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We have tested the hypothesis that alpha-adrenergic drive is involved in the nocturnal increase in TSH in man. Seven mildly hypothyroid women (basal TSH levels 5.0-11.0 mU/l), aged 38-60 years, and nine euthyroid women, aged 27-60 years, were studied. Subjects underwent alpha-adrenergic blockade by infusion of thymoxamine (210 micrograms/min from 19.00 to 24.00 h); the same women were used as controls, with saline infused on different nights. Subjects were not allowed to sleep during the study period. A clear evening rise in basal TSH levels was apparent in both normal subjects and patients. Although overall secretion of TSH was slightly decreased in normal subjects (mean +/- S.E.M. area under the curve, 29.93 +/- 0.96 vs 30.71 +/- 0.80 mU/l per h; P less than 0.05), thymoxamine infusion did not produce any major alteration in the gradual rise in TSH levels during the evening (incremental change above baseline +0.96 +/- 0.21 during control infusion and +0.97 +/- 0.27 mU/l during thymoxamine infusion). In mildly hypothyroid patients the TSH changes were exaggerated and alpha-adrenergic blockade caused a reduction in basal TSH levels and a delayed rise in TSH (incremental change above baseline +2.93 +/- 1.42 during control infusion and +2.26 +/- 0.73 mU/l during thymoxamine infusion; P less than 0.02). Overall TSH secretion was significantly decreased by thymoxamine (mean +/- S.E.M. area 106 +/- 2.45 mU/l per h vs 123.32 +/- 3.68 in the control study; P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

It is well known that muscarinic cholinergic blockade either reduces or abolishes stimulated GH release in normal subjects. In this study we have investigated whether cholinergic muscarinic blockade could reduce the GH responses to GRF 1-29 and TRH in acromegalic subjects. Eight acromegalic subjects underwent two GRF tests (GRF 1-29, 1 microgram/kg i.v.) with and without pirenzepine (0.6 mg/kg, i.v.). A further four of these patients received TRH (200 micrograms/kg, i.v.) on separate occasions with and without pirenzepine (0.6 mg/kg, i.v.). Cholinergic muscarinic blockade did not alter the GH responses to GRF and TRH in patients with acromegaly. These findings are in contrast with previous data reported on the effects of cholinergic blockade on stimulated GH levels in normal subjects and in patients with type I diabetes mellitus and are compatible with the view that somatotroph adenomas are functionally disconnected from hypothalamic control mechanisms.