Preliminary Evidence of Linkage of Salt Sensitivity in Black Americans at the β 2 -Adrenergic Receptor Locus

Abstract

Salt sensitivity is a heritable trait that is a hallmark of hypertension in black Americans. Genes encoding adrenergic receptors are candidate loci for the inheritance of this hypertension-related trait because of the role of these receptors in the regulation of renal sodium excretion and vascular tone. We performed this study to determine whether these loci are responsible for some of the phenotypic variation in salt sensitivity. Hypertensive black American probands were ascertained, followed by sequential ascertainment of adult sib pairs among the first-, second- and third-degree relatives of the proband. Both hypertensive and normotensive siblings were tested for salt sensitivity by an intravenous sodium-loading, lasix volume-depletion protocol. Genotyping was performed with restriction fragment length polymorphisms in genomic DNA probed with clones containing the β ₂ - and α _2c10 -adrenergic receptor genes. A total of 109 sib pairs was evaluated. Salt sensitivity was defined as the change in blood pressure in each individual, comparing the sodium-loaded with the volume-depleted state. Systolic pressure decreased by an average of 9.0±9%, diastolic pressure by 1.5±11%, and mean arterial pressure by 5.0±9%. Neither blood pressure nor salt sensitivity was linked at the α _2c10 -adrenergic receptor locus. No evidence suggested that systolic salt sensitivity and baseline blood pressure were linked at the β ₂ -adrenergic receptor locus. Model-independent sib pair linkage analysis suggested that diastolic blood pressure response to sodium loading/volume depletion is linked at the β ₂ -adrenergic receptor locus ( P <.006). Evidence for linkage was significant at the .05 level after adjustment for the number of phenotypic traits examined.