Effects of growth hormone-releasing factor on growth hormone secretion in acromegaly

Twenty-nine patients with acromegaly (8 untreated and 21 previously treated in various ways) and 16 normal men were given iv bolus doses of human pancreatic tumor GH-releasing factor (hpGRF-40). Twenty-five of the 29 patients responded to hpGRF-40 with elevations of plasma GH. The magnitude of the responses varied widely. Responses of untreated patients were generally similar to those of the normal subjects. Previously treated patients had a significantly lower response than normal individuals [change in GH, 7.5 +/- 1.8 vs. 42.0 +/- 11.0 ng/ml (mean +/- SEM); P less than 0.01], and 4 patients who had received radiation therapy failed to respond to hpGRF-40. There was no significant correlation between the magnitude of the response and patients' age, sex, baseline GH levels, GH responsiveness of TRH, or GH suppression after oral glucose administration. Patients studied both pre- and postoperatively were responsive to hpGRF-40 at all times tested, but the magnitude of the response decreased after successful surgical removal of the adenoma. Thus, most patients with treated or untreated acromegaly respond to hpGRF-40, but their responses do not clearly distinguish them from normal subjects. GH-releasing hormone testing is unlikely to replace other endocrine tests available for the diagnosis and evaluation of acromegaly.