Effect of vasoactive intestinal polypeptide on growth hormone secretion in perifused acromegalic pituitary adenoma...

The effects of vasoactive intestinal polypeptide (VIP), dopamine, and somatostatin (SRIF) on GH secretion were examined in vitro in perifused pituitary adenoma tissues obtained at surgery from seven patients with acromegaly. The perifusion of VIP at 5 x 10(-8) M resulted in a significant increase in effluent GH levels in five of the seven adenomas. A dose-related GH response was observed from 5 x 10(-9) to 5 x 10(-7) M VIP in two adenomas examined. SRIF at 5 x 10(-8) to 10(-7) M suppressed not only baseline secretion of GH but also inhibited GH rises elicited by VIP in six of the seven adenomas. Dopamine at 5 x 10(-7) to 5 x 10(-6) M decreased the baseline secretion of GH in six of the seven adenomas. In four of the six adenomas responsive to dopamine, dopamine suppressed VIP-induced GH release when perifused simultaneously. In the remaining two dopamine-sensitive adenomas in which VIP alone failed to affect GH release, the inhibition by dopamine of GH release was blocked by VIP perifused concomitantly with dopamine. Synthetic TRH or theophylline perifused at the end of the experiment stimulated GH release in all of the adenomas, indicating the viability of tumor cells throughout the study. These results suggest that VIP stimulates GH release by its direct action on pituitary adenoma cells of acromegalic patients and that VIP, SRIF, and dopamine interact at the pituitary level in modulating GH secretion from these adenomas.