN H U M A N P E N I S
263
TABLE 1 Percentage distribution of types of responses and threshold concentration of histamine and methylhistamines on c o r p u s c a v e r n o s a muscle o f h u m a n penis. Drug
No. o f penes
Histamine
15
Total No. o f strips
Contraction
53
33
62.3
No.
%
Relaxation
Biphasic
Threshold dose (ng/ml)
No.
%
Threshold dose (ng/ml)
No.
%
Threshold dose (ng/ml)
1 1 2 +_ 24 1
15
28.3
7 1 6 +- 3 3 0
5
9.4
4 0 0 -+ 87
.
6.7
2
2-Me h i s t a m i n e
6
9
9
100.0
2 5 0 +- 58
4-Me h i s t a m i n e
6
15
5
33.3
9 1 2 +- 5 7 0
. 9
60.0
.
. 6 3 4 _+ 2 1 0
.
. 1
1 +S.E.M. 2 20 n g / m l c o n t r a c t e d ; 1 0 0 n g / m l relaxed.
the contractions of the corpus cavernosa produced by histamine and 4-methylhistamine. This effect of burimamide could be reversed by changing the bathing fluid (fig. 3). The relaxant effect of histamine and 4methylhistamine was blocked by burimamide (0.8--3.2 pg/ml). In the presence of a higher concentration of burimamide (6.4pg/ml), doses of histamine and 4-methylhistamine which had previously relaxed the muscle now produced contractions. This reversed (contractile) effect of histamine was blocked by mepyramine (40 ng/ml) (fig. 4).
4ng/ml Tension ~
•
Nepyrclmlne - -
3.5. Other antagonists Phentolamine (0.4 pg/ml) selectively antagonised the contractions of the corpus cavernosa which were produced by adrenaline (40 ng/ml) and polyphloretin phosphate (40 pg/ ml) antagonised those produced by prostaglandin F2~ (100ng/ml). Contractions produced by histamine and 2-methylhistamine were not affected by these antagonists. Isoprenaline (70 ng/ml) relaxed the strips of corpus cavernosa muscle. This effect of isoprenaline was blocked by propranolol (0.4
~
5rain
,~.
•
o
•
o
~-
o Adr
• Hist
• Hist
/,OOng/ml
t,,lepyromine -
o Adr
-
I
• Hist
o Adr
• H~st
Fig. 2. E f f e c t of m e p y r a m i n e (4 n g / m l a n d 4 0 0 n g / m l - - d i f f e r e n t strips) o n h i s t a m i n e (o Hist, 4 0 0 n g / m l ) a n d a d r e n a l i n e (© Adr, 16 n g / m l ) i n d u c e d c o n t r a c t i o n s o f c o r p u s c a v e r n o s a m u s c l e strips o f h u m a n penis.
264
P.G. A D A I K A N , S.M.M. K A R I M
I
c ,mr~o "
5 ml,, ~ m
/
recover} "
I
10
m~n
35-
15
•
• /
/ o~/
/
•
o~,
I
•
•
•
•
o~
Bur~rnamlde ~/ug/m~ }
Fig. 3. P o t e n t i a t i o n b y b u r i m a m i d e o f r e p e a t e d doses o f h i s t a m i n e i n d u c e d (o Hist, 4 0 0 n g / m l ) c o n t r a c t i o n s of c o r p u s c a v e r n o s a muscle of h u m a n penis.
pg/ml). Doses of up to 3.2 pg/ml propranolol did n o t have any effect on the relaxant effects of histamine or 4-methylhistamine.
4. Discussion To our knowledge, studies on pharmacological effects of drugs on the h u m a n penis have so far not been reported, possibly because of the difficulty in obtaining the material. Such studies could prove useful in studying the physiology of h u m a n penile erection and ejaculation, and in evaluating the possible roles of naturally occurring substances in these processes. Material obtained from sex change operations in transsexual subjects provides an ideal opportunity to investigate the effect of drugs on the human penis. In this first investigation, we have studied the effects of histamine on the corpus cavernosa muscle of the h u m a n penis. The presence of histamine in high amounts in the rabbit penis (Penttil~i and Vartainen, 1964) and the contractile effect reported for this c o m p o u n d on the isolated retractor penis muscle of the dog (Bottazi, 1916; L u d u e n a and Grigas, 1966), bull (Klinge, 1970) and ox (Ambache et al., 1975) make this study of particular interest. Histamine caused contraction, relaxation or a biphasic effect (contraction followed by relaxation) in the corpus cavernosa muscle of the human penis. The stimulant action of histamine was selectively antagonized by mepyramine, a histamine H~-receptor antagonist but not by other drugs e.g. polyphloretin
Burlmcmlde 0 8,ucJ/ml
Burimomide 3 2 ug/ml
Burimamide
i'~epy ro m i n e
Fig. 4. E f f e c t o f b u r i m a m i d e o n t h e r e l a x a n t e f f e c t o f h i s t a m i n e o n c o r p u s c a v e r n o s a m u s c l e o f h u m a n penis ( e Hist, 4 0 0 ng/ml).
