HORMONAL STATUS AND THE NEUROENDOCRINE RESPONSE TO A NOVEL HETEROTYPIC STRESSOR INVOLVING SUBCHRONIC NOISE EXPOSURE

Despite a number of studies on noise-induced health effects, it is sti ll unclear to what extent different neuroendocrine pathways are affect ed by noise exposure. Male Wistar rats were housed in sound-attenuated rooms isolated for noise from outside. Three groups of chronically ca nnulated rats were exposed to either background noise (+/- 64 dB) only or irregular experimental white noise (90 dB, 2-22 kHz). Two protocol s, with approximately the same total amount of noise but with differen t densities, were used: protocol N1 (180 min random noise per day for 18 days) or protocol N2 (540 min random noise per day for 8 days). Bas al levels of circulating hormones (ACTH, corticosterone, prolactin and catecholamines) and plasma glucose were measured. In control animals, no significant changes in any of these parameters were observed over 18 days. Except for plasma prolactin, N1 did not induce a significant elevation in basal hormonal levels. N2 however induced significant ele vation in basal prolactin, corticosterone and noradrenaline levels. At the end of the exposure period, all animals were subjected to a novel heterotypic stressor (restraint stress) to monitor differences in neu roendocrine activation (ACTH, corticosterone and prolactin). Compared to nonexposed control animals, N1 animals showed a normal ACTH and an enhanced corticosterone response, whereas N2 animals showed an increas ed ACTH but a normal corticosterone response. The prolactin response o f both N1 and N2 animals was significantly decreased. Adrenal cell sus pension experiments revealed that in noise-exposed rats both basal- an d ACTH-stimulated corticosterone production were significantly increas ed as compared to control animals. These results indicate that chronic noise exposure at mild intensities induces subtle but significant cha nges in hormonal regulation.