Abstract
Xiao, Daliao, Xiaohui Huang, Lawrence D. Longo, and Lubo Zhang. PKC regulates α1-adrenoceptor-mediated contractions and baseline Ca2+ sensitivity in the uterine arteries of nonpregnant and pregnant sheep acclimatized to high alttude hypoxia. High Alt. Med. Biol. 11:153–162, 2010.—Chronic hypoxia has a profound effect on uterine artery adaptation to pregnancy. The present studies tested the hypothesis that pregnant kinase C (PKC) differentially regulates α1-adrenoceptor-mediated contractions and Ca2+ sensitivity in the uterine arteries of nonpregnant and pregnant sheep acclimatized to high altitude hypoxia. Uterine arteries were isolated from nonpregnant (NPUA) and near-term pregnant (PUA) ewes maintained at high altitude (3801 m, Pao2 ∼60 torr) for 110 days. Phorbol 12,13-dibutyrate (PDBu) decreased phenylephrine-induced contractions in PUA but not in NPUA, which was partly inhibited by the PKC inhibitor GF109203X. Additionally, GF109203X shifted the concentration–response curve of phenylephrine-induced contractions to the right in PUA. In β-escin-permeabilized arteries, Ca2+-induced increases in 20-kDa myosin light chain phosphorylation (MLC20-P) were similar in NPUA and PUA. However, Ca2+ produced a concentration-dependent increase in the ratio of tension to MLC20-P in PUA, as compared with NPUA. PKC inhibition decreased Ca2+-induced contractions in both NPUA and PUA. PDBu induced contractions of PUA in the absence of changes in MLC20-P, which was not affected by PD098059. There was a significant increase in the basal activity of PKCɛ in PUA, but not in NPUA, in hypoxic sheep, as compared with normoxic animals. The results demonstrate that the inhibitory effect of PKC on α1-adrenoceptor-mediated contractions of uterine arteries is preserved in pregnant sheep at high altitude. However, the PKC-mediated thin-filament regulatory pathway is upregulated, resulting in increased baseline Ca2+ sensitivity in the uterine artery during pregnancy at high altitude.
