Calcium and Inorganic Phosphorus Metabolism in Naked Mole Rats Heterocephalus glaber Is Only Indirectly Affected by Cholecalciferol

Abstract

Naked mole rats seem to be naturally deficient in cholecalciferol yet exhibit net calcium and inorganic phosphorus absorption efficiencies that approach a physiological maximum (i.e., exceed 94%). Oral supplementation with cholecalciferol therefore does not markedly enhance the efficiency of gastrointestinal absorption of these minerals, but rather exerts indirect effects on mineral metabolism by increasing food intake (1.7 ×) from 3.6 ± 0.4 to 6.2 ± 0.3 g/100 g body wt day -1. This, in turn, results in a concomitant increase in the daily rate of calcium absorption from 2.9 ± 0.3 to 4.4 ± 0.4 (mmol/100 g body wt day -1) and inorganic phosphorus absorption from 4.5 ± 0.4 to 7.9 ± 0.4 (mmol/100 g body wt day -1) with cholecalciferol supplementation. Excretion of calcium decreases from 2.9 ± 0.5 to 1.2 ± 0.4 μmol/100 g body wt day -1 with cholecalciferol supplementation whereas inorganic phosphorus excretion is unchanged (4.3 ± 0.9 to 4.3 ± 1.2 μmol/100 g body wt day -1), to give a positive mineral balance, without any evident pathology. Indeed serum calcium (2.3 ± 0.1 vs 2.5 ± 0.1 mmol/liter) and inorganic phosphorus (1.5 ± 0.3 vs 1.6 ± 0.2 mmol/liter) concentrations remain tightly regulated irrespective of vitamin D 3 status. Mineral balance in naked mole rats is concluded not to he directly influenced by cholecalciferol, rather it may be affected by pleiotropic actions of cholecalciferol on gut function.