Duodenal Ca2+ absorption is not stimulated by calcitriol during early postnatal development of pigs.
The role of calcitriol in stimulating intestinal active Ca2+ absorption during postnatal life was studied in newborn, suckling, and weaned control (Con) piglets and piglets suffering from inherited calcitriol deficiency (Def piglets). In addition, a group of Def piglets was treated with vitamin D3 (Def-D3 piglets), which normalized plasma calcitriol levels. Regardless of age, duodenal calbindin-D9k concentrations ranged between 1,839 and 2,846 microg/g mucosa in Con piglets, between 821 and 1,219 microg/g mucosa in Def piglets, and between 2,960 and 3,692 microg/g mucosa in Def-D3 animals. In weaned animals, active Ca2+ absorption as calculated from in vitro 45Ca2+ flux rate measurements in Ussing chambers could be related to calbindin-D9k levels. Thus active Ca2+ absorption was completely absent in Def animals but was reconstituted in Def-D3 animals. In contrast, in newborn Def piglets active Ca2+ absorption functioned normally despite the low plasma calcitriol and mucosal calbindin-D9k levels and could not be affected by treatment with vitamin D3. Similar results were obtained from suckling Def piglets. The microtubule-disrupting agent colchicine caused significant inhibition of transepithelial net Ca2+ absorption in duodenal epithelia from newborn piglets without exerting an effect in suckling and weaned animals. Colchicine had no effect on Ca2+ uptake across the brush border membrane of mucosal enterocytes or on glucose-dependent electrogenic net ion flux rates in duodenal preparations from newborn Con piglets. In conclusion, our findings reveal intestinal active Ca2+ absorption during early postnatal life of pigs that involves calcitriol-independent mechanisms and that may include intact microtubule actions.
Schroeder
B
B
Department of Physiology, School of Veterinary Medicine, D-30173 Hannover, Germany.
Dahl
M R
MR
Breves
G
G
D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling; D064026:Calbindins; D002117:Calcitriol / Q000172:deficiency / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D004386:Duodenum / Q000254:growth & development / Q000502:physiology* / Q000503:physiopathology; D005260:Female; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D007413:Intestinal Mucosa / Q000254:growth & development / Q000502:physiology* / Q000503:physiopathology; D007700:Kinetics; D008297:Male; D008353:Mannitol / Q000493:pharmacokinetics; D008871:Microvilli / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D012279:Rickets / Q000503:physiopathology*; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D013552:Swine; D014886:Weaning
D064026:Calbindins; D010710:Phosphates; D064030:S100 Calcium Binding Protein G; D008353:Mannitol; D002117:Calcitriol; D002118:Calcium