Genetic variants in the alpha2C-adrenoceptor and G-protein contribute to ethnic differences in cardiovascular stress responses

Takotsubo Syndrome in Black Americans: Insights From the National Inpatient Sample

BACKGROUND

Data on race-related differences in the clinical outcomes of Takotsubo syndrome are limited, particularly for Black patients. This study aimed to assess whether race and sex may have an additional impact on the inpatient mortality of patients with Takotsubo syndrome.

METHODS

A total of 4,628 patients from the United States' National Inpatient Sample from 2012 to 2016 were identified; propensity score analysis revealed a similar propensity score between Black patients (n = 2,314) and White patients (n = 2,314), which was used to balance observed covariates. Sex and age distributions were identical between the 2 groups. The groups were also similar in baseline characteristics, including cardiovascular risk factors. White patients were compared with Black patients on in-hospital outcomes and inpatient mortality. A logistic regression analysis was conducted to measure the difference in mortality based on race and sex.

RESULTS

Compared with White patients, Black patients had a higher percentage of in-hospital complications, including cerebrovascular accidents (4.9% vs 2.5%, P ≤ .01), acute kidney injury (25% vs 19%, P ≤ .01); longer lengths of stay (8 vs 7 days, P ≤ .01); and higher inpatient mortality (6.1% vs 4.5%, P < .01). When analysis was conducted with race and sex combined, inpatient mortality was higher among Black men than among White women (odds ratio, 2.7 [95% CI, 1.80-3.95]; P ≤ .01).

CONCLUSION

This study showed that Black patients with Takotsubo syndrome have higher in-hospital complications and inpatient mortality rates. When race and sex were combined, inpatient mortality was significantly higher among Black men than among either White men and women or Black women.

Racial differences in takotsubo cardiomyopathy outcomes in a large nationwide sample

Aims

Takotsubo cardiomyopathy (TC) is characterized by transient ventricular impairment, often preceded by emotional or physical stress. Racial differences affect the outcomes of several cardiovascular conditions; however, the effect of race on TC remains unknown. This investigation aims to assess the effect of race on in‐hospital outcomes of TC in a large national sample.

Methods and results

We conducted a US‐wide analysis of TC hospitalizations from 2006 to 2014 by querying the National Inpatient Sample database for the International Classification of Diseases‐ninth Revision TC code, characteristics, and inpatient outcomes. Patients with a primary diagnosis of acute coronary syndrome were excluded to reduce selection bias. Caucasians were compared with African Americans (AA) for differences in baseline characteristics and in‐hospital outcomes. Multivariate regression models were created to adjust for potential confounders. Of 97 650 TC patients, 83 807 (86.9%) were women, 89 624 (91.8%) identified as Caucasians, and 8026 (8.2%) as AA. The annual number of TC hospitalizations increased significantly from 2006 to 2014 in both races (from 335 to 21 265 annual cases, P < 0.001). In‐hospital mortality initially increased (1–2% in 2006 to 5–6% in 2009, P < 0.001) and subsequently remained relatively stable around 5–7% with no significant difference between races. In unadjusted analysis, AA had more cardiac arrests [304 (3.8%) vs. 2569 (2.9%), P = 0.04], invasive mechanical ventilation [1671 (20.8%) vs. 15 897 (17.7%), P = 0.002], tracheostomies [242 (3%) vs. 1600 (1.8%), P = 0.001], acute kidney injuries [1765 (22%) vs. 14 608 (16.3%), P < 0.0001], and longer hospital stays [4.5 (3.2–4.8) vs. 3.8 (3.7–3.9) days, P < 0.0001] compared with Caucasians. After the adjustment for differences in age, gender, comorbidities (using the enhanced Charlson comorbidity index), hospital location/teaching status, and socio‐economic factors, all differences were significantly attenuated or eliminated. Additionally, the adjusted risk was lower in AA compared with Caucasians, for cardiogenic shock [odds ratio (OR) 0.61 (0.47–0.78), P < 0.0001], mechanical ventilation [OR 0.8 (0.70–0.92), P = 0.002] and intraaortic balloon pump insertion [OR 0.63 (0.41–0.99), P = 0.04].

