Gender differences in protein kinase G-mediated vasorelaxation of rat aorta

Although gender and oestrogen treatment influence production of the vasorel axant, NO, their influence on factors downstream in the NO signal-transduct ion pathway, specifically protein kinase G (PKG), remains unknown. We aimed to study the influence of sex hormones on PKG, along with the endothelial modulation of these effects, in rat thoracic aortic rings in two separate g roups, control male and female rats and ovariectomized female rats after tr eatment with oestrogen or vehicle. Vessel preparations were preconstricted with phenylephrine (0.1 muM). Constrictions were greater in male than femal e aortas. This differential effect was attenuated by endothelium removal, a ddition of the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quino xalin-1-one (ODQ, 1 muM) and the nitric oxide synthase (NOS) inhibitor NG-m onomethyl-L-arginine (L-NMMA, 100 muM), supporting the role of NO in mainte nance of basal relaxation and vascular tone in females. We have examined th e relative activity of the specific PKG subtypes 1 alpha and 1 beta in vasc ular smooth muscle, based on relaxation of rat aortas by two cGMP analogues with different selectivity, beta -phenyl-1-N-2-ethano-8-bromo-cGMP (8-Br-P ET-cGMP) and 8-(2-amino-phenylthio)cGMP (8-APT-cGMP). 8-Br-PET-cGMP was mor e potent than 8-APT-cGMP in both sexes, suggesting that PKG 1 alpha is the primary subtype involved in vasorelaxation. The gender differences in PKG a ctivity were examined based on relaxation responses in male and female rat aortas. Both 8-Br-PET-cGMP and 8-APT-cGMP were more potent in aortas from m ale than female rats. In further studies on the endothelial modulation of r elaxation with 8-APT-cGMP, the differential gender-vasorelaxation response was negated by endothelium removal and addition of the guanylate cyclase in hibitor ODQ (1 muM), but not by the NOS inhibitor L-NMMA (100 muM), suggest ing that an endothelial-dependent factor other than NO may be responsible f or the observed differential PKG-mediated vasorelaxation between the sexes. To further investigate oestrogen influence on PKG, treated female rats wer e studied. Contrary to our hypothesis, in the presence of 1 muM ODQ, there were no differences in either the phenylephri ne constriction, or the relax ation with 8-APT-cGMP from either sham-operated, vehicle-treated or oestrog en-treated ovariectomized rats. In conclusion, female rat aortas have great er basal NO production compared with males. Relaxant responses to PKG activ ation are greater in aortas from male compared with female rats. These find ings suggest hormonal regulation of PKG; however, oestrogen treatment of ov ariectomized rats did not affect PKG activity, suggesting factors other tha n oestrogen may be responsible for the gender differences noted in this stu dy.