Flunarizine, a calcium influx blocker, inhibits TRH-but not potassium-stimulated prolactin secretion.

The effect of flunarizine on the secretion of prolactin from monolayer cultures of normal rat pituitary cells has been determined. Both basal and TRH-stimulated secretion were found to be significantly inhibited by micromolar concentrations of flunarizine, whereas depolarization (high K+)-stimulated secretion was virtually unaffected. These results indicate that TRH-stimulated prolactin secretion probably involves calcium influx and that flunarizine may be useful as a probe for particular Ca2+ channels.