Effect of atropine on the exercise-heat performance of man.

This paper summarizes the findings from two recent studies involving the physiological effects of atropine (0 to 4 mg, im) on soldiers performing physical exercise in hot-dry environments. Study I determined the threshold of physiological effects and the gradation of these effects with increasing dosage of atropine. Study II examined the effects of exercise-heat acclimation on the reduced physical exercise performance that occurs following atropine administration. The following new observations were made: (1) a 0.5-mg dose of atropine elevates heart rate, rectal temperature, and mean skin temperature; (2) atropine exerts its peak physiological effects approximately 70 min after intramuscular injection; (3) within the dosage levels tested, the magnitude of the elevated heart rate response is curvilinearly related to atropine dosage, whereas, the magnitude of the elevated rectal temperature response is linearly related to atropine dosage; (4) repeated administration of atropine over a number of days does not alter thermo-regulatory responses; (5) heat acclimation improves exercise-heat performance of individuals under the influence of atropine by enabling a reduced rectal temperature; and (6) heat acclimation increases the sweat output of individuals under the influence of atropine; however, the absolute reduction in sweat output from atropine is the same pre-and post-heat acclimation.