Evidence for autoregulation of growth hormone secretion via the central nervous system

The ability of growth hormone (GH() to regulate its own secretion at the level of the central nervous system was examined in chronically cannulated freely-moving rats. Six-hour GH secretory profiles were obtained from 2 groups of rats administered either normal saline or rat GH via the lateral ventricle of the brain. The typical pulsatile pattern of GH secretion was evident in normal saline-treated control rats with most peak GH values > 400 ng/ml. Injection of rat GH (15 microgram/10 microliter) resulted in a significant suppression in amplitude of GH secretory pulses after an interval of 1 hour and plasma GH levels remained markedly depressed for up to 6 h after injection. Peak GH values did not exceed 76 ng/ml during the latter 3 h of the sampling period. These findings clearly demonstrate that GH can regulate its own secretion via a negative feedback system. Furthermore, the results suggest that the central nervous system is an important site of action for GH autoregulation.