ISTITUTO DI CLINICA MEDICA GENERALE E TERAPIA MEDICA DELL'UNIVERSITA DI SIENA DOPAMINERGIC STIMULATION OF H G H IN DIABETES MELLITUS AND IN OBESITY GIORGIO GRAGNOLI

VINCENZOPALAZZUOLI

ITALO TANGANELLI

ROBERTOFAVILLI

GIOVANNA MIGLIARESE

Many authors have studied the behavior of growth hormone in diabetes mellitus, in order to contribute to the knowledge on the role of this hormone in diabetic angiopathy 11. ~4. is. However, research carried out to date has not led to any definite conclusions. In fact, in every clinical form of diabetes, some authors have found human growth hormone ( H G H ) to be within the normal range, others have found increased, and others still decreased levels a" ~8.21. In obesity, on the other hand, the deficit in H G H secretion 1~ has been confirmed by numerous case studies and in relation to different types of stimulation i. 19. 20 However, at present these phenomena have not been fully clarified, owing to the difficulty of studying and evaluating the complex metabolic and neuroendocrinological mechanisms involved in the secretion of somatotropin. Recently, the importance of dopaminergic mediation in the maintenance of H G H homeostasis has been demonstrated 5. 4. 0; thus, the hypothesis can be suggested that the particular behavior of this hormone, which has been demostrated in obesity and in diabetes mellitus, may also be related to an abnormal sensitivity of the hypothalamic receptors, or to an alteration in the availability of neurotransmitters at the level of the structures which control its secretion. A contribution to the solution of this problem may come from a study of the variations in somatotropin, in relation to dopaminergic stimulation by i.v. administration of L-Dopa. MATERIALS A N D METHODS

Three ~oups of patients were studied. The first included 6 male and 2 female controls, aged 20 to 62, who were free from endocrine or metabolic disease. The second group included 8 diabetics, 5 male and 3 female, aged 38 to 68, with normal weight and metabolic balance, who had been undergoing insulin therapy for some time, and were suffering from Key-words: Diabetes mellitus; Essential obesity; Growth hormone inhibiting [actor; Growth hormone releasing [actor; Human growth hormone; L-Dopa. Received: October 27, 1975. Acta diabet, lat. 14, 137, 1977. 137

DOPAi~ItNERGIC STID4ULATION OF HGH IN DIABETES M E L L I T U S AND IN O B E S I T Y

stage II and III retinopathy. The third group included 9 patients, 5 female and 4 male, aged 19 to 57, suffering from essential obesity, with body weight at least 3098 above normal. At the time of the experiment, all subjects had been on a balanced, normal-calorie diet for 6 days; insulin therapy had been withheld in the diabetics from 18~° the previous evening; there were no serious alterations in the acid-base balance, however. In all cases, the pattern of blood sugar and HGH plasma levels was studied in basal conditions and 15, 30, 45, 60 and 90 rain after rapid infusion of L-Dopa, at the dosage

L - Dopa

16]

*

'

T

T II I\

\

104

T/

-S 6J

/

\\

\ \

\

\

// // i

4!

\T

1

~"

901

.... @

-3b

-;s

6

;s

( Ogoo) O-----O

Fig.

I -

\

3'0

k

(I0 oo)

rain

HGH

;

6o

•

glucose

Blood glucose and HGH plasma levels (~ ± SEM) in control subjects after i,v.

L-Dopa infusion.

time (rain)

* p < 0.05

glucose ( mg/lO0 ml)

HGH

( ng/ml )

--30

81 ± 4.5

3.04 ± 0.81

0

83 ± 5.1

2.95 ± 0.73

15

88 ± 4.0

3.84 ± 0.88

30

83 ± 6.6

8.01 4- 1.85 *

45

86 _ 6.1

13.47 4- 2.56 **

60

78 ± 6.3

14.2

90

81 ± 5.4

4- 3,40 **

5.4 + 1.20

** p < 0.005

Table I - Blood glucose and HGH plasma values (~ +__SE/Vl) in control subjects after i.v.

L-Dopa infusion.

138

G. GRAGNOLI~ V. PALAZZUOLI, R. FAVILLI~ I, TANGANELLI, G. MIGLIARESE

of 1.5 m g / k g of body wright, The drug was administered over a period of i 0 min and none of the subjects suffered nausea or showed other signs of intolerance, or significant variations in blood pressure during the experiment. Gtycemic levels were measured by B~OWN's method3; H G H was assayed radioimmunologieally *a using a CEA-IRE-Sorin (Saluggia) kit. Statistical analysis of the results within ~ o u p s was performed using Student's t-test. Comparisons between groups were made using Tukey's test.

