DISTRIBUTION OF 1,25-DIHYDROXYVITAMIN D-3[22-OXA] IN-VIVO RECEPTOR-BINDING IN ADULT AND DEVELOPING SKIN

Because of the therapeutic potential of oxacalcitriol (OCT, 22-oxa-dih ydroxyvitamin D-3), in vivo studies were conducted in adult and neonat al rats to identify the nuclear receptor sites of action in different tissues of the skin. Results were compared with those for 1,25-dihydro xyvitamin D-3 (1,25(OH)(2)D-3) and oestradiol from previous studies. A utoradiograms were prepared from the dorsal skin of adult rats and the skin of the leg and head regions of neonatal rats 1 or 2 h after the injection of H-3-OCT, Specific nuclear concentrations of radioactivity , eliminated by competition with unlabelled OCT or 1,25(OH)(2)D-3, wer e found in cells of the epidermis, outer hair sheath, hair bulb and se baceous glands, but were absent or low in most fibroblasts of the derm is and hypodermis. The strongest nuclear binding of OCT was conspicuou s in outer hair sheaths, where it was 1.5 to 3.2 times higher than in keratinocytes of the epidermis. The distribution of nuclear receptors for OCT was similar to that for 1,25(OH)(2)D-3 but in part dissimilar to that for oestradiol. Oestradiol binding was found in the epidermis and hair sheaths, and also predominantly in fibroblasts of the dermis and hair dermal papillae. The results suggest genomic regulatory effec ts of OCT, similar to the effects of vitamin D, on proliferation, diff erentiation and activity of keratinocytes, growth and maintenance of h air, and proliferation and secretion of sebaceous glands. This may be utilized therapeutically, since OCT has a lower calcaemic effect than 1,25(OH)(2)D-3.