ONTOGENETIC DEVELOPMENT OF THE INHIBITION OF GROWTH HORMONE RELEASE BY SOMATOSTATIN IN THE RAT: IN-VIVO AND IN-VITRO (PERIFUSION) STUDY

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Abstract
An in-vitro study of GH secretion by rat fetal and neonatal pituitary glands was conducted using a perifusion system. After a 2 h period the GH content of the effluent was constant. Theophylline, thyrotrophin releasing hormone (TRH) and rat stalk median eminence extract (SME) were effective stimuli of GH release from the pituitary glands of the 19·5-day-old fetuses. Somatostatin, added to the medium (10 μg/ml), had no inhibitory effect on GH release (basal or stimulated by either theophylline or SME) before day 4 after birth. After postnatal day 5, somatostatin always inhibited GH secretion. These findings were consistent with the results of experiments in vivo. In rats tested within 4 days of birth, sodium pentobarbitone-stimulated plasma GH levels were not reduced by somatostatin; on day 4 and thereafter somatostatin depressed the response to pentobarbitone injection. These results indicate a postnatal maturation of the regulation of GH release by the hypothalamo–hypophysial system in the rat.