LOCALIZATION OF ENDOTHELIN ET(A) AND ET(B) RECEPTOR-MEDIATED CONSTRICTION IN THE RENAL MICROCIRCULATION OF RATS

1. The aim of the study was to visualize endothelin-1 (ET-1)-mediated constriction in renal vessels of cortical and juxtamedullary glomeruli in the split hydronephrotic rat kidney in vivo and to functionally ch aracterize the ET receptor subtypes involved. 2. ET-1 (10(-9) M) const ricted preglomerular vessels (by 6-18%) and efferent arterioles (by 11 -13%), and decreased glomerular blood flow (GBF, by 55%) of cortical a ny juxtamedullary glomeruli. 3. The ET(A) antagonist BQ-123 (10(-6) M) , as well as the ET(B) antagonist BQ-788 (2 x 10(-7) M) and IRL 1038 ( 10(-6) M), shifted the concentration-response currie of GBF for ET-1 t o the right by one order of magnitude. While BQ-123 antagonized ET-1 c onstriction only in preglomerular vessels, BQ-788 and IRL 1038 were ef fective both in preglomerular vessels and efferent arterioles. 4. The ET(B) agonist IRL 1620 (10(-8) M) reduced GBP by 50% and constricted e fferent arterioles (by 20-33%) about two times more than preglomerular vessels (by 6-14%). 5. Our results suggest that in renal cortical and juxtamedullary vessels of rats, ET-1-induced preglomerular vasoconstr iction is mediated by ET(A) and ET(B) receptors, while efferent vasoco nstriction is predominantly mediated by ET(B) receptors, which might h ave important consequences for the regulation of glomerular filtration pressure by ET.