Evidence for vitamin D-independent active calcium absorption in newborn piglets

Abstract

The role of 1,25-dihydroxycholecalciferol (calcitriol) for intestinal calcium (Ca2+) absorption was studied in newborn (< 1 week old) and weaned piglets (> 6 weeks old). In both groups, normal piglets and piglets suffering from inherited pseudo vitamin D-deficiency rickets, type I (PVDRI) were used. In this inherited disorder, renal production of calcitriol is absent. Plasma samples were assayed for calcitriol and total Ca, and dissociation constants (Kd) and maximum binding capacities (Bmax) of intestinal calcitriol receptors were determined under equilibrium conditions at 4 degrees C. Unidirectional Ca(2+)-flux rates were measured across stripped duodenal mucosae in Ussing chambers in the absence of electrochemical gradients. The plasma calcitriol concentrations of neonatal (26.5 +/- 7.1 pg/ml, n = 11; mean +/- SEM) and weaned PVDRI piglets (18.8 +/- 5.7 pg/ml, n = 8) were unphysiologically low and differed significantly from control animals (83.6 +/- 14.8 pg/ml, n = 8, and 86.9 +/- 9.6 pg/ml, n = 11, respectively). However, newborn PVDRI piglets had normal plasma Ca levels at least during the first days of life. They became hypocalcemic and developed clinical symptoms of rickets during the following weeks. In newborn PVDRI and control piglets, Bmax was significantly lower (84 +/- 28 fmol/mg protein and 127 +/- 55 fmol/mg protein, n = 9, respectively) than in weaned piglets (741 +/- 82 fmol/mg protein, n = 9, and 778 +/- 121 fmol/mg protein, n = 8, respectively). Significant net Ca(2+)-fluxes were found in both newborn PVDRI and control piglets (88.8 +/- 25.1 nmol.cm-2 x h-1, n = 6, and 86.5 +/- 10.5 nmol.cm-2 x h-1, n = 9, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Transport of nutrients and electrolytes across the intestinal wall in pigs

“…This protein has been proposed to facilitate the movement of Ca 2+ across the cytosol from the apical to the basolateral side of the enterocyte (Bronner, 1992(Bronner, , 2003Kumar, 1995;Christakos et al, 1996). Evidence for the contribution of similar cytosolic processes has also been described for pigs (Fox et al, 1985;Schröder et al, 1993Schröder et al, , 1998a.…”

“…Whereas the individual proportions of distinct pathways in overall Ca 2+ net absorption in different intestinal segments are not clear, it is obvious that at least in weaning piglets and adult pigs an intact vitamin Dhormone system is obligatory (Schröder et al, 1993). This indicates that only passive Ca 2+ net absorption would not be sufficient to keep the animals in health (Schlumbohm and Harmeyer, 2004).…”

Prolactin is an important regulator of intestinal calcium transport

“…Interestingly, in vitamin D-deficient neonatal piglets caused by inherited pseudovitamin D-deficient rickets type I, the duodenal active calcium absorption appeared to be normal despite the low plasma 1,25-(OH) 2 D 3 and low mucosal calbindin-D 9K levels (Schröder et al 1993). This normal rate of active calcium absorption was maintained during the first week postpartum, but was completely absent at weaning (Schröder et al 1993;Schroeder et al 1998).…”

Luminal and endocrine factors for regulation of intestinal monosaccharide and Ca2+ transport

“…This protein has been proposed to facilitate the movement of Ca 2+ ("cytoplasmic ferry model"; Khanal and Nemere, 2008) in a still unknown manner across the cytosol from the apical to the basolateral side of the enterocyte (Bronner, 1992(Bronner, , 2003Kumar, 1995;Christakos et al, 1996). Evidence for the contribution of similar cytosolic processes has also been described for pigs (Fox et al, 1985;Schröder et al, 1993Schröder et al, , 1998a.…”

“…Although, the individual proportions of distinct pathways in overall Ca 2+ net absorption in different intestinal segments are not clear, it is obvious that at least in weaning piglets and adult pigs an intact vitamin D-hormone system is obligatory (Schröder et al, 1993). This indicates that passive Ca 2+ net absorption alone would not be sufficient to maintain the health status of the animals (Schlumbohm and Harmeyer, 2004).…”