Abstract
The intrarenal gradient of renin activity was determined in rats by using superficial (S) and deep (D) cortical juxtaglomerular apparatuses (JGA's), identified and microdissected after silicone-rubber compound injection. Angiotensin generated from single JGA's using partially purified sheep renin substrate was quantified by rat bioassay. When, in rats on a normal NaCl diet, silicone-rubber was injected into a carotid artery, alone or with abdominal aorta catheterization, S:D renin activity ratios were 1.18+/-0.08 (SEM) and 1.21+/-0.12, respectively. The S:D renin activity ratios obtained when silicone-rubber was injected into the abdominal aorta (2.52+/-0.09) or a chronic carotid artery catheter (3.44+/-0.40) were significantly higher (P < 0.001). The lower S:D renin activity ratios after carotid artery manipulation were due to significantly higher D-JGA renin activities. This increased D-JGA renin activity and the lack of a renin gradient appear to be related to acute carotid artery manipulation. Alterations in JGA renin activity were examined relative to NaCl intake. 2 wk after high-NaCl diet the absolute net renin activity decreased (P < 0.001) more in S (5.84+/-0.11 ng AI.JGA(-1).h(-1)) than D (1.73+/-0.06 ng AI.JGA(-1).h(-1)) JGA's, and the intrarenal renin gradient was lost (S:D-JGA renin activity, 1.00+/-0.07), as compared to the regular NaCl diet. 2 wk of a low-NaCl diet resulted in a greater (P < 0.01) increase in S (14.28+/-1.47 ng AI.JGA(-1).h(-1)) than D (9.62+/-1.19 ng AI.JGA(-1).h(-1)) JGA renin activity and a renin gradient (S:D-JGA renin activity) of 1.75+/-0.12. These results demonstrate that NaCl intake clearly influences total JGA renin content and may also affect the relative intrarenal distribution of renin activity.