CONTRALATERAL INHIBITION OF ECCRINE SWEATING IN RATS AFTER TOPICAL APPLICATION OF DRUGS

¹ The National Drug Company Research Laboratories, Division of Richardson-Merrell Inc., Philadelphia, Pennsylvania

Sweat prints were obtained by placing hind paws of rats on moisture-sensitive paper strips saturated with bromphenol blue. The intensity of color change was an indication of degree of sweating and hidrosis scores were determined according to an eight-point scale. Topical application of 0.016 to 10% scopolamine hydrobromide, 2 to 10% atropine sulfate or 30 to 40% aluminum chloride resulted in inhibition of heat-enhanced sweating on both treated and contralateral (nontreated) paws. Drug effects, in each case, increased in magnitude and duration with increasing concentration. In an attempt to elucidate the mechanism of action of the contralateral inhibition, the following observations were made. 1) Intravenously injected aluminum chloride (6.25 mg/kg) failed to produce anhidrosis. 2) In parabiosis experiments, topically applied 2% scopolamine inhibited sweat secretion of ipsilateral and contralateral paws of the treated rat but did not significantly affect paw sweating in the untreated parabiont. 3) Topically applied 2% scopolamine exerted no obvious mydriasis, nor did the treatment exert significant effects on either paw skin or rectal temperature responses after heat exposure. These results suggest that the contralateral inhibitory effects of the test drugs are not due to l) postabsorptive circulation of the drugs to the contralateral paw, 2) a humoral mechanism or 3) inhibition of the thermoregulatory response to heat. The exact mechanism of the contralateral inhibition is not known, but a neurally mediated effect appears to be implicated.