Approximately 20 -40% of adolescents have shown a reduction of urinary sodium excretion (U Na V) in response to blood pressure (BP) increase during behavioral stress. G protein-coupled receptor kinase 4 (GRK4) mediates the pressure and natriuresis relation. The present study investigated the impact of GRK4 genetic variants on U Na V under stress. A total of 664 normotensive adolescents including whites and blacks (17.6 Ϯ 3.3 yrs, 43.4% blacks) were recruited. Participants were subjected to a stress-protocol including three 10-min tasks (a social competence interview, a virtual reality car driving simulation test, and a video game challenge), concluded by a urine collection. Three functional polymorphisms including R65L, A142V and A486V were genotyped. Given blacks compared with whites had significantly higher systolic BP (SBP) levels during rest (p Ͻ 0.001) and stress (p Յ 0.001), there was no statistical difference in U Na V in response to stress between the two ethnic groups. In blacks, compared with R65R homozygotes, individuals with R65L or L65L genotype had significantly lower levels of stress-induced U Na V (8.42 Ϯ 0.63 versus 9.85 Ϯ 0.37 mEq/h, p ϭ 0.01). In summary, BP elevation seems uncoupled with U Na V increase during behavioral stress in black adolescents. The 65L allele of the GRK4 gene is associated with stress-induced U Na V reduction, suggesting impaired sodium handling in affected black youth. E ssential hypertension is determined by gene and environment interactions, and has its origin in childhood. Blood pressure (BP) increase during a sustained period of behavioral stress is typically accompanied by a compensatory increase in urinary sodium excretion (U Na V) (1,2). Our previous data show that an inadequate compensatory increase in U Na V in response to stress occurs in 20 -40% of adolescents aged 15-19 y (Harshfield et al. Annual Meeting of Society of Behavioral Medicine, April 13-16, 2005, Boston), which may predict the development of hypertension (1,2). In particular, we have recently demonstrated that U Na V in response to stress is a heritable phenotype in a multi-ethnic cohort of adolescents (Ge et al., Annual meeting of the American Society of Human Genetics, October 25-29, 2005, Salt Lake City). However, no candidate gene association study has been performed to date. Dopamine enhances renal sodium excretion, diuresis and natriuresis via dopamine receptors D (DRD) in the renal proximal tubules (3-5). G protein-coupled receptor kinase 4 (GRK4) regulates DRD1 phosphorylation, desensitization and internalization (6,7). Although functional single nucleotide polymorphisms (SNPs) of the GRK4 gene have been associated with hypertension in adult populations (8 -11), the impact of these variants on sodium homeostasis in humans remains unknown. Thus we conducted association analyses of the GRK4 polymorphisms in relation to stress-induced U Na V in a sample of young normotensive white and black twins.
METHODS
Study population.A total of 664 normotensive twin subjects including whites a...