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 (1,25(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 (%) 95.33 (SEM 1.36); inorganic P (P(i)) AFA (%) 93.49 (SEM 0.81)). Furthermore, plasma mineral content was tightly regulated (Ca 2.57 (SEM 0.08) mmol/l; Mg 1.23 (SEM 0.05) mmol/l; P(i) 2.12 (SEM 0.15) mmol/l). 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.
Pitcher
T
T
Physiology Department, Medical School, University of the Witwatersrand, Parktown, South Africa.
Buffenstein
R
R
D000818:Animals; D001692:Biological Transport; D001693:Biological Transport, Active; D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006706:Homeostasis; D007408:Intestinal Absorption / Q000502:physiology*; D007420:Intestine, Large / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008903:Minerals / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012377:Rodentia / Q000378:metabolism*; D014070:Tooth / Q000033:anatomy & histology / Q000378:metabolism; D014807:Vitamin D / Q000378:metabolism
D008903:Minerals; D014807:Vitamin D; D008274:Magnesium; D011188:Potassium; D002118:Calcium