Release of corticosteroid by the interrenal gland is one step in the sequence of energy-mobilizing responses to stressors, including pollutants. Chronic field exposures to mixtures are associated with a depressed cortisol profile in fish and it has been proposed that a prolonged toxicant-invoked hyperstimulation may lead to an exhaustion of the secretory system. The functional integrity of the corticosterone-producing axis was tested in an amphibian, the mudpuppy (Necturus maculosus). Circulating levels of corticosterone following a standardized capture and handling stress were compared among nine populations in two hydrographic systems impacted by persistant organochlorines. This initial study revealed a weak trend for lower plasma corticosterone in females with higher organochlorines or PCBs in the tissues. The high intra-site variability may have compromised our capacity to detect subtle differences. In a follow-up study, the responsiveness to an ACTH challenge was compared between a contaminated and a reference population. Exogenous ACTH injected after a 24 hrs acclimation in a field-adapted flow-through system elicited a significantly lower surge in plasma corticosterone in the contaminated males and females compared to reference. Corticosterone levels measured after the rest period were higher in the contaminated group. In conclusion, the ACTH-challenge revealed a reduced responsiveness of the interrenal gland and some deficiency of the system to recover from an initial stress in a contaminated population, while previous monitoring only detected a tendency for lower circulating corticosterone. Plasma glucose levels, liver glycogen stores and histology of the interrenal tissue will be also used to assess the physiological competence of the corticosterone-producing axis of the mudpuppy.
Key Words: Amphibian, Corticosterone secretion, ACTH, Organochlorines
Andrée Gendron
Département des Sciences Biologiques
Université du Québec à Montréal
C.P. 8888, succ. Centre-ville
Montréal, Québec, Canada
H3C 3P8
Phone: (514)762-9836
d345510@er.uqam.ca
Presented at SETAC conference in Vancouver (November 1995)