Dual effect of osmotic cell swelling on prolactin secretion by acutely dispersed adenohypophyseal cells

Abstract

Cell swelling induced by acute exposure to the permeant molecule urea or by medium hyposmolarity evoked a prompt PRL secretory burst from dispersed rat anterior pituitary cells. However, during continuous exposure ≥10 min to these conditions inhibition of basal and TRH-induced PRL secretion occurred and there was an “off” burst of PRL secretion following return to basal conditions. Compared with continuous TRH stimulation which causes biphasic PRL secretion with a rapid high amplitude first phase secretory burst followed by a sustained low level second phase of secretion, cell swelling induced only “first phase” secretion. Removing Ca 2+ from the medium or adding 50 μM verapamil markedly depressed the “off” secretory burst following return to basal conditions but had no effect on the initial high amplitude burst. Our data suggest that the effect of cell swelling on PRL secretion is complex and that there are at least two mechanisms for PRL secretion in normal anterior pituitary cells; these are differently affected by cell swelling and Ca 2+ influx.