A protective effect of dietary calcium against acute waterborne cadmium uptake in rainbow trout.
The present study examined the interactions between elevated dietary calcium (as ionic Ca2+ in the form of CaCl2 x 2H2O) and acute waterborne Cd exposure (50 microg/l as CdNO3 for 3 h) on whole body uptake and internal distribution of newly accumulated Cd, Ca2+, and Na+ in juvenile rainbow trout (Oncorhynchus mykiss). Fish were fed with three diets 20 (control), 30 and 60 mg Ca2+/g food: for 7 days before fluxes were measured with radiotracers over a 3h period. The two elevated Ca2+ diets reduced the whole body uptake of both Ca2+ and Cd by >50% and similarly reduced the internalization of both newly accumulated metals in most tissues, effects which reflect the shared branchial uptake route for Ca2+ and Cd. As the Ca2+ concentrations of the fluid phases of the stomach and intestinal contents were greatly elevated by the experimental diets, increased gastrointestinal Ca2+ uptake likely caused the down-regulation of the branchial Ca2+ (and Cd) uptake pathway. Waterborne Na+ uptake and internal distribution were not affected. While plasma Ca2+ surged after the first two feedings of the 60 mg Ca2+/g diet, internal homeostasis was quickly restored. Total Ca2+, Na+, and Cl- levels in tissues were not affected by diets. While dietary Ca2+ protected against waterborne Cd uptake, it did not protect against the relative inhibition of waterborne Ca2+ uptake caused by waterborne Cd. Acute exposure to 50 microg/l Cd reduced the uptake and internalization of newly accumulated Ca2+ (but not Na+) by 70% or more, regardless of diet. Since elevated dietary Ca2+ reduces waterborne Cd uptake, fish eating a Ca(2+)-rich invertebrate diet may be more protected against waterborne Cd toxicity in a field situation.
Baldisserotto
B
B
Departamento de Fisiologia, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil. bernardo@smail.ufsm.br
Kamunde
C
C
Matsuo
A
A
Wood
C M
CM
D000704:Analysis of Variance; D000818:Animals; D002104:Cadmium / Q000493:pharmacokinetics*; D002136:Calcium, Dietary / Q000378:metabolism* / Q000493:pharmacokinetics; D004781:Environmental Exposure; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D012964:Sodium / Q000493:pharmacokinetics; D014874:Water Pollutants, Chemical / Q000493:pharmacokinetics*
D002136:Calcium, Dietary; D014874:Water Pollutants, Chemical; D002104:Cadmium; D012964:Sodium