Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in the diuretic and natriuretic effect of dopamine.

KIRCHHEIMER, C; FEDERIK M DEL M; NOWICKI, S

Miami- Estados Unidos

Congreso; XVII Sesion of the Interamerican Society of Hypertension and the Consortium for Southeastern Hypertension Control; 2007

Inter-american Society of Hypertension

Role of 20-hydroxyeicosatetraenoic acid (20-HETE) in the diuretic and natriuretic effect of dopamine. Kirchheimer Carolina, Federik Maria del Milagro, Nowicki Susana Renal dopamine (DA) plays an important role in regulating sodium excretion and blood pressure. The participation of arachidonic acid metabolites in DA-induced inhibition of Na+,K+-ATPase activity has been suggested. The principal cytochrome P450 (CYP)-derived arachidonic acid metabolite in the kidney is 20-hydroxieicosatetraenoic acid (20-HETE). We have previously shown the role of 20-HETE in Na+,K+-ATPase inhibition. The aim of the present study was to investigate the role of 20-HETE in both DA-induced Na+,K+-ATPase inhibition and natriuresis. Na+,K+-ATPase activity was quantified in microdissected rat proximal tubules by measuring [g32P]-ATP hydrolysis. Treatment of proximal tubules with 10-5M DA resulted in 41% inhibition of Na+,K+-ATPase activity. Inhibition of  20-HETE synthesis by the CYP inhibitor 17-octadecynoic acid (17-ODYA, 10-6M), which had no effect per se, abolished the effect of DA. The role of 20-HETE in PKCa activation, a necessary step for DA-induced Na+,K+-ATPase inhibition, was studied on isolated proximal tubule cells by measuring PKCa translocation from the cytosol to the membrane. Incubation of tubule cells with 10-5M DA or 10-6M 20-HETE resulted in PKCa redistribution. Pre-incubation with the CYP inhibitor 1-aminobenzotriazole (ABT 5x10-4M, 20 min) precluded DA-induced PKCa translocation without modifying the effect of 20-HETE. To study the effect of DA in vivo,  an acute volume expansion (5% body weight, isotonic NaCl, 30 min) was induced in control and in ABT-treated rats (50 mg /kg, i.p,12h before experiments). Rats were prepared for clearence studies. Urine samples were collected during basal (B), expansion (E)  and recovery (R) periods. As expected, volume expansion induced an increase in DA excretion (ng/min/100g, B: 271.5±25.3, E: 680,3±224.2) in control rats, which was not affected by ABT.  There were no differences in diuresis (V) and natriuresis (UNa+V) between control and ABT-treated rats in B. However, ABT reduced both V and UNa+V during E (V; control: 3.60±0.22#, ABT: 1.82±0.32*; UNa+V; control: 0.299±0.062#, ABT: 0.055±0.006*). ABT modified neither Na+ clearence (CNa+) nor fractional sodium excretion (FE Na+) during B, but reduced both during E (CNa+; ul/min/100g, control: 4.90±1.04, ABT: 0.95±0.13*; FE Na+, %, control: 0.147±0.004, ABT: 0.067±0.008*) and also during R (CNa+; control: 3.30±0.05, ABT: 1.25±0.29*; FENa+, control: 0.389±0.117, ABT: 0.107±0.023*). (# p<0.05 vs basal, * p<0.05 vs control). Our results indicate that 20-HETE is involved in DA-induced Na+,K+-ATPase inhibition, acting as a second messenger in its intracellular signalling. 20-HETE also participates in the natriuretic response to moderate extracellular volume expansion, probably acting at the tubule level.