Adiposity Is Related to Gender Differences in Impaired Stress-Induced Pressure Natriuresis

Abstract

Abstract-The purpose of this study was to determine if there are gender differences in stress-induced pressure natriuresis and to examine the effects of adiposity on these differences. The subjects were 151 boys and 141 girls 15 to 18 years of age who underwent a 5-hour stress protocol (2-hour prestress, 1-hour stress, 2-hour poststress) after being brought into similar levels of sodium balance. The gender-by-condition interaction was significant for systolic and diastolic blood pressure (Pϭ0.001 for both), and the effect of condition was significant for sodium excretion (Pϭ0.001). Key Words: gender Ⅲ obesity Ⅲ stress Ⅲ sodium Ⅲ blood pressure Ⅲ natriuresis Ⅲ hypertension, sodium-dependent W e hypothesized 1 that impaired stress-induced pressure natriuresis contributes to the development of essential hypertension (HTN) and blood pressure (BP)-related target organ damage by increasing the cardiovascular load experienced as a result of the stress. Our definition of impaired stress-induced pressure natriuresis is an increase in BP during an extended period of stress without an adequate compensatory increase in urinary sodium excretion (U Na V). We provided indirect support for our hypothesis in a recent study 1 in which black compared with white youths had slower natriuresis across a series of stressors. This pattern was associated with cardiac remodeling. We provided additional support for our hypothesis in another recent study 2 that demonstrated that a significant percentage of black youths showed impaired stress-induced pressure natriuresis during an extended stress period, with BP remaining elevated as long as 2 hours after the cessation of the stressor. Subsequently, we reported 3 that obese compared with lean youths had slower natriuresis during an extended stress period despite similar levels of BP.The well-documented gender differences in cardiovascular disease and HTN have received increased attention in recent years (for recent reviews, see References 4 through 7) 4 -7 . Furthermore, gender differences in cardiovascular responses to acute stress have long been recognized. 8,9 The first goal of this study was to determine if there are gender differences in changes in BP and U Na V during extended stress. A second goal was to determine if these differences are related to adiposity. A final goal was to examine the roles of angiotensin (Ang) II and insulin on the response patterns in a subgroup of boys and girls. Methods Study PopulationThe protocol was approved by the Human Assurance Committee of the Medical College of Georgia. Written informed parental consent and subject assent were obtained before testing. The subject characteristics are provided in ProtocolOur protocol has been described previously in detail. 2,3 Briefly, the subjects were placed on a controlled sodium diet of 4000Ϯ200 mg/d for 3 days before testing. 10 On the fourth day, the subjects performed the stress protocol. The stress protocol included a pretest period of 2 hours, during which the subjects watched movies and/or listened to

Update on G-protein polymorphisms in hypertension

“…Previously, our group, led by Harshfield, developed a theoretical model and protocol to study the impact of stress on sodium handling in the hypertensive process by examining the pressure natriuresis response to a period of extended competitive stress [30,31]. Using this model, impaired stress-induced pressure natriuresis (SIPN) is defined as an increase in BP during a period of extended stress without an adequate compensatory increase in urinary sodium excretion (U Na V) to contribute to the return of BP to pre-stress levels-that is, homeostasis.…”

Stress-induced sodium retention and hypertension: A review and hypothesis

“…We did not observe changes in adrenocorticotropic hormone, or in relationships between adrenocorticotropic hormone and sodium excretion during stress in our initial study on adults [7]. In addition, we did not observe an association between changes in insulin and sodium retention throughout our protocol [15,16]. …”

“…Percent of body fat independently accounted for 4.6% of the variance of the stress-induced change in sodium excretion and 11.2% of the variance of sodium excretion during stress. In our third study on 151 boys and 141 girls, Harshfi eld et al [15] reported that body mass index was inversely related to sodium excretion during the stress period in boys. The magnitude of the correlation became greater when considering only boys with a body mass index greater than 25.…”

“…Studies in youths (ages 15-18 years) provided additional support [15,41]. In one study, our group reported a marginal inverse correlation between angiotensin II and sodium excretion during stress in a cohort of boys [15]. In a second study, our group reported that angiotensin II accounted for 6.1% of variance of sodium excretion during stress in a model that included race, sex, and measures of adiposity [41].…”

“…This increase was blocked with ACE inhibition. Studies in youths (ages 15-18 years) provided additional support [15,41]. In one study, our group reported a marginal inverse correlation between angiotensin II and sodium excretion during stress in a cohort of boys [15].…”