Maintenance of endothelin-induced renal arteriolar constriction in rats is cyclooxygenase dependent

Influence of arachidonate cyclooxygenase (COX) prod ucts on endothelin (ET)-evoked renal vasoconstriction was assessed. In microperfused rat afferent (AA) and efferent arterioles (EA), indomethacin had no effects on the maximal contraction of both AA and EA by ET, but reduced the duration of ET-induced constriction in both arterioles. ET infusion to rats in vivo resulted in a selective increase in efferent but not afferent arteriolar resistance, leading to a dramatic increase in transcapillary hydraulic pressure difference. Glomerular filtration rate (GFR), which fell progressively during infusion of ET alone, was markedly preserved by COX inhibition, but not during selective thromboxane A₂ antagonism. In isolated glomeruli, release of prostaglandin (PG) F_2α in response to 10^-6 mol/l ET exceeded that of PGE₂ by a ratio of 3:2. Collectively, these data provide strong evidence that locally released COX products, possibly PGF_2α, play a key role in sustaining ET-induced renal arteriolar constriction. COX inhibition leads to acute vasorelaxation of AA despite continued ET administration, without affecting EA constriction in vivo, thereby resulting in a dramatic reversal of the effects of ET on GFR.