Fatigue of the Sweat Glands

Abstract

The rate of sweat secretion has been shown to decrease during prolonged exposure to heat (1-3). This phenomenon has practical importance in the etiology of heat stroke, since the evaporation of sweat is the only significant means for dissipating heat when the environmental temperature equals or exceeds the body temperature.It is not known whether this decrease in sweating rate is due to a failure of the sudomotor center or to an exhaustion of the peripheral glandular units. The present, investigation was undertaken in an attempt to answer this question. The' results indicate that the decrease in sweating rate is due primarily to fatigue of the secretory mechanism of the glands. Apparently sweating can continue indefinitely at the same rate only as long as the demand upon the secretory mechanism does not exceed the capacity of the simultaneous restorative processes. Whenever the demand upon the secretory mechanism exceeds restorative capacity the rate of sweating decreases. PROCEDUREFour young, un-acclimatized, healthy males served as subjects for the experiments which were conducted during the winter months. Sweating was stimulated in a hot room, temperature 400 to 450 C., relative humidity 60 to 90 per cent. The carbon dioxide and oxygen concentrations of the air were controlled and kept constant at normal values prevailing outside the gas-tight chamber. The subjects entered the room nude except for a pair of light shorts and remained at rest lying uncovered on top of a bed during the entire experiment. Room temperature and rectal temperature were recorded every 30 minutes.The total amount of sweat secreted from the entire body surface was estimated at accurately timed intervals of 30 to 60 minutes' duration. The subject removed his shorts. His skin was dried thoroughly with towels and body weight measured to the nearest 50 gm. Water, approximately at body temperature, was imbibed in amounts equivalent to the loss in body weight; sodium chloride was taken to replace an estimated average loss of 50 mEq. of sodium per liter of sweat produced. The total amount of sweat secreted in any period was calculated from the weight loss with corrections for water intake and urine flow. The insensible water loss from the skin and through the expired air and the metabolic weight loss were taken into account and did not introduce a significant error into this calculation at the sweating rates which prevailed in these experiments.Local collections of sweat, using special collection chambers (4), were obtained from the ventral surfaces of the forearms. The sweat was absorbed into filter paper discs and the rate of flow calculated by the weight increment of the disc during exactly timed periods of 20 to 30 minutes' duration.Prints of the sweating areas were obtained and analyzed by methods previously described (5). In brief, paper impregnated with iodine was placed in special holders and pressed against the skin of the local collection areas for timed periods of 1 to 10 seconds. The water emerging from the sweat glands reacted wi...

Studies on the nature of sweat gland ‘fatigue’ in the goat

“…Similar patterns of evaporative loss have been found in some wild East African bovids (Robertshaw & Taylor, 1969). A prominent feature of sweating in sheep and goats is the rapid decline in the amount of sweat produced at each discharge, an apparent 'fatigue' (Robertshaw, 1968 gland function has been noted in man after prolonged exposure to hot humid conditions and also after repeated administration of acetyl-/5-methylcholine (Thaysen & Schwartz, 1955; Collins, Sargent & Weiner, 1959). It can also be produced in a localized area of skin by preventing the evaporation of sweat and it has been suggested that sweat gland 'fatigue' in man is caused by hydration of the skin and obstruction of the sweat gland ducts.…”

“…The 'fatigue' of sweat gland activity induced in man by exposure to severe heat is similar in nature, i.e. the number of active glands does not diminish (Thaysen & Schwartz 1955).…”

Proceedings of the Physiological Society

“…Eccrine sweat glands exhibit a relatively high resistance to failure during continuous stimulation by low concentrations of acetylcholine (ACh), although high concentrations rapidly desensitize the glands (Collins, Sargent & Weiner, 1959). After 6 hr of thermal sweating the response to methacholine is reported to decrease (Thaysen & Schwartz, 1955) and this has been taken as evidence for 'fatigue' of the sweat glands. In the present experiments on seven subjects in environments of 460 C dry bulb/30°C wet bulb or 400 C dry bulb/32°C wet bulb, it was found that the sweat response to ACh did not decrease significantly, that sweat rate decreased by less than 30 % of the initial maximum, and that skin and rectal temperatures increased steadily during 3-5 hr of heat exposure.…”

Proceedings of the Physiological Society

“…In an area of the skin repeatedly injected with 400 Kg ACh or methacholine without atropine there was little reaction to the test doses and a slow recovery from the depression took place during the following 12 hr. Thaysen & Schwartz (1955) suggest that the decrease in sweat gland activity by repeated injections of drugs is due to 'fatigue' of the glands. We have found, however, that the depression by drugs does not necessarily entail prolonged or intense secretory activity and that the NaCl concentration of the sweat does not increase as is the case in thermal sweat gland 'fatigue' (Robinson & Robinson, 1954).…”