L - Dopa

10 l 8 ¸

, //

.....

0J 90 (09oo) q l ~ - - - - - e HGH

rain H

Fig. 2 - Blood glucose and H G H plasma levels (,~ ±

(10oo) glucose

SEM) in diabetic subjects after i.v.

L-Dopa infusion.

* p < 0.05

time (rain)

glucose (rag/100 ml )

HGH (ng/ml )

--30

-189 4. 12.8

t.88 4. 0.33

0

184 ± 7.5

1.95 4. 0.36

15

202 ± 12,2

2.66 + 0.55

30

192 4- 7.8

6.75 4. 0.66 **

45

192 4. 9.6

5.90 + 0.99 *

60

190 4. 11.2

5.07 + 0,8t *

174 4. 9,2

2,38 + 0,55

** p < 0.001

T a b l e 2 - Blood glucose and H G H plasma vatues (~ ± SEM) in diabetic subiects after i.v. L-Dopa infusion.

139

DOPAMINERGIC STIMULATION OF HGH IN DIABETES MELLITUS AND IN OBESIT~f

RESULTS Glycemic values in the group of control subjects (fig. 1, tab. 1) ranged between 71 and 90 rag/100 ml and did not show significant variation (p 0.05) after L-Dopa loading. In basal conditions, HGH was 3.04 +___0.81 ng/mi. After infusion of the drug, HGH levels increased, and 45 and 60 rain after L-Dopa administration plasma levels of 13.47 ± 2.56 and 14.2 _4- 3.4 ng/ml were found, which were statistically higher (p ~ 0.005 than those found in fasting patients.

~27 d

L - Dopa

1

oo! 80 J

-s~

6

-;~

;5

a,-----o

3'o

4'5

rain

(09°°) HGH

•

6'o

7s

9'o

(10oo) • glucose

Fig. 3 - Blood glucose and HGH plasma levels (:~ + SEM) in obese subjects after i.v.

L-Dopa infusion.

time

* p < 0.05

HGH

(mg/lO0ml)

--30

89.8 + 6.32

0

83.2 ± 3.86

1.05 + 0.28

15

90.6 _+ 4.44

1.32 + 027

30

95.2 4- 6.86

3.12 + 0,67 *

45

87.7 ± 6.45

4.29 + 0.72 **

60

91.3 _+ 7.11

2.95 4- 0.65 *

90

90.7 J: 5.84

1.25 4- 026

(nglml) 1.06 + 0.30

** p < 0.005

Table 3 - Blood glucose and HGH L-Dopa infusion.

140

gltmose

(mia)

p l a s m a v a l u e s (~ ± S E M ) i n o b e s e s u b j e c t s a f t e r i.v.

G. GRAGNOLI, V. PALAZZUOLI, R. FAVILLI, I. TANGANELLI, G. MIGLIARESE

In the diabetics (fig. 2, tab. 2), whose insulin therapy had been withheld, as mentioned above, from 1800 the previous evening, blood sugar levels were 189 ~ 12.8 rag/100 ml at the beginning of the experiment and did not show statisticatly significant differences (p > 0.05) after administration of the drug. In this group, too, H G H levels, which were within normal limits at the start of the experiment, showed a progressive increase after L-Dopa infusion. However, during the observation period, H G H plasma levels never exceeded 10 ng/ml in any of the cases studied. The peak (6.75 i 0.66 ng/ml) was not only dearly lower (p < 0.05) but also occurred 30 rain earlier than in the controls; this made the differences between the two groups 45 and 60 rain after the i.v. load of the drug even more obvious (tab. 4). In obese subjects (fig. 3, tab. 3) the glycemic levels, which were within normal limits at the beginning of the experiment, did not show any significant variation in response to the L-Dopa stimulus (p > 0.05).

