Absence of alkaline phosphatase-linked inorganic phosphate transport in the chick jejunum.

The role of non-specific alkaline phosphatase-linked inorganic phosphate (Pi) transport in the chick jejunum was investigated by using the everted gut sac technique. The highest intensity of transport was observed for free Pi. The maximal transport rate was considerably reduced when beta-glycerophosphate was used as a single source of phosphorus. These results suggested absence of the alkaline phosphatase-linked transport system for inorganic phosphate in the epithelium of the chick jejunum. Studies of Mg effect on Pi absorption as well as examination of temporal changes in Pi transport rate and beta-glycerophosphate hydrolysis rate by intestinal brush border alkaline phosphatase gave further backing to this suggestion.

Vitamin D3 and 1,25-dihydroxyvitamin D3 stimulate the skeletal muscle-calcium mobilization in rachitic chicks.

The Ca content in skeletal muscle relative to vitamin D3 intake was studied in chicks. It was found that the Ca content in rachitic chick muscle was significantly higher than normal and it decreased with vitamin D3 treatment. In 4-week-old chicks fed a vitamin D-deficient diet, the Ca content in leg muscle reached 9.86 +/- 1.07 mg/100 g wet wt, although in chicks receiving vitamin D3 in doses of 100 and 500 IU/kg diet, it was 7.80 +/- 0.72 and 6.08 +/- 0.61 mg/100 g wet wt, respectively. A single i.m. dose of 0.50 micrograms of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) or vitamin D3 caused a dramatic decrease in the muscle Ca content by 3 to 6 h after the injection. A simultaneous rise in the Ca level in blood serum was observed. However, at this time the Ca binding protein content in duodenal mucosa and the stimulation of Ca absorption were negligible. These findings allow the conclusion that the vitamin D deficiency in chicks leads to a surplus Ca accumulation in skeletal muscle. The administration of vitamin D3 or its metabolites causes rapid Ca release during the first 6 h. This may be the source of the Ca level increase in blood serum. In this respect 1,25(OH)2D3 was much more effective than vitamin D3.

Reversal of prednisolone-induced inhibition of intestinal calcium-binding protein synthesis by 1 alpha-hydroxycholecalciferol in chicks.

Effects of prednisolone on the biochemical indices of blood serum, ash content in bones, calcium absorption and calcium-binding protein (CaBP) in the intestinal mucosa were studied. The oral administration of prednisolone (10 mg/kg) for 2 weeks reduced CaBP content and calcium absorption to the level typical for D-avitaminosis. The oral administration of 1 alpha-hydroxycholecalciferol (390 pmoles/day) in combination with prednisolone for a week returned calcium absorption and CaBP to the control value.