Human pancreatic growth hormone-releasing factor (hpGRF-44) in acromegaly before and after adenomectomy : modifications induced by somatostatin (GHRIH) infusion

The influence of human pancreatic growth hormone-releasing factor (hpGRF-44) on GH secretion was investigated in 15 patients with active acromegaly. Following the administration of hpGRF-44 (1 microgram/kg, iv) mean (+/- SE) serum GH level increased from 22.4 +/- 6.3 ng/ml to 42.9 +/- 8.2. ng/ml (peak, p less than 0.01). The pattern and the magnitude of the GH rises were widely variable and it was possible to identify three types of responses: in fact in 2 cases a very large serum GH rise, eight folds over baseline, was observed, in 7 patients a clear GH stimulation, two-three fold over baseline was noticed and in 6 patients no significant GH modifications were seen. No correlation was found between the response to hpGRF-44 and the existence of abnormal GH responses to dopamine infusion, TRH and dopamine-sulpiride test. In 5 acromegalic patients hpGRF-44 was injected again after transsphenoidal adenomectomy. The magnitude of serum GH response decreased in one hyperresponsive patient, increased in 2 previously unresponsive cases and did not change in the remaining cases. In 6 GH responsive patients hpGRF-44 was injected at 120 min during a 4 hour infusion of somatostatin (GHRIH, 3.33 micrograms/min). GHRIH infusion significantly suppressed GH levels in all the patients and blunted the hpGRF-44 stimulated GH increase. The different patterns of GH response to hpGRF-44 in acromegalic patients suggest a different sensitivity of the adenomatous somatotrophs and a possible contribution by normal GH-secreting cells to hpGRF-44 induced GH response.