Stimulation of growth hormone (GH) and somatomedin C in idiopathic GH-deficient subjects by intermittent pulsatile administration of synthetic human pancreatic tumor GH-releasing factor.

After initial challenges with vehicle alone and then 10 micrograms/kg human pancreatic tumor GH-releasing factor (hpGRF)-40, six adult subjects who had presented in childhood with idiopathic GH deficiency were given 0.33 micrograms/kg hpGRF-40, iv, every 3 h for 5 days. Serum GH levels were monitored daily for 90 min after the 0800 h doses of 0.33 micrograms/kg hpGRF-40, and serum somatomedin C was measured at 0800 and 2000 h. In addition, plasma levels of cholesterol, high density lipoprotein cholesterol, and triglycerides were measured daily at 0800 h. Three hours after the last 0.33 micrograms/kg dose, all subjects were rechallenged with 10 micrograms/kg hpGRF-40. In response to the initial 10 micrograms/kg challenge with hpGRF-40, and although serum GH levels rose in two of six subjects, the mean maximum GH level achieved was no different from that after treatment with vehicle alone. Within 12 h after initiation of the intermittent administration of hpGRF-40, mean +/- SEM serum somatomedin C had risen by 0.1 +/- 0.05 U/ml, and at the end of the 5-day period, had increased from 0.24 +/- 0.07 to 0.78 +/- 0.32 U/ml. In response to the second challenge with 10 micrograms/kg hpGRF-40, serum GH levels rose in three of the four subjects who initially failed to respond or had a less than 1 ng/ml GH response. The increase in serum GH was greater in one of the two subjects who had responded to the first dose. In addition, unlike the first dose, the mean maximal serum GH level achieved in response to the second 10 micrograms/kg dose of hpGRF-40 was higher than that in response to vehicle (P = 0.031). Although there was no statistically significant change during the 5-day period, in plasma cholesterol, high density lipoprotein cholesterol, or triglycerides, the latter exhibited a trend toward increased levels. Our preliminary data show that 5 days of intermittent hpGRF-40 administration augment GH secretion in some adults with GH deficiency, suggesting that somatotropes are present in idiopathic GH deficiency and may be primed by hpGRF-40. The rise in serum somatomedin C to normal levels after multiple injections of hpGRF-40 is encouraging, since circulating levels of somatomedin C may be more important than the increase in immunoreactive GH levels as an index of response for induction of linear growth. The demonstration of biological effects of hpGRF-40 in all six subjects without any serious adverse effects suggests that hpGRF-40 has promise in the treatment of GH deficiency.