Regulation of α₁-adrenoceptor-mediated contractions of uterine arteries by PKC: Effect of pregnancy

Protein kinase C (PKC) plays an important role in the regulation of uterine artery contractility and its adaptation to pregnancy. The present study tested the hypothesis that PKC differentially regulates α1- adrenoceptor-mediated contractions of uterine arteries isolated from nonpregnant (NPUA) and near-term pregnant (PUA) sheep. Phenylephrine-induced contractions of NPUA and PUA sheep were determined in the absence or presence of the PKC activator phorbol 12,13-dibutyrate (PDBu). In NPUA sheep, PDBu produced a concentration-dependent potentiation of phenylephrine-induced contractions and shifted the dose-response curve to the left. In contrast, in PUA sheep, PDBu significantly inhibited phenylephrine-induced contractions and decreased their maximum response. Simultaneous measurement of contractions and intracellular free Ca2+ concentrations ([Ca2+]i) in the same tissues revealed that PDBu inhibited phenylephrine-induced [Ca 2+]i and contractions in PUA sheep. In NPUA sheep, PDBu increased phenylephrine-induced contractions without changing [Ca 2+]i. Western blot analysis showed six PKC isozymes, α, βI, βII, δ, ε, and ζ, in uterine arteries, among which βI, βII, and ζ isozymes were significantly increased in PUA sheep. In contrast, PKC-α was decreased in PUA sheep. In addition, analysis of subcellular distribution revealed a significant decrease in the particulate-to-cytosolic ratio of PKC-ε in PUA compared with that in NPUA sheep. The results suggest that pregnancy induces a reversal of PKC regulatory role on α1-adrenoceptor-mediated contractions from a potentiation in NPUA sheep to an inhibition in PUA sheep. The differential expression of PKC isozymes and their subcellular distribution in uterine arteries appears to play an important role in the regulation of Ca2+ mobilization and Ca 2+ sensitivity in α1-adrenoceptor-mediated contractions and their adaptation to pregnancy. Copyright © 2006 the American Physiological Society.