Dietary fish oil promotes positive inotropy of ouabain in the rat heart

We tested the hypothesis that a fish oil (FO) diet promotes positive inotro py of ouabain without increased toxicity. For 2 mo, two groups of adult mal e rats were fed I) a regular food diet supplemented with dietary long-chain polyunsaturated fatty acid from FO or 2) a regular food diet (control). Th e responsiveness to ouabain was evaluated for the two groups in Langendorff -perfused hearts, by P-31 nuclear magnetic resonance spectroscopy, and on p urified membrane-bound Na-K-ATPase. The maximum positive inotropy achieved with ouabain was nearly two times higher in the FO than in the control grou p and was not associated with significant changes in energetics. Alteration of function and energetic metabolism and inhibition of Na-K-ATPase in resp onse to 3 x 10(-4) M ouabain were delayed in the FO group. This study demon strates that dietary FO, by a cardiac membrane incorporation of n-3 polyuns aturated fatty acid, promotes positive inotropy of ouabain without toxicity and changes in cardiac metabolism.