In vivo testing of the functional integrity of the corticosterone-producing axis in mudpuppy (amphibia) exposed to chlorinated hydrocarbons in the wild

Abstract

Abstract The functional integrity of the hypothalamo–pituitary–interrenal (HPI) axis was tested in an aquatic salamander, the mudpuppy (Necturus maculosus), exposed in the wild to HPI axis disrupters. The response to stress challenges was compared in mudpuppies sampled at nine sites of the St. Lawrence and Ottawa rivers during winter. Polychlorinated biphenyls and organochlorine pesticides measured in gonads indicated that the exposure was highly variable among sites. Females subjected to a standardized capture and confinement stress, a treatment that induces a surge of circulating corticosterone, had significantly lower levels of corticosterone at a number of contaminated sites compared to animals from the reference areas. Among-site differences could not be distinguished in males that had very low corticosterone levels overall. The reduced corticosterone response at contaminated sites was not associated with an atrophy of the interrenal corticosterone-releasing cells. A corticotrophin (adrenocorticotrophic hormone, ACTH) challenge imposed in situ after a 24-h postcapture recovery elicited a corticosterone surge significantly lower in contaminated females and males, pointing to disruptions along the HPI axis downstream of the pituitary ACTH-secreting cells. Corticosterone levels measured after recovery were higher at the contaminated site, suggesting an increase in resting levels. Liver glycogen, whose replenishment is partly mediated by corticosterone, was significantly depleted in salamanders collected at most contaminated sites. Our results suggest xenobiotic-induced disruptions within the HPI axis of an amphibian species, but the role of alternative factors is also discussed.