Conclusions

Our investigation is the first large US‐wide analysis studying racial variations in TC outcomes. AA overall have more in‐hospital complications; however, the differences are driven by racial disparities in demographics, comorbidities, and socio‐economic factors.

Usefulness of Malignancy as a Predictor of WorseIn-Hospital Outcomes in Patients With Takotsubo Cardiomyopathy

Takotsubo cardiomyopathy (TC) is a form of dilated cardiomyopathy often associated with physical or emotional stress. Association with cancer has been reported, however, in-hospital outcomes in TC patients with history of malignancy have not been fully characterized. We conducted a retrospective chart review of hospitalized patients with diagnosis of TC between January 2006 and January 2017. Patients were divided into 2 groups based on the previous history of malignancy. Presenting symptoms, cardiac imaging and short-term events including in-hospital complications and mortality, were compared. Of 318 patients with TC, 81 (25.4%) had a previous diagnosis of cancer. Mean age was 67.5 (SD 12.6), 151 (47.5%) were African American, 122 (38.4%) Caucasian, and 10 (3.1%) of other ethnicities. Patients with history of malignancy were older (70.0 [SD 10.6] vs 66.6 [SD 13.1] years, p = 0.03), had higher heart rate on presentation (93 [SD 19] vs 87 [SD 25] beats/minute, p = 0.03), higher prevalence of severely decreased cardiac function (left ventricular ejection fraction <25%) (29.6% vs 16%, p = 0.01), longer hospitalization (7 (4-13) vs 4 (3-8) days, p = 0.001) and experienced more in-hospital cardiac arrests (6 [7.4%] vs 5 [2.1%], p = 0.035) compared with patients without malignancy history. Higher percentage of longer hospitalization and left ventricular ejection fraction <25% in the cancer group persisted after controlling for sepsis, chemotherapy exposure, and metastatic disease. In conclusion, in a racially diverse hospitalized population of TC, prevalence of cancer history is high, and diagnosis of previous malignancy is associated with adverse in-hospital outcomes.

Genetic variation in the alpha1B-adrenergic receptor and vascular response

The alpha1B (α1B)-adrenergic receptors contribute to vasoconstriction in humans. We tested the hypothesis that variation in the ADRA1B gene contributes to interindividual variability and ethnic differences in adrenergic vasoconstriction. We measured dorsal hand vein responses to increasing doses of phenylephrine in 64 Caucasians and 41 African Americans and genotyped 34 ADRA1B variants. We validated findings in another model of catecholamine-induced vasoconstriction, the increase in mean arterial pressure (ΔMAP) during a cold pressor test (CPT). One ADRA1B variant, rs10070745, present in 14 African-American heterozygotes but not in Caucasians, was associated with a lower phenylephrine ED50 (geometric mean (95% confidence interval), 144 (69-299) ng ml-1) compared with 27 African-American non-carriers (208 (130-334) ng ml-1; P=0.015) and contributed to the ethnic differences in ED50. The same variant was also associated with a greater ΔMAP during CPT (P=0.008). In conclusion, ADRA1B rs10070745 was significantly associated with vasoconstrictor responses after adrenergic stimulation and contributed to the ethnic difference in phenylephrine sensitivity.

