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Abstract
The effect of intrarenal infusion of ouabain (90 μg/kg) on renin release was examined in the anaesthetized dog. Ouabain reduced cortical Na-K-ATPase activity to 23% and outer medullary activity to 18% of the control level. During renal arterial constriction to a perfusion pressure below the autoregulatory range, renin release rose from 1.2 ± 0.4 to 47.4 ± 6.9 μg/min (P=0.02) This response was abolished by ouabain. When superimposed on renal arterial constriction, beta-adrenergic stimulation enhanced renin release from 25.6 ± 10.7 to 56.9 ± 9.5 μg/min(P=0.02) at a urinary sodium excretion of 2 ± 1 μmol/min. After ouabain, the corresponding increment substantially decreased since release rose from 5.6 ± 2.0 to 19.9 ± 5.3 μg/min only (P = 0.02), at a urinary sodium excretion of 140 ± 67 μmol/min. When glomerular filtration was reduced to zero by ureteral occlusion in one series, renin release increased to 22.6 ± 5.1 but was reduced (P<0.05) by ouabain to 13.5 ± 5.5 μg/min and superimposed isoproterenol had no effect. According to these observations, ouabain inhibits renin release by a direct effect on the afferent arteriole through constriction of the autoregulating renin-secreting segment.