Evidence for genetic determination of specific food choices of rats.

To study the contributions of genetics to food selection in an omnivorous species, rats of two strains and rats derived from reciprocal crosses of the two strains were compared. In addition, offspring of rats that accepted a specific food (ham) were compared with offspring of rats that refused the same food, and food selection of males was compared with that of females. Both homozygous nonobese Zucker rats and Zucker x Sprague-Dawley hybrid rats ate butterscotch, semisweet chocolate, and ground beef more often than Sprague-Dawley rats did. In contrast, Zucker rats ate ham more often than hybrid rats did, and hybrid rats in turn ate ham more often than Sprague-Dawley rats did. Rats produced by the two reciprocal crosses were similar to each other in food selection, ruling out maternal environment effects as the explanation for differences between Zucker and Sprague-Dawley rats. Hybrid rats selected for rejecting ham produced offspring that ate ham less often than did offspring of rats that accepted ham. Females ate semisweet chocolate more often than males did. We conclude that, contrary to the widely accepted view, heredity significantly influences specific food choices in an omnivorous species.

Adipocyte diameter distributions and body fat contents of sedentary and exercised female Zucker rats.

The objective was to determine whether adipocyte diameter distributions were asymmetric in lean and obese female Zucker rats under conditions of ordinary activity (sedentary controls) as well as under conditions of enforced treadmill exercise. In sedentary animals, adipocyte diameter distributions were asymmetric in both lean and obese rats. Exercise abolished the asymmetry and markedly reduced body fat content of lean rats but had no such effects in obese ones. In contrast, exercise had no effect on average adipocyte diameter in either lean or obese rats. Results suggest that ability of exercise to reduce body fat content is more closely related to a decreased proportion of small adipocytes than to decreased average adipocyte diameter in female Zucker rats.

Isoproterenol-induced mortality and cardiac lipids of aspirin-pretreated rats with various fat intakes.

The effect of altering cardiac concentrations of precursors and inhibitors of prostaglandin synthesis by varying fat intake was determined in rats injected with the cardiotoxic drug isoproterenol, following pretreatment with aspirin or potassium phosphate buffer solution. Prior to injection, four groups of rats were fed either a low-fat diet (3.7 energy percent coconut oil or 3.7 energy percent safflower oil) or a high-fat diet (3.7 energy percent safflower oil-36.4 energy percent coconut oil mixture or 40.1 energy percent safflower oil.) Mortality as well as fatty acid composition of cardiac lipids changed in response to altered kinds and amounts of fats. Mortality and cardiac C20:4/C22:6 ratio were lowered by feeding 3.7 energy percent coconut oil, and increased by feeding 40.1 energy percent safflower oil. Aspirin reduced mortality in rats fed 40.1 energy percent safflower oil, but not in rats fed other diets. Results suggest that dietary manipulations which increase tissue content of polyunsaturated fatty acids of the n-6 type relative to those of n-3 type may increase sensitivity to isoproterenol, and that effectiveness of aspirin in reducing isoproterenol-induced mortality depends upon the n-6/n-3 ratio of cardiac fatty acids.