Renin distribution in the rabbit renal microvasculature

Immunocytochemical studies have shown that renin, which is normally located in the juxtaglomerular afferent arteriole, may also be found farther upstream toward the interlobular artery during chronic stimulation of the renin-angiotensin system. We assessed the renin distribution along the renal microvasculature using both quantitative analysis and immunocytochemistry in rabbits that received a normal sodium diet (0.48% NaCl), a low sodium diet (0.04% NaCl), or enalapril (1 mg/kg/day) for 4 weeks. From the outer cortex we microdissected 1) the proximal portion of the afferent arteriole (p-AF) extending from the interlobular artery to a point 50 μm from the glomerulus, 2) the distal 50 μm including its intact terminus (d-AF), and 3) the glomerulus without the vascular pole (GL) and measured their renin content In controls, renin was 0.3±0.2, 27.0±5.2, and 2.8±0.5 ng angiotensin I/hr/arteriole (or GL) in the p-AF, d-AF, and GL, respectively. The low sodium diet and enalapril increased renin in the d-AF (53.1±6.9 and 68.4±8.1, respectively) but not in the GL (3.3±1.0 and 3.6±0.7). In the p-AF, both caused a small increase (Δ=1.5); however, this increase was minuscule compared with the large increase in the d-AF (Δ=41). Although the average length of positive immunostaining along the afferent arteriole was increased during chronic stimulation, only a small percentage of afferent arterioles showed staining farther than 50 μm from the GL. We conclude that in the rabbit 1) approximately 90% of active renin is located in the d-AF, 1% in the p-AF, and 9% in the glomerulus during a normal sodium diet; and 2) renin content increases almost exclusively in the d-AF during a low sodium diet or enalapril treatment Thus, the GL and p-AF contribute little to the increased renal renin content seen with these chronic stimuli.