Abstract 055: Sex Differences in the Development of Age-Dependent Hypertension and the Salt Sensitivity of Blood Pressure

Abstract

Aim: Age-dependent hypertension (HTN) develops at different rates in men versus women. These studies tested the hypothesis that in a model of normal aging, the Sprague Dawley rat, alterations in fluid and electrolyte balance contribute to age-dependent HTN in a sex-dependent manner. Methods: Three, 8 and 16-month old male and female SD rats on a normal salt (NS; 0.6% NaCl) diet underwent an acute IV volume expansion (VE; 5% body weight) and mean arterial pressure (MAP), diuresis and natriuresis were assessed. In separate groups of aged rats fed a 21-day NS or high salt (HS; 4% NaCl) diet in vivo MAP and NCC activity (ΔUNaV to IV hydrochlorothiazide, 2mg/kg) were assessed. N=4-6/gp. Results: The diuretic and natriuretic responses to an acute VE are profoundly blunted in aged male, but not female, rats. In contrast to female rats, male rats exhibit age-dependent HTN on a lifelong NS intake and develop age-dependent salt sensitivity of blood pressure. Female rats exhibit higher baseline sodium chloride cotransporter (NCC) activity and both young male and female rats exhibit dietary sodium evoked suppression of the NCC that is lost with age. Conclusion: Aging in the Sprague Dawley rat is associated with the sex specific development of age dependent HTN and the salt sensitivity of blood pressure in the male vs. female rat. We speculate that this sex specific difference is related to the impaired ability of male rats to maintain fluid and electrolyte homeostasis - potentially via a mechanism involving increased age-dependent baseline NCC-mediated sodium retention.