Regulation of growth hormone and prolactin secretion in patients with acromegaly and/or excessive prolactin secretion

Reproducible changes in serum growth hormone (GH) concentrations in the majority of acromegalic patients following oral glucose, intravenous arginine and insulin induced hypoglycemia, and marked variation during the more subtle stimuli of a 24 hour observation period indicate that GH secretion, though quantitatively excessive, remains responsive to regulatory influences in these patients. Since at least some of these secretory stimuli are mediated through the hypothalamus, it is suggested that the primary defect in some acromegalic patients lies at the level of the hypothalamus rather than the pituitary. Reports of bioassayable GH releasing activity in the plasma of acromegalic patients are consistent with the hypothesis that excessive GH releasing factor production from the hypothalamus underlies GH hypersecretion in these acromegalic patients. Marked variation in the serum prolactin concentrations occurs during serial observation of patients with prolactin secreting pituitary tumors. In some of these patients, the serum prolactin levels are suppressed following L DOPA ingestion. Thus, there is considerable similarity between the patterns of GH and prolactin secretion in disorders characterized by pituitary tumors and excessive secretion of GH or of prolactin.