Dietary obesity and weight cycling in rats: a model of stress-induced hypertension?

The present study was designed to reproduce the mild hypertension seen in dietary obese weight-cycled rats [P. Ernsberger and D. O. Nelson. Am. J. Physiol. 254 (Regulatory Integrative Comp. Physiol. 23): R47-R55, 1988] and determine whether this mild hypertension was associated with changes in sodium excretion and pressor responsiveness to angiotensin II (ANG II). Male Sprague-Dawley rats were fed pelleted chow (Pellet group) or chow plus sweetened condensed milk (Milk group) or were exposed to four cycles of a 4-day fast alternated with 2 wk of refeeding of pelleted chow and sweetened condensed milk (Cycled group). Blood pressure and heart rate were measured by tail cuff at the onset and last day of each fast and after 3 days of refeeding. During fasting, urine sodium excretion was measured. Mean arterial pressure and heart rate responses to intravenous administration of ANG II (40, 80, and 120 ng/kg), metoprolol (1 mg/kg), and methyl scopolamine (2 mg/kg) were obtained from the femoral artery in awake unrestrained rats. Weight cycling did not lead to mild hypertension or increased bradycardic response to sympathetic blockade with metoprolol. ANG II-elicited pressor responses were similar for Pellet, Milk, and Cycled groups. Sodium excretion did not change with fasting. Mild hypertension developed when obese weight-cycled rats were housed together in groups and not when housed individually. Our preliminary data are consistent with the notion that stress associated with group housing may be a factor in the mild hypertension of obese weight-cycled rats.