Gender-related distinctions in protein kinase C activity in rat vascular smooth muscle

Gender differences in vascular reactivity have been suggested; however, the cellular mechanisms involved are unclear. We tested the hypothesis that th e gender differences in vascular reactivity reflect gender-related, possibl y estrogen-mediated, distinctions in the expression and activity of specifi c protein kinase C (PKC) isoforms in vascular smooth muscle. Aortic strips were isolated from intact and gonadectomized male and female Wistar-Kyoto ( WKY) rats and spontaneously hypertensive rats (SHR). Isometric contraction was measured in endothelium-denuded aortic strips. PKC activity was measure d in the cytosolic and particulate fractions, and the amount of PKC was mea sured using Western blots and isoform-specific anti-PKC antibodies. In inta ct male WKY rats, phenylephrine (Phe, 10(-5) M) and phorbol 12,13-dibutyrat e (PDBu, 10(-6) M) stimulated contraction to 0.37 +/- 0.02 and 0.42 +/- 0.0 2 g/mg tissue wt, respectively. The basal particulate/cytosolic PKC activit y ratio was 0.86 +/- 0.06, and Western blots revealed alpha-, delta-, and z eta -PKC isoforms. Phe and PDBu increased PKC activity and caused significa nt translocation of a- and d- PKC from the cytosolic to particulate fractio n. In intact female WKY rats, basal PKC activity, the amount of alpha-, del ta-, and zeta -PKC, the Phe- and PDBu-induced contraction, and PKC activity and translocation of a- and d- PKC were significantly reduced compared wit h intact male WKY rats. The basal PKC activity, the amount of alpha-, delta -, and zeta -PKC, the Phe and PDBu contraction, and PKC activity and a- and d- PKC translocation were greater in SHR than WKY rats. The reduction in P he and PDBu contraction and PKC activity in intact females compared with in tact males was greater in SHR (similar to 30%) than WKY rats (similar to 20 %). Phe and PDBu contraction and PKC activity were not significantly differ ent between castrated males and intact males but were greater in ovariectom ized (OVX) females than intact females. Treatment of OVX females or castrat ed males with 17 beta -estradiol, but not 17 alpha -estradiol, subcutaneous implants caused significant reduction in Phe and PDBu contraction and PKC activity that was greater in SHR than WKY rats. Phe and PDBu contraction an d PKC activity in OVX females or castrated males treated with 17 beta -estr adiol plus the estrogen receptor antagonist ICI-182,780 were not significan tly different from untreated OVX females or castrated males. Thus a gender- related reduction in vascular smooth muscle contraction in female WKY rats with intact gonads compared with males is associated with reduction in the expression and activity of vascular alpha-, delta-, and zeta -PKC. The gend er differences in vascular smooth muscle contraction and PKC activity are a ugmented in the SHR and are possibly mediated by estrogen.