The genetics of anxiety-related negative valence system traits

NIMH's Research Domain Criteria (RDoC) domain of negative valence systems (NVS) captures constructs of negative affect such as fear and distress traditionally subsumed under the various internalizing disorders. Through its aims to capture dimensional measures that cut across diagnostic categories and are linked to underlying neurobiological systems, a large number of phenotypic constructs have been proposed as potential research targets. Since "genes" represent a central "unit of analysis" in the RDoC matrix, it is important for studies going forward to apply what is known about the genetics of these phenotypes as well as fill in the gaps of existing knowledge. This article reviews the extant genetic epidemiological data (twin studies, heritability) and molecular genetic association findings for a broad range of putative NVS phenotypic measures. We find that scant genetic epidemiological data is available for experimentally derived measures such as attentional bias, peripheral physiology, or brain-based measures of threat response. The molecular genetic basis of NVS phenotypes is in its infancy, since most studies have focused on a small number of candidate genes selected for putative association to anxiety disorders (ADs). Thus, more research is required to provide a firm understanding of the genetic aspects of anxiety-related NVS constructs. © 2016 Wiley Periodicals, Inc.

GNB3 C825T Polymorphism and Myocardial Recovery in Peripartum Cardiomyopathy: Results of the Multicenter Investigations of Pregnancy-Associated Cardiomyopathy Study

BACKGROUND

Black women are at greater risk for peripartum cardiomyopathy (PPCM). The guanine nucleotide-binding proteins β-3 subunit (GNB3) has a polymorphism C825T. The GNB3 TT genotype more prevalent in blacks is associated with poorer outcomes. We evaluated GNB3 genotype and myocardial recovery in PPCM.

METHODS AND RESULTS

A total of 97 women with PPCM were enrolled and genotyped for the GNB3 T/C polymorphism. Left ventricular ejection fraction (LVEF) was assessed by echocardiography at entry, 6 and 12 months postpartum. LVEF over time in subjects with the GNB3 TT genotype was compared with those with the C allele overall and in black and white subsets. The cohort was 30% black, age 30+6, LVEF 0.34+0.10 at entry 31+25 days postpartum. The % GNB3 genotype for TT/CT/CC=23/41/36 and differed markedly by race (blacks=52/38/10 versus whites=10/44/46, P<0.001). In subjects with the TT genotype, LVEF at entry was lower (TT=0.31+0.09; CT+CC=0.35+0.09, P=0.054) and this difference increased at 6 (TT=0.45+0.15; CT+CC=0.53+0.08, P=0.002) and 12 months (TT=0.45+0.15; CT+CC=0.56+0.07, P<0.001.). The difference in LVEF at 12 months by genotype was most pronounced in blacks (12 months LVEF for GNB3 TT=0.39+0.16; versus CT+CC=0.53+0.09, P=0.02) but evident in whites (TT=0.50++0.11; CT+CC=0.56+0.06, P=0.04).

CONCLUSIONS

The GNB3 TT genotype was associated with lower LVEF at 6 and 12 months in women with PPCM, and this was particularly evident in blacks. Racial differences in the prevalence and impact of GNB3 TT may contribute to poorer outcomes in black women with PPCM.

Genome-wide linkage and regional association study of blood pressure response to the cold pressor test in Han Chinese: the genetic epidemiology network of salt sensitivity study

BACKGROUND

Blood pressure (BP) response to cold pressor test (CPT) is associated with increased risk of cardiovascular disease. We performed a genome-wide linkage scan and regional association analysis to identify genetic determinants of BP response to CPT.

METHODS AND RESULTS

A total of 1961 Chinese participants completed the CPT. Multipoint quantitative trait linkage analysis was performed, followed by single-marker and gene-based analyses of variants in promising linkage regions (logarithm of odds ≥2). A suggestive linkage signal was identified for systolic BP response to CPT at 20p13 to 20p12.3, with a maximum multipoint logarithm of odds score of 2.37. On the basis of regional association analysis with 1351 single nucleotide polymorphisms in the linkage region, we found that marker rs2326373 at 20p13 was significantly associated with mean arterial pressure responses to CPT (P=8.8×10(-6)) after false discovery rate adjustment for multiple comparisons. A similar trend was also observed for systolic BP response (P=0.03) and diastolic BP response (P=4.6×10(-5)). Results of gene-based analyses showed that variants in genes MCM8 and SLC23A2 were associated with systolic BP response to CPT (P=4.0×10(-5) and 2.7×10(-4), respectively), and variants in genes MCM8 and STK35 were associated with mean arterial pressure response to CPT (P=1.5×10(-5) and 5.0×10(-5), respectively).

