Renal and extra-renal excretion of calcium in the marine teleost, Gadus morhua

Abstract

The calcium turnover, with particular emphasis on the routes and rates of excretion, was investigated in the Atlantic cod, Gadus morhua. A very rapid internal redistribution of injected 45Ca was demonstrated, with the decline in the plasma concentration conforming to the power function f(t) = 8.83% X t-0.585. The clearance for 45Ca and [3H]inulin were both linearly correlated to urine flow and showed a ratio (Cca/CIn) of 2.6:1. Likewise a linear correlation between the renal and extra-renal excretion of 45Ca could be demonstrated with a ratio of 1:0.47, indicating that the renal route of excretion is of major importance in this species. The renal excretion of calcium was estimated to be 4.2 mumol X kg-1 X h-1 and the total calcium excretion to be 6.2 mumol X kg-1 X h-1. Calculations are presented, suggesting that the balance between intake and excretion of calcium can be explained in terms of growth of the animal, which would allow for an increase in the amount of body calcium of approximately 5 g X yr-1. It is also concluded that because about two-thirds calcium is excreted via the renal route, the kidneys may be the most important site for the regulation of calcium excretion in the cod.