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.
Physiology Department, Medical School, University of the Witwatersrand, Parktown, South Africa.
T
T
Pitcher
R
R
Buffenstein
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