CONCLUSIONS

Within a suggestive linkage region on chromosome 20, we identified a novel variant associated with BP responses to CPT. We also found gene-based associations of MCM8, SLC23A2, and STK35 in this region. Additional work is warranted to confirm these findings.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov; Unique identifier: NCT00721721.

Angiotensin AT1 - α2C-Adrenoceptor Interaction Disturbs α2A-auto-Inhibition of Catecholamine Release in Hypertensive Rats

α₂-Adrenoceptors lower central sympathetic output and peripheral catecholamine release, and thus may prevent sympathetic hyperactivity and hypertension. α₂AR also influence vascular tension. These α₂AR are malfunctioning in spontaneously hypertensive rats (SHR). Here I tested if an interaction between α₂AR subtypes and the angiotensin AT1 receptor (AT₁R) precipitated these disorders. Blood pressure was monitored through a femoral artery catheter and cardiac output by ascending aorta flow in anesthetized rats. Catecholamine concentrations were determined in plasma collected at the end of a 15-min tyramine-infusion. Tyramine stimulates norepinephrine release through the re-uptake transporter, thus preventing re-uptake. Presynaptic control of vesicular release is therefore reflected as differences in overflow to plasma. Previous experiments showed surgical stress to activate some secretion of epinephrine, also subjected to α₂AR-auto-inhibition. Normotensive rats (WKY) and SHR were pre-treated with (1) vehicle or α₂AR-antagonist (L-659,066), followed by fadolmidine (α_2C>B>A + α₁AR-agonist), ST-91 (α_2non-A-selective agonist), or m-nitrobiphenyline (α_2CAR-agonist + α_2A+B-antagonist), or (2) AT1R-antagonist losartan, losartan + L-659,066, or losartan + clonidine. In WKY, L-659,066 alone, L-659,066 + agonist or losartan + L-659,066 increased catecholamine overflow to plasma after tyramine and eliminated the norepinephrine-induced rise in total peripheral vascular resistance (TPR). In SHR, L-659,066 + fadolmidine/ST-91/m-nitrobiphenyline and losartan + L-659,066 greatly increased, and losartan + clonidine reduced, catecholamine concentrations, and L-659,066 + ST-91, losartan + L-659,066 and losartan + clonidine eliminated the tyramine-induced rise in TPR. Separately, these drugs had no effect in SHR. In conclusion, peripheral α_2CAR-stimulation or AT₁R-inhibition restored failing α_2AAR-mediated auto-inhibition of norepinephrine and epinephrine release and control of TPR in SHR.

Association between genetic variants of the ADD1 and GNB3 genes and blood pressure response to the cold pressor test in a Chinese Han population: the GenSalt Study

