Normal rabbit intestinal cytosol as a source of binding protein for the 1,25-dihydroxyvitamin D3 assay

Duncan, William E.; Aw, T. Choon; Walsh, P.G; Haddad, John G.

doi:10.1016/0003-2697(83)90449-9

Cited by 28 publications

(2 citation statements)

References 18 publications

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“…The partially purified 1,25-(OH)2D3 was quantitated using the radioligand assay of Eisman, Hamstra, Kream & DeLuca (1976). Binding protein was obtained from the duodena of New Zealand White rabbits (Duncan, Aw, Walsh & Haddad, 1983). This assay could detect as little as 3 fmol l,25-(OH)2D3/tube and was linear between 3 and 120 fmol/tube using a logit transformation.…”

Section: Methodsmentioning

confidence: 99%

Effect of age on renal responsiveness to parathyroid hormone and calcitonin in rats

Armbrecht¹,

Wongsurawat²,

Paschal³

1987

Journal of Endocrinology

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The purpose of these studies was to determine whether the responsiveness of the kidney to parathyroid hormone (PTH) and calcitonin changed with age. Experiments were performed in young (3 months old), adult (12-14 months old) and old (22-24 months old) male Fischer 344 rats fed normal diets and thyroparathyroidectomized. Parathyroid hormone was administered i.p. at 24, 12 and 2 h before death and calcitonin was given i.p. at 12 and 2 h before death. Parathyroid hormone significantly increased the conversion of 25-hydroxyvitamin D3 to 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) by renal slices from young but not adult or old animals. A similar age-related decline in the capacity of PTH to raise serum 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels was also seen. Parathyroid hormone significantly decreased tubular reabsorption of phosphorus, increased concentrations of urinary cyclic AMP (cAMP) and increased serum concentrations of calcium in all age groups. In contrast, calcitonin significantly increased 1,25-(OH)2D3 production by renal slices from both young and adult animals. Calcitonin decreased serum concentrations of calcium in young but not in adult rats. These results suggest that there are maturational changes in the PTH- and cAMP-dependent pathways in the kidney but not in the calcitonin- and cAMP-independent pathways. The changes in the PTH- and cAMP-dependent pathways affect the stimulation of 1,25-(OH)2D production but not the inhibition of phosphate transport.

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Section: Methodsmentioning

confidence: 99%

Effect of age on renal responsiveness to parathyroid hormone and calcitonin in rats

Armbrecht¹,

Wongsurawat²,

Paschal³

1987

Journal of Endocrinology

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show abstract

“…Unbound [3H]l,25(OH)2D3 was separated out from bound label using dextrancoated charcoal. Binding protein was obtained from duodena of male New Zealand white rabbits extract (Duncan et al 1983). This assay could detect as little as 5 pg of l,25(OH)2D3 and was linear between 5 and 50 pg using a Logit transformation.…”

Section: Methodsmentioning

confidence: 99%

Insulin modulates the stimulation of renal 1,25-dihydroxyvitamin D3 production by parathyroid hormone

Wongsurawat¹,

Armbrecht²

1985

Acta Endocrinologica

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Abstract. Previous studies have shown that there is an impairment in renal production of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the major biologically active metabolite of vitamin D3, in diabetes. This impairment is not due to a deficiency in the parathyroid hormone (PTH), a major stimulator of renal 1,25(OH)2D3 production. Therefore, we have investigated the capacity of PTH to stimulate 1,25(OH)2D3 production in insulin deficiency and with insulin replacement. Experiments were performed in rats fed a 0.6% calcium, vitamin D sufficient diet for 2 weeks. Thyroparathyroidectomy was performed on all rats. Rats to be rendered diabetic were injected with streptozotocin immediately after surgery. In non-diabetic rats, PTH administration significantly increased renal 1,25(OH)2D3 production (11 ± 2 vs 46 ± 5 pg/min/g; P < 0.05). In diabetic rats, however, PTH caused only a modest increase in 1,25(OH)2D3 production (11 ± 1 vs 19 ± 4 pg/min/g; P < 0.05). With insulin replacement, PTH stimulation of 1,25(OH)2D3 production was markedly increased over that seen in diabetic rats (48 ± 12 vs 19 ± 4 pg/min/g; P < 0.05). PTH was equally effective in raising serum calcium, depressing serum phosphorus and tubular reabsorption of phosphate in non-diabetic as well as in diabetic rats. These results demonstrate that insulin is necessary for the maximal stimulation of renal 1,25(OH)2D3 production by PTH. However, insulin is not necessary for PTH action in terms of renal handling of phosphate and inducing hypercalcaemia. These results suggest multiple pathways for the action of PTH, only some of which are insulin requiring.

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Effect of theophylline on calcium metabolism and circulating vitamin D metabolites

Fortenbery

McDermott

Duncan

1990

Journal of Bone and Mineral Research

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Theophylline has been shown to induce the hepatic microsomal enzyme system. These same enzymes increase the metabolism of vitamin D and 25-hydroxyvitamin D when induced by chronic barbiturate or phenytoin administration. To assess the long-term effects of theophylline on vitamin D and calcium metabolism, young rats were treated for 4 weeks with constant subcutaneous theophylline infusions. Theophylline-treated animals had a significantly increased urinary calcium excretion (p less than 0.0001), a significantly decreased total body calcium per gram body weight (p less than 0.05), and significantly decreased serum 25-hydroxy-vitamin D concentrations (p less than 0.002) when compared to control animals. These alterations in the concentration of 25-hydroxyvitamin D may impair the ability to increase 1,25-dihydroxyvitamin D-dependent intestinal calcium absorption to compensate for excessive urinary calcium losses. These data suggest that theophylline promotes skeletal calcium loss, and its use may be a risk factor for the development of osteopenia in humans.

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Normal rabbit intestinal cytosol as a source of binding protein for the 1,25-dihydroxyvitamin D3 assay

Cited by 28 publications

References 18 publications

Effect of age on renal responsiveness to parathyroid hormone and calcitonin in rats

Effect of age on renal responsiveness to parathyroid hormone and calcitonin in rats

Insulin modulates the stimulation of renal 1,25-dihydroxyvitamin D3 production by parathyroid hormone

Effect of theophylline on calcium metabolism and circulating vitamin D metabolites

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