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Biomedical subjects

S U Toverud

Publications and source records attributed to S U Toverud.

72 records · Page 4Linked to original sources
PubMed1975

The effect of vitamin D on the structural crosslinks and maturation of chick bone collagen.

The quantitative relationships were determined between the structural crosslinks, dihydroxylysinonorleucine (Lys(OH)2-Nle) and hydroxylysinonorleucine (Lys (OH) -Nle) in NaB 3H4-reduced diaphyseal bone collagen from 1-, 2-, 3- and 4-week-old chicks fed either a vitamin D-deficient diet, a normal-vitamin D diet or a high-, but non toxic, vitamin D diet from time of hatching. Chicks fed the normal diet showed a progressive decrease in the ratio of Lys(OH)2-Nle/Lys(OH)-Nle with age. This decrease was accelerated in chicks receiving the High-vitamin D diet. In the vitamin D-deficient group, the ratio was higher than controls at 1 and 2 weeks and increased further at 3 and 4 weeks. Similar changes in Lys(OH)2-Nle/Lys(OH)-Nle ratio did not occur in skin collagen. Compared to Control-vitamin D animals, the increased crosslink ratios in the vitamin D-deficient bone collagen occurred prior to changes in growth rate and could not be correlated with lysine hydroxylation or the hypocalcemia seen in this group. These results suggest that the type of crosslink analysis used in this study provides one of the earliest and most sensitive indications of a bone disturbance due to vitamin D deficiency and that vitamin D specifically acts to increase the rate of maturation of bone collagen.

Age Factors↗
PubMed1975

Vitamin D, dietary calcium and parathyroid hormone interactions in chicks.

The effect of dietary vitamin D levels on the response to iv injected parathyroid hormone (PTH) was studies in chicks fed one of three diets: D-deficient, Control-D (1.4IU cholecalciferol/g diet), or High-D (70 IU cholecalciferol/g diet) during the first 4 weeks post-hatching. Compared to chicks on Control-D diet, chicks on the D-deficient diet had significantly decreased plasma Ca levels at 2 and 4 weeks and increased plasma P levels at 17 and 21 days. The plasma Ca response to a low dose of PTH (15 USP U/100 g body wt) 1 hr postinjection was normal at 1 week, reduced at 2 weeks and absent at 4 weeks in D-deficient chicks. However, a 4-16-fold higher dose of PTH did elicit a significant, though subnormal, response in this group at 3 and 4 weeks. Chicks fed the D-deficient diet with 2.8% Ca, compared to 1.4% Ca, showed a near normal plasma Ca level and bone ash content and only a small increase in plasma P at 17 and 21 days. However, the plasma Ca response to 15 U PTH/100 g body wt in this group was significantly increased only at 17 days and not at 21 days. In contrast, the hyperphosphatemic response to PTH was not markedly diminished in the D-deficient group, and it was restored to Control-D levels in the D-deficienyt High Ca group. These data suggest that different mechanisms may be involved in the Ca and P responses.

Animals↗
PubMedDate not supplied

Circulating calcitonin in lactating women.

As part of an initial study we have attempted to ascertain whether lactating women exhibit high, clearly measurable levels of immunoreactive calcitonin (CT). Plasma levels of CT were measured in women who had been lactating for either a short time (less than 4 months) or a very long time (17-73 months). In 2 of 18 women lactating for only a short time CT levels were high and easily measured (greater than 200 pg/ml) while, in contrast, CT levels were undetectable (less than 60 pg/ml) in all of 16 nonlactating control subjects. In all six of the women studied who had been lactating for a long time, measurable levels of CT were observed, although provocative testing of women with measurable plasma CT using iv pentagastrin and calcium did not show a consistent pattern of CT secretory response. Thus, out of the total of 24 lactating women studied, one third were found to have measurable plasma levels of CT. The findings agree with studies in experimental animals which have indicated hypercalcitoninemia during lactation, but the factors responsible for the elevated CT levels during lactation remain to be elucidated.

Calcitonin↗
PubMedDate not supplied

Calcium absorption during development: experimental studies of the rat small intestine.

During the period of natural weaning in the rat (beginning during the third week) the mechanisms of calcium absorption from the duodenum change from an efficient nonsaturable process, which is insensitive to vitamin D, to a combination of a less efficient nonsaturable process and a saturable vitamin D-dependent component. The stimulatory effect of vitamin D on active calcium transport requires the development of mucosal receptors for 1,25-(OH)2D3 and increasing circulating levels of 1,25-(OH)2D3. Concurrent increases in the concentration of the cytosolic calcium-binding protein (CaBP) support the suggestion that the CaBP mediates, in part, the effect of 1,25-(OH)2D3 on active calcium transport. The decline in the efficiency of nonsaturable calcium absorption during the third week coincides with, but is probably not due to, the loss of pinocytotic capacity of the small intestine. The time of appearance of the receptors for 1,25-(OH)2D3 and the decline in nonsaturable calcium absorption are under glucocorticoid control as are several other maturational events in the intestine at this time.

Aging↗