Biological activity of 1,25-dihydroxyvitamin D sub 2 and 24-epi-1,25-dihydroxyvitamin D sub 2

Journal Article · Fri Apr 01 04:00:00 EST 1988 · American Journal of Physiology; (USA)

OSTI ID:6746958

DeLuca, H F; Sicinski, R R; Tanaka, Y; Stern, P H; Smith, C M ^[1]

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1. Univ. of Wisconsin, Madison (USA) Northwestern Univ., Chicago, IL (USA)

The biological activity of 1,25-dihydroxyvitamin D{sub 2} (1,25(OH){sub 2}D{sub 2}) and 24-epi-1,25-dihydroxyvitamin D{sub 2} (24-epi-1,25(OH){sub 2}D{sub 2}) has been determined in vitamin D-deficient rats. The biological effectiveness of 1,25(OH){sub 2}D{sub 2} is equal to that reported previously for 1,25-dihydroxyvitamin D{sub 3} (1,25(OH){sub 2}D{sub 3}) in intestinal calcium transport, mineralization of bone, mobilization of bone calcium, and elevation of plasma inorganic phosphorus of rachitic rats. However, 24-epi-1,25(OH){sub 2}D{sub 2} is at best one-half as active as 1,25(OH){sub 2}D{sub 2} in stimulating intestinal calcium transport and in the mineralization of rachitic bone. The 24-epi-1,25(OH){sub 2}D{sub 2} is one-third as active as 1,25(OH){sub 2}D{sub 3} in binding to the chick intestinal receptor for 1,25(OH){sub 2}D{sub 3}. Thus receptor discrimination may account for the twofold difference in intestinal calcium transport activity. 24-Epi-1,25(OH){sub 2}D{sub 2} appeared inactive in in vivo mobilization of bone calcium or bone phosphorus. On the other hand, in fetal rat bone culture, the epi compound was only five times less active than 1,25(OH){sub 2}D{sub 2} in inducing resorption. Short-term experiments on bone mineral mobilization in vivo show that the 24-epi-1,25(OH){sub 2}D{sub 2} does induce bone calcium mobilization but that its activity in this respect is short lived. It is suggested that 24-epi-1,25(OH){sub 2}D{sub 2} is more rapidly degraded in vivo than 1,25(OH){sub 2}D{sub 2}, and, as a result, it shows preferential activity on intestine whose response to a single dose of 1,25(OH){sub 2}D{sub 2} remains for several days, whereas the short-lived bone system does not remain stimulated during the 24-h period between doses.

• OSTI ID: 6746958
• Journal Information: American Journal of Physiology; (USA), Journal Name: American Journal of Physiology; (USA) Vol. 254:4; ISSN 0002-9513; ISSN AJPHA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
ABSORPTION
ALKALINE EARTH ISOTOPES
ANIMAL TISSUES
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIODEGRADATION
BODY
BONE TISSUES
CALCIUM 45
CALCIUM ISOTOPES
CHEMICAL REACTIONS
CHOLECALCIFEROL
CONNECTIVE TISSUE
CROSS-LINKING
DAYS LIVING RADIOISOTOPES
DECOMPOSITION
DOSE-RESPONSE RELATIONSHIPS
ERGOCALCIFEROL
EVEN-ODD NUCLEI
HYDROGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOTOPES
MAMMALS
MEMBRANE PROTEINS
MINERALIZATION
NUCLEI
NUTRITIONAL DEFICIENCY
ORGANIC COMPOUNDS
POLYMERIZATION
PROTEINS
RADIOISOTOPES
RATS
RECEPTORS
RODENTS
TISSUES
TRITIUM COMPOUNDS
VERTEBRATES
VITAMIN D
VITAMINS