Current knowledge about hypertension suggests that an elevated peripheral resistance maintains high levels of arterial pressure. This increase in peripheral resistance may be caused by a vasoconstriction resulting from an alteration in vascular smooth muscle which makes it more sensitive to normal stimuli. Experimental observations suggest that this increased sensitivity reflects, at least in part, an abnormal regulation of intracellular calcium ion (Ca2+) by the phosphoinositide system. In this signal transduction system, activated receptors (i.e., alpha-adrenergic and serotonergic) act on a guanine nucleotide binding regulatory protein (G protein). Once activated, the G protein stimulates a phospholipase C that generates two second messengers: diacylglycerol (the physiological activator of protein kinase C) and inositol 1,4,5- trisphosphate (IP3), which activates a receptor-operated channel that releases Ca2+ from the sarcoplasmic reticulum. The activation of protein kinase C and other kinases contributes to the intracellular signal producing contraction. Previous work from this laboratory has demonstrated that components of this signal transduction pathway are increased in arteries of rats with genetic and experimental hypertension. This previous work used both pharmacological and biochemical assays and characterized the following: 1) receptor affinity and number; 2) inositol phosphate turnover and phospholipase C activity; 3) Ca2+ mobilization from the sarcoplasmic reticulum; and 4) protein kinase C activity. The goal of this research is to extend our understanding of the phosphoinositide signaling system in vascular smooth muscle from hypertensive rats. The research will be guided by the working hypothesis that augmented vascular reactivity in hypertension is due to an increase in the functional activity of a G protein (Gq) involved in agonist- promoted phosphoinositide hydrolysis. The research will focus on four aspects in rats with either genetic or experimentally-induced hypertension: 1) functional activity of G proteins and vascular reactivity; 2) regulation of G protein activity by nitric oxide- stimulated ribosylation; 3) antihypertensive therapy, blood pressure and G protein activity; and 4) genetic aspects of G protein coupling. The proposed experiments will be performed on isolated blood vessel segments (aorta, mesenteric arteries and arterioles, tail artery, femoral artery) from hypertensive and normotensive rats. The techniques used to evaluate functional characteristics of G protein activity include: 1) isometric recording of contractile behavior (intact and permeabilized preparations); 2) measurement of G protein levels using antibody techniques; 3) pharmacological characterization of G protein activity (agonists and antagonists of G protein activity coupled with antagonists of phospholipase C; 4) analysis of vascular traits in a genetic experiment; 5) analysis of vascular function in rats receiving antihypertensive therapy; 6) characterization of G protein function in arteries transplanted from hypertensive rats into normotensive rats (and vice versa) and 7) characterization of G protein function in blood vessels that are protected from elevated blood pressure by a ligation procedure. It is anticipated that this study will yield important information about functional determinants of vascular reactivity in hypertension.
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