Mechanism of increased renin release during sodium deprivation

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Abstract
During Na deprivation more renin is released and more is stored than during Na loading. These studies sought to determine whether the increased release was directly proportional to the increased renin content, or whether there was in addition an increase in the responsiveness of the release mechanism. Plasma renin activity in Na-deprived rats (46.0 .+-. 2.2 ng/ml per h) (n, 55) was 6-fold greater than that in Na-loaded rats (7.3 .+-. 0.8 ng/ml per h) (n, 29), but renal renin content was only 3-fold greater (45.12 .+-. 2.54 compared to 15.84 .+-. 1.46 .mu.g/g). Basal rate of renin release from the isolated perfused kidneys of Na-deprived rats was 10-fold greater (2.41 .+-. 0.26 .mu.g/h per g) (n, 19) than that from kidneys of Na-loaded rats (0.25 .+-. 0.07 .mu.g/h per g) (n, 8). These values represented 5.6 .+-. 0.9 and 1.6 .+-. 0.4%/h of the amount of renin stored. Lowering the perfusion pressure from 150 to 50 mmHg or perfusing with isoproterenol (2.43 .mu.M) produced a 4-fold increase in renin release and fraction released in kidneys from Na-deprived rats, but not in those from Na-loaded rats, despite a substantial amount of renin stored. During Na deprivation both increased renal renin content and increased responsiveness of the renin release mechanism contribute to the enhanced renin response.