Renal function and renin secretion after administration of ouabain and ouabain plus furosemide in conscious sheep.

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Abstract
The effects of ouabain or ouabain and furosemide on renal function and renin secretion were studied in conscious isovolemic sheep. The sheep received a continuous renal arterial infusion of papaverine, 7 mg/min, throughout the experiment. Ouabain alone (7 X 10(-7) M in the renal plasma) produced significant decreases in glomerular filtration rate (GFR) and renal plasma flow (RPF) but not in renal perfusion pressure. Plasma [K+] rose after ouabain administration. Fractional (FENa) and absolute (UNaV) Na+ excretion were 2.9 +/- 1.0% (mean +/- SE) and 78 +/- 54 muEq/min, respectively, during the papaverine infusion and rose to 19 +/- 5.1% (P less than 0.05) and 528 +/- 116 muEq/min (P less than 0.01) after ouabain administration. Despite the large changes in Na+ reabsorption, renin secretion was not stimulated. During the control period, renin secretion was 281 +/- 131 ng/min and the average renin secretion after ouabain administration was 310 +/- 78 ng/min (not significant). A smaller dose of ouabain (2 X 10(-7) M) infused into the renal artery with 40 mg of furosemide, iv, did not decrease GFR but RPF was suppressed. FENa and UNaV averaged 4.4 +/- 1.6% and 121 +/- 44 muEq/min, respectively, while papaverine was infused into the renal artery and increased to 18 +/- 4.8% (P less than 0.05) and 636 +/- 209 muEq/min (P less than 0.05) after ouabain and furosemide were infused. Renin secretion was 118 +/- 62 ng/min during the control period and averaged 240 +/- 67 ng/min after ouabain plus furosemide. The difference was not statistically significant. Thus ouabain alone does not stimulate renin secretion in the conscious, isovolemic sheep despite a presumed increase in [NaCl] at the macula densa and inhibition of NaCl transport by the loop of Henle. Ouabain also blocks the normal stimulatory effects of furosemide on renin secretion.