Objectives-Black subjects may be less responsive to β-blockers than whites. Genetic variants in the β 1 -adrenergic receptor (β 1 -AR) associated with lesser response to β-blockers are more common in blacks than whites. The purpose of this study was to determine whether ethnic differences in response to β-blockade can be explained by differing distributions of functional genetic variants in the β 1 -AR.Methods-We measured sensitivity to β-blockade by the attenuation of exercise-induced tachycardia in 165 subjects (92 whites) who performed a graded bicycle exercise test before and 2.75 hours after oral atenolol (25 mg). We determined heart rate at rest and at 3 exercise levels from continuous ECG recordings and calculated the area-under-the-curve (AUC). We also measured plasma atenolol concentrations and determined genotypes for variants of the β 1 -AR (Ser49Gly, Arg389Gly) and α 2C -AR (del322-325). The effects of ethnicity, genotype, and other covariates on the heart rate reduction after atenolol were estimated in multiple regression analyses.Results-Atenolol resulted in a greater reduction in exercise heart rate in whites than blacks (P=0.006). β 1 -AR Arg389 (P=0.003), but not the α 2C -AR 322-325 insertion allele (P=0.31), was independently associated with a greater reduction in heart rate AUC. Ethnic differences in sensitivity to atenolol remained significant (P=0.006) after adjustment for β 1 -AR and α 2C -AR genotypes.Conclusions-Ethnic differences in sensitivity to the β 1 -blocker atenolol persist even after accounting for different distributions of functional genetic β 1 -AR variants, suggesting that additional, as yet unidentified factors contribute to such ethnic differences.

This study demonstrates the feasibility of using olfactory receptor neurons to examine alterations in intracellular signaling in neuronal cells from living patients. Our results, although based on a small number of subjects, suggest that altered intracellular calcium signaling in olfactory receptor neurons may be a trait of bipolar disorder.

Purpose There is a large interindividual variability in dexmedetomidine dose requirements for sedation of patients in intensive care units (ICU). Cytochrome P450 2A6 (CYP2A6) mediates an important route of dexmedetomidine metabolism, and genetic variation in CYP2A6 affects the clearance of other substrate drugs. We examined whether CYP2A6 genotypes affect dexmedetomidine disposition. Methods In 43 critically ill ICU patients receiving dexmedetomidine infusions adjusted to achieve the desired level of sedation, we determined a median of 5 plasma dexmedetomidine concentrations each. Forty subjects were genotyped for five common CYP2A6 alleles and grouped into normal (n=33), intermediate (n=5), and slow metabolizers (n=2). Results Using a Bayesian hierarchical nonlinear mixture model, estimated dexmedetomidine clearance was 49.1 L/hr (posterior mean; 95% credible interval, 41.4 to 57.6 L/hr). There were no significant differences in dexmedetomidine clearance among normal, intermediate, and slow CYP2A6 metabolizer groups. Conclusion Genetic variation in CYP2A6 is not an important determinant of dexmedetomidine clearance in ICU patients.

Objectives: Cardiovascular responses to stressors are regulated by sympathetic activity, increased in black Americans, and associated with future cardiovascular morbidity. Our aim was to determine whether two functional variants in genes regulating sympathetic activity, a deletion in the α 2C -adrenergic receptor (ADRA2C del322-325) and a G-protein β3 subunit variant (GNB3 G825T), affect cardiovascular responses to physiologic stressors and contribute to their ethnic differences. Methods:We measured heart rate and blood pressure responses to a cold pressor test (CPT) in 79 healthy subjects (40 blacks, 39 whites), aged 25.7 ± 5.3 years, and determined genotypes for the ADRA2C and GNB3 variants. We examined the response variables (increase in heart rate and blood pressure) in multiple linear regression analyses adjusting first for baseline measures, ethnicity, and other covariates, and then additionally for genotypes. Results:Black subjects had a greater heart rate response to CPT than whites (mean difference, 9.9 bpm; 95% confidence interval (CI), 4.1 to 15.6; P=0.001). Both the ADRA2C del/del (15.8 bpm; 95% CI, 8.0 to 23.7; P<0.001) and GNB3 T/T genotypes (6.8 bpm; 95% CI, 0.9 to 12.7; P=0.026) were associated with greater heart rate response. After adjusting for genotypes, the ethnic difference was abrogated (1.3 bpm; 95% CI, −5.4 to 8.0; P=0.70), suggesting that the genetic variants contributed substantially to ethnic differences. Conclusions:Variation in genes that regulate sympathetic activity affects hemodynamic stress responses and contributes to their ethnic differences. This study elucidates how genetic factors may in part explain ethnic differences in cardiovascular regulation.

