Effects of 17β-estradiol and progesterone on agonist-stimulated inositol phospholipid breakdown in uterine smooth muscle

Inositol phospholipid breakdown, from a [³H]inositol-labelled pool, induced by a variety of contractile agents was monitored in uterine smooth muscle slices pretreated with estradiol-17β or estradiol-17β and progesterone by measuring the accumulation of [³H]inositol phosphates. Agonist potencies for stimulating [³H]IP accumulation were not affected by hormone treatment but the maximum responses were dependent upon hormonal state. Maximum responses to carbachol, norepinephrine, prostaglandin F_2α were increased in progesterone-dominated tissues but maximum responses to oxytocin were unaffected. Inhibition of agonist-induced responses by competitive receptor antagonists confirmed the receptor specificity of carbachol-, norepinephrine- and oxytocin-mediated responses. Partial membrane depolarization (25 mM K⁺) did not affect agonist-induced maximal responses in either estrogen- or progesterone-dominated tissue. These data suggest that gonadal steroid hormones affect agonist-dependent intracellular calcium mobilization processes.