glucose time

Tukey

diabetics VS

VS

~S

( rain )

test

controls

controls

obese

diabetics obese

--30

64

108 *

8

I00

0

86

101 *

0

101

15

98

114 *

2

112

30

76

109 *

12

97 *

45

75

106 *

1

105 *

60

88

112 *

13

99*

90

62

93 *

9

84 *

*

HGH time

Tukey

controls V$

~2.~

VS

(rain)

test

diabetics

controls obese

diabetics obese

--30

1,57

1.16

1.98 *

0.82

0

I25

1.00

1.90

0.90

15

1.28

118

2,25 *

1.34 *

30

2.84

1.26

4.89 *

3.63 *

45

3.87

7.57 *

9.18 *

1.61

60

6.84

9.13 *

11.25 *

2.12

90

3.88

3.02

4.1.5 *

1.13

* p < 0.05

Table 4 - Statistical analysis, according to Tukey's test for muhiple comparisons, of glucose and HGH values found in the groups of subjects examined in basal conditions and after i.v. L-Dopa infusion.

141

DOPMVIINERGIC STIMULATION OF HGH IN DIABETES MELLITUS AND IN OBESIT'* ~

H G H plasma levels were found to be lower than those of the controls (p < 0.05) in basal conditions, increasing steadily after infusion of L-Dopa. However, the peak which was reached 45 min after the end of the infusion was never found to exceed 6 ng/ml and was significantly lower than in the control and diabetic groups (p < 0.05). DISCUSSION Our studies have shown that in diabetics and in obese subjects tlae i.v. administration of L-Dopa causes a less marked H G H increase than in control subjects (tab. 4). Statistical analysis of the results also demonstrated t h a t in simple obesity the H G H increase induced by infusion of the drug i s even smaller than in patients with insulin-dependent diabetes meUitus (tab. 4 ). If we accept MIMS's theory 1., according to which, in addition to adrenergic receptors in the hypothalamus, there are chemoceptors re~malating t h e secretion of H G H , the phenomenon we have demonstrated in diabetics could be interpreted on the basis of a reduced GRF response to L-Dopa stimulation, secondary to raised glycemic leveIs. This metabolic situation could have modified the response of the ~-adrenergic receptor to dopaminergic stimulation as a result of changes of the chemoceptor. In obese subjects, we also found a reduced H G H response to g-Dopa infusion. This behavior has been found in essential obesity using various tests, such as hypoglycemia, oral administration of L-Dopa, infusion of arginine, adrenaline and propranolol, which normally elicit a significant increase in H G H 1. 8. 6. z0. On the basis of our data it can be, however, maintained that this is not related to reduced dopamine availability at the level of the hypothalamic structures controlling H G H secretion. It can therefore be suggested that in GRF secreting neurons, the dopaminergic effect is lost through metabolic factors which are in excess in obese subjects and which, in particular experimental conditions, can 'override the neural signals' 7. O n the other hand, it cannot be excluded that the diminished secretion of somatotropin may be due to excessive GIF production, also capable of inhibiting the HGH-stimulating action of L-Dopa 17. Therefore, at present a definite contribution to the interpretation of the diencephalo-hypophyseal alterations involved in essential obesity can o n l y be expected from the radioimmunoassay of factors inhibiting and stimulating the liberation of HGH. SUMMARY The behavior of HGH in basal conditions and after L-Dopa infusion was studied in a group of patients with diabetic retinopathy, in 9 obese and 8 control subjects. In both diabetics and obese subjects, increases found in HGH plasma levels after administration of the drug were slighter than in the controls. On the basis of these results it can be concluded that in diabetics the availability of energetic substrates may modify the HGH response to the L-Dopa stimulus. In obesity, the possibility is considered of a reversible defect in the sensitivity of the dopaminergicreceptors, induced by metabolic and endocrine factors. REFERENCES I) BECKP., KOUMaS J. H. T., WINTERLINGC.A.: Studies of Insulin and Growth Hor. mone Secretion in Human Obesity - J. Lab. din. Med. 64, 654, 1964. 142

