NOREPINEPHRINE KINETICS IN OLDER WOMEN: RELATIONSHIP TO PHYSICAL ACTIVITY AND BLOOD PRESSURE

Abstract

1552 The sympathetic nervous system (SNS) participates in the regulation of carbohydrate, lipid, and energy metabolism, and has been implicated in the pathogenesis of hypertension and obesity. Increased SNS activity with age may alter disease risk and contribute to the development of certain chronic diseases. Thus, we examined possible determinants of SNS activity in older normotensive women from infusions of tritiated norepinephrine (NE) to estimate rates of plasma NE appearance and clearance. A secondary aim was to examine the association between NE kinetics and mean supine arterial blood pressure. Twenty-two older women (65.7 ± 5.7 y) were characterized for resting NE kinetics, body composition, body fat distribution, peak aerobic capacity, leisure time physical activity energy expenditure (LTA), dietary carbohydrates, and daily energy intake. Analysis of univariate correlations revealed that only the LTA was significantly correlated with plasma NE appearance (r = 0.54, p <.01). Stepwise regression analysis identified LTA as the only significant predictor of plasma NE appearance rate with a total R2 = 0.30. Waist-to-hip ratio was selected as the only significant predictor of mean arterial blood pressure with an R2 = 0.29. When forced into the model, plasma NE appearance explained only 1% of the unique variance in mean arterial blood pressure. In summary, we found that: 1) higher levels of physical activity are related to higher plasma NE appearance in older women; 2) greater central body fatness is an independent predictor of mean arterial blood pressure; and 3) plasma NE appearance rate is a minor contributor to variation in mean arterial blood pressure in older, normotensive women.