This is a proposal to investigate the mechanisms regulating renal vascular and tubular (medullary thick ascending limb; mTAL) synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) during pregnancy. 20-HETE is a major cytochrome P450 (CYP) 4A-derived eicosanoid in the rat kidney whose potent effects on vascular tone and tubular ion transport implicate it in the regulation of renal function and in the control of blood pressure. Normal pregnancy in humans and rats is associated with increases in the glomerular filtration rate and renal blood flow along with a significant decrease in arterial pressure and total peripheral resistance. The exact mechanisms mediating these physiological changes are not fully understood. Preliminary studies demonstrated distinct patterns of CYP4A isoform expression and 20-HETE synthesis in renal microvessels and mTAL during pregnancy and a transient reduction in systolic blood pressure and urinary sodium excretion following administration of an inhibitor of 20-HETE synthesis in pregnant rats. We hypothesize that renal 20-HETE synthesis is affected during gestation and that 20-HETE is involved in the regulation of renal function and blood pressure during pregnancy. Experiments will be performed in Aim 1 to characterize vascular and mTAL 20-HETE synthesis and CYP4A expression in pregnant rats at different gestational days, and in Aim 2 to determine the consequence of inhibition and over-expression of CYP4A proteins in pregnant rats on renal 20-HETE synthesis, vascular reactivity, mTAL potassium channel activity, urinary electrolyte levels, and blood pressure. It has been shown that nitric oxide (NO) inhibits CYP4A activity and expression; inhibition of its production results in signs similar to preeclampsia. Experiments in Aims 3 and 4 will examine the possibility that NO presents a mechanism that regulates CYP4A expression and 20-HETE synthesis during pregnancy. The present proposal sets the basis for understanding mechanisms that regulate 20-HETE synthesis in the kidney during pregnancy. Ultimately, this knowledge can uncover new therapeutic targets and provide novel loci for the control and treatment of pregnancy-induced hypertension.