The Effect of Glucose on the Growth Hormone Response to Glucagon and Propranolol-Glucagon in Normal Subjects Clark

T. Sawin,

Cynthia

K. Silbert,

The mean (* SE) peak level of serum growth hormone (GH) after intramuscular injection of glucagon in ten normal adult men was 15.1 l 2.1 ng/ml; glucose infusion suppressed the mean peak GH to 9.6 f 3.7 u&ml ( p < 0.05). Pretreatment of eight of these subjects with propranolol caused a modest increase in the mean

and Marvin

L. Mitchell

jects the peak GH was suppressed but in three it was not. Conclusions: (1) The GH response after glucagon is usually due to a fall in serum glucose after the initial rise in serum glucose induced by glucagon. (2) Nevertheless, since glucose does not consistently inhibit the GH response after glucagon, a second mechanism probably exists by which glucagon stimulates GH secretion. (3) Glucose completely suppresses the propranolol-induced increase in the GH response to glucagon; an adrenergic mechanism may be involved in the control of GH secretion by glucose.

peak GH after glucagon (19.4 * 2.8 ng/ml) but did not improve the mean peak OH after glucagon when glucose was infused (8.7 f 2.8 r&ml). Individual analysis of the peak GH showed that glucose infusion did not uniformly suppress the peak GH after glucagon; in seven sub-

I

N NORMAL SUBJECTS the intramuscular or subcutaneous injection of glucagon’ causes a rise in serum growth- hormone (GH) in addition to the rise in serum glucose. The peak level of GH usually occurs 2-3 hr after the glucagon injection, a time when the level of serum glucose has fallen to normal. The sequence of events suggests that the fall in glucose might cause the rise in GH, since a fall in serum glucose can stimulate GH secretion even though overt hypoglycemia does not occur.’ If so, prevention of the fall in glucose should block the rise in serum GH. In addition, propranolol is known to enhance the GH response to glucagon.3 Therefore, we studied the effect of glucose infusion on the GH response to both glucagon and propranolol-glucagon in normal subjects. MATERIALS Ten normal

adult men, aged 18-25, intramuscularly

METHODS

were studied after an overnight

30 min. two basal blood samples were obtained was then injected

AND

and blood samples obtained

Serum was assayed for glucose using an Autoanalyzer each subject after an interval

fast. After

I5 min apart. One mg glucagon

of at least 2 days with

at 30, 60, 120,

and for GH’. the addition

g of glucose was infused

studies were repeated with the addition

From the Medical and the Departments

Service,

in each subject.

of propranolol

Tufts

University

of

180 min.

of an intravenous

in

infusion

of

for the subsequent

3 hr;

In eight of the ten subjects,

both

which was given (40 mg po) 2 hr before the

Boston Veterans Administralion

of Medicine,

150, and

The study was repeated

20% glucose beginning at the time of the glucagon injection and continuing a total of 200-240

a rest period

(Eli Lilly and Co.)

Hospital,

and Boston

State

University

Laboratory Schools

Insritule.

of Medicine,

Boston, Mass.

Received for

publicarion

April I, 1975.

Reprinr requests should be addressed to Clark Hospiral.

IS0 S. Huntingron

T. Sawin,

M.D.,

Boston

Veterans

Administration

Ave., Boston. Mass. 02130.

0 1975 by Grune & Stratton.

Inc.

Metabolism, Vol. 24, No. 9 (September), 1975

1009

1010

SAWIN, SILBERT,AND MITCHELL

glucagon injection in each study. For statistical purposes, values of GH greater than 25 ng/ml were treated as 25 ng/ml and values < 1 ng/ml were treated as 1 ng/ml; differences between means were analyzed using paired and unpaired t tests.6

