DIETARY-PROTEIN DOES NOT ALTER INTRINSIC REACTIVITY OF RENAL MICROCIRCULATION TO ANGIOTENSIN-II IN RODENTS

The effect of dietary protein on renal function and on renal microvasc ular reactivity to angiotensin II was determined in rats fed a high-pr otein diet (40% protein), a low-protein diet (6% protein), or a normal diet (23% protein). Inulin clearance was higher in high-protein-fed r ats (n = 7) than in rats fed a low-protein diet (n = 7), 0.88 +/- 0.14 (means +/- SE) vs. 0.54 +/- 0.07 ml.min(-1).g kidney wt(-1) (P < 0.05 ). We also used videomicroscopy to assess the effect of angiotensin II on the renal microcirculation in a hydronephrotic kidney preparation. The afferent and efferent arterioles constricted to angiotensin II an d norepinephrine in both high- and low-protein-fed rats; this constric tion was diminished to angiotensin II but not to norepinephrine, in ra ts fed a high-protein diet (-24.3 +/- 4.5, -20.2 +/- 4.2%) compared wi th rats fed a low-protein diet (-39 +/- 5.1, -39.1 +/- 5.7%). The vaso constrictor responses to angiotensin II in rats fed a high-protein die t and a normal diet were significantly greater following inhibition of angiotensin II formation with captopril but not in low-protein-fed ra ts. The apparent high-endogenous level of angiotensin II among rats fe d a high-protein diet may account for the diminished reactivity to exo genous angiotensin II. Thus alterations in intrinsic vascular reactivi ty to angiotensin II are not responsible for the altered hemodynamics associated with dietary protein.