Chick brain calcium binding protein: response to cholecalciferol and some developmental aspects

Following oral administration of 3H-cholecalciferol to rachitic chicks, the radioactive metabolites found in brain tissues were separated by Sephadex LH-20 chromatography. The parent vitamins and two biologically important metabolites, 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol were detected in the brain, although at relatively low levels. A comparison with other tissues suggested the brain was much less permeable to the vitamin D steroids than were other tissues. However, chronic cholecalciferol administration for 4 weeks to severely vitamin D deficient chicks elicited a significant increase in the cerebellar content of a calcium-binding protein (CaBP). The lowest level administered, 2 IU/day (130 pmole), increased the CaBP content by more than 50%, while 16 IU/day (1.04 nmole) doubled the CaBP content. Chick brain CaBP has the same physical characteristics and is immunologically identical to the vitamin D-induced CaBP present in chick intestine, it differs in that single acute doses of vitamin D do not increase the content of brain CaBP while intestinal CaBP synthesis is stimulated significantly. The time course of appearance and content of brain CaBP in embryonic chicks was monitored. It was first detectable in the brain at day 15 of incubation and increased to a near post-hatch level by day 20. It differed in its initial time of appearance from both kidney CaBP which first appears at day 10 and intestinal CaBP which is not detectable until hatch day.