The effect of diazepam on the responsiveness of human eccrine sweat glands to carbachol: influence of ambient temperature.

The effect of diazepam (10 mg, p.o.) on the responsiveness of eccrine sweat glands to intradermally injected carbachol and on critical flicker fusion frequency was compared in 6 male healthy volunteers under two ambient temperature conditions, 22 degrees C and 35 degrees C. Carbachol evoked dose-related increases in sweat gland activity. Responsiveness to carbachol was significantly enhanced under the 35 degrees C condition as compared to the 22 degrees C condition, this being reflected in a higher value of Emax of the dose-response curve for carbachol under the 35 degrees C condition. Diazepam had no significant effect on responses to carbachol under the 22 degrees C condition, but prevented the increase in responsiveness produced by high ambient temperature. High ambient temperature had no significant effect on critical flicker fusion frequency. Diazepam significantly reduced critical flicker fusion frequency under both temperature conditions. It is suggested that diazepam may block the increase in sympathetic outflow normally evoked by high ambient temperature, thereby preventing the development of sweat gland hyper-responsiveness.