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Regulation of ₁-adrenoceptor-mediated contractions of uterine arteries by PKC: effect of pregnancy

Center for Perinatal Biology, Department of Physiology and Pharmacology, Loma Linda University School of Medicine, Loma Linda, California

Submitted 28 March 2006 ; accepted in final form 11 May 2006

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 ₁-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 [Ca²⁺]_i and contractions in PUA sheep. In NPUA sheep, PDBu increased phenylephrine-induced contractions without changing [Ca²⁺]_i. Western blot analysis showed six PKC isozymes, , _I, _II, , , and , in uterine arteries, among which _I, _II, and isozymes were significantly increased in PUA sheep. In contrast, PKC- was decreased in PUA sheep. In addition, analysis of subcellular distribution revealed a significant decrease in the particulate-to-cytosolic ratio of PKC- in PUA compared with that in NPUA sheep. The results suggest that pregnancy induces a reversal of PKC regulatory role on ₁-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 Ca²⁺ sensitivity in ₁-adrenoceptor-mediated contractions and their adaptation to pregnancy.

calcium mobilization; calcium sensitivity; adaptation; sheep

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