Diurnal variation of growth hormone secretion following thyrotropin-releasing hormone infusion in normal men.

Abstract

Growth hormone (GH) secretion following a standard intravenous dose of thyrotropin-releasing hormone (TRH) was studied in eight healthy young men in the morning (0800h), in the evening (2000h), and after an acute 12-hr shift of the rest-activity cycle. The maximal increment in serum GH concentration following TRH administration was significantly greater in the evening than in either the morning or evening after reversal of the rest-activity cycle (p less than 0.02). Seven of the eight subjects showed an increase in serum GH following TRH in the evening but not after rest--activity reversal (p less than 0.01). Only one subject showed a GH response during one of two morning trials. Serum GH concentration was also increased in two of six subjects following saline infusion in the evening. These findings indicate that the GH response to TRH may depend on the phase of GH secretory activity at the time of testing. The GH responses to TRH reported in various disease states may, therefore, reflect alterations in the GH secretory rhythm or disturbances in circadian rest--activity patterns.