Bordetella pertussis, the causative organism of whooping cough, produces a calmodulin-sensitive adenylate cyclase. Confer & Eaton [(1982) Science 217, 948-950] have shown that an extract from B. pertussis increases intracellular cyclic AMP levels in neutrophils and suggested that this increase is caused by the bacterial adenylate cyclase which penetrates these cells. We demonstrate in the present study that adenylate cyclase activity in lysates from lymphocytes exposed to a partially purified preparation of the bacterial enzyme has properties completely different from those of the intrinsic membrane-bound enzyme. Adenylate cyclase activity in lysates from lymphocytes exposed to the invasive enzyme is insensitive to N-ethylmaleimide, readily inactivated by acetic anhydride and relatively stable to SDS. Similar properties are exhibited by the bacterial enzyme itself. By contrast, the intrinsic membrane-bound enzyme activated by forskolin and guanosine 5'-gamma-thiotriphosphate is sensitive to N-ethylmaleimide and SDS and relatively stable to acetic anhydride. This strongly supports the notion that B. pertussis adenylate cyclase penetrates cells. Using the partially purified preparation of the invasive enzyme, we have studied the kinetics of its penetration. The intracellular catalytic activity reaches a steady state within 20 min, irrespective of enzyme or cell concentration. Steady-state levels are maintained for at least 2 h provided that the invasive enzyme is present in the incubation medium. Upon its removal, a rapid decrease (t1/2 approximately equal to 15 min) in the intracellular cyclase level is observed. This decrease reflects intracellular inactivation of the bacterial enzyme and is not caused by the release of the enzyme to the cell medium.

Abstract-The ␣ 2 -adrenoceptor agonist clonidine reduces blood pressure more effectively in White than Black Americans despite similar degrees of sympatholysis. Functional genetic variation in receptor signaling mechanisms, for example in the ␤3 G-protein subunit (GNB3 C825T) and in the ␣ 2C -adrenoceptor subtype (ADRA2C del322-325), may affect drug responses. We examined the hypothesis that there are ethnic differences in the responses to the highly selective ␣ 2 -agonist, dexmedetomidine, and that these genetic variants contribute to interindividual variability in drug responses. In a placebo-controlled, single-masked study, 73 healthy subjects (37 whites and 36 blacks) received 3 placebo infusions and then 3 incremental doses of dexmedetomidine (cumulative dose, 0.4 g/kg), each separated by 30 minutes. Blood pressure, heart rate, and plasma catecholamine concentrations were determined after each infusion. We measured dexmedetomidine concentrations after the last infusion and determined ADRA2C del322-325 and GNB3 C825T genotypes. Dexmedetomidine lowered blood pressure and plasma catecholamine concentrations significantly (all PϽ0.001). There was substantial interindividual variability in the reduction of systolic blood pressure (range, 1 to 34 mm Hg) and plasma norepinephrine concentrations (range, 24 to 424 pg/mL). However, there were no differences between black and white subjects in dexmedetomidine responses (PϾ0.16 for all outcomes) before or after adjustment for covariates. Neither ADRA2C del322-325 nor GNB3 C825T genotypes affected the responses to dexmedetomidine (all PϾ0.66). There is large interindividual variability in response to the selective ␣ 2 -AR agonist dexmedetomidine, and neither ethnicity nor ADRA2C and GNB3 genotypes contribute to it. Further studies to identify determinants of ␣ 2 -AR-mediated responses will be of interest. Key Words: cardiovascular physiology Ⅲ receptors, adrenergic, ␣-2 Ⅲ G-protein beta3 subunit Ⅲ dexmedetomidine Ⅲ pharmacogenetics Ⅲ ethnic groups ␣ 2 -Adrenoceptors (␣ 2 -ARs) in the central nervous system and on presynaptic sympathetic nerve terminals play a key role in the regulation of the sympathetic response and thus cardiovascular control. The systemic administration of an ␣ 2 -AR agonist causes a reduction in sympathetic tone resulting in a decrease in blood pressure and heart rate, and the ␣ 2 -AR agonist clonidine is widely used as antihypertensive medication. There is, however, substantial interindividual variability in response to ␣ 2 -AR agonists, and black hypertensive patients achieved blood pressure control with clonidine monotherapy less often than whites. 1,2 Concordant with that observation, we found that clonidine reduced blood pressure less in healthy black subjects than white subjects, despite similar decreases in norepinephrine spillover. 3 The reasons for these ethnic differences remain unclear.Functionally significant genetic variants of ␣ 2 -ARs and other proteins in their signaling pathways have been identified. The prevalence of these allelic...

