Abstract
Progesterone enhanced the contractile effect of epinephrine on the ductus deferens of the guinea pig in vitro. In relation to this mechanical phenomenon, we examined the phosphatidylinositol metabolism. In the 3H-myoinositol labeled ductus deferens, radioactivity in phosphatidylinositol bisphosphate was about 2.6 times as high as that in phosphatidylinositol. Phosphatidylinositol and phosphatidylinositol phosphate were not changed by epinephrine (100 μM), but phosphatidylinositol bisphosphate was increased at 10 sec and 1 min after the administration of epinephrine (100 μM). Progesterone (100 μM) added 5 min before the administration of epinephrine increased the stimulatory effect of epinephrine on the phosphatidylinositol bisphosphate metabolism, but had no effect on the phosphatidylinositol and phosphatidylinositol phosphate metabolism. These studies suggest that progesterone expresses its activity not through the cytoplasmic progesterone receptor but through the epinephrine-mediated smooth-muscle contractile mechanism.
