[The effect of synthetic human pancreatic growth hormone-releasing factor (hpGRF-44) on serum growth hormone response in normal and obese subjects].

Synthetic human pancreatic growth hormone-releasing factor (hpGRF-44) was given by i.v. bolus injection to 15 normal non-obese and 32 obese subjects who were divided into two groups according to their ages--group A: young subjects, 20-50 yrs., and group B: old subjects, more than 60 yrs. In normal subjects, hpGRF-44 had no effect on the secretion of PRL, TSH, LH, FSH, IRI and cortisol. hpGRF-44 stimulated GH secretion selectively. However, the serum GH responses were different between the young and old groups, the peak GH levels being significantly higher in the young group than in the old group (20.1 +/- 4.2 vs. 7.5 +/- 1.6 ng/ml; group A vs. B; p less than 0.05). At the doses of 0.5, 1.0, 2.0 and 4.0 micrograms/kg B.W., the serum GH responses were similar in an individual subject. In young obese subjects, the peak GH levels to hgGRF-44, 1.0 microgram/kg B.W. were significantly lower than those in young normal subjects (4.3 +/- 0.6 vs. 20.1 +/- 4.2 ng/ml; obese vs. normal; p less than 0.01). In old subjects, the peak GH levels to hpGRF-44, 1.0 microgram/kg B.W. were similarly diminished in both normal and obese subjects. However, the integrated response of GH was significantly lower in obese subjects than in normal subjects (405.9 +/- 58.7 vs. 755.9 +/- 134.2 ng X min/ml; obese vs. normal; p less than 0.05). In 5 young obese subjects, regular insulin (RI) injection (0.15 U/kg B.W.) and arginine drip infusion (0.5 g/kg B.W.) alone, and simultaneous injection of hpGRF-44, 1.0 microgram/kg B.W. and RI, 0.15 U/kg B.W. were done. In these subjects, GH responses to RI or arginine infusion were diminished as in the case of hpGRF-44 administration, whereas the peak GH levels were higher in the RI stimulation. The combination of hpGRF-44 and RI partially restored GH response. (peak GH levels; 14.6 +/- 0.8 ng/ml). These results confirm the age difference of serum GH response to hpGRF-44 and also indicate that obese subjects show low or no response to hpGRF-44 administration. The fact that insulin hypoglycemia induced larger serum GH response that hpGRF-44 in obese subjects may suggest the existence of GH-releasing substances other than hpGRF-44.