Influence of dietary polyunsaturated fatty acids on contractility, lusitropy and compliance of isolated rat myocardium

Two groups of 15 rats were fed for 4 weeks with diets containing 15% by weight of fat varying in polyunsaturated fatty acids (PUFA) content and type. Diet C18:2 (n-6) contained 20% of total fatty acids as linoleic acid and small amount of (n-3) PUFA (0.4% of the total fatty acids). Diet LC (n-3) contained the same amount of 18:2 (n-6) and of long chain (n-3) C20 and C22 PUFA (10% of the total fatty acids). Contents of both saturated fatty acids and amount of total PUFA were kept constant in the two diets. Left ventricular papillary muscle mechanics were studied blind at Lmax and over the entire load-continuum, in terms of inotropy, characteristics of the force-velocity relationship, relaxation and compliance. Inotropy, force-velocity relationships and muscle compliance were similar in both groups. There was a trend towards a lower peak lengthening velocity at preload in the LC (n-3) group (P=0.10) together with an unchanged peak rate of isometric force decline. This resulted in a significant impairment of the two mechanical indexes testing the load dependence of myocardial relaxation (P=0.019 and P=0.002). In conclusion, short-term differences in PUFA regimen were associated with an unchanged myocardial contractility and economy of force generation. The decreased load dependence of relaxation together with unchanged myocardial compliance strongly favored a physiological relevance of the previously reported modifications of sarcoplasmic reticulum phospholipid composition and calcium transport under (n-3) PUFA regimen.