Genetic polymorphism of the alpha-2 adrenergic receptor and blood pressure in South American Blacks.

The gene for the alpha-2 adrenergic receptor encoded by chromosome 10 (A2AR) is polymorphic, and Southern blotting with a cDNA probe following restriction enzyme digest of this gene results in fragments of either 6.7 kb or 6.3 kb in size. We reported an association between homozygosity for the 6.3 kb allele and hypertension in urban Detroit Blacks. To determine whether the results of this population-based study were due to genetic admixture rather than an effect of the environment, we studied a group of Blacks living in relative isolation in rural, Chicaloma, Bolivia. When compared to Blacks in Detroit, similar frequencies of the polymorphic A2AR alleles were found in 37 Chicaloman Blacks. However, in Chicaloma, high blood pressure, by North American standards, was nonexistent. Furthermore, among Bolivian Blacks, there were no differences between those individuals homozygous for the 6.7 allele or those subjects carrying at least one 6.3 kb allele in systolic blood pressure (117 ± 5 vs. 125 ± 5 mm Hg) or salt excretion (17 ± 3 vs. 18 ± 2 mEq/h, P= n.s.). Similar to Detroit Blacks, systolic blood pressure was correlated with salt excretion (y = 92.8 + 1.42x, r2=.5, P=0.001) and age (y = 75.7 + 1.2x, r2=.3, P = 0.04), but only in those Chicalomans carrying the 6.3 kb allele. It can be suggested from these data that environmental influences affect susceptibility to high blood pressure as much as genetic admixture.