A rapid and precise method for the determination of vitamin D3 in rat skin by high-performance liquid chromatography

Vitamin D: Photobiological and Ecological Aspects

Vitamin D was discovered as a result of its ability to cure rickets, but recently a wide range of other functions for it in the human body has been suggested. Vitamin D is not a vitamin in the strict sense as it can be synthesised in the human body following exposure of the skin to ultraviolet radiation. Provitamin D (7-dehydrocholesterol) is converted to previtamin D which is further modified by a series of reactions to the active form, 1,25-dihydroxyvitamin D. This Chapter summarises the discovery of vitamin D and reviews the chemistry and photochemistry of its precursors, transformations and metabolites. The production of vitamin D in various human populations is described, and how to assess vitamin D status. The skeletal and non-skeletal effects of vitamin D are discussed, particularly its role in immunomodulation with consequences for protection against a variety of human diseases. The Chapter concludes with evolutionary aspects, the occurrence and role of vitamin D in the plant kingdom, biogeographical considerations, and the nonphotochemical production of vitamin D in certain plants.

Estimation of vitamin D3 and 25-hydroxyvitamin D3 in muscle and adipose tissue of rats and man

An assay is described based on a high pressure liquid chromatography system for measurement of vitamin D3 and 25-hydroxyvitamin D3 concentration in adipose tissue and muscle. The sensitivity of the assay is less than 1 ng/g of tissue. Neither vitamin D3 nor 25-hydroxyvitamin D3 were found in tissues of vitamin D-deficient rats using this method. 25-Hydroxyvitamin D3 could not be detected in adipose tissue and very little was found in muscle of normal rats. The mean vitamin D3 concentrations in 15 samples of human perirenal adipose tissue was 45.3 ng/g +/- 22.2 (SD) and in 6 samples of axillary tissue 115.6 ng/g +/- 52.4 (SD). Human adipose tissue contains a substantial amount of vitamin D3 and its contribution to the maintenance of vitamin D status is discussed.

Spectral character of sunlight modulates photosynthesis of previtamin D3 and its photoisomers in human skin

The photosynthesis of previtamin D3 from 7-dehydrocholesterol in human skin was determined after exposure to narrow-band radiation or simulated solar radiation. The optimum wavelengths for the production of previtamin D3 were determined to be between 295 and 300 nanometers. When human skin was exposed to 295-nanometer radiation, up to 65 percent of the original 7-dehydrocholesterol content was converted to previtamin D3. In comparison, when adjacent skin was exposed to simulated solar radiation, the maximum formation of previtamin D3 was about 20 percent. Major differences in the formation of lumisterol3, and tachysterol3 from previtamin D3 were also observed. It is concluded that the spectral character of natural sunlight has a profound effect on the photochemistry of 7-dehydrocholesterol in human skin.

Application of high-performance liquid chromatography to the study of esterified 7-dehydrocholesterol in rat skin

A novel and precise method for determining free and esterified 7-dehydrocholesterol in rat skin was developed by using a two-step high-performance liquid chromatography system. This method involves initial lipid extraction, separation of the free and esterified 7-dehydrocholesterol by, firstly, preparative high-performance liquid chromatography, saponification, and determination by, secondly, analytical high-performance liquid chromatography. This method was applied to the study of the 7-dehydrocholesterol in rat skin. Almost all of the 7-dehydrocholesterol in rat skin was present in an esterified form (78-93%). Ultraviolet exposure of the skin increased total 7-dehydrocholesterol content, however, the percentage of esterified 7-dehydrocholesterol was not altered appreciably. Application of this method to the study of the photo-metabolism of 7-dehydrocholesterol in rat skin revealed that almost all of the vitamin D3 produced by ultraviolet rays was in the esterified form.

Isolation and identification of tachysterol3 in rat skin exposed to ultraviolet light

In order to investigate the mechanism of the cutaneous synthesis of vitamin D3 in vivo, a photolysis by-product of previtamin D3 in organic solvent, namely, tachysterol3 was isolated and identified in ultraviolet-exposed rat skin. Tachysterol3 was identified by chromatographic comigration of an ultraviolet-absorbing peak wih authentic tachysterol3 in straight-phase HPLC (Zorbax SIL column) and reversed-phase HPLC (Nucleosil 5C18 column), and by the ultraviolet absorption spectrum. The comparison of the extent of formation of tachysterol3 between in rat skin in vivo and in ethanol solution indicated that the yield in rat skin is similar to that in organic solvent. The results suggest that the reaction mechanism in rat skin in vivo may be identical wit that in organic solvents.