LONG-TERM CALORIE RESTRICTION ENHANCES BAROREFLEX RESPONSIVENESS IN FISCHER 344 RATS

Diet influences many aspects of cardiovascular function. Restriction of caloric intake represents a major nonpharmacological means of reducing blood pressure. The aim of the present work was to determine the effects of long-term calorie restriction on mean arterial pressure (MAP) and baroreflex responsiveness of the conscious, normotensive, nonobese Fischer 344 male rat. From 6 wk of age rats ate either ad libitum or 60% of the amount consumed by those eating ad libitum. Calorie restriction had no effect on MAP of rats 12-14 mo of age; the MAP for the ad libitum fed and calorie-restricted groups were 114.6 +/- 1.6 and 111.6 +/- 0.8 mmHg, respectively. Basal heart rate (HR), however, was reduced from 396 +/- 6 beats/min in the ad libitum-fed group to 333 +/- 5 beats/min in the calorie-restricted group. Administration of sodium nitroprusside (SNP) (both as bolus and constant infusion) and phenylephrine (PE) (bolus alone) elicited tachycardia and bradycardia in both groups. The calorie-restricted group exhibited greater baroreflex responsiveness to hypotensive stress than did the ad libitum-fed group. For constant infusion of SNP, the baroreflex gain of the calorie-restricted group (-5.43 +/- 0.56 beats.min-1.mmHg-1) was significantly greater than that of the ad libitum-fed group (-2.14 +/- 0.19 beats.min-1.mmHg-1). Bolus injections of SNP elicited similar results. Calorie restriction only minimally altered the baroreflex responsiveness to hypertensive stress elicited by bolus injections of PE, although the relationship between HR and MAP was shifted to the left in the calorie-restricted group. These results indicate that, although long-term calorie restriction exerts no effect on MAP, it enhances baroreflex responsiveness and decreases HR.