[Effect of active metabolites of vitamin D 3 on the status of rat bone tissue in various experimental models of hypokinesia].

Rats were for 6 weeks either kept in small cages or suspended. The caged rats showed hypocalcemia and lowered active transport of calcium in the intestine and no changes of PTH in blood. Femoral bone measurements in these rats revealed reduced density and content of calcium and phosphorus in proximal epiphyses, slight increase of these parameters in diaphyses and lack of changes in distal epiphyses. The suspended rats exhibited normocalcemia, noticeable but insignificant increase of PTH and calcium absorption as well as decreased density and content of calcium and phosphorus in distal epiphyses and their slight increase in diaphyses. Administration of active vitamin D3 metabolites led to an increase of bone mineral density and content only in those femur compartments where hypokinesia-induced changes were seen. It is concluded that during hypokinesia bone disorders are predominantly produced by local factors that may increase bone sensitivity to systemic influences.