[Role of calcium ions and cyclic nucleotides in the regulation of somatotroph functional activity in rats as a function of age].

Somatotropic hormone (STH) biosynthesis and secretion were studied in primary adenohypophyseal cultures of neonatal, prepubertal, and adult rats. It was shown by disc PAAG electrophoresis of products synthesized in incubation of neonatal rat hypophyseal cells that L-14C leucin incorporates predominantly in the STH containing fraction. The share of prelabeled STH secreted into the culture virtually did not depend on the age of animals, this indicating the maturity of mechanisms of basal somatotroph secretion as early as in the neonatal period of development. Ca-regulating agents (ionophore A23187, EGTA) caused quantitatively similar changes of somatotroph secretory activity in cultures of hypophyseal cells from rats of different ages. At the same time, clear-cut age-specific features of stimulating effect of dibutyryl derivatives of cAMP and cGMP on secretion of immunoreactive STH were detected. The results indicate that somatotropic function in neonatal hypophysis is a dominant one and demonstrates increased reactivity to secretogenic action of cyclic nucleotide analogs.