Central and peripheral effects of repeated noise stress on hypothalamic-pituitary-adrenocortical axis in pigs

The present study was performed to examine the effects of a repeated noise exposure (4 weeks) on basal and noise-induced plasma adrenocorticotrophin (ACTH), cortisol and corticosteroid binding globulin (CBG) levels, brain glucocorticoid receptors (GR) and corticotropin-releasing hormone (CRH) concentrations as well as on the morphology of adrenal glands in German Landrace pigs. Chronically cannulated pigs were exposed to either a daily stimulation with broad-band noise (2 h, 90 dB) (N1), or to the same stimulus three times a week (N2), or to an equal handling procedure without noise stimulation. Noise exposure caused an increase of basal CBG concentrations in N1 animals in the first week. During noise session, an increase of plasma ACTH and cortisol levels in N1 animals was measured in week 1 followed by a subsequent decrease until week 4. The ACTH and cortisol response of the N2 animals increased after week 1 and was significantly elevated in week 4. Furthermore, noise stress caused an increased hippocampal GR binding of N2 pigs, but had no effects on GR binding in the amygdala and on hypothalamic CRH levels. There were also significant structural modifications in the adrenal gland of N1 pigs resulting in differentiated effects on the adrenal cortex and medulla. The present results show that repeated noise exposure of pigs causes considerable alterations at different levels of the HPA system in association with the frequency of noise stimulation. This may have substantial impact on the general vulnerability of the animal with respect to productivity, health and welfare.