Ectopic growth hormone releasing factor stimulates growth hormone release from human somatotroph adenomas in vitro

The effects of an ectopic growth hormone releasing factor (E-GHRF) from a carcinoid tumor were studied in three human GH-secreting pituitary adenomas in monolayer culture. GH release by the adenomas was stimulated by 55 +/- 10%, 57 +/- 8%, and 59 +/- 17% during a 4 h exposure to E-GHRF at concentrations of 3, 0.8, and 24 Units/ml, respectively. Two of the tumors also secreted prolactin (PRL) and in one, E-GHRF (0.8 Units/ml) stimulated PRL release by 48 +/- 8%. GH and PRL release were both suppressed by somatostatin (10(-8)M) in two of the adenomas. These results 1) demonstrate for the first time E-GHRF stimulation of GH release from human pituitary tissue in vitro, 2) support an etiologic role for E-GHRF in the development of acromegaly, and 3) indicate that GH-secreting adenomas retain the capability of responding to GHRF.