Local effect of vasoactive intestinal polypeptide on human sweat-gland function

Physiological significance of vasoactive intestinal polypeptide (VIP), a putative co-transmitter of the cholinergic neuron innervating sweat glands, was investigated by its local effect on drug-induced sweating. VIP, methacholine chloride (MCH), or VIP plus MCH dissolved in 0.1ml of 0.9% NaCl solution to a specified concentration was injected intradermally at the center of a forearm test area of 15cm2 and the sweat rate was recorded continuously by capacitance hygrometry. In a cool environment (Ta, 23°C), VIP failed to cause sweat secretion, but increased the rate of MCH-induced sweating, most markedly at a concentration of 10-5g/ml, where the rise in local skin temperature was the greatest. On an area anesthetized by nerve block in a hot environment (Ta, 35°C), the effect was less obvious and less consistent, indicating that the sweat-facilitatory effect of VIP is reduced under the condition of passive cutaneous vasodilation. It may be postulated that VIP plays a role in securing ample oxygen supply to functioning sweat glands, especially with a relatively high cutaneous vasoconstrictor tone.