Dietary manipulation of cardiac and aortic smooth muscle reactivity to isoproterenol

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Abstract
The responsiveness to isoproterenol of isolated atria and aortic strips was examined in 2 groups of male Fischer 344 rats. Group A (control) was composed of 5 mo.-old rats fed ad libitum; group R (experimental) was composed of rats whose food intake had been restricted for 2 mo. to 60% of that consumed by group A. Aortic strips obtained from group R and preconstricted with 30 mM K+ relaxed by 18% when challenged by a maximal concentration of isoproterenol (1 .mu.M). This relaxation was significantly less than the 28% relaxation observed with strips from group A. No effect on the inotropic response of the left atria or on the chronotropic response of the right atria to maximal concentrations of isoproterenol was observed. A slight but statistically significant increase in sensitivity to isoproterenol was observed in the inotropic response of the left atria. The 50% effective concentration (EC50) for the isoproterenol-stimulated increase in force development observed with group R was 0.87 .+-. 0.16 .times. 10-8 M, which was significantly less than the value of 1.56 .+-. 0.28 .times. 10-8 M obtained with atria from group A. Food restriction exerted no significant effect on the EC50 for the chronotropic response of right atria to isoproterenol. Both the body weight and the heart weight of group A were greater than those of group R. The ratio of heart weight to body weight was significantly greater in group R than in group A. Food restriction imposed for periods even as short as 2 mo. can evidently elicit changes in vascular smooth muscle function. Cardiac muscle reactivity can also be altered by dietary manipulation.