AREGU February 47/2

Kanashiro, Celia A., Kathy L. Cockrell, Barbara T. Alexander, Joey P. Granger, and Raouf A. Khalil. Pregnancy-associated reduction in vascular protein kinase C activity rebounds during inhibition of NO synthesis. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 278: R295– R303, 2000.—Vascular reactivity has been shown to be reduced during pregnancy and to be enhanced during chronic inhibition of nitric oxide (NO) synthesis in pregnant rats; however, the cellular mechanisms involved are unclear. The purpose of this study was to investigate whether the pregnancy-induced changes in vascular reactivity are associated with changes in the amount and/or activity of vascular protein kinase C (PKC). Active stress as well as the amount and activity of PKC was measured in deendothelialized thoracic aortic strips from virgin and pregnant rats untreated or treated with the NO synthase inhibitor N G-nitro-Larginine methyl ester (L-NAME). In virgin rats, the PKC activator phorbol 12,13-dibutyrate (PDBu, 1026 M) and the a-adrenergic agonist phenylephrine (Phe, 1025 M) caused significant increases in active stress and PKC activity that were inhibited by the PKC inhibitors staurosporine and calphostin C. Western blot analysis in aortic strips of virgin rats showed significant amount of the a-PKC isoform. Both PDBu and Phe caused significant translocation of a-PKC from the cytosolic to the particulate fraction. Compared with virgin rats, the PDBuand Phe-stimulated active stress and PKC activity as well as the amount and the PDBuand Phe-induced translocation of a-PKC were significantly reduced in late pregnant rats but significantly enhanced in pregnant rats treated with L-NAME. The PDBuand Pheinduced changes in active stress and the amount, distribution, and activity of a-PKC in virgin rats treated with L-NAME were not significantly different from that in virgin rats, whereas the changes in pregnant rats treated with L-NAME 1 the NO synthase substrate L-arginine were not significantly different from that in pregnant rats. These results provide evidence that a PKC-mediated contractile pathway in vascular smooth muscle is reduced during pregnancy and significantly enhanced during chronic inhibition of NO synthesis. The results suggest that one possible mechanism of the pregnancy-associated changes in vascular reactivity may involve changes in the amount and activity of the a-PKC isoform.