Racial differences in drug response: isoproterenol effects on heart rate in healthy males

Autonomic responses to stress in Black versus Caucasian Africans: the SABPA study

Underlying mechanisms of increased pressor responses to stress in Blacks are poorly understood. Cardiovascular regulation of normotensive Black (n=43) and Caucasian (n=90) Africans was studied during a cold pressor and color-word conflict test. Autonomic evaluation was performed by spectral analysis. Higher diastolic pressor and heart rate responses to the cold pressor test were observed in Black compared to Caucasian Africans. Autonomic efferent outflow to stress was comparable between groups. Transient downregulation of baroreflex during stress was evident in Blacks but not in Caucasians. Greater diastolic pressor responses were related to a higher cardiac reactivity, a baroreflex desensitization, and higher stress perception in Black Africans. Thus, increased stress perception may facilitate cardiac and diastolic hyperreactivity, indirectly affecting baroreflex function in Black Africans.

Heart failure-the importance of ethnicity

Heart failure is a major public health problem in the Western world. Aetiological factors involved in its development include hypertension, diabetes, and ischaemic heart disease--all of which differ in prevalence, and possibly mechanism, between patients of differing ethnicity. Unfortunately, epidemiological and therapeutic trials have involved almost exclusively white populations, and evidence from these trials cannot necessarily be assumed to be generalisable to populations that include high proportions of patients from other ethnic origins. This review will discuss the mechanistic and therapeutic differences that exist in heart failure between those of European origin, and patients from the major ethnic minority groups of the UK.

Hypertension in black people: study of specific genotypes and phenotypes will provide a greater understanding of interindividual and interethnic variability in blood pressure regulation than studies based on race

Hypertension is more frequent and more severe in some Black populations. Although many studies have focused on hypertension in black people in an attempt to understand the genetic and environmental factors that regulate blood pressure, this approach has not been productive. Study of the relationship between specific phenotypes and genotypes, both within and across ethnic groups, is more likely to advance our understanding of the regulation of blood pressure than studies focused on race and blood pressure.

Blunted blood pressure response to central sympathoinhibition in normotensive blacks: increased importance of nonsympathetic factors in blood pressure maintenance in blacks

Enhanced sympathetic reactivity may predispose blacks to the development of hypertension and may occur because of increased sympathetic stimulation and/or attenuated sympathoinhibition. A potential site for such attenuated sympathetic inhibition may be at the level of central alpha2-adrenergic receptors, which play an important role in the feedback inhibition of norepinephrine release. We used cumulative doses (1, 2, and 3 microg/kg I.V.) of the centrally acting alpha2-adrenergic agonist clonidine to measure the sensitivity of alpha2-adrenoceptor-mediated sympathoinhibition and the resultant hypotensive response in 8 normotensive blacks and 10 normotensive whites. Sympathetic activity was determined by radioisotope dilution methodology. Basal norepinephrine spillover was similar in blacks (0.80+/-0.14 microg/min) and whites (0.73+/-0.19 microg/min, P=NS) and after clonidine decreased significantly in both blacks (0.21+/-0.07 microg/min, P<.0001) and whites (0.24+/-0.06 microg/min, P<.0001), with no difference between the groups (P=NS). Despite this similar degree of sympathoinhibition, the hypotensive response to clonidine was markedly blunted in blacks, such that mean arterial pressure decreased by only 10% in blacks but by 21% in whites (P<.0001). The smaller blood pressure decrement after clonidine in normotensive blacks, in the face of an equal degree of sympathoinhibition, suggests that even when sympathetic tone is decreased to the same level in blacks and whites, normotensive blacks have less reduction in blood pressure than whites, implying that nonadrenergic mechanisms contribute more to blood pressure maintenance in blacks than whites. Whether a similar interethnic difference in response to sympathoinhibition occurs in hypertensive patients is as yet unknown.

Inter-ethnic differences in xenobiotic metabolism

The aim of safety assurance procedures is to determine a level of intake (the acceptable daily intake (ADI) or tolerable daily intake (TDI)) that is without adverse health effects in the human population. The majority of studies on inter-ethnic differences in xenobiotic metabolism have concentrated in the incidence of expression of the poor metaboliser phenotype for a number of drug metabolising enzymes. Such ethnic differences can result in different incidences of individuals at higher risk, but this would not affect the safety assurance/risk assessment outcome unless poor metaboliser status was not recognised in the database used for the initial assessment and calculation of ADI or TDI. Of far greater importance are ethnic differences which result in population differences in the mean values, and/or the extent of variability within the population, for key kinetic parameters such as the internal dose or area under the plasma concentration time curve (AUC). There are few studies on inter-ethnic differences in sensitivity and most of these relate to in vivo differences for therapeutic/pharmacological agents, so that the reported data reflect both kinetic and dynamic variability. Inter-ethnic differences are limited in extent and well within the uncertainty factor of 10 used for human variability.

Reduced beta 2-receptor mediated vasodilation in African Americans

It is well recognized that African Americans have a higher prevalence of cardiovascular disease than White Americans although the underlying mechanisms are not entirely understood. This study was perfumed to evaluate racial differences in the chronotropic and vasodilatory effects of the beta-receptor agonist, isoproterenol. We compared cardiovascular responses to intravenous infusion of isoproterenol in 27 African Americans and 27 White men and women. African Americans showed significantly smaller beta 2-receptor mediated falls in diastolic pressure than Whites. In contrast, isoproterenol produced similar increases in heart rate in both races. The findings suggest that African Americans have decreased beta 2-receptor mediated vasodilatory capacity, and may help explain the higher prevalence of hypertension and cardiovascular disease in African Americans compared to Whites.

Are there beta-adrenergic receptor response differences between racial groups?

Beta-adrenergic receptor (BAR) agonists and antagonists are among the most widely used drugs in America today. This review highlights the importance of cross-racial studies in evaluating BAR effects because heterogeneity in pharmacologic response among humans exists. Clinicians and basic scientists in the drug development industry need to acknowledge racial differences in antihypertensive drug responses and prevent various racial groups from being underrepresented in clinical trials. This article reviews the influence of race on BAR responses with emphasis on blacks and whites. Information from patients with hypertension, healthy volunteers, and in vitro studies is presented.

Racial differences in drug response: isoproterenol effects before and after propranolol

The aim of this study was to determine in young, healthy men the relative contribution of pharmacodynamic factors inherent between two groups known to respond differently to hypertensive therapy. Black (n = 10) and white (n = 10) men received an isoproterenol sensitivity test before and after propranolol (0.1 mg/kg, then 50 micrograms/min). There were greater increases (twofold) in systolic BP following the 1.0- and 1.5-microgram isoproterenol dose (P less than 0.05) in the black group. During propranolol there were no differences in free (1)-propranolol concentrations between the groups; however, propranolol decreased resting heart rate in the white group more than in the black group (P less than 0.05). Cardiac index decreased less in the black group compared to the white group (P less than 0.05). Following the second isoproterenol challenge, there again were greater increases in systolic BP in the black group at both the 10- and the 20-micrograms isoproterenol dose (P less than 0.05). Our study has highlighted the importance of cross-racial studies in evaluating drug effects.