TOPICAL TACALCITOL (1,24-(R)-DIHYDROXYVITAMIN D-3) INDUCES A TRANSIENT INCREASE IN THYMIDINE INCORPORATION AND CALMODULIN CONTENT IN PIG EPIDERMIS FOLLOWING TAPE STRIPPING IN-VIVO

Tape stripping induces transient increase in keratinocyte proliferatio n in vivo. The effects of tacalcitol (1.24-(R)-dihydroxyvitamin D-3) o intment on the cell kinetics of pig epidermis after the tape stripping were investigated. The tacalcitol ointment (2 mu g/g) was applied onc e to the back of pigs immediately after the tape stripping. The pig ep idermal cell kinetics were analyzed at various times following the tre atment. Tape stripping transiently increased thymidine incorporation o f keratinocytes: the maximal effect was observed at 24 h. Tape strippi ng-induced increase in thymidine incorporation was markedly augmented by tacalcitol treatment. At 24 h following the tape stripping DNA-flow cytometry revealed an accelerated transition from G0 1 to S phase of cell cycle in tacalcitol treated epidermis. There was no significant d ifference. however. in mitotic counts and G2M phase fractions between tape stripping-treated and tape stripping plus tacalcitol ointment-tre ated epidermis. We also measured calmodulin content of pig epidermis f ollowing the treatments. Although tape stripping slightly increased ca lmodulin content of pig epidermis, this was statistically not signific ant. Tape stripping plus tacalcitol ointment treatment resulted in a s ignificant increase in calmodulin content at 24 h following the treatm ent. There was no significant difference in calmodulin content between tape stripping treated- and tape stripping plus tacalcitol-treated ep idermis.