RESULTS Serum

GH After Glucagon

The pattern of serum GH (mean values * SE at several points in time) and the mean peak GH after glucagon alone are shown in Fig. 1, IA. The peak GH after glucagon alone ranged from 6.2-25 ng/ml (Table 1). Glucose infusion prevented the serum glucose from rapidly returning to basal levels after the glucagon injection; while there was a moderate fall from the highest serum glucose during the infusion, the mean serum glucose was still 190 f 12 (SE) at the end of the study (Fig. 2A). The mean peak GH after glucagon was significantly suppressed by glucose (p < 0.01) (Table 1). However, suppression of the GH response was not uniform. On examining individual subjects, it was evident that the peak GH was suppressed in seven of the ten subjects (Fig. 1, IB; Fig. 3; Table 1) but not at all in the other three (Fig. 1, IC; Fig. 3; Table 1). There was no difference in glucose levels during glucose infusion when those whose GH was suppressed were compared with those whose GH was not suppressed nor was there any difference between the two groups in the peak GH after glucagon without glucose infusion.

3

5

IO -

es

-’ 0 (n=3)

IC

60

I20

180

Peak

KC

(II=31

0

60

120

180

Peak

M/NUTES POST GLUCAGCW Fig. 1. Serum GH levels (mean + SE) after glucagon (I) and propranolol-glucagon (II). (A) response in all subjects studied; (8) response with added glucose infusion in all subjects ruppressed by glucose; (C) rorponso with added glucose infusion in all subjects not suppressed by glucose.

1011

GLUCOSE

Table 1. Peak OH Values (ng/ml)

After Glucagon and Propmnolol-Glucagon With

And Without Glucose Infusion PropranololGlUCClQOll

Glucagon Propronolol-

and Subject

GhKag.Xl

GlUCOSe

GlUCagOlI

and GlUCOS.3

1

9.4

a.2

> 25.0

12.4

2

6.2

2.2

11.4

5.2

3

23.3

5.3

4

12.7

5.7

11.2

5

7.8

2.0

7.8

6

15.0

17.6

7

13.0

6.8

>25.0 -

8

18.4

4.0

>25.0

5.2

>25.0 -

23.0 -

9

>25.0

25.0

10

20.4

4.0

Mean

15.1

9.6*

2.1

SE *p < 0.01 verrvr glucagon

>25.0

2.4 2.0 1.0 16.8 -

19.4

3.7

0.7**

2.8

2.8

alone.

l*p < 0.01 versvspropranoloCglucagon

chne.

Serum GH After Propranolol-Glucagon

The mean peak GH was greater, though not significantly so (p > 0.05), after propranolol-glucagon than after glucagon alone (Fig. 1, IIA). Nevertheless, with propranolol pretreatment, the peak GH was clearly higher in five of the eight subjects; and the one subject with an equivocal response to glucagon alone (peak GH > 5 < 7 rig/ml) now had a normal response (peak GH > 7 ng/ml) (Table 1, Fig. 3). As before, glucose infusion prevented the serum glucose from returning to normal (Fig. 2B); the glucose levels during glucose infusion after propranolol-glucagon were not different than those found during glucose infusion after glucagon alone. Glucose infusion suppressed the mean peak GH after propranolol-glucagon (Table 1). The individual peak GH was suppressed by glucose in all eight subjects (Fig. 3, Table 1); however, the only subjects who still had a normal response, i.e., peak GH > 7 ng/ml, were the same three who continued to respond normally to glucagon alone when glucose was infused (Fig. 1, IIC; Fig. 3) while the serum GH was essentially completely suppressed in the other five subjects (Fig. 1, IIB). With glucose infusion, the mean peak

1R PROPRANaLOL-GLC(

1A. GLUCAGON 2

p

-z

I oGlucoseInfusion *No Glucose

400 t

(mean f SE) after glucagon injection with (0) and with-

treatment (n = with propranolol ment (n = 8).

10); (B) pmtreat-

60

(20

160

0

60

MNU TES POST GLUCAGON

120

180

SAWIN,

1012

4 GLUCAGON

SILBERT, AND MITCHELL

G. FWOPRANOLOLGLUCAGON

24

Fig. 3.

4 0

I

BEFORE GLUCOSE

I AFTER GLUCOSE

i BEFORE GLUCOSE

AFTER GLUCOSE

(A) Effect of glucose infusion on the

peak OH level after glucogon. (B) Effect of glucose infusion on the peak GH level after propmnolol-glucogon. Horizontal dashed lines indicate the limits of an equivocal peak GH level after glucagon in normal subjects; a higher level is considered normal and a lower level abnormal.

