β₂-adrenergic Receptor Gene Arg16Gly Polymorphism And Essential Hypertension

Objective: Now essential hypertension(EH) is thought to arise from an interaction between susceptible genes and environmental factors .To date ,investigation of the genetic basis of hypertension has largely focused on candidate genes from the rennin-angiotensin system. Indeed,there is support for linkage and association of the angiotensinogen gene to hypertension in two different population of white European origin and African Caribbean ethnicity.The sympathetic nervous system represents the second important regulator of blood pressure through alterations in vascular responsiveness,rennin release ,renal sodium handling,and cardiac output.Accordingly,genetic variation in either the α-adrenoceptor,leading to enhanced vasoconstriction,or β₂-adrenoceptors ,leading to attenuated vasodilatation, might be important for increasing total peripheral resistance and hence blood pressure. Significant evidence has been provided for the pathophysiological involvement of the β₂-adrenergic receptor ( β₂ -AR) in hypertension ,and alteredβ₂-adrenergic regulation has been reported in individuals with hypertension .In the promoter and coding regions ofβ₂-AR ,a total of 17 single-nucleotide polymorphisms have been reported,of which 2 amino-terminal polymorphisms were shown to impart distinct agonist-mediated regulatory properties.That is, an Arg16 →Gly substitution exaggerates agonist-mediated receptor downregulation, whereas Gln27→Glu reduces it .A subsequent conditional analysis suggested that the Arg16Gly polymorphism exerted the predominant effect . Despite intense effort, the relationship betweenβ₂-adrenergic Receptor Gene Arg16Gly Polymorphism and Essential Hypertension remains eclusive. The aim of this study is to test the distribution of β₂AR genotypes in essential hypertensives and normal controls of Chinese Han nation using PCR-RFLP and to investigate the association between β₂-AR Arg16Gly polymorphism and blood pressure,rest heart rate,body mass index and lipide in hypertensive subjects,and analyze the relationship between β₂-AR Arg16Gly polymorphism and hypertension, revealing the functional effects of this polymorphism in vivo, thus supply possible evidence for gene treatment on hypertension. Methods: The hypertensive group consisted of 114 subjects(62 men and 52 women), aged 54.5±11.6 years,who did not take antihypertensive medication for at least three months. 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. Hypertension diagnosed according to the criteria of WHO/ISH in Feb, 1999 (without antihypertensive medication, systolic blood pressure ≥140 mmHg and/or diastolic bloodpressure ≥90 mmHg; or diagnosed and receiving antihypertensive therapy), without secondary factors. The normal control group included 150 cases (89 men and 61 women), aged 55.7±9.0years, from the outpatient clinic for physical examination. All participants were Han national people who had no consanguineous relationship and lived in ShiJiaZhuang or nearby. Height and body weight was measured in all subjects. 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. Plasma and leukocytes were tested for lipid and drawn for DNA respectively. Determination of Arg16Glygenotypes: Genomic DNA was extracted from leucocytes by a classical procedure, then β2AR 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 NcoI, and the resulting fragments were separated on 12% polyacrylamide gel, visualized by AgNo₃ staining. Products yielded four fragments of 146bp,128bp,22bp,18bp,subject containing 146 bp,22bp was classified Arg/Arg genotype (Arg/Arg homozygotes); containing 146bp,128bp,22bp,18bp was classified Arg /Gly genotype(Arg 16Gly heterozygous) ;containing...