Role of Ca2+ and cyclic nucleotides in the control of prostaglandin E production in the rat anterior pituitary gland

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Abstract
In an attempt to relate changes in the intracellular concentration of prostaglandin [PG] E to the secretion process, 2 agents known to increase cyclic nucleotide concentrations and hormone release were added to dispersed rat anterior pituitary cells. They caused increases in the intracellular PGE concentrations. Increasing the K+ concentration in the medium (which stimulates hormone release) caused a rapid rise in PGE concentrations. The addition of the Ca2+ ionophore A23187 [2-[(3.beta.,9.alpha.,11.beta.-trimethyl)-8-(2-pyrrole carboxymethyl)1,7-dioxaspiro[6.6] undecyl-2.beta.-methyl]5-methyl aminobenzoxazole-4-carboxylic acid] had a similar effect. The effects of changes in the K+ and Ca2+ concentrations and the addition of EDTA were measured on the redistribution of radioactivity in pituitary glands prelabeled with [3H]arachidonic acid. Elevated K+ concentrations stimulated the transfer of label to PG and free arachidonic acid, suggesting an increased phospholipase A activity. The absence of extracellular CaCl2 and the addition of EDTA had the opposite effect, which could be canceled by the addition of sufficient amounts of CaCl2. The addition of agents that increase membrane permeability to bivalent cations probably results in an influx of Ca2+ and this appears to result in increased phospholipase A activity, which in turn leads to an increase in PG production.