Differing effect of atropine on heart rate in Chinese and white subjects.

To determine if differences exist between Chinese and white subjects in their response to atropine and if the intrinsic heart rate and the autonomic contribution to the heart differ between the two races, eight white and eight Chinese males were studied. In all subjects the heart rate decreased after the first dose of atropine (0.003 mg/kg) with no difference in the bradycardia between the two races. However, as further doses were administered, the heart rate increased in both groups, resulting in a significantly (p less than 0.05) greater increase in Chinese subjects than in white subjects. The increase in heart rate for each nanogram per milliliter of atropine was 2.8-fold higher (p less than 0.05) in the Chinese subjects (19.24 +/- 4.41 beats/min) compared with white subjects (6.83 +/- 1.62 beats/min). There was no difference in the intrinsic heart rate, in the relative vagal contribution, or in relative sympathetic contribution to the heart rate between the Chinese and white subjects. These data indicate that Chinese subjects are more sensitive to the effect of atropine, which is not related to the contribution of autonomic tone to the heart.