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Dietary Fish Oil Confers Direct Antiarrhythmic Properties on the Myocardium of Rats¹

Department of Physiology, The University of Adelaide, SA 5000 ^* Cardiac Research Unit, Commonwealth Scientific and Industrial Research Organisation, Division of Human Nutrition, Adelaide, SA 5000, Australia

This study tested the hypothesis that in vivo antiarrhythmic effects of dietary fish oil can be attributed directly to changes in myocardial properties. Sixty adult male rats were fed a fish oil diet (FO), an isoenergetic saturated fat diet (SAT) or a low fat reference diet (REF) for 16 wk. hearts isolated from these rats were perfused with washed porcine erythrocytes (0.4 hematocrit) in working heart mode. Dietary fish oil prevented reperfusion-induced ventricular fibrillation (VF) (% of rats with VF: REF 50%, SAT 80% P = 0.35, FO 0% P < 0.05 n = 10) and reduced arrhythmias in ischemia. In a separate set of hearts from rats fed the three diets, FO increased while SAT reduced the stimulation threshold for programmed electrical induction of VF during control perfusion compared with REF (mean ± SD: REF 7.1 ± 0.2 mA; SAT 5.8 ± 0.2 mA, P < 0.001; FO 15.1 ± 1.0 mA, P < 0.001, n = 10) and during subsequent ischemia (REF 5.9 ± 0.2 mA; SAT 3.8 ± 0.3 mA, P < 0.001; FO 8.9 ± 0.2 mA, P < 0.001, n = 10). The isolated working heart model used physiological workload and oxygenation but excluded extracardiac influences. Dietary fish oil prevented the initiation and reduced the severity of arrhythmias in the isolated hearts in response to a variety of stimuli. These results establish that irrespective of any effects on blood pressure or platelet function in vivo, dietary fish oil directly affects myocardial properties which may contribute to observed clinical reductions in cardiac mortality associated with fish consumption.

KEY WORDS: • dietary fats (n-3) fatty acids • myocardial ischemia • arrhythmia • rats

¹ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

² Current address: Dr. Salvatore Pepe, Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Johns Hopkins Bayview Research Campus, 4940 Eastern Avenue, Baltimore, MD 21224.

³ To whom correspondence and reprint requests should be addressed.

Manuscript received 5 April 1995. Revision accepted 15 August 1995.