FATIGUE OF THE SWEAT GLANDS

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Abstract
Decrease in the rate of sweat secretion during prolonged exposures to environmental temperatures above 40[degree]C is due primarily to a decline in the activity of each glandular unit and secondarily to reduction in the number of functioning units. The relative activities of the sweat glands remain unchanged during exposure to heat, indicating that the absolute decrease in the function of each gland is proportional to its original or maximal functional capacity. Repeated intradermal injections or constant infusion of [beta]-methyl-acetylcholine hydrochloride, Mecholyl, evoked decreasing outputs of sweat until a refractory state was reached; as in the case of general reflex sweating the decrease in secretion rate was due chiefly to decline in the flow per gland, and less to decline in the number of functioning glands. The time needed for recovery of glandular function following a single maximal stimulation with Mecholyl proved to be 5-6 hours. Sweat glands which were rendered refractory to Mecholyl showed no response to the stimulus of general heat; conversely, the output of sweat following intradermal injection of Mecholyl was diminished by preliminary reflex sweating. Results suggest that the decrease in reflex sweating produced by environmental heat is due to fatigue of the glandular units and not to decreased central nervous stimulation. Apparently sweating can continue indefinitely at the same rate only if the demand on the secretory mechanism does not exceed simultaneous processes that operate to restore secretory function. When the demand upon the secretory mechanisms exceeds the capacity for restoration of function, the sweating rate decreases.

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