The metabolism and biological activity of esterified vitamin D in the rat

Abstract

I . [~-~H]Cholecalciferol and [1-~H]cholecalcifero1 palmitate in amounts equivalent to z pg cholecalciferol were injected into rachitic rats as aqueous preparations (intravenously) or in arachis oil (intramuscularly). 2.The radioactive faecal metabolites collected for up to 17 days were fractionated according to their polarity. The same pattern of excreted radioactivity was seen with intravenous and intramuscular cholecalciferol and intravenous cholecalciferol palmitate. Intramuscular cholecalciferol palmitate produced a higher proportion of the most polar metabolites in faeces.3. Parenterally administered cholecalciferol palmitate in a rickets-healing biological assay had activity equivalent to unesterified cholecalciferol. Evidence has been presented that fatty acid esters of vitamin D are formed in the rat by enzymes with low specificity for the vitamin (Fraser & Kodicek, 1968~) and that these esters remain in tissues while vitamin D alcohol is metabolized and excreted (Fraser & Kodicek, 1968b). However, it is not apparent whether the esterified vitamin is available to the vitamin D-requiring processes in the animal. To investigate this point an examination was made of the metabolic fate and utilization of parenterally administered synthetic vitamin D ester. I n one experiment the faecal radioactivity was measured after paren teral injection of [I -3H]cholecalciferol palmitate. Another experiment compared the biological activities of free and esterified vitamin D.

Metabolism of vitamin D. A new cholecalciferol metabolite, involving loss of hydrogen at C-1, in chick intestinal nuclei

“…They also prepared a number of tritiated vitamins D, namely [24,25,26,27-3H9]-, [7-3H]-, [6-3H]-, [3-3H]and [loc-3H]-cholecalciferol, and showed that the expired air of the rats dosed with [la-3H]cholecalciferol contained the lowest amount of radioactivity. Therefore [la-3H]cholecalciferol ofspecific radioactivity 141mc/m-mole has been used in this laboratory in a series of studies of vitamin D metabolism (Fraser & Kodicek, 1965, 1966, 1969Bell & Kodicek, 1967). Neville & DeLuca (1966) prepared [1,2-3H]cholecalciferol of specific radioactivity 180mc/m-mole and showed the existence of another biologically active metabolite of vitamin D, originally designated Peak IV (Norman, Lund & DeLuca, 1964), in rats.…”

“…In the rat the nuclear radioactivity was characterized by its chromatographic properties (Stohs & DeLuca, 1967) as corresponding to the Peak IV material described by . However, Haussler, Myrtle & Norman (1968) showed that the chick intestinal nuclear radioactivity could be fractionated into three substances (4a, 4b and 4c), of which only one (4b) was found in the nuclear chromatin. They were not able to state which of the three substances was 25-hydroxycholecalciferol.…”

“…The supernatant from the first 800g centrifugation, containing the mitochondria, microsomes and cytoplasm, was frequently analysed without further fractionation and is referred to as the supernatant fraction. Purified chromatin was prepared by the method of Haussler et al (1968) from the nucleardebris fraction.…”

The Metabolic Fate of (26,27) 3H‐25‐Hydroxyvitamin D3 in Normal, Uremic and Rachitic Rats

“…Our interpretation of this metabolic phenomenon is only speculative, but we presume that the formation of such high amounts of peak1 could be only explained by an entirely disturbed enzymatic activity. Provided that this metabolite constitutes an ester of 25-HCC, one could at least speculate on its importance, as esterified vitamin D, has been shown to possess some biological activity [39,48]. However, we do not think that the formation of peak I should be regarded as a biological adaptation of rats severely depleted of vitamin D or phosphate.…”

The intracellular distribution of [1-3H]cholecalciferol in the intestine of vitamin D-deficient and -supplemented rats

“…Recently the long-chain fatty acid esters of calciferol have been reported in rat liver and kidney after an oral dose of [1-3H]cholecalciferol (Fraser & Kodicek, 1965). Occasionally radioactivity was detected in the calciferol ester region of a thin-layer chromatogram (Tables 4 and 5, chromatographic Table 3.…”