Effect of Thyrotropin-Releasing Hormone and Bromoergocriptine on Growth Hormone and Prolactin Secretion in Perfused Pituitary Adenoma Tissues of Acromegaly

To determine the site of action of TRH and 2-brom-alpha-ergocriptine (CB154) on pituitary hormone release in acromegalic patients, the effect of these substances on GH and PRL secretion was examined in perfused pituitary adenoma tissues obtained at surgery from subjects with acromegaly. Relatively stable baseline secretion levels of GH and PRL were followed by an abrupt and marked discharge of the hormones after TRH infusion in all of the experiments. The pattern of GH response was essentially the same as that of PRL. Moreover, a dose-response relationship was obtained between the TRH concentrations infused and the magnitude of GH and PRL responses. The infusion of CB154, on the other hand, inhibited both GH and PRL secretion in three experiments performed on different adenoma tissues. This effect of CB154 was prompt and lasted for a long period even after the infusion was discontinued. When TRH was perfused concomitantly with CB154, the stimulatory effect of TRH on GH release was maintained, while TRH-induced PRL secretion was completely blocked. The results suggest that both TRH and CB154 possess a direct action on pituitary adenoma cells of acromegaly and that aberrant GH responses to TRH and dopaminergic agonists in acromegalic patients may be explained by the altered cellular membrane receptors of the adenoma of these subjects.