Low-calcium diets increase both production and clearance of 1,25-dihydroxyvitamin D3 in rats

Journal Article · Thu Feb 01 00:00:00 EST 1990 · American Journal of Physiology; (USA)

OSTI ID:7191866

Fox, J; Bunker, J E; Kamimura, M; Wong, P F ^[1]

---

1. Tulane Univ. School of Medicine, New Orleans, LA (USA)

Administration of large doses of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) to animals induces 1,25(OH)2D3 side-chain oxidative pathways. This study determined if the elevated plasma 1,25(OH)2D3 seen in rats fed low-Ca diets is associated not only with an increased production rate (PR) but also with an increased metabolic clearance rate (MCR) of the hormone. In vitamin D-replete rats fed a Ca-deficient diet for 3-4 wk, the PR increased 21-fold, plasma levels 15-fold, and the MCR by 37%. The increased MCR in Ca-deficient rats was associated with a 48% increase in hepatic microsomal UDP glucuronyl transferase enzyme activity, whereas 1,25(OH)2D3 catabolism by homogenates of liver and small intestinal mucosa was unchanged. In contrast to the effects of low-Ca diets, acute (7 h) pharmacological elevation of plasma 1,25(OH)2D3 to 1.5 ng/ml in normal rats did not influence the MCR. Thus chronically elevated 1,25(OH)2D3 levels are necessary to stimulate clearance. In conclusion, 1,25(OH)2D3 clearance in rats can be stimulated not only by chronic pharmacological doses of 1,25(OH)2D3 but also by the physiological stimulus of a low-Ca diet. Hence, plasma 1,25(OH)2D3 levels can be regulated by changes in both PR and MCR.

• OSTI ID: 7191866
• Journal Information: American Journal of Physiology; (USA), Vol. 258; ISSN 0002-9513
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CALCIUM
NUTRITIONAL DEFICIENCY
TRANSFERASES
ENZYME ACTIVITY
VITAMIN D
METABOLISM
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL PATHWAYS
CLEARANCE
DIET
HORMONES
RATS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALKALINE EARTH METALS
ANIMALS
ELEMENTS
ENZYMES
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
KINETICS
MAMMALS
METALS
REACTION KINETICS
RODENTS
VERTEBRATES
VITAMINS
550201* - Biochemistry- Tracer Techniques