GRK5 Gln41Leu polymorphism is not associated with sensitivity to beta(1)-adrenergic blockade in humans

Abstract

Aims: A common, functionally significant polymorphism in GRK5 (Gln41Leu) encodes a gain-of-function enzyme that enhances desensitization of the beta(1)-adrenergic receptor. GRK5 Leu41 has been postulated to confer endogenous 'genetic beta-blockade' and contribute to an attenuated response to beta-blockers in black subjects. The effects of this GRK5 variant on sensitivity to a beta-blocker have not been studied in humans. We hypothesized that the GRK5 Gln41Leu variant contributes to interindividual variability in response to beta-blockade and to the ethnic difference in sensitivity between black and Caucasian individuals.

Materials & methods: We measured the heart rate at rest and during a graded incremental exercise in 154 healthy subjects (85 white and 69 black) before and after an oral administration of 25 mg atenolol. We determined the genotypes of GRK5 (Gln41Leu), beta(1)-adrenergic receptor (ADRB1 Ser49Gly and Arg389Gly) genotypes and plasma atenolol concentrations. The effects of genotype and covariates on sensitivity to atenolol, measured as the reduction in exercise-induced tachycardia, were determined using multiple regression analyses.

Results: The minor allele frequency of GRK5 Leu41 was 32.6% in blacks and 0% in whites. Black individuals were less sensitive to atenolol than white individuals (p < or = 0.011) but this was not explained by the GRK5 genotype. The GRK5 genotype had no effect on resting heart rate before (p = 0.61) and after adjustment for age, sex, ethnicity, atenolol concentrations, BMI and ADRB1 genotypes (p = 0.81). The decrease in heart rate after atenolol administration did not differ significantly according to the GRK5 genotype at rest or after exercise, before (all p > 0.14) and after statistical adjustment for covariates (all p > 0.17).

Conclusion: The GRK5 Gln41Leu polymorphism does not affect sensitivity to the beta(1)-adrenergic blocker, atenolol, during acute physiological adrenergic stimulation, nor does it contribute to the ethnic differences in sensitivity to atenolol among black and Caucasian individuals.

Figures

Figure 1. Heart rate reduction after atenolol administration in GRK5 genotypes

(A) Unadjusted reduction in heart rate at rest and incremental exercise in GRK5 Gln41Leu genotypes after atenolol administration for both black and white subjects. Data points represent the unadjusted mean reduction in heart rate in the three genotype groups; error bars represent standard deviation. There was no significant difference between genotypes at any point (all p > 0.14), and the area under the curve was not significantly different among genotypes (p = 0.29). (B) Unadjusted reduction in heart rate at rest and incremental exercise in GRK5 Gln41Leu genotypes after atenolol administration for black subjects only. Data points represent the unadjusted mean reduction in heart rate in the three genotype groups; error bars represent standard deviation. There was no significant difference between genotypes at any point (all p > 0.33), and the area under the curve was not significantly different among genotypes (p = 0.49).