Genetic factors influence blood pressure (BP) response to the cold pressor test (CPT), which is a phenotype related to hypertension risk. We examined the association between variants of the α-adducin (ADD1) and guanine nucleotide binding protein (G protein) β-polypeptide 3 (GNB3) genes and BP response to the CPT. A total of 1998 Han Chinese participants from the Genetic Epidemiology Network of Salt Sensitivity completed the CPT. The area under the curve (AUC) above the baseline BP during the CPT was used to measure the BP response. Twelve single-nucleotide polymorphisms (SNPs) of the ADD1 and GNB3 genes were selected and genotyped. Both single-marker and haplotype association analyses were conducted using linear mixed models. The rs17833172 and rs3775067 SNPs of the ADD1 gene and the rs4963516 SNP of the GNB3 gene were significantly associated with the BP response to CPT, even after adjusting for multiple testing. For the ADD1 gene, the AA genotype of SNP rs17833172 was associated with lower systolic BP (SBP) reactivity (P<0.0001) and faster BP recovery (P=0.0003). The TT genotype of rs3775067 was associated with slower SBP recovery (P=0.004). For the GNB3 gene, the C allele of SNP rs4963516 was associated with faster diastolic BP recovery (P=0.002) and smaller overall AUC (P=0.003). Haplotype analysis indicated that the CCGC haplotype of ADD1 constructed by rs1263359, rs3775067, rs4961 and rs4963 was significantly associated with the BP response to CPT. These data suggest that genetic variants of the ADD1 and GNB3 genes may have important roles in BP response to the CPT. Future studies aimed at replicating these novel findings are warranted.

Catecholamine pathway gene variation is associated with norepinephrine and epinephrine concentrations at rest and after exercise

OBJECTIVE

To examine the hypothesis that genetic variation in enzymes and transporters associated with synthesis, storage, release, and metabolism of catecholamines contributes to the interindividual variability in plasma catecholamine concentrations at rest and after exercise.

METHODS

We measured plasma norepinephrine (NE) and epinephrine concentrations at rest and after a standardized exercise protocol in 165 healthy individuals (60% White, 40% African-American) and examined 29 functional or common variants in 14 genes involved in synthesis, transport, or metabolism of catecholamines. We examined the relationship between genotypes and NE concentrations at rest and the increase after exercise (ΔNE) by multiple linear regression with adjustment for covariates [age, race, sex, BMI, fitness, and resting NE (for ΔNE)]. As a secondary outcome, we carried out similar analyses for epinephrine concentrations.

RESULTS

There was large interindividual variability in resting NE (mean, 204±102 pg/ml; range, 39-616 pg/ml) and ΔNE (mean, 256±206 pg/ml; range, -97 to 953 pg/ml). Resting NE was significantly associated with variants of four genes: CYB561 (P<0.001), VMAT2 (P=0.016), CHGA (P=0.039), and PNMT (P=0.038). ΔNE after exercise was associated with three variants of PNMT (P=0.041) and COMT (P=0.033 and 0.035), and resting and exercise epinephrine concentrations were associated with two variants each.

CONCLUSION

The findings of this exploratory study suggest that variation in catecholamine pathway genes contributes to the interindividual variability in plasma NE and epinephrine concentrations at rest and after exercise.

Alpha-adrenergic receptor gene polymorphisms and cardiovascular reactivity to stress in Black adolescents and young adults

Cardiovascular reactivity to stress and α-adrenergic receptor (α-AR) function may contribute to the development of hypertension. As Black Americans have an increased risk of hypertension, we evaluated associations between α(1A) -AR (Arg492Cys), α(2A) -AR (-1291C/G), and α(2B) -AR (Ins/Del301-303) gene variants and cardiovascular reactivity in 500 normotensive Black youth. Heart rate, preejection period, total peripheral resistance, and blood pressure were measured during cold and psychological stress. The Arg492Cys polymorphism in the α(1A) -AR gene was associated with heart rate reactivity to stress, but the association depended on sex. The -1291C/G promoter polymorphism in the α(2A) -AR gene was associated with vascular reactivity to stress; vasoconstriction increased as a linear function of the number of copies of the variant G allele. Thus, specific associations emerged between genetic variations in α-Ars and cardiovascular reactivity in young Blacks.

