Effect of trifluoperazine, a calmodulin antagonist, on prostaglandin output from the guinea-pig uterus.

Trifluoperazine, a calmodulin antagonist, inhibited the A23187-induced increase in outputs of prostaglandin (PG) F-2 alpha and 6-oxo-PGF-1 alpha from the Day 7 and Day 15 guinea-pig uterus superfused in vitro. The basal outputs of, and the arachidonic acid-induced increase in outputs of PGF-2 alpha, PGE-2 and 6-oxo-PGF-1 alpha from the guinea-pig uterus were not inhibited by trifluoperazine. In contrast, indomethacin inhibited A23187-stimulated, arachidonic acid-stimulated and the basal outputs of PGs from the guinea-pig uterus, indicating that trifluoperazine was not inhibiting cyclo-oxygenase. Since the action of A23187 is dependent upon extracellular Ca2+, the present findings provide evidence that calmodulin is involved in Ca2+-induced increases in uterine PG output from the guinea-pig uterus. Trifluoperazine, but not indomethacin, inhibited A23187-induced contraction of the guinea-pig uterus, which is consistent with calmodulin being involved in smooth muscle contraction. Arachidonic acid treatment did not contract the guinea-pig uterus. These findings indicate that PGs are not involved in the contraction induced by A23187. Other findings of interest were (i) trifluoperazine caused a small, sometimes significant (P less than 0.05), increase in uterine PG output, (ii) exogenous arachidonic acid failed to increase PGF-2 alpha output from the Day 15 uterus in contrast to the stimulant action of A23187, and (iii) exogenous arachidonic acid caused a fairly large increase in uterine PGE-2 output in contrast to the small effect with A23187.