Investigations on vitamin D esters synthesized in rats. Detection and identification

Abstract

1. Vitamin D-deficient rachitic rats were given [1-(3)H]cholecalciferol by gastric intubation. After 24hr., diethyl ether extracts of liver and kidney contained 5-11% and 4.5-20% respectively of total vitamin D apparently esterified with long-chain fatty acids. 2. A two-dimensional thin-layer chromatographic technique was devised that completely separated seven synthetic vitamin D esters according to the chain length and number of double bonds in the fatty acid component. When the ;vitamin D ester' fraction from liver or kidney was co-chromatographed with the standard esters, radioactivity appeared mainly in vitamin D palmitate, stearate, oleate and linoleate regions. The proportion of radioactivity in the saturated fatty acid esters was higher in kidney than in liver. 3. The same percentage of tissue vitamin D in the esterified form was found at each of two dosages of vitamin D. 4. The possible specificity of a vitamin D esterification mechanism is discussed.

Deposition in and release of vitamin D3 from body fat: evidence for a storage site in the rat

“…Thus, by 6 wk after treatment was stopped, 20% of all radioactivity in fat was in the form of esters. It is known that a small quantity of these is formed during intestinal absorption (28,29), and they have been detected in liver and kidney (26,30 (31,32) to a high pharmacological dose), and that release is very slow and approximately proportional to the concentration of vitamin D in adipose tissue over this same large dose range. Thus, adipose tissue serves as a depot of large capacity which accumulates vitamin D proportionate to its concentration in plasma and releases it at a much slower rate that is proportionate to its concentration in fat.…”

Vitamin D Metabolism Revised: Fall of Dogmas

“…The fate of the other vitamin D (or 25OHD) molecules is unclear, but esterification is most likely involved as part of the degradation pathway. This involves conjugations with sulfate (into vitamin D/25‐hydroxyvitamin D3‐3‐sulfate), glycosides (eg, vitamin D and 25‐hydroxyvitamin D3‐3‐glucuronide), taurine, or long‐chain fatty acids . The esterification of vitamin D is already found early in evolution as some glycosides of vitamin D are even found as toxic agents in plants and most vitamin D found in fish liver is in the form of fatty acid esters .…”

“…This involves conjugations with sulfate (into vitamin D/25-hydroxyvitamin D3-3-sulfate), glycosides (eg, vitamin D and 25-hydroxyvitamin D3-3-glucuronide), taurine, or long-chain fatty acids. (102,103) The esterification of vitamin D is already found early in evolution as some glycosides of vitamin D are even found as toxic agents in plants (104) and most vitamin D found in fish liver is in the form of fatty acid esters. (105) The regulation of these esterifications and the potential recovery of vitamin D metabolites by de-esterification (eg, hepato-biliary-intestinal recycling) are largely unexplored.…”

Degradation of vitamin D3 in a stressed formulation: The identification of esters of vitamin D3 formed by a transesterification with triglycerides

“…This interest stems from the observations that vitamin D 3 in salt-water fish is esterified [38,39], and that esters (mainly palmitate, stearate, linoleate and oleate) are synthesized in rats that are fed the vitamin [40]. Human pancreatic carboxyl esterase has been shown to catalyze the esterification of vitamin D 3 with oleic acid [41], and the gastro-intestinal absorption of the palmitate ester has been studied in human neonates [42].…”