Ontogeny of the GH response to phorbol ester and phospholipase C in rat pituitary cells

GH secretory patterns undergo marked change during early mammalian development. The factors that underlie these changes and the major components of signal transduction in the immature somatotrophs are not fully understood. Increasing evidence suggests that protein kinase C (PKC) plays a central role in perinatal organ differentiation and function. To evaluate the possible role of PKC as a mediator of GH secretion from immature pituitaries, we tested the effects of the PKC activating phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), alone or together with GH-releasing factor (GRF), somatostatin (SRIF), and Ca2+ modifying agents; an inactive phorbol analogue (4 alpha-12-13-didecanoate; 4 alpha-PDD), and phospholipase C on GH release from pituitary cell cultures from perinatal and mature rats. Pituitary primary cell cultures were prepared from fetal (day 20 of 21.5 days of gestation), 2-day-old, 12-day-old, and adult male (2- to 4-month-old) rats. Each experiment was performed on at least three separate occasions. The magnitude of TPA (0.15-150 nM)-induced GH release was markedly age-dependent, fractional GH release being greatest from pituitaries of fetal and newborn rats, and least from those of adults (P < 0.001). Further, the minimum dose of TPA required to stimulate GH release over basal levels was tenfold higher for adult pituitaries (15 nM) than for perinatal pituitaries (1.5 nM). Phospholipase C (1 and 10 U/ml) also caused greater fractional GH release from neonatal pituitaries than from adult pituitaries (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)