Modulation of α(2C) adrenergic receptor temperature-sensitive trafficking by HSP90

Decreasing the temperature to 30°C is accompanied by significant enhancement of α(2C)-AR plasma membrane levels in several cell lines with fibroblast phenotype, as demonstrated by radioligand binding in intact cells. No changes were observed on the effects of low-temperature after blocking receptor internalization in α(2C)-AR transfected HEK293T cells. In contrast, two pharmacological chaperones, dimethyl sulfoxide and glycerol, increased the cell surface receptor levels at 37°C, but not at 30°C. Further, at 37°C α(2C)-AR is co-localized with endoplasmic reticulum markers, but not with the lysosomal markers. Treatment with three distinct HSP90 inhibitors, radicicol, macbecin and 17-DMAG significantly enhanced α(2C)-AR cell surface levels at 37°C, but these inhibitors had no effect at 30°C. Similar results were obtained after decreasing the HSP90 cellular levels using specific siRNA. Co-immunoprecipitation experiments demonstrated that α(2C)-AR interacts with HSP90 and this interaction is decreased at 30°C. The contractile response to endogenous α(2C)-AR stimulation in rat tail artery was also enhanced at reduced temperature. Similar to HEK293T cells, HSP90 inhibition increased the α(2C)-AR contractile effects only at 37°C. Moreover, exposure to low-temperature of vascular smooth muscle cells from rat tail artery decreased the cellular levels of HSP90, but did not change HSP70 levels. These data demonstrate that exposure to low-temperature augments the α(2C)-AR transport to the plasma membrane by releasing the inhibitory activity of HSP90 on the receptor traffic, findings which may have clinical relevance for the diagnostic and treatment of Raynaud Phenomenon.

Genetic variants in the renin-angiotensin system and blood pressure reactions to the cold pressor test

OBJECTIVES

The purpose of this study was to examine the association between genetic variants in the renin-angiotensin system and blood pressure (BP) responses to the cold pressor test (CPT).

METHODS

The CPT was conducted among 1998 Han Chinese participants. BP measurements were obtained before and after the CPT using a standard sphygmomanometer according to a standard protocol. The association between SNP genotypes and BP responses to the CPT was assessed using a mixed linear model.

RESULTS

Of 68 SNPs genotyped in six renin-angiotensin system genes, two were strongly associated with DBP responses to CPT (P ≤ 0.001; false discovery rate q value < 0.05): rs2006765 and rs943580 in the angiotensinogen (AGT) gene. Compared to C allele carriers of rs2006765, the TT homozygotes had a significantly decreased DBP response to the CPT. For participants with the TT genotype, percentage DBP responses were 5.68% (4.25-7.10%), compared to corresponding responses of 9.17% (8.66-9.68%) among participants with the CC+CT genotype. In addition, SNP rs4681443 of the angiotensin type 1 receptor (AGTR1) gene was significantly associated with percentage SBP responses to CPT (P ≤ 0.001; q-value <0.05).

CONCLUSION

Briefly, our study identified variants in the AGT and AGTR1 genes that may influence BP responses to CPT in the Han Chinese population. These results show that genetic variants in the renin-angiotensin system play an important role in BP responses to CPT and, therefore, in predicting future hypertension.

β-blocker therapy and heart rate control during exercise testing in the general population: role of a common G-protein β-3 subunit variant

AIM

Impaired heart rate (HR) response to exercise is associated with increased cardiovascular morbidity and mortality. We analyzed whether common variants (rs5443/C825T and rs5442/G814A) in the G-protein β3 subunit (GNB3) gene modulate interindividual variation in β-blocker responses with respect to HR.

MATERIALS & METHODS

Among 1614 subjects (347 current β-blocker users) of a population-based study, HR during symptom-limited exercise testing was analyzed by multilevel linear regression models adjusted for potential confounders.

RESULTS

In β-blocker users, but not in nonusers, HR was attenuated in rs5443 T allele carriers (TC/TT vs CC) with lower adjusted HR over the entire exercise period from rest to peak workload (3.5 bpm; 95% CI: 1.1-5.8; p < 0.01), and during recovery (4.2 bpm; 95% CI: 0.6-7.8; p = 0.02). The genotype-related HR reducing effect at peak exercise varied by up to 7.5 bpm (CC vs TT), more than a third (35.9%) of the total β-blocker effect (20.9 bpm). By contrast, rs5442 had no impact on any HR-related parameter.

