1,25-DIHYDROXYCHOLECALCIFEROL ANALOGS CANNOT REPLACE VITAMIN-D IN NORMOCALCEMIC MALE-RATS

A possible role of vitamin D in the growth and development of rats was investigated. Impaired development was observed in normocalcemic, vit amin D-deficient male and female rats, as revealed by low intestinal c alcium transport, low renal vitamin D receptor levels and poor bone mi neralization. Analogs of 1,25-dihydroxycholecalciferol, possessing red uced calcium-mobilizing activity in intestine and bone but retaining d ifferentiation activity in cultured cells, were unable to support norm al development of normocalcemic, vitamin D-deficient male rats. These results suggest that either the calcium-mobilizing activity alone or b oth the calcium-mobilizing activity and differentiating activity of vi tamin D are required for normal development or that the analogs are in active in vivo. We also demonstrated sex-related differences in intest inal calcium transport, renal vitamin D receptor regulation and bone m ineralization that were independent of vitamin D status.