title: Estradiol impairs hyposmoregulatory capacity in the euryhaline tilapia, Oreochromis mossambicus.
abstract: Freshwater (FW)-adapted tilapia (Oreochromis mossambicus) were treated with estradiol (E(2)) for 4 days to stimulate protein synthesis and sampled at 0, 4, and 24 h after exposure to 50% seawater (SW). E(2) increased circulating vitellogenin (VTG) levels in large amounts, indicative of unusually high rates of hepatic protein synthesis. E(2) treatment prevented the recovery of plasma osmolality in 50% SW that was evident in the sham group. Plasma sodium concentration was significantly elevated with E(2) in FW, but the levels did not change in 50% SW. Gill Na(+)-K(+)-ATPase activity was significantly lower in the E(2) group compared with sham-injected tilapia in 50% SW. No significant differences were noted in plasma cortisol, thyroxine, triiodothyronine, or glucose concentration with E(2) in 50% SW. E(2) significantly lowered several key liver enzyme activities and also decreased gill lactate dehydrogenase and malate dehydrogenase activities over a 24-h period. Together, our results suggest that E(2) impairs ion regulation in tilapia, partially mediated by a decreased metabolic capacity in liver and gill. The decreased tissue metabolic capacity is likely due to E(2)-induced energy repartitioning processes that are geared toward VTG synthesis at the expense of other energy-demanding pathways.
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. mvijayan@sciborg.uwaterloo.ca
authors.forename: M M
authors.initials: MM
authors.lastname: Vijayan
authors.forename: A
authors.initials: A
authors.lastname: Takemura
authors.forename: T P
authors.initials: TP
authors.lastname: Mommsen
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology*; D005618:Fresh Water; D005880:Gills / Q000187:drug effects / Q000201:enzymology; D006854:Hydrocortisone / Q000097:blood; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008291:Malate Dehydrogenase / Q000378:metabolism; D008297:Male; D009929:Organ Size / Q000187:drug effects; D009994:Osmolar Concentration; D012623:Seawater; D012964:Sodium / Q000097:blood; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013974:Thyroxine / Q000097:blood; D017210:Tilapia; D014284:Triiodothyronine / Q000097:blood; D014819:Vitellogenins / Q000097:blood; D014882:Water-Electrolyte Balance / Q000187:drug effects*
chemical_list: D001786:Blood Glucose; D014819:Vitellogenins; D014284:Triiodothyronine; D012965:Sodium Chloride; D004958:Estradiol; D012964:Sodium; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase; D000254:Sodium-Potassium-Exchanging ATPase; D013974:Thyroxine; D006854:Hydrocortisone