Previous studies on the effects of ethanol on circulating pituitary hormones have been carried out mostly during daytime when the secretion of these hormones is generally at a nadir. Therefore, we studied the effects of ethanol on the nocturnal secretion of GH, PRL, TSH, and thyroid hormones (protocol I, nine healthy subjects, five women) and on the TSH and PRL responses to synthetic TRH (protocol II, healthy subjects, four women). Ethanol was given in doses of 0, 0.5 or 1.0 g/kg of BW(protocol I) and 0 or 1.0 g/kg (protocol II) and ingested po at 1900-1945 h. In protocol I, plasma GH rose from 0.6 +/- 0.2 microgram/L (mean +/- SE) at 2200 h to 25.0 +/- 4.3 micrograms/L at 0100 h in control subjects and was almost completely inhibited at 4.5 +/- 1.7 micrograms/L at 0100 h in subjects receiving 1.0 g/kg ethanol (P