Relationship between PPARα activation and NO on proximal tubular Na(+ )transport in the rat

BACKGROUND: Nitric oxide (NO) regulates renal proximal tubular (PT) Na(+ )handling through modulation of Na(+)-K(+ )ATPase. Peroxisome Proliferator Activated Receptorα (PPARα), a nuclear transcription factor, is expressed in PTs and has been reported to influence NO generation/activity in renal tissues. This study tested the hypothesis that PPARα interacts with NO and thereby affects renal tubular Na(+ )transport. Urinary excretion of nitrite (UNO(X)V) and Na(+ )(U(Na)V) and PT Na(+ )transport (Na(+)-K(+ )ATPase activity) were determined in rats treated with clofibrate (250 mg/kg i.p) or WY14643 (45 mg/kg; i.p.), a PPARα ligand, 2% NaCl (orally), clofibrate/NaCl, L-NAME, an inhibitor of NO production (100 mg/kg; orally), L-NAME/Clofibrate. RESULTS: Clofibrate or WY14643 increased PPARα expression by 106 ± 7% (p < 0.05) and 113 ± 8% (p < 0.05), respectively. Similarly, clofibrate and WY14643 increased expression of MCAD, a downstream target protein of PPARα by 123 ± 8% (p < 0.05) and 143 ± 8% (p < 0.05), respectively. L-NAME attenuated clofibrate-induced increase in PPARα expression by 27 ± 2% (p < 0.05) but did not affect MCAD expression. UNO(X)V excretion increased 3–4 fold in rats treated with clofibrate, WY14643 or NaCl from 44 ± 7 to 170 ± 15, 144 ± 18 or 132 ± 11 nmol/24 hr, respectively (p < 0.05). Similarly, clofibrate, WY14643 or NaCl elicited a 2–5 fold increase in U(Na)V. L-NAME significantly reduced basal UNO(X)V and U(Na)V and abolished the clofibrate-induced increase. Clofibrate, WY14643, NaCl or clofibrate + NaCl treatment reduced Na(+)-K(+)-ATPase activity in the PT by 89 ± 23, 62 ± 10, 43 ± 9 and 82 ± 15% (p < 0.05), respectively. On the contrary, L-NAME or ODQ, inhibitor of sGC, abolished the inhibition of Na(+)-K(+)-ATPase activity by clofibrate (p < 0.05). Clofibrate either alone or with NaCl elicited ~2-fold increase in the expression of the α1 subunit of Na(+)-K(+ )ATPase in the PT while L-NAME abolished clofibrate-induced increase in Na(+)-K(+ )ATPase expression. CONCLUSION: These data suggest that PPARα activation, through increased NO generation promotes renal excretion of Na(+ )through reduced Na(+)-K(+ )ATPase activity in the PT probably via post translational modification of Na(+)-K(+)-ATPase

Differential effects of 20-hydroxyeicosatetraenoic acid on intrarenal blood flow in the rat

ABSTRACT We recently demonstrated that endothelin-1-induced medullary vasodilation despite a potent cortical vasoconstriction in the rat kidney may be accounted for by 20-hydroxyeicosatetraenoic acid (20-HETE) production. This study characterized the effects of 20-HETE and its metabolites, 20-hydroxy prostaglandin E 2 (20-OH PGE 2 ) and 20-hydroxy prostaglandin F 2␣ (20-OH PGF 2␣ ), and the contribution of nitric oxide (NO) and prostanoids to the changes evoked in cortical blood flow (CBF) and medullary blood flow (MBF). We tested the hypothesis that 20-HETE produces qualitatively different regional hemodynamic effects in the kidney with 20-OH PGF 2␣ or 20-OH PGE 2 , accounting for the vasoconstriction or vasodilation, respectively, in the cortex and medulla. Renal intra-arterial infusion of 1, 2.5, 5, and 10 ng/min 20-HETE decreased CBF by 10 Ϯ 3, 24 Ϯ 4, 40 Ϯ 7, and 58 Ϯ 9 perfusion units (PU), respectively, but increased MBF by 4 Ϯ 2, 16 Ϯ 4, 27 Ϯ 3, and 41 Ϯ 10 PU, respectively. 20-OH PGF 2␣ mimics the effects of 20-HETE, as did PGF 2␣ . However, 20-OH PGE 2 increased both CBF and MBF, as did PGE 2 . Indomethacin (5 mg/kg) blunted the effects of 20-HETE but not that of 20-OH PGE 2 and 20-OH PGF 2␣ . -5-heptenoic acid) (0.1 mg/kg), a prostaglandin H 2 /thromboxane A 2 receptor antagonist, blunted the cortical and medullary hemodynamic effects elicited by 20-HETE, 20-OH PGE 2 , 20-OH PGF 2␣ , and PGF 2␣ but not PGE 2 . N -L-nitro arginine methyl ester (5 mg/kg), the inhibitor of NO synthase, exacerbated the cortical constrictor effects of 20-HETE and 20-OH PGF 2␣ without affecting the medullary perfusion produced by 20-HETE or its metabolites. These findings suggest that 20-HETE, through its hydroxyl metabolites, produced differential effects in the kidney. The medullary perfusion appears to be independent of NO. 20-Hydroxyeicosatetraenoic acid (20-HETE), the major eicosanoid in the kidney, is widely known as a constrictor hormone eliciting potent vasoconstriction of the peripheral arteries of the rabbit, the renal afferent arteriole of the rat, dog, and rabbit 20-HETE and other CYP450 products are good substrates for COX, and their production occurs throughout the kidney. Although the specific metabolic pathways for 20-HETE in the kidney has not been fully identified, a priori, the presence of CO

