title: Species-specific sensitivity to selenium-induced impairment of cortisol secretion in adrenocortical cells of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis).
abstract: Species differences in physiological and biochemical attributes exist even among closely related species and may underlie species-specific sensitivity to toxicants. Rainbow trout (RT) are more sensitive than brook trout (BT) to the teratogenic effects of selenium (Se), but it is not known whether all tissues exhibit this pattern of vulnerability. In this study, primary cultures of RT and BT adrenocortical cells were exposed to selenite (Na(2)SO(3)) and selenomethionine (Se-Met) to compare cell viability and ACTH-stimulated cortisol secretion in the two fish species. Cortisol, the primary stress hormone in fish, facilitates maintenance of homeostasis when fish are exposed to stressors, including toxicants. Cell viability was not affected by Se, but selenite impaired cortisol secretion, while Se-Met did not (RT and BT EC(50)>2000mg/L). RT cells were more sensitive (EC(50)=8.7mg/L) to selenite than BT cells (EC(50)=90.4mg/L). To identify the targets where Se disrupts cortisol synthesis, selenite-impaired RT and BT cells were stimulated with ACTH, dbcAMP, OH-cholesterol, and pregnenolone. Selenite acted at different steps in the cortisol biosynthesis pathway in RT and BT cells, confirming a species-specific toxicity mechanism. To test the hypothesis that oxidative stress mediates Se-induced toxicity, selenite-impaired RT cells were exposed to NAC, BSO and antioxidants (DETCA, ATA, Vit A, and Vit E). Inhibition of SOD by DETCA enhanced selenite-induced cortisol impairment, indicating that oxidative stress plays a role in Se toxicity; however, modifying GSH content of the cells did not have an effect. The results of this study, with two closely related salmonids, provided additional evidence for species-specific differences in sensitivity to Se which should be considered when setting thresholds and water quality guidelines.
authors.affiliation: University of Lethbridge, Department of Biological Sciences, Alberta Water and Environmental Science Building, 4401 University Drive, Lethbridge, Alberta, Canada T1K 3M4. lana.miller@uleth.ca
authors.forename: L L
authors.initials: LL
authors.lastname: Miller
authors.forename: A
authors.initials: A
authors.lastname: Hontela
mesh_terms: D000302:Adrenal Cortex / Q000187:drug effects* / Q000378:metabolism; D000324:Adrenocorticotropic Hormone / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002478:Cells, Cultured; D005978:Glutathione / Q000378:metabolism; D006854:Hydrocortisone / Q000378:metabolism*; D015227:Lipid Peroxidation / Q000187:drug effects; D017686:Oncorhynchus mykiss; D012645:Selenomethionine / Q000633:toxicity*; D018038:Sodium Selenite / Q000633:toxicity*; D013045:Species Specificity; D014337:Trout
chemical_list: D000975:Antioxidants; D000324:Adrenocorticotropic Hormone; D012645:Selenomethionine; D005978:Glutathione; D018038:Sodium Selenite; D006854:Hydrocortisone