β₁-Adrenergic Receptor Arg389Gly Polymorphism And Essential Hypertension

Objective: Essential hypertension (EH) is an important risk factor for cardiovascular disease. Epidemiology indicates that EH is a complicated hereditary disease involving both genetic and environmental factors. Between 30% and 50% of blood pressure variation in the population is determined by genetic factor. Researchers pay much attention to the candidate genes of EH. The blood pressure level is determined by two factors: cardiac output and peripheral resistance, both of which are tightly regulated by the sympathetic nervous system. The β1-adrenergic receptor (β1-AR) is the dominant β-AR subtype expressed on myocyte. A number of single nucleotide polymorphisms were identified in the human β1-AR gene. Researchers pay much attention to the two common polymorphisms in the β1-AR. The first polymorphic locus at nucleic acid 145 (A→G) resulted in substitution of Ser for Gly at position49. The second was observed at nucleic acid 1165 (G→C) resulting in substitution of Gly for Arg at position 389. The codon 389 polymorphism is located in the proximal region of the carboxyterminus cytoplasmic tail, and the region is believed to be an important site for receptor coupling to the G-protein. In vitro mutagenesis studies of the codon 389 polymorphism revealed nearly twofold greater basal and threefold greater agonist-mediated adenylyl cyclase activities with the Arg389 receptor form, so we hypothesized that the β1-AR genotype may have functional significance in humans. Although this polymorphism has clearly been shown to be functional in vitro, data on its consequences in vivo are conflicting. And there are ethnic differences in the distribution of the functionally important Arg389Gly polymorphism of the β1-AR. Because the β1-AR is crucial in regulating cardiac output and agents blocking it lower blood pressure, we hypothesized that genetic variants of the β1-AR could be of importance in the development of EH. The aim of the present study was to investigate whether the functionally important Arg389Gly polymorphism of the β1-AR was associated with EH by the technique of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) .Methods: The EH group consisted of 171 subjects (88 men and 83 women), aged 55.67±10.81 years. EH was diagnosed according to the criteria of WHO/ISH in Feb, 1999 (without antihypertensive medication, systolic blood pressure≥140 mmHg and/or diastolic blood pressure≥90 mmHg), without secondary factors. All patients had not used antihypertensive medicine at least for three month. The control group included 124 cases (63 men and 61 women), aged 54.69±10.43 years, from the outpatient clinic for physical examination, excluding acute or chronic disease. All participants were Han national people who had no consanguineous relationship and lived in ShiJiaZhuang or nearby region. Blood pressure was measured in the seated position with a sphymomanometer after 20 minutes of rest, and heart rate was recorded by palpation of the radial artery and recorded for 60 seconds. 5 ml elbow vein blood was drawn from each participant after a fasting period of 12 hours, and injected into test-tube which contained EDTA. leukocytes were drawn for DNA. Determination of Arg389Gly genotypes: Genomic DNA was extracted from leukocytes by a classical procedure, then β1 AR gene was amplified by polymerase chain reaction enzymes, and the resulting fragments were separated on 2% agarose gel electrophoresis, visualized by ethidium bromide staining. The PCR products were digested by BcgI, the resultant DNA fragments are separated by electrophoresis on a 2% agarose gel containing ethidium bromide and visualized under UV light. Statistical analysis: The frequencies of the alleles and genotypes in EH and control groups were compared using Chi- square test, numerical data among two groups using independent-samples t tests. P < 0.05 was considered statistically significant. The statistical software SPSS (version 11.0) was used for all analyses.Results: The baseline characteristics (age, gen...