Sulpiride and thyrotrophin releasing hormone loading test in patients with acromegaly

The effects of sulpiride, a dopamine receptor blocking agent, and of thyrotrophin-releasing hormone (TRH) were studied on prolactin secretion in 17 patients with acromegaly and 25 control subjects. THe basal serum prolactin level was increased in 9 acromegalic patients. After sulpiride loading, maximum changes in prolactin level were significantly smaller in acromegalic patients, irrespective of the basal prolactin concentration. TRH loading resulted in a decrease of prolactin secretion predominantly in the patients with high basal serum hormone levels. A blunted thyrotrophin response to TSH was found only in those acromegalic patients who had concomitant thyroid disease. Higher than normal basal prolactin levels in some of the acromegalic patients and abnormal prolactin responses following sulpiride and TRH loading in most of the patients with acromegaly are attributed to deranged hypothalamo-hypophyseal regulation.