Growth hormone inhibits growth hormone secretion from the rainbow trout pituitary in vitro

Growth hormone (GH) secretion in salmonids and other fish is under the cont rol of a number of hypothalamic factors, but negative feed-back regulation by circulating hormones can also be of importance for the regulation of GH secretion. Mammalian studies show that GH has a negative feed-back effect o n its own secretion. In order to elucidate if GH levels present a direct ul tra-short negative feedback loop at the pituitary level GH secretion was st udied in intact pituitaries from 50 g fish in an in vitro perifusion system . Following an initial equilibrium period pituitaries were exposed to five increasing concentrations (1-1000 ng ml(-1)) of ovine CH (oGH) in 20-min st eps, before being returned to a GH-free perifusion. Ovine GH caused a signi ficant dose-dependant inhibition of GH secretion and it is concluded that G H can exert a direct negative feedback control on GH secretion at the pitui tary level. (C) 2000 Elsevier Science Inc. All rights reserved.