Comparison of the effects of vitamin D3, dihydrotachysterol, and parathormone on calcium kinetics in the rat.

Rats were treated with 100 I.U. (= 2.5 mcg) Vit. D3/day during 14 days and submitted to a radio-Calcium assay of Calcium kinetics. The results were compared with those obtained in weight-matched pair-fed controls, and with those obtained in former experiments applying dihydrotachysterol and parathormone. Vit. D3, which is transformed to a hormone, increased the fast exchange compartment, the exchange rate between the compartments, the endogenous fecal Calcium excretion rate, and the bone uptake and release rates. These findings indicate that the Vit. D-hormone is more similar in its action to the other hormone, parathormone, than to its close chemical relative dihydrotachysterol.