Cyclic GMP accumulation during cholinergic stimulation of eccrine sweat glands

The possibility that guanosine 3'5'-cyclic monophosphate (cGMP) may be an intracellular mediator of cholinergic stimulation [methacholine chloride (MCh)] was explored by comparing the relationship between the time course of cGMP accumulation and sweat secretion by use of isolated monkey palm eccrine sweat glands. Isolated sweat glands were incubated with MCh or other agents, and tissue levels of cGMP were determined by radioimmunoassay. In parallel experiments, sweat secretion was induced from cannulated single sweat glands in vitro. Stimulation with MCh produced a Ca-dependent transient elevation of cGMP level from 10 to 80 fmol/gland, peaking at 1-2 min but returning to the basal level by 5 min. The MCh-induced cGMP level was dose dependent and was inhibited by atropine. Ionophore A23187 (2 X 10(-4) M), however, caused persistent elevation of cGMP level for at least 20 min. Neither 10(-4) M MNNG, which elevated the cGMP level comparably with MCh stimulation, nor 8-bromo-cGMP (2 mM) induced sweat secretion. Thus although a parallelism between the cGMP level and sweating rate appears to hold for the initial stage of MCh-induced sweating, it does not hold for the steady state of sweat secretion. Data could not be interpreted to favor the notion that cGMP may be the intracellular mediator of cholinergic sweat secretion.