Racial differences in beta-adrenoceptor-mediated responsiveness.
Previous studies have suggested that racial differences may exist in beta-adrenoceptor-mediated responsiveness. However, no clear conclusions can be drawn based on these studies because of the confounding effect of the parasympathetic nervous system on responses to isoproterenol bolus doses. In this study, we blocked the effects of the parasympathetic nervous system with atropine, to determine whether racial differences exist in sensitivity to beta-adrenoreceptor stimulation and blockade. Sixteen healthy black and white men participated in the study. Atropine was administered before all studies to induce parasympathetic blockade. Isoproterenol sensitivity studies and treadmill exercise were then performed in the with and without beta-adrenoceptor blockade by propranolol. Responses measured included heart rate (HR), blood pressure (BP), and tremor. The average isoproterenol dose producing a 25-beat/min increase in HR was more than twofold higher in blacks than in whites (3.4 +/- 1.2 vs. 1.6 +/- 0.4 micrograms, respectively, p < 0.05). There were no racial differences in response to beta-adrenoreceptor blockade. Our results showed that during parasympathetic blockade blacks were less sensitive to the chronotropic effects of isoproterenol than whites. We conclude that these response differences are due to greater beta-adrenoceptor sensitivity in whites than in blacks.
Johnson
J A
JA
Department of Clinical Pharmacy, College of Pharmacy, University of Tennessee, Memphis 38163.
Burlew
B S
BS
Stiles
R N
RN
D000328:Adult; D000704:Analysis of Variance; D001285:Atropine / Q000494:pharmacology; D044383:Black People; D001794:Blood Pressure / Q000187:drug effects; D004562:Electrocardiography / Q000187:drug effects; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects; D011433:Propranolol / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000187:drug effects; D014202:Tremor / Q000139:chemically induced; D044465:White People
D011943:Receptors, Adrenergic, beta; D001285:Atropine; D011433:Propranolol; D007545:Isoproterenol