F2  A COMPARISON OF TWO RODENT MODELS FOR THE ASSESSMENT OF POTASSIUM CHANNEL OPENERS ON HAIR GROWTH IN VIVO

Davies, G.C., Chen, Y.C., Thornton, M.J., Randall, V.A., Department of Biomedical Sciences, University of Bradford, Bradford, West Yorkshire, UK

Potassium channel openers such as minoxidil can induce hair growth in vivo, although there is a need for a more effective therapeutic agent.  Therefore, it is important to have a reproducible in vivo model for the assessment of novel pharmaceuticals upon the hair follicle.

We have compared the effects of two potassium channel openers, minoxidil and diazoxide, in two rodent species.  Male C57 BL/6 mice (n=7/group) were dosed daily with either the vehicle, or 30 mg/kg diazoxide.  The vehicle, minoxidil (10 mg/kg), or diazoxide (3, 10, 30 mg/kg) were also orally administered daily to male Wistar rats (n=6/treatment).

The passing of the anagen wave was synchronous in the rat, in contrast to patchy eruptions in the mice, allowing for more accurate assessment of drug effects. Diazoxide (30 mg/kg) tended to advance anagen onset on the dorsum of both species.  Whereas both 3 mg/kg (p<0.005), 10 mg/kg (p<0.05) diazoxide, and 10 mg/kg minoxidil (p<0.005) significantly advanced anagen in the rat.

In mice, diazoxide (30 mg/kg) caused a significant (p<0.05) increase in terminal hair length. In the rat, minoxidil (10 mg/kg) significantly (p<0.05) increased terminal length, diazoxide at 3, 10, and 30 mg/kg had no effect.

Both models responded to potassium channel openers, with minoxidil acting as a more potent stimulator of rodent hair growth. In conclusion, the rat has a highly synchronised anagen wave, making it a better model, and would be recommended for future studies.