GH after propranolol-glucagon is the same as after glucagon thus glucose abolishes propranolol’s moderate enhancement sponse to glucagon.

alone (Table of the GH

1); re-

DISCUSSION

Limited previous data suggested that serum GH does not rise when glucose and glucagon were given together, 7-9 although one subject was noted to have a normal GH response to glucagon despite hyperglycemia.” Our results indicate that glucose suppresses the GH response to glucagon in most but not all normal subjects. Thus, in most subjects, the GH response may result primarily from a fall in serum glucose after the initial rise in serum glucose. However, glucagon must act through some other mechanism as well since the GH response was not suppressed by glucose in some subjects. That a second mechanism exists is also suggested by the fact that the rise in GH after a glucose load is generally not as consistent as that after glucagon injection despite a similar rise and fall in serum glucose.“-‘5 It appears that glucose can override this second mechanism in most but not all subjects. Propranolol is known to enhance the GH response to glucagon in some normal subject? as it did in most of the subjects studied here. Nevertheless. glucose suppressed the GH response to propranolol-glucagon to the same extent as it suppressed the response to glucagon alone. Thus, the propranolol-induced enhancement of the GH response to glucagon is uniformly abolished by glucose which suggests that an adrenergic mechanism may be involved in the control of GH secretion by glucose. The response of serum GH to other stimuli is variably affected by glucose. Glucose obviously would blunt the GH response to hypoglycemia induced by insulint6 or other means. However, the GH response to other stimuli normally associated with little or no change in serum glucose may or may not be blunted by glucose. The GH response to arginine and L-dopa is sometimes blunted by glucose’7-‘9 and sometimes not.‘9-23 Moderate elevation of serum glucose does not block the GH response to pyrogen,24*25 surgical stress,26 or sleep.27~28

GLUCOSE

1013

Whether or not the GH response to exercise is blunted by glucose depends on the severity of the exercise. 29 There appears to be no simple way to integrate the effect of changes in serum glucose with the effects of most of these agents on GH secretion. One gains the impression that these agents stimulate GH independently of changes in serum glucose but that glucose can sometimes override the stimulus. The GH response to glucagon appears, however, to be related both to a fall in serum glucose and to a mechanism independent of a fall in serum glucose. The enhancement of the GH response due to propranolol is suppressible by glucose; perhaps glucose suppresses GH secretion in part by acting at P-adrenergic sites. The mechanism independent of a fall in serum glucose is nevertheless usually suppressed by glucose in a manner reminiscent of the effect of glucose on the GH response to arginine, L-dopa, and exercise noted previously; the nature of this interaction is unknown.

REFERENCES 1. Mitchell ML, Byrne MJ, Sanchez Y. Sawin CT: Detection of growth-hormone deficiency. The glucagon stimulation test. New Engl J Med 282:539-541, 1970 2. Click SM: Hypoglycemic threshold for human growth hormone release. J Clin Endocrinol Metab 30:619-623, 1970 3. Mitchell ML, Suvunrungsi P, Sawin CT: Effect of propranolol on the response of serum growth hormone to glucagon. J Clin Endocrinol Metab 32:470-475, 1971 4. Hoffman WS: A rapid photoelectric method for the determination of glucose in blood and urine. J Biol Chem 120:51-55, 1937 5. Mitchell ML, Collins S, Byron J: Radioimmunoassay of growth hormone by enzyme partition. J Clin Endocrinol Metab 29:257-264, 1969 6. Bradford Hill A: Principles of Medical Statistics (ed 8). New York, Oxford University Press. 1966, p 146 7. Roth J, Glick SM. Yalow RS, Berson SA: Secretion of human growth hormone: physiologic and experimental modification. Metabolism 12:577-579, 1963 8. Mitchell ML, Byrne MJ, Silver J: Growthhormone release by glucagon. Lancet 1:289290, 1969 9. Eddy RL, Jones AL, Hirsch RM: Effect of exogenous glucagon on pituitary polypeptide hormone release. Metabolism 19:904-912, 1970 10. Spathis GS, Bloom SR, Jeffcoate WJ, Millar JGB, Kurtz A, Pyasena MRD, Smith JA, Nabarro JDN: Subcutaneous glucagon as a test of the ability of the pituitary to secrete

