Possible mechanism of prostaglandin-induced renal vasoconstriction in the rat.

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Abstract
We studied the role of the renin-angiotensin system in the vasoconstrictor effect induced by prostaglandins (PG) on the renal microcirculation in 25 euvolemic Munich-Wistar rats. Infusions of subvasodepressor doses of PgE2 and PGI2 led to lower mean values for single nephron (SN) glomerular filtration rate (GFR), total kidney GFR, glomerular plasma flow rate, QA, and ultrafiltration coefficient (Kf) than were found in animals given vehicle alone (control group). On the other hand, the mean values for glomerular transcapillary hydraulic pressure difference, delta P, and total renal arteriolar resistance, RTA, tended to be higher in the experimental groups. The effects of PGI2 on the renal microcirculation were more pronounced than for PGE2. These increases in delta P and RTA and decreases in QA and Kf are typical of changes induced by angiotensin II (AII). To further explore this AII-like phenomenon, an infusion of saralasin, a competitive AII antagonist, was used. Indeed, when saralasin was infused together with either PGE 2 or PGI2 the previously noted effects on delta P, QA, RTA and Kf were largely abolished. Thus, saralasin transformed the renal action of PGE2 and PGI2 from vasoconstrictor (low QA, high RTA) to vasodilator (high QA and low RTA). Therefore, the effects of nonvasodepressor doses of PGE2 and PGI2 on the renal microcirculation appear to depend on an intermediate action of AII.