The evaluation of hypothalamic somatostatin tone using pyridostigmine and thyrotropin releasing hormone in patients with acromegaly

To indirectly evaluate the hypothalamic somatostatin (SS) tone in patients with acromegaly, the effects of pyridostigmine (PD), a Cholinesterase inhibitor which can inhibit hypothalamic SS secretion, on TRH-induced TSH secretion and the effects of SMS 201–995 on TSH or GH secretion 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 pretreatment with PD (60 mg po, -30 min), normal young subjects showed significantly enhanced TSH responses to TRH (500 μg iv, 0 min) compared to single administration of TRH, whereas normal old and acromegalic patients did not show such enhancement. Plasma TSH response to a single administration of TRH in acromegalic patients was significantly lower than that of normal young and old subjects. Although normal young and old subjects showed significantly enhanced GH responses to GHRH (100 μg 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 similar between normal subjects (5 young 5 old) and 7 acromegalic patients. Further, the maximal plasma GH decrement after administration was significantly 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 young and probably old subjects.