DUODENAL CA2-DEVELOPMENT OF PIGS( ABSORPTION IS NOT STIMULATED BY CALCITRIOL DURING EARLY POSTNATAL)

The role of calcitriol in stimulating intestinal active Ca2+ absorptio n during postnatal life was studied in newborn, suckling, and weaned c ontrol (Con) piglets and piglets suffering from inherited calcitriol d eficiency (Def piglets). In addition, a group of Def piglets was treat ed with vitamin D-3 (Def-D-3 piglets), which normalized plasma calcitr iol levels. Regardless of age, duodenal calbindin-D-9k concentrations ranged between 1,839 and 2,846 mu g/g mucosa in Con piglets, between 8 21 and 1,219 mu g/g mucosa in Def piglets, and between 2,960 and 3,692 mu g/g mucosa in Def-D-3 animals. In weaned animals, active Ca2+ abso rption as calculated from in vitro Ca-45(2+) flux rate measurements in Ussing chambers could be related to calbindin-D-9k levels. Thus activ e Ca2+ absorption was completely absent in Def animals but was reconst ituted in Def-D-3 animals. In contrast, in newborn Def piglets active Ca2+ absorption functioned normally despite the low plasma calcitriol and mucosal calbindin-D-9k levels and could not be affected by treatme nt with vitamin Ds Similar results were obtained from suckling Def pig lets, The microtubule-disrupting agent colchicine caused significant i nhibition of transepithelial net Ca2+ absorption in duodenal epithelia from newborn piglets without exerting an effect in suckling and weane d animals. Colchicine had no effect on Ca2+ uptake across the brush bo rder membrane of mucosal enterocytes or on glucose-dependent electroge nic net ion flux rates in duodenal preparations from newborn Con pigle ts. In conclusion, our findings reveal intestinal active Ca2+ absorpti on during early postnatal life of pigs that involves calcitriol-indepe ndent mechanisms and that may include intact microtubule actions.