Passive uptake in the small intestine and active uptake in the hindgut contribute to the highly efficient mineral metabolism of the common mole-rat. cryptomys hottentotus

Cryptomys hottentotus has no access to dietary or endogenous sources of cholecalciferol (D3). Serum concentrations of calcifediol (25(OH)D3) were undetectable (5 ng/ml) and calcitriol (l,25(OH)2D3), although detectable in plasma, was at a low concentration (31.40 (sem 3.06 pg/ml). Despite their naturally impoverished vitamin D status, these animals exhibited highly efficient mineral absorption processes (Ca apparent fractional absorption efficiency, AFA (%) 9533 (sem 1.36); inorganic P (Pi) AFA (%) 93.49 (sem 0.81)). Furthermore, plasma mineral content was tightly regulated (Ca 2 57 (sem 0.08) mmol/1; Mg 1.23 (sem 0.05) mmol/1; Pi 2–12 (sem 0.15) mmol/1). Mode of uptake in C. hottentotus was unlike that in other D3-replete mammals. First, passive (rather than active) uptake occurred in the traditional site of active Ca absorption (with serosal:mucosal (S:M) ratios in the duodenum of 1.32 (sem 0.13)), and the only site of active Ca uptake was the hindgut (caecum S :M 3.35 (sem 0.46); proximal colon S: M 2.13(sem 0.30)). Despite the presence of active uptake in these hindgut regions, their overall contribution to the daily rate of mineral absorption was small (9.53 (sem 1.27) %). These underground inhabitants rely upon highly efficient, passive mineral uptake. This is adequate to meet their mineral requirements and maintain mineral homeostasis in the absence of vitamin D.