Vitamin D metabolism in the Damara mole-rat is altered by exposure to sunlight yet mineral metabolism is unaffected.
Vitamin D may be endogenously synthesized in the skin in the presence of sunlight or, alternatively, acquired from dietary sources. Cryptomys damarensis appear to have a naturally impoverished vitamin D status with low plasma concentrations of both 25-hydroxyvitamin D (25(OH)D; < 5 ng/ml) and 1,25-dihydroxyvitamin D (1,25(OH)2D; < 20 pg/ml). We attribute this to their underground habitat and herbivorous habits. We questioned whether these subterranean mammals could utilize sunlight-mediated pathways and therefore compared vitamin D metabolism and function when animals were (a) housed naturally (control), (b) given an oral vitamin D3 (D3) supplement (1 IU/g dry matter food eaten per day) and (c) exposed to 10 h of sunlight. Control animals exhibited a highly efficient apparent fractional absorption of both calcium (Ca) and inorganic phosphorus (Pi) (> 90%), passive mode of intestinal mineral uptake, yet tightly regulated serum ionized calcium (Ca2+). The ratio of 25(OH)D-1 alpha-hydroxylase (1-OHase) to 25(OH)D-24R-hydroxylase (24-OHase) activity in the kidney, corresponded with a state of vitamin D deficiency. Cryptomys damarensis responded to both oral D3 supplementation and sun exposure by an increase in plasma concentration of 1,25(OH)2D with a commensurate decline (P < 0.05) in 1-OHase activity, and a resulting decrease (P < 0.05) in the ratio of 1-OHase:24-OHase activity. Despite these changes, the intestinal mode of Ca uptake and plasma total Ca, Ca2+ and Pi remained unchanged with either treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Pitcher
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Department of Physiology, Medical School, University of the Witwatersrand, Johannesburg, South Africa.
Sergeev
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IN
Buffenstein
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D000818:Animals; D002118:Calcium / Q000378:metabolism; D002762:Cholecalciferol / Q000008:administration & dosage; D053493:Cholestanetriol 26-Monooxygenase; D004032:Diet; D007408:Intestinal Absorption; D007668:Kidney / Q000378:metabolism; D008903:Minerals / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D012377:Rodentia / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000378:metabolism; D013472:Sunlight; D014807:Vitamin D / Q000378:metabolism*
D008903:Minerals; D014807:Vitamin D; D002762:Cholecalciferol; D010758:Phosphorus; D013250:Steroid Hydroxylases; D053493:Cholestanetriol 26-Monooxygenase; D002118:Calcium