GH and ACTH. Clin Endocrinol 3:175-186, 1974 11. Street0 JM: Late post-glucose rise in plasma growth hormone as a test of pituitary function. J Clin Endocrinol Metab 31:84-85, 1970 12. Hunter WM. Clarke BF, Duncan LIP: Plasma growth hormone after an overnight fast and following glucose loading in healthy and diabetic subjects. Metabolism 15:596-607, 1966 13. Boden G, Soeldner JS, Steinke J, Thorn GW: Serum human growth hormone (HGH) response to IV glucose: Diagnosis of acromegsly in females and males. Metabolism 17:1-9, 1968 14. Misbin RI, Edgar PJ, Lockwood DH: Influence of adrenergic receptor stimulation on glucose-metabolism during starvation in man: Effects on circulating levels of insulin-growth hormone and free fatty acids. Metabolism 20: 544-554, 1971 15. Okada Y, Hibita T, lshitobi K, Wada M, Santo Y, Harada Y: Human growth hormone secretion after exercise and oral glucose administration in patients with short stature. J Clin Endocrinol Metab 34:1055-1058, 1972 16. Roth J, Glick SM, Yalow RS, Berson SA: The influence of blood glucose on the plasma concentration of growth hormone. Diabetes 13:3555361, 1964 17. Mims RB, Scott CL, Modebe OM, Bethune JE: Prevention of L-dopa-induced growth hormone stimulation by hyperglycemia. J Clin Endocrinol Metab 37:660-663, 1973 18. Burday SZ, Fine PH, Schalch DS: Growth hormone secretion in response to ar-

SAWIN,

1014

ginine infusion in normal and diabetic subjects: Relationship to blood glucose levels. J Lab Clin Med 7 1897-9 I I, 1968 19. Merimee TJ, Rabinowitz D, Fineberg SE: Arginine-initiated release of human growth hormone. Factors modifying the response in normal man. New Engl J Med 280:1434-1438. 1969 20. Boyd AE 111. Lebovitz HE, PfeiIIer JB: Stimulation of human-growth-hormone secretion by L-dopa. New Engl J Med 283:14251429. 1970 21. Boyd AE III, Lebovitz HE, Feldman JM: Endocrine function and glucose metabolism in patients with Parkinson’s disease and their alteration by L-dopa. J Clin Endocrinol Metab 33:8299837, 1971 22. Rabinowitz D. Merimee TJ. Burgess JA, Riggs L: Growth hormone and insulin release after arginine: Indifference to hyperglycemia and epinephrine. J Clin Endocrinol Metab 26: 1170-l 172, 1966 23. Tyson JE, Fiedler A: Hyperglycemia and arginine-initiated growth-hormone release during pregnancy. Obstet Gynecol 34:319-321. 1969

SILBERT,

AND MITCHELL

24. Greenwood FC, Landon J: Growth hormone secretion in response to stress in man. Nature

210:540-541.

1966

25. Kohler PO, O’Malley BW, Rayford PL, Lipsett MB, Odell WD: Effect of pyrogen on blood levels of pituitary trophic hormones. Observations of the usefulness of the growth hormone response in the detection of pituitary disease. J Clin Endocrinol Metab 27:219-226. 1967 26. Click SM. Roth J, Yalow RS. Berson SA: The regulation of growth hormone secretion. Ret Prog Horm Res 21:241 -283, 1965 27. Lucke C. Click SM: Experimental modification of the sleep-induced peak of growth hormone secretion. J Clin Endocrinol Metab 321729-736. 1971 28. Vanderlaan LG, Vanderlaan hormone release 897, 1970

WP, Parker DL. Rossman EF: Implications of growth in sleep. Metabolism 19:89 I

29. Hansen AP: Serum growth hormone response to exercise in non-obese and obese normal subjects, Stand J Clin Lab Invest 31: l75178, 1973