Caloric restriction alters arterial blood pressure and baroreflex responsiveness of the spontaneously hypertensive rat

Aging is associated with an increase in blood pressure and the occurrence of hypertension. Caloric restriction retards the aging process, in general, and is a commonly used therapeutic approach to the control of high blood pressure. The aim of this study was to examine the effects of long term caloric restriction on mean arterial blood pressure, heart rate and the baroreflex responsiveness of spontaneously hypertensive (SH) rats. Male, 3-month-old SH rats were allowed to eat ad libitum or were fed only 60% of the ad libitum amount. After 4 months, cannulas were inserted in the left femoral artery and vein under anesthesia. On the following day the blood pressure and heart rate were measured in the conscious rat. The basal mean arterial pressure of the calorie restricted rats (166±4 mm Hg, N=5) was significantly less than that of the ad libitum fed rats (182±4 mm Hg, N=4). The basal heart rates of the calorie restricted and ad libitum fed rats were 296±12 beats/min and 323±8 beats/min, respectively. The difference between the means was not significant (p>0.1). Nitroprusside and phenylephrine infusions were used to induce hypotensive and hypertensive episodes, respectively. For nitroprusside, the relationship between the change in mean arterial pressure and the reflex heart rate response was significantly steeper in the calorie restricted group (1.90±0.37 beats/min/mm Hg) than in the ad libitum fed group (0.86±0.1 beats/min/mm Hg). For phenylephrine the relationships were 0.98±0.09 and 0.52±0.18 beats/min/mm Hg, respectively. These results demonstrate that chronic caloric restriction reduces mean arterial pressure and enhances baroreflex responsiveness in the SH rat.