CONCLUSION

In this population-based sample, a common GNB3 polymorphism (C825T) was significantly related with response to β-blocker therapy with respect to HR during exercise and HR recovery, respectively. Further prospective studies are needed to confirm these associations and to examine their potential clinical relevance.

Genetic influences on cardiovascular stress reactivity

Individual differences in the cardiovascular response to stress play a central role in the reactivity hypothesis linking frequent exposure to psychosocial stress to adverse outcomes in cardiovascular health. To assess the importance of genetic factors, a meta-analysis was performed on all published twin studies that assessed heart rate (HR) or blood pressure (BP) reactivity to the cold pressor test or various mental stress tasks. For reactivity to mental stress, the pooled heritability estimate ranged from 0.26 to 0.43. Reactivity to the cold pressor test yielded heritability estimates from 0.21 to 0.55. An ensuing review of genetic association studies revealed a number of genes, mostly within the sympathoadrenal pathway, that may account for part of the heritability of cardiovascular stress reactivity. Future progress in gene finding, that should include measures of sympathetic and vagal stress reactivity, may help uncover the molecular pathways from genetic variation to stress reactivity.

Spinal cord and peripheral nerve stimulation techniques for neuropathic pain

When comprehensive medical pharmacological therapy titrated to maximum doses fails to provide an appropriate level of analgesia, or side effects associated with these therapies impair the ability to increase the doses to obtain appropriate therapeutic effects in patients with a variety of chronic neuropathic pain conditions, alternative methods, such as spinal cord stimulation and peripheral nerve stimulation, are effective alternative options. This article discusses important concepts to consider when implementing spinal cord and peripheral nerve stimulation therapy for the treatment of neuropathic pain conditions other than failed back surgery syndrome. The focus is primarily on post-surgical pain syndromes, which are frequently encountered in daily clinical practice.

Effects of variation in the human alpha2A- and alpha2C-adrenoceptor genes on cognitive tasks and pain perception

BACKGROUND

The mechanisms underlying interindividual variability in pain perception and cognitive responses are undefined but highly heritable. alpha(2C)- and alpha(2A)-adrenergic receptors regulate noradrenergic activity and are important mediators of pain perception and analgesia. We hypothesized that common genetic variants in these genes, particularly the ADRA2C 322-325 deletion variant, affect pain perception or cognitive responses.

METHODS

We studied 73 healthy subjects (37 Caucasians and 36 African-Americans) aged 25.4+/-4.6years. Pain response to a cold pressor test was measured using a 10cm visual analog scale and again on the next day, after three infusions of the selective alpha(2)-agonist dexmedetomidine. Standardized cognitive tests were administered at baseline and after each infusion. The contribution of ADRA2C deletion genotype, dexmedetomidine concentration, and other covariates to pain perception and cognitive responses was determined using multiple linear regression models. Secondary analysis examined the effects of ADRA2A and other ADRA2C variants on pain perception.

RESULTS

ADRA2C Del homozygotes had higher pain scores in response to cold at baseline (6.3+/-1.8cm) and after dexmedetomidine (5.6+/-2.2cm) than insertion allele carriers (4.6+/-2.1cm [baseline] and 3.8+/-1.9cm [after dexmedetomidine]; adjusted P-values=0.019 and 0.004, respectively). Cognitive responses were unrelated to ADRA2C Ins/Del genotype. None of the other ADRA2A and ADRA2C variants was significantly related to cold pain sensitivity before dexmedetomidine; after dexmedetomidine, ADRA2A rs1800038 was marginally associated (P=0.03).

CONCLUSION

The common ADRA2C del322-325 variant affected pain perception before and after dexmedetomidine but did not affect other cognitive responses, suggesting that it contributes to interindividual variability in pain perception.