Contribution of cytochrome P450 4A isoforms to renal functional response to inhibition of nitric oxide production in the rat

20-Hydroxyeicosatetraenoic acid (20-HETE), a major renal eicosanoid, regulates renal function and contributes to renal responses following withdrawal of nitric oxide (NO). However, the role of 20-HETE-synthesizing isoforms in renal function resulting from NO inhibition is unknown. The present study evaluated the role of cytochrome (CYP)4A1, −4A2 and −4A3 isoforms on renal function in the presence and absence of NO. Antisense oligonucleotides (ASODN) to CYP4A1, −4A2 and −4A3 reduced 20-HETE synthesis and downregulated the expression of CYP4A isoforms in renal microsomes. Nω-L-nitromethyl arginine ester (L-NAME, 25 mg kg−1), an inhibitor of NO production, increased mean arterial blood pressure (MABP, Δ=+18 to 26 mmHg), reduced renal blood flow (RBF, Δ= −1.8 to 2.9 ml min−1), increased renal vascular resistance (RVR, Δ=+47 to 54 mmHg ml−1 min−1), reduced glomerular filtration rate (GFR), but increased sodium excretion (UNaV). ASODN to CYP4A1 and −4A2 but not −4A3 reduced basal MABP and RVR and increased basal GFR, while ASODN to CYP4A2 significantly reduced basal UNaV suggesting a differential role for CYP4A isoforms in the regulation of renal function. ASODN to CYP4A2 but not −4A1 or −4A3 blunted the increase in MABP by L-NAME (38 ± 9 %, P < 0.05). ASODN to CYP4A1, −4A2 and −4A3 attenuated the reduction in RBF and the consequent increase in RVR by L-NAME with a potency order of CYP4A2 = CYP4A1 > CYP4A3. ASODN to CYP4A1 and −4A2 but not −4A3 attenuated L-NAME-induced reduction in GFR, but ASODN to all three CYP4A isoforms blunted the L-NAME-induced increase in UNaV (CYP4A3 > CYP4A1 >> CYP4A2). We conclude from these data that CYP4A isoforms contribute to different extents to basal renal function. Moreover, CYP4A2 contributes greatest to haemodynamic responses while CYP4A3 contributes greatest to tubular responses following NO inhibition. We therefore propose that NO differentially regulates the function of CYP4A1, −4A2, and −4A3 isoforms in the renal vasculature and the nephron

The Research Centers in Minority Institutions (RCMI) Translational Research Network: Building and Sustaining Capacity for Multi-Site Basic Biomedical, Clinical and Behavioral Research.

The Research Centers in Minority Institutions (RCMI) program was established by the US Congress to support the development of biomedical research infrastructure at minority-serving institutions granting doctoral degrees in the health professions or in a health-related science. RCMI institutions also conduct research on diseases that disproportionately affect racial and ethnic minorities (ie, African Americans/Blacks, American Indians and Alaska Natives, Hispanics, Native Hawaiians and Other Pacific Islanders), those of low socioeconomic status, and rural persons. Quantitative metrics, including the numbers of doctoral science degrees granted to underrepresented students, NIH peer-reviewed research funding, peer-reviewed publications, and numbers of racial and ethnic minorities participating in sponsored research, demonstrate that RCMI grantee institutions have made substantial progress toward the intent of the Congressional legislation, as well as the NIH/NIMHD-linked goals of addressing workforce diversity and health disparities. Despite this progress, nationally, many challenges remain, including persistent disparities in research and career development awards to minority investigators. The continuing underrepresentation of minority investigators in NIH-sponsored research across multiple disease areas is of concern, in the face of unrelenting national health inequities. With the collaborative network support by the RCMI Translational Research Network (RTRN), the RCMI community is uniquely positioned to address these challenges through its community engagement and strategic partnerships with non-RCMI institutions. Funding agencies can play an important role by incentivizing such collaborations, and incorporating metrics for research funding that address underrepresented populations, workforce diversity and health equity