ACTH does not mediate divergent stress responsiveness in rainbow trout.
Two lines of rainbow trout selected for high (HR) and low (LR) responsiveness to a standardised confinement stressor displayed a sustained divergence in plasma cortisol levels during a 3-h period of confinement (max.: HR: 167+/-13 ng ml(-1); LR: 103+/-8 ng ml(-1); P<0.001). However, no significant difference in plasma ACTH levels was evident (max: HR: 153+/-9 pg ml(-1); LR: 142+/-7 pg ml(-1)). Dexamethasone (DEX) was administered to HR and LR fish to block endogenous adrenocorticotropin (ACTH) release. Administration of a weight-adjusted dose of ACTH to the DEX-blocked fish elevated plasma cortisol levels to a significantly greater extent in HR (233+/-24 ng ml(-1)) than LR (122+/-14 ng ml(-1)) fish (P<0.001). Plasma cortisol levels in DEX-blocked HR and LR fish after sham injection were low but also significantly different (HR: 6.7+/-1 ng ml(-1); LR: 2.2+/-0.2 ng ml(-1); P<0.001). These results indicate that modulation of cortisol responsiveness to stressors in HR and LR fish resides, at least in part, downstream of the hypothalamic-pituitary axis.
Pottinger
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TG
NERC Centre for Ecology and Hydrology, Windermere Laboratory, The Ferry House, Far Sawrey, Ambleside, Cumbria LA22 0LP, UK. tgp@ceh.ac.uk
Carrick
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TR
D000222:Adaptation, Physiological; D000324:Adrenocorticotropic Hormone / Q000097:blood* / Q000494:pharmacology / Q000502:physiology; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D006854:Hydrocortisone / Q000097:blood*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology; D008297:Male; D017686:Oncorhynchus mykiss / Q000502:physiology*; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology; D013312:Stress, Physiological
D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone