Figure 5.

Vasodilatory effects of estrogenic compounds are unrelated to changes in Ca²⁺-sensitization of contraction but are enhanced in the presence of an L-type Ca²⁺ channel agonist. Permeabilized placental arteries exhibited U46619-induced Ca²⁺-sensitization of contraction at sub-maximal activating Ca²⁺ (pCa6.7) that was similar in magnitude to contraction in pCa4.5 solution alone (representative raw data tracing of A). 17β-estradiol (30 µM) did not affect this agonist-mediated Ca²⁺-sensitization. In intact preconstricted placental arteries, 17β-estradiol-mediated relaxation (B) was enhanced by preincubation with the L-type Ca²⁺ channel agonist Bay K8644 (C and D). Similar effects were observed on DPN-mediated relaxation (D). *Significant differences between 17β-estradiol alone and in the presence of Bay K8644.