The platelet thrombus is the major pathologic entity in acute coronary syndromes, and antiplatelet agents are a mainstay of therapy. However, individual patient responsiveness to current antiplatelet drugs is variable, and all drugs carry a risk of bleeding. An understanding of the complex role of Prostaglandin E2 (PGE2) in regulating thrombosis offers opportunities for the development of novel individualized antiplatelet treatment. However, deciphering the platelet regulatory function of PGE2 has long been confounded by non-standardized experimental conditions, extrapolation of murine data to humans, and phenotypic differences in PGE2 response. This review synthesizes past and current knowledge about PGE2 effects on platelet biology, presents a rationale for standardization of experimental protocols, and provides insight into a molecular mechanism by which PGE2-activated pathways could be targeted for new personalized antiplatelet therapy to inhibit pathologic thrombosis without affecting hemostasis.

Background-␣ 2A -Adrenoceptors (␣ 2A -ARs) have important roles in sympathetic cardiovascular regulation. Variants of ADRA2A affect gene transcription and expression and are associated with insulin release and risk for type 2 diabetes. We examined whether ADRA2A variants are also associated with cardiovascular responses to the selective ␣ 2 -ARagonist dexmedetomidine. Methods and Results-Seventy-three healthy subjects participated in a placebo-controlled, single-blind study. After 3 infusions of placebo, subjects received 3 incremental infusions of dexmedetomidine (cumulative dose, 0.4 g/kg). Primary outcomes were changes in systolic blood pressure (SBP) and plasma norepinephrine concentrations, measured as difference of the area-under-the-curve during placebo and dexmedetomidine infusions (⌬AUC). We used multiple linear regression analysis to examine the associations between 9 ADRA2A tagging variants and 5 inferred haplotypes and ⌬AUC after adjustment for covariates. Homozygous carriers of rs553668 and the corresponding haplotype 4, previously associated with increased ␣ 2A -AR expression, had a 2.2-fold greater decrease in AUC SBP after dexmedetomidine (adjusted Pϭ0.006); similarly, the maximum decrease in SBP was 24.7Ϯ8.1 mm Hg compared with 13.6Ϯ5.9 mm Hg in carriers of the wild-type allele (Pϭ0.007). Carriers of haplotype 3, previously associated with reduced ␣ 2A -AR expression, had a 44% smaller decrease in AUC SBP (Pϭ0.013). Haplotype information significantly improved the model predicting the decrease in SBP (PϽ0.001). There were similar but nonsignificant trends for diastolic blood pressure and heart rate. Genotypes were not significantly associated with norepinephrine responses. Conclusions-Common