EPIDERMAL GROWTH-FACTOR STIMULATES THE PROLACTIN SYNTHESIS AND SECRETION IN RAT PITUITARY-CELLS IN CULTURE (GH4C1 CELLS) BY INCREASING THE INTRACELLULAR CONCENTRATION OF FREE CALCIUM

Epidermal growth factor (EGF) stimulated the prolactin (PRL) synthesis and release from the GH4C1 cells in a dose-dependent manner. The ED50 was between 10(-11) and 10(-10) mol/l. The maximal effect was obtained at 10(-9) mol/I EGF for the release, and 10(-8) mol/l EGF for the synthesis. EGF stimulated the release of PRL from cell perfusion columns after a lag period of about 30 s. The maximal secretion of PRL occurred about 60 s after the start of stimulation. The PRL secretion declined to basal levels within 2 min. The EGF-stimulated PRL release was additive to the secretion evoked by thyrotropin-releasing hormone (TRH) and vasoactive intestinal peptide (VIP). An instantaneous increase in the intracellular concentration of free calcium, [Ca2+]i, of the GH4C1 cells was observed after the administration of EGF. EGF modified neither the basal nor the TRH-stimulated inositoltrisphosphate production in the GH4C1 cells, and EGF did not show any effect on the cyclic adenosine monophosphate production of these cells.