ROLE OF THE NA-CA2(+) AND NA+-H+ ANTIPORTERS IN PROLACTIN-RELEASE FROM ANTERIOR-PITUITARY-CELLS IN PRIMARY CULTURE()

2',4'-dimethylbenzamilamiloride (DMB), a somewhat selective inhibitor of the Na+-Ca2+ exchanger, in concentrations of 10, 30 and 100 mu M di d not produce any significant effect on baseline prolactin release fro m anterior pituitary cells in primary culture. When prolactin secretio n was stimulated by the inhibitor of the Na+-K+-ATPase, ouabain, that activates the Na+-Ca2+ exchanger as a Ca2+-influx pathway, DMB was abl e to produce inhibition of prolactin secretion. 5-(N, N-hexamethylene) amiloride (HMA), another amiloride analog which specifically inhibits the Na+-H+ antiporter and has no inhibitory activity on the Na+-Ca2exchanger, at the concentrations of 0.1, 1 and 10 mu M, did not affect basal prolactin release whereas it significantly reduced prolactin re lease stimulated by thyrotropin releasing hormone (TRH) (1 mu M). Thes e results suggest that the Na+-Ca2+ antiporter is involved in the proc ess of prolactin release elicited by the inhibition of the Na+-K+-ATPa se whereas the Na+-H+ antiporter is involved in the prolactin secretio n elicited by TRH.