THE EVALUATION OF HYPOTHALAMIC SOMATOSTATIN TONE USING PYRIDOSTIGMINEAND THYROTROPIN-RELEASING-HORMONE IN PATIENTS WITH ACROMEGALY

To indirectly evaluate the hypothalamic somatostatin (SS) tone in pati ents with acromegaly, the effects of pyridostigmine (PD), a cholineste rase inhibitor which can inhibit hypothalamic SS secretion, on TRH-ind uced TSH secretion and the effects of SMS 201-995 on TSH or GH secreti on were studied in acromegalic patients (31-69 yr, n=10), normal young (21-24 yr, n=7) and normal old male subjects (62-71 yr, n=7). After p retreatment with PD (60 mg po, -30 min), normal young subjects showed significantly enhanced TSH responses to TRH (500 mu g iv, 0 min) compa red to single administration of TRH, whereas normal old and acromegali c patients did not show such enhancement. Plasma TSH response to a sin gle administration of TRH in acromegalic patients was significantly lo wer than that of normal young and old subjects. Although normal young and old subjects showed significantly enhanced GH responses to GHRH (1 00 mu g iv at 0 min) after the pretreatment with PD (60 mg, -30 min), no such enhancement was observed in acromegalic patients. In contrast, the decrement in plasma TSH after SMS 201-995 administration was simi lar between normal subjects (5 young 5 old) and 7 acromegalic patients . Further, the maximal plasma GH decrement after administration was si gnificantly greater in acromegalic patients than in the 5 normal young and 5 old subjects p<0.01). In conclusion, hypothalamic SS tone does not appear to be elevated in acromegalic patients compared to normal y oung and probably old subjects.