(Verbatim from the application): Heme oxygenase (HO) catalyzes the conversion of heme to biliverdin, free iron and carbon monoxide (GO). Heme is required for synthesis/activity of heme proteins that can affect vascular and renal function such as the eicosanoid biosynthetic enzymes, cytochrome P450 (GYP) monooxygenases, thromboxane and prostacyclin synthases and cyclooxygenases (COX). HO controls cellular heme concentrations and is solely responsible for the generation of the vasodepressor CO which, by itself, can bind to the heme moiety of heme proteins causing either enzyme activation or inhibition. Induction of HO suppresses renal arachidonic acid (AA) metabolism to pressor metabolites via GYP and COX/thromboxane synthase activities, is associated with natriuresis and blood pressure reduction, and is prevented by HO inhibitors, suggesting that HO-derived heme depletion and/or CO generation underlie these effects. CO or HOheme-generated CO elicits vasodilation in vitro and in vivo and reduces blood pressure in the SHR. Two HO isoforms have been identified as the primary source of HO activity, the inducible HO-i and the constitutively-expressed HO-2. The newly discovered HO-3 isoform share 90 percent homology with HO-2 and lack significant catalytic activity. The distribution and contribution of each isoform to HO activity within the kidney is unknown. We demonstrated relatively high levels of HO-2 in the renal microvessels and the medullary thick ascending limb, whereas proximal tubules exhibit high levels of HO-i. We propose that HO isoforms are differentially localized in kidney structures and contribute to the regulation of GYP and COX activities, thereby regulating the formation of eicosanoids that affect vasomotion and modulate ion transport. The proposed studies will: 1) localize HO isoforms expression and activity within the rat kidney; 2) examine the effect of HO inducers and selective inhibitors on HO isoforms expression and distribution in the kidney; and 3) study the effect of these maneuvers in determining the functional relationship of HO isoforms to renal COX and GYP-dependent eicosanoid biosynthesis. Studying HO in renal structures of normotensive and hypertensive rats and in rats in which renal HO has been altered will establish local changes in the expression of HO isoforms as they relate to the expression of COX and CYP-AA metabolism. Studies that examine the influence of HO activity on these heme proteins will shed light on possible mechanisms by which underexpression/overexpression of HO affects vascular tone, ion transport and blood pressure.
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