RENAL-ARTERY STENOSIS AND ISCHEMIA - EFFECT ON RENAL BLOOD-FLOW AND EXTRACTION FRACTION

The clearances of [I-131]orthoiodohippurate and Tc-99m-mercaptoacetylt riglycine provide a measure of effective renal plasma flow, yet these clearances are proportional to renal plasma flow only if the extractio n fraction remains constant. To determine the effect of unilateral ren al artery stenosis, captopril, renal ischemia, and partial renal vein occlusion on renal blood how and the extraction fraction of [I-131]ort hoiodohippurate, Tc-99m-mercaptoacetyltriglycine, and [I-125]iothalama te, we conducted a series of constant infusion studies in Sprague-Dawl ey rats. Renal artery flow reduction of approximately 70% decreased th e extraction fraction of all three agents (P less than or equal to.05) . Captopril had no effect on extraction fraction in controls, but it p roduced a further decrease in extraction fraction of Tc-99m-mercaptoac etyltriglycine and [I-131]orthoiodohippurate in rats with renal artery stenosis (P less than or equal to.05). Ischemia resulted in a 16% dec rease in flow (P<.01) but a much larger (47% to 65%) decrease in extra ction fraction of all three agents (P<.002). Partial renal vein occlus ion also decreased the extraction fraction of all three agents (P less than or equal to.05). The changes in extraction fraction imply that t he clearances of [I-131]orthoiodohippurate and Tc-99m-mercaptoacetyltr iglycine in disease states may not be proportional to renal plasma flo w. Furthermore, in rats with renal artery stenosis it appears that ren al blood flow must fall below a critical threshold of approximately 58 % before extraction fraction decreases; as renal blood flow is further reduced below this threshold, there is a corresponding reduction in e xtraction fraction (P<.01).