Hormonal control of intestinal calcium-binding protein concentrations at weaning in rats.

In rats, the intestinal concentration of immunoreactive Ca-binding protein was shown to increase at weaning. We now report that injections of 1,25-dihydroxycholecalciferol (1,25(OH)2D3, 25 ng or 10 ng/day) in suckling rats on days 11, 12 and 13 induce a premature rise of the intestinal Ca-binding protein concentrations, associated with increased plasma Ca concentrations. No effect is seen after 25-hydroxycholecalciferol, or after hydrocortisone administration. L-Thyroxine, at high doses (50 micrograms/day) and at more physiological doses (2 micrograms/day) induces a significant rise of the intestinal Ca-binding protein concentrations and a decrease of plasma Ca concentrations. The association of 1,25(OH)2D3 (at 10 ng/day) and L-thyroxine (at 2 micrograms/day) does not cause an additive effect on Ca-binding protein concentrations and does not change plasma Ca. These results suggest that 1,25(OH)2D3 and thyroxine are probably involved in the regulatory mechanisms of the intestinal Ca-binding protein synthesis at weaning.