N.A. Jorgensen

The effect of age on calcium absorption and accumulation of 1,25-hydroxyvitamin D3 in intestinal mucosa of rats

Abstract Calcium transport in the proximal duodenum was measured in male rats of various ages by the everted intestinal sac method. Calcium transport markedly and progressively diminished from 54 days to 384 days of age despite adequate intakes of vitamin D 3 (10 IU/day). Additionally, feeding low phosphorus and/or low calcium diets for 24 days did not result in an enhanced calcium transport in old (1 year) rats while showing the expected enhancement in young rats (24 days). The administration of 325 pmoles of either 1,25-dihydroxyvitamin D 3 or 1α-hydroxyvitamin D 3 daily increased intestinal calcium transport in both young and old rats. This response was accompanied by increased serum calcium in young rats and increased serum phosphorus in old rats. Administration of vitamin [1,2 3 H]D 3 daily (10 IU) for 6 days orally and chromatography of the extracts of serum and intestine permitted the demonstration that the diminished calcium transport with age is positively correlated with diminished levels of 1,25-dihydroxy-[1,2 3 H] D 3 in serum and intestinal mucosa. It appears that the decreased intestinal absorption with age is a result of a diminished formation of 1,25-dihydroxyvitamin D 3 . The inability of aged rates to alter this condition under dietary depletion of calcium and/or phosphorus may play a significant role in the development of bone disease in the aged.

The determination of the vitamin D metabolites on a single plasma sample: Changes during parturition in dairy cows☆

Abstract Methods have been developed for the precise measurement of the major known vitamin D metabolites in a single sample of cow plasma (~5 ml). The procedure involves initial extraction with methylene chloride-methanol followed by chromatography on Sephadex LH-20. 25-Hydroxyvitamin D 2 and 25-hydroxyvitamin D 3 were determined using high-pressure liquid chromatography and comparing ultraviolet absorption peak height with absorption peak heights of standards. The dihydroxylated metabolites were further purified and resolved by high-pressure liquid chromatography and determined by radioligand binding assays. The assays were employed to measure the total vitamin D metabolite levels in the plasma of paretic and normal dairy cows at parturition. Parturition had no effect on 25-hydroxyvitamin D levels in either group of cows (paretic, 37–44 ng/ml; normal, 35–38 ng/ml). However, normal cows did show lower mean 25-hydroxyvitamin D levels at every sampling period with the lowest levels in both groups occurring at 7 days postpartum. Plasma 25, 26-dihydroxyvitamin D was higher in paretic animals prepartum and at parturition (0.7–1.0 ng/ml) when compared to nonparetic animals (0.4–0.45 ng/ml). Similar levels (0.6 ng/ml) were observed in both groups postpartum. Cows developing parturient paresis showed a significant ( P P

Action of Solanum malacoxylon on calcium metabolism in the rat

Abstract The administration of an aqueous extract of the leaves from Solanum malacoxylon to vitamin D-deficient rats fed a normal calcium, normal phosphorus diet markedly increased serum calcium concentration within 48 hours. The Solanum malacoxylon extract also stimulated intestinal calcium transport in the vitamin D-deficient rat but was without effect on the mobilization of calcium from bone. The extract from 100 mg of dry Solanum malacoxylon leaves was more effective than 25 units of vitamin D given daily to vitamin D-deficient rats in stimulating intestinal calcium transport but its effect was not additive to that of the vitamin D. The results demonstrate that the action of Solanum malacoxylon is independent of vitamin D and, although it can substitute for vitamin D in the stimulation of intestinal calcium transport activity, it cannot substitute for vitamin D in the mobilization of calcium from bone.

Intestine, Bone, and Mammary Gland Contributions to Maternal Plasma Calcium Increase after Abrupt Weaning

Abstract The response of maternal plasma calcium concentration to the abrupt and permanent removal of the suckling pups on Day 13 of lactation was investigated. Maternal plasma calcium did not change at 6 hr or 12 hr following pup removal. At 18 hr and 24 hr after weaning, the maternal plasma calcium concentration increased in mothers consuming either 0.47% calcium or 0.02% calcium diets. At 24 hr after weaning, the plasma calcium increase in mothers consuming low dietary calcium was 55% that of mothers consuming adequate dietary calcium. The contribution of the mammary gland to the plasma calcium increase in rats consuming the low dietary calcium was investigated by removing the mammary glands. Following mammary gland removal, plasma calcium increased 50% compared with mothers that had intact mammary glands. The data suggest that intestinal absorption of calcium and bone calcium mobilization remain stimulated by the lactation process for at least 24 hr after removal of the nursing pups.