Antihypertensive effects of food-intake restriction in aortic coarctation hypertension

OBJECTIVE: To test the hypothesis that reductions in mean arterial pressure (MAP) induced by food-intake restriction in aortic coarctation hypertension are the result of a reduction of the sympathetic support of the MAP. We also wanted to determine whether the baroreflex control of the heart rate, and alpha- and beta-adrenergic responsivenesses were influenced by chronic food-intake restriction. METHODS: Four days after aortic coarctation, female Sprague-Dawley rats were assigned to a group that had access ad libitum to food (CON; n = 19) or to a food-intake-restricted group (FRG; n = 17) that was allowed 60% of the CON group's food intake per rat. After 3 weeks, carotid and jugular catheters were implanted for measurement of the MAP and infusion of drugs into conscious rats. The sympathetic contribution to the blood pressure was assessed by measuring the depressor response to ganglionic blockade by hexamethonium plus atropine (30.0 and 0.1 mg/kg intravenously). The baroreflex control of the heart rate was assessed by administering alternating bolus doses of phenylephrine and nitroprusside. The alpha-adrenergic sensitivity was assessed by measuring the response of the MAP to phenylephrine in areflexive rats (after ganglionic blockade), and the beta-adrenergic sensitivity was assessed by measuring the responses of the MAP and heart rate to isoproterenol administration both in reflexive and in areflexive rats. RESULTS: Four days after catheterization, both the MAP (CON 150 +/- 5 mmHg, FRG 116 +/- 4 mmHg) and the heart rate (CON 414 +/- 8 beats/min, FRG 365 +/- 11 beats/min) were significantly lower in rats of the FRG. That the sympathetic support of the MAP had diminished in FRG rats was evidenced by an attenuated depressor response to ganglionic blockade (40 +/- 3 versus 65 +/- 3 mmHg). FRG rats exhibited significantly greater reflex bradycardia in response to phenylephrine (slope -1.44+/- 0.07 versus -0.54 +/- 0.05 beats/min per mmHg), whereas their reflex tachycardia was not altered (slope -1.58 +/- 0.08 versus -1.53 +/- 0.13 beats/min per mmHg). FRG rats also displayed blunted responses of the heart rate and MAP to isoproterenol administration. CONCLUSION: Food-intake restriction attenuates the rise in MAP which occurs after aortic coarctation significantly. The antihypertensive effect of food-intake restriction may be mediated via a reduction in sympathetic tone.