NEUROENDOCRINE CONTROL OF SWEAT GLANDS

Eccrine glands perform two functions: those on the foot pads of animals and the palms of humans facilitate prehension and are controlled by both adrenergic and cholinergic nerves; those on the general body surface regulate body heat and are controlled by cholinergic nerves. The adrenergic effect in the glands of the palms and soles is mediated through α-receptors. The function of these glands is also modified by humoral agents. Circulating catecholamines increase sweating by stimulating the β-receptors, a matter of physiologic significance because sweating facilitates dissipation of heat induced by exercise. Circulating catecholamines do not seem to cause the sweating observed in pheochromocytoma, insulin hypoglycemia, and hypotension, all of which arc associated with elevated levels of plasma catecholamines. Aldosterone acts on the epithelium lining the excretory duct and stimulates the absorption of sodium, in partial exhange for potassium, from the fluid secreted by the cells of the secretory coil. This absorption produces a hypotonic secretion. In some species, e.g., horses and cows, apocrine glands perform a thermoregulatory function. In all animals so far studied, an adrenergic nerve supply to apocrine sweat glands has been demonstrated; in some species, however, nerve terminals have not been detected histologically. A neurohumoral type of sudomotor transmission has been proposed in which the transmitter is released into the circulatory system in close proximity to the sweat glands. In equine species, circulating catecholamines have been shown to supplement neural stimulation during exercise