INTRARENAL DISTRIBUTION AND ATPase INHIBITING ACTIVITY OF OUABAIN IN DOGS

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Abstract
Experiments were undertaken to substantiate the hypothesis that the mechanisms of the direct effect of ouabain on the renal excretion of electrolytes is the result of inhibition of the transport enzyme, (Na, K)-ATPase. In dogs hydrated with saline, 3H-ouabain injection into the unilateral renal artery produced a continuing marked increase in excretion of H2O and Na from the kidney, but not from the counter kidney. At maximal diuresis-90 min after ouabain injection, both kidneys were removed to assay microsomal ATPase activity and determine radioactivity distributed in subcellular structures. 3H-ouabain was deposited in the microsome fraction obtained from the injected kidney in concentrations ranging from 10-7 to 10-6 M/kg wet wt, and (Na, K)-ATPase activity of this fraction was inhibited as compared with that of the microsomal fraction obtained from control kidneys. Since (Na, K)-ATPase activity of renal microsomes was significantly inhibited in vitro by more than 10-7 M of ouabain, ouabain concentration in microsomes obtained from the injected kidney was considered to be sufficient to inhibit ATPase activity. Ouabain diuresis under these conditions is closely related to direct inhibitory effect of ouabain on (Na, K)-ATPase activity of microsomes in tubular cells.

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