Effects of vitamin D on calcium regulation in vitamin-D-deficient pigs given a phytate-phosphorus diet

Abstract

1. Vitamin-D-deficient pigs were fed on a phytate-phosphorus diet and treated with vitamin D, (+D) to examine the time-course of adaptative changes in plasma minerals, vitamin D metabolites, parathyroid hormone (PTH) and calcium balance and intestinal Ca-binding protein (CaBP).2. The 5-week vitamin D repletion (25 pg cholecalciferol/kg diet) regimen restored plasma Ca, P and alkaline phosphatase (EC 3.1.3.1) to normal, decreased PTH and markedly and rapidly increased plasma 25-hydroxycholecalciferol (25-OHD, sevenfold after 4 d) and 1,25-dihydroxycholecalciferol (I, 25(OH),D,, 1.8-fold after 4 d).3. CaBP concentrations were markedly elevated all along the digestive tract, especially in the distal regions. 4. Ca absorption and retention were enhanced (fourfold and sixfold respectively) by the + D diet. 5. The improved Ca absorption, coupled with increased CaBP and 1,25(OH),D, levels, suggest that vitamin D metabolism in phytate-P-fed pigs is sensitive to the depressed Ca availability due to phytate feeding. It also indicates that CaBP may play an important role in the adaptation of Ca absorption.6. Persistent hypercalciuria indicates that mineral metabolism was still affected by the phytate nature of the dietary P in spite of the vitamin D treatment.Phosphorus depletion induces increases in circulating 1,25-dihydroxycholecalciferol (1,25(OH),D,), intestinal calcium-binding protein (CaBP) and Ca absorption (for review, see Sommerville et al. 1985b). Phytate-P, which is the predominant P source in pig feeds, leads to P deficiency if no additional inorganic P is provided (Pointillart et al. , 1985, and phytate-P absorption is improved by vitamin D supplementation (Fontaine et al. 1985) demonstrating the importance of this form of P for pig husbandry. Diets in which the bulk of the phosphate is in the form of phytate also give rise to major disturbances of Ca metabolism (hypocalcaemia, hypercalciuria) and cause significant reductions in the utilization of Ca by the formation of poorly absorbed insoluble Ca phytate (Pointillart et al. 1985). These disturbances are aggravated by vitamin D deficiency (Pointillart et al. 1985). In the present study, we have used vitamin-D-deficient pigs to examine the capacity of vitamin D repletion to overcome the disturbances of Ca metabolism caused by consumption of a diet whose phosphate content, while normal, is largely (80%) in the form of phytate.We have also examined the changes in the principal plasma variables linked to plasma phosphate and Ca regulation, 25-hydroxycholecalciferol~25-OHD), 1,25(OH),D,, alkaline phosphatase (EC 3 . 1 . 3 . 1 ; AP) and parathyroid hormone (PTH) levels, throughout the experimental period. They were measured before and during the period of vitamin D supplementation and compared with those of non-supplemented vitamin-D-deficient pigs, At the end of the experimental period the pigs were killed and the CaBP contents of a number of areas of the small intestine were measured to determine what, if any, correlation existed between the values and the Ca ab...

Effects of calcitriol on stimulation of ion transport in pig jejunal mucosa.

“…This estimate was made for duodenal mucosa which possesses relatively high calbindin concentrations. Similar results, however, are obtained when the calculation is made for jejunal mucosa in which total calbindin concentration is less but in which calbindin concentrations between control and vitamin D-deficient mucosa are reported to be more different (Pointillart et al 1986).…”

“…For the calculation we used the observation of Maenz et al (1987) (Bronner, 1988) and an unspecific cytosolic Ca2+-buffering capacity of about 700 fM with an apparent single KD of 0 55 /M (Muallem, 1989) This estimate was made for duodenal mucosa which possesses relatively high calbindin concentrations. Similar results, however, are obtained when the calculation is made for jejunal mucosa in which total calbindin concentration is less but in which calbindin concentrations between control and vitamin D-deficient mucosa are reported to be more different (Pointillart et al 1986). …”

“…Finally, the I., response was greater with LC than with NC mucosa when intracellular Ca2+ and cyclic nucleotide concentrations were increased by sequential addition of A23187 and theophylline both in the presence and in the absence of indomethacin (Fig. 1 Calbindin possibly acts as a cytosolic Ca2+ buffer in Ca2+-dependent I., stimulation Harrison, Hitchman & Brown (1975), Fox et al (1985) and Pointillart, Fontaine & Thomasset (1986) have shown that calbindin concentrations in duodenal and jejunal mucosa of calcitriol-deprived piglets were 50% less compared to vitamin Dreplete piglets. Bronner (1988) has estimated that about 40 % of total cytosolic Ca2l in vitamin D-replete duodenal and jejunal mucosa is trapped by calbindin, while the remaining portion appears to be bound to other Ca2+-binding substances.…”

High-performance ion chromatography method for separation and quantification of inositol phosphates in diets and digesta

“…InsP 6 bound P is poorly available to monogastric animals like pigs causing excessive P excretion, which results in environmental pollution in areas with high densities of animals [8,9]. Naturally occurring plant phytase in the feed [10][11][12][13] or added commercial microbial phytase [14][15][16] catalyses the hydrolysis of InsP 6 , producing myo-inositol pentakis-, tetrakis-, tris-, bis-, monophosphates (InsP 5 -InsP 1 ) and finally myo-inositol [17]. The extent to which InsP 6 and its degradation products are hydrolysed before and during digestion is of significance for the availability of P. Therefore, it is of great interest to investigate the InsP 6 degradation pathways and products.…”

The effect of dietary protein content on calcium and phosphorus retention in the growing Iberian pig

“…They reported deficient bone mineralization combined with increased bone resorption leading to bone loss and fragility with the two latter diets. Hypercalciuria associated to low P intake has also been reported by Vipperman et al (1974), Pointillart et al (1986), Pointillart (1991) and Fernández (1995) in growing pigs. This effect can be expected even in the case of sufficient Ca being present in the diet.…”