Irregular activation of individual sweat glands in human sole observed by a videomicroscopy

Sweat secretion from individual sweat glands on the human sole was observed in four male subjects by using a videomicroscope and correlated with sudomotor neural activity recorded from the tibial nerve by means of microneurography. Individual sweat glands could be distinguished as active, less active and inactive according to the incidence of sweat secretion during spontaneous sweating. The threshold amplitude of the sudomotor burst necessary for sweat secretion varied from gland to gland. The number of sweat secretion was significantly related to the threshold amplitude. Sweat glands often failed to produce sweat secretion even when a suprathreshold burst occurred: only 46.1+/-3.8% (mean +/- S.E.M.) of the suprathreshold bursts elicited sweat secretion. Failure of the sweat secretion tended to appear after several bursts occurred consecutively with short intervals. In spite of the variability in sweat gland activity, the number of sweat glands recruited was linearly related to the amplitude of the sudomotor burst (P < 0.001). Thus, although sweat secretion from each sweat gland depends primarily on the intensity of sudomotor neural activity. the activity of each sweat gland may fluctuate temporally as the result of irregular activation of sudomotor fibers and possibly some intrinsic factors of the gland.