phosphate (a prostaglandin antagonist) or phentolamine (an a-adrenoreceptor blocker). The corpus cavernosa was also contracted by 2-methylhistamine which is known to stimulate mainly Hi-receptors (Black et al., 1972) and this effect was also selectively antagonised by mepyramine. The relaxant action of histamine was selectively blocked by burimamide, a selective H2-receptor antagonist, but not affected by propranolol (a ~-adrenoreceptor blocker). The results thus show that the corpus cavernosa muscle of the human penis contains both histamine H1- and H~-receptors. Although muscle strips from different penes usually respond to histamine by a contraction or a relaxation, it is likely that all penes possess both H1- and H2-receptors, and that the responses depend upon the relative proportion of these receptors. On a penis muscle which responded by a contraction (Hi-receptors), burimamide potentiated the contractile effect of histamine, presumably by blocking the relaxing action on H~-receptors which may have been limiting the stimulating action of histamine. Similar potentiation of stimulant action of histamine with burimamide has been reported to occur with the isolated guinea pig ileum and d u o d e n u m (Bareicha and Rocha e Silva, 1975). Blocking the H~-receptors of the penile muscle (which responds to histamine by a contraction) with mepyramine produces a reversal of effect i.e. a relaxation. This relaxant effect can be blocked by the H2receptor antagonist, burimamide.
HISTAMINE RECEPTORS IN HUMAN PENIS C o n v e r s e l y , tissues t h a t r e s p o n d t o hista m i n e b y a r e l a x a t i o n , are capable o f cont r a c t i n g with t h e same dose o f h i s t a m i n e w h e n the r e l a x a n t H2-receptors are b l o c k e d with b u r i m a m i d e . T h e ensuing c o n t r a c t i o n s can be b l o c k e d with t h e H i - r e c e p t o r b l o c k e r , mepyramine. Whether the effect of histamine on t h e penis is o f physiological i m p o r t a n c e is not known. T h e r e t r a c t o r penis muscle o f d o g and bull possesses post-ganglionic i n h i b i t o r y nerves ( L a n g l e y a n d A n d e r s o n , 1 8 9 5 ) with atropineresistance transmission. L u d u e n a and Grigas (1966, 1972) showed that the stimulation of sacral p a r a s y m p a t h e t i c fibres w h i c h p r o d u c e s r e l a x a t i o n o f the r e t r a c t o r penis muscle o f d o g , is n o t cholinergic or purinergic. R e c e n t l y A m b a c h e et al. ( 1 9 7 5 ) have r e p o r t e d t h a t t h e r e l a x a t i o n o f t r a n s m u r a l l y s t i m u l a t e d isolated steer r e t r a c t o r penis was n o t a f f e c t e d b y mep y r a m i n e o r b u r i m a m i d e . H o w e v e r , it is n o t e w o r t h y that histamine produces only c o n t r a c t i o n in the r e t r a c t o r penis muscle o f d o g , steer and bull (Bottazi, 1 9 1 6 ; L u d u e n a and Grigas, 1 9 6 6 , 1 9 7 2 ; Klinge, 1 9 7 0 and A m b a c h e et al., 1 9 7 5 ) . C o r p u s c a v e r n o s a and c o r p u s s p o n g i o s a muscles o f h u m a n penis possess b o t h i n h i b i t o r y and e x c i t a t o r y hista m i n e r e c e p t o r s . T h e possibility o f h i s t a m i n e i n v o l v e m e n t in p o s t g a n g l i o n i c i n h i b i t o r y nerve transmission t o h u m a n penile muscle c a n n o t t h e r e f o r e be ruled o u t . This possibility is n o w u n d e r investigation.
265 Acknowledgements We are grateful to Professor S.S. Ratnam for providing the surgical materials and to Miss Lo Pia Yong and Miss Tai Mei Yoon for technical assistance. The work was carried out under research grants from The Lee Foundation, Singapore and the Singapore Turf Club. References Ambache, N., S.W. Killick and M. Aboo Zar, 1975, Extraction from ox retractor penis of an inhibitory substance which mimics its atropine-resistant neurogenic relaxation, Brit. J. Pharmacol. 54,409. Bareicha, I. and M. Rocha e Silva, 1975, Occurrence of H2-receptors for histamine in the guinea pig intestine, Biochem. Pharmacol. 24, 1215. Black, J.W., W.A.M. Duncan, C.J. Gurant, C.R. Canellin and E.M. Parsons, 1972, Definition and antagonism of histamine H2-receptors, Nature (London) 236,395. Bottazi, F., 1916, Recherches sur Le 'M. retractor penis' et sur d'autres preparations musculaires lisses, Arch. Ital. Biol. 65,265. Klinge, E., 1970, The effect of some substances on the isolated bull retractor penis muscle, Acta. Physiol. Scand. 78,280. Langley, J.N. and H.K. Anderson, 1895, The innervation of the pelvic and adjoining viscera. Pt. III. The external generative organs, J. Physiol., 19, 85. Luduena, F.P. and E.O. Grigas, 1966, Pharmacological study of autonomic innervation of dog retractor penis, Amer. J. Physiol. 210,435. Luduena, F.P. and E.O. Grigas, 1972, Effect of some biological substances on the dog retractor penis in vitro, Arch. Intern. Pharmacodyn. 196,269. Penttil~, O. and A. Vartiainen, 1964, Acetylcholine, histamine, 5-hydroxytryptamime and catecholamine contents of mammalian penile erectile and urethral tissue, Acta Pharmacol. (Khb). 21, 145.
