Sweat Secretion by Human Axillary Apoeccrine Sweat Gland in Vitro

Functional characteristics of isolated single human axillary apoeccrine sweat glands have been studied using in vitro sweat induction methods. Sustained copious clear fluid secretion was evoked by methacholine (MCh), epinephrine (EP), isoproterenol (ISO), and phenylephrine (PL) in decreasing order in a pharmacologically specific manner. Apoeccrine glands showed a higher cholinergic sensitivity than eccrine sweat glands, as shown by the apparent association constant for MCh of 2.7 X 10(-7) M compared with 2.1 X 10(-6) M for the axillary eccrine sweat gland. The average total sweat rate of the apoeccrine gland for a 30-min period was sevenfold higher than that of the eccrine sweat gland. In contrast, isolated apocrine glands showed intermittent pulsatile turbid sweat secretion in response to MCh or EP. The Na+ and K+ concentration of apoeccrine glands was nearly isotonic, whereas those of apocrine sweat was 120-140 mM for Na+ and 10-20 mM for K+. Apoeccrine ductal Na+ absorption was also observed in the apoeccrine glands and was no more efficient than that of the axillary eccrine sweat gland. Thus apoeccrine sweat glands are functionally and pharmacologically distinct from axillary apocrine glands and significantly contribute to overall axillary sweating in humans.