Renal renin content and release decrease from outer to inner cortex; this may be due to a cortical-to-medullary gradient in glomerular density and/or renin content per afferent arteriole. Although low sodium diets have been reported to decrease the tissue renin gradient, little information is available on renin release by different areas of the renal cortex or the effect of a low sodium diet. In the present study, we examined basal- and isoproterenol-stimulated renin release and content in microdissected superficial, midcortical, and juxtamedullary afferent arterioles from rabbits on normal and low sodium diets. Renin content was 25.8 ± 3.6, 1.4 ± 0.32, and 0.27 ± 0.09 ng angiotensin I (Ang I)/hour/arteriole in the superficial, midcortical and juxtamedullary arterioles, respectively. Dietary sodium restriction significantly increased it to 60.1 ± 7.3, 13.8 ± 3.1, and 1.48 ± 0.6, respectively. Renin release was 0.64 ± 0.13, 0.15 ± 0.04, and 0.025 ± 0.013 ng Ang I/hour/arteriole/hour incubation of arteriole in the superficial, midcortical and juxtamedullary arterioles, respectively. With sodium restriction it increased significantly for the superficial, (1.77 ± 0.27) and midcortical (0.62 ± 0.11) but not the juxtamedullary arterioles (0.038 ± 0.02). With either diet, renin release and content among the three types of arterioles were significantly different. Isoproterenol (1.6 × 10-4 M) significantly stimulated renin release from all three types of arterioles whether rabbits were fed a normal or low sodium diet; however, only in the superficial arterioles was the increase (Δ) greater with dietary sodium restriction. In summary, in microdissected rabbit afferent arterioles, there are steep cortical-to-medullary gradients in renin content and release per arteriole which are maintained after dietary sodium restriction; the effect of dietary sodium restriction on both renin content and basal or isoproterenol-stimulated release is greater in superficial than deeper arterioles.
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