G. GRAGNOLt, V. PALAZZUOLI, R. FAVILL[~ I. TANGANELLI, G. MIGLIARESE

2) BOYDA.E. III, LEBOVITZH. E., PI:EIFFERJ. 13.: Stimulation of Human-Growth-Hormone Secretion by L-Dopa - New Engl. J. Med. 283, 1425, 1970. 3) BRowN M.E.: Ultra-Micro Sugar Detemfinations Using 2,9-DimethyI-l,10-Phenantoine Hypochloride (Necuproine) - Diabetes 10, 60, 1961. 4) CAVAamNIF., PZm~CCHIM., SCOTTIG., RaCGI U., PONTIZOLIA.E., B2u~AR.: Effect of L-Dopa Administration on Growth Hormone Secretion in Normal Subiects and Parkinsonian Patients - J. Endocr. 54, 425, 1972. 5) ET--KHODARYA.Z., BaLL M.F., SaXlN B., CANARYJ.J.: The Effect of Weight Loss on the Growth Hormone Response to ArNnine Infusion in Obesity - J. din. Endocr. 32, 42, 1971. 6) FINGEm-IUTM., KalEGER D.T.: Plasma Growth Hormone Response to bDopa in Obese Subiects - Metabolism 23, 267, 1974. 7) Fzova~aN L.A., STAC'~em~M.E.: Neuropharmacologie Control of Neuroendocrine Function in Man -Metabolism 24, 21i, 1975. 8) t-L~NsENAa. P.: Abnormal Serum GH Response to Exercise in Maturity-Onset Diabetics - Diabetes 22, 619, 1973. 9) K~SAL P.C., Bus~ J., TALLESTO.R., BUSE M.: The Effect of L-Dopa on Plasma Growth Hormone, Insulin and Thyroxine - J. clin. Endocr. 34, 99, 1972. 10) LEsso:v M. H., YOUNGS.M., GREENWOODF.C.: Gt'owth Hormone Secretion in Obese Subjects - Guy's Hosp. Rep. t15, 65, 1966. 11) L~BmCK K., CHRISTENS~ N. J., JENSEN V.A., JOVaNSEN K., OLS~N T. S., HANSm'¢ Aa. P., ORsI.:ov H., OST~rdrZ R.: Diabetes, Diabetic Angiopathy and Growth Hormone - Lancet 2, 13t, 1970. 12) MI,-as R.B., SCOTT C.L., MOImBE O.M., BETI~IJNE J.E. - Prevention of L-Dopa Induced Growth Hormone Stimulation by HyperNycemia - J. din. Endocr. 37, 660, 1973. 13) MOLINA:rTIG.M., MASSAZAF., STZU~vIIAE., PENNISI F., SCASSELLATIG.A., VANCHEZI L.: Radioimmunoassay of Human Growth Hormone - J. nucl. Biol. Med. 13, 26, 1969. 14) Muc~zo M., CREPALDIG., FEDELED., TIENGOA.: Growth Hormone Secretion in Diabetic Retinopathy - Acta diabet, lat. 10, 737, 1973. 15) POWELL E.D., F ~ T Z G.A., P~'~:BKINM.T., FIELD R.A.: Growth Hormone in Relation to Diabetic Retinopathy - New Engl. J. Med. 275, 922, 1966. 16) ROTHJ., GLmK S.M., YALOWR. S., BERSONS.A.: Secretion of Human Growth Hormone: PhysioloNc and Experimental Modification - Metabolism I2, 577, 1963. 17) SIBERT. M., VANI)EN~EXGG., YEN S. S.C.: Inhibition of Growth Hormone Release in Human by Somatostatin - J. clin. Endocr. 37, 632, 1973. 18) TCI-IOBROUTSKYG.: Plasma Growth Hormone Levels after Lunch in Diabetic and Non-Diabetic Subjects - Acta endocr. (Kbh.) 74, 67, 1973. 19) TClmBRotrrsKYG., ROSSELIN G., ASSAN R., FP,XYCHET P., DERo~r M.: Growth Hormone Secretion in Obese Subjects with and without Diabetes. Comparison with NonObese Patients - In: VAGUEJ. (Ed.): PhysiopathologT of Adipose Tissue. Excerpta Medica Foundation, Amsterdam, 1969; p. 269. 20) YALOWR. S., GLICK S.M., ROa'H J., BEI~SONS.A.: Plasma Insulin and Growth Hormone Leveis in Obesity and Diabetes - Ann. N. Y. Acad. Sci. I31,357, 1965. 21 ) YDE H.: The Immunoreaetive Growth Hormone in Serum from Patients with Various Types of Diabetes Mellitus - Acta endocr. (Kbh.) 64, 339, 1970.

Requests for reprints should be addressed to: GtOZGIO GRAGNOLI

Istituto di Clinica bfedica Generale e Terapia Medica ddl'Universit~ degti Studi di Siena Piazzetta della Selva, 7, 53100 Siena- Italy

143