Ca2+-insensitive vascular protein kinase C during pregnancy and NOS inhibition

Pregnancy-induced hypertension is associated with increased vascular resist ance: however, the cellular mechanisms involved are unclear. We have previo usly found that the relation between Ca2+ entry and the developed force in vascular smooth muscle is altered during normal pregnancy and in a rat mode l of pregnancy-induced hypertension produced by long-term treatment with th e nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME ). The purpose of this study was to investigate whether the pregnancy-assoc iated changes in the vascular Ca2+ entry-force relation reflect changes in the amount and/or activity of Ca2+-insensitive protein kinase C (PKC) isofo rms. Active stress and the amount and activity of PKC were measured in deen dothelialized aortic strips from nonpregnant and pregnant rats untreated or treated with L-NAME and incubated in Ca2+-free (2 mmol/L EGTA) I(I cbs sol ution. In nonpregnant rats, the PKC activator phorbol 12,13-dibutyrate (PDB u. 10 mol/L) and the alpha-adrenergic agonist phenylephrine (Phe, 10(-5) mo l/L) caused significant, maintained increases in active stress and PKC acti vity that were inhibited by the PKC inhibitors staurosporine and calphostin C. Western blots in aortic strips of nonpregnant rats revealed the Ca2+-in sensitive delta-PKC and zeta-PKC isoforms. Both PDBu and Phe caused translo cation of delta-PKC from the cytosolic to the particulate fraction. Compare d with nonpregnant rats, the amount of delta-PKC and zeta-PKC and the PDBu- stimulated and Phe-stimulated stress, PKC activity and translocation of del ta-PKC were significantly reduced in late pregnant rats but significantly e nhanced in pregnant rats treated with L-NAME. The PDBu-induced and Phe-indu ced responses in nonpregnant rats treated with L-NAME were not significantl y different from nonpregnant mts, whereas the responses in pregnant rats tr eated with L-NAME+L-arginine were not significantly different from pregnant rats. These results provide evidence that a signaling pathway in vascular smooth muscle possibly involving the Ca2+-insensitive delta-PKC and zeta-PK C isoforms is reduced in late pregnancy and enhanced during long-term inhib ition of nitric oxide synthesis. The changes in the amount and activity of vascular PKC isoforms may, in part, explain the changes in vascular resista nce during normal pregnancy and pregnancy-induced hypertension.