title: Effect of direction (epidermis-to-dermis and dermis-to-epidermis) on the permeation of several chemical compounds through full-thickness skin and stripped skin.
abstract: OBJECTIVE
  Compound permeation through stratum corneum-stripped skin is generally greater than that through full-thickness skin. In addition, epidermis-to-dermis permeation profile should be the same as dermis-to-epidermis permeation profile. However, stripped skin permeability of some compounds was lower than full-thickness skin permeability and different permeabilities were found for some compounds between the two directions of skin permeation. The reasons for these findings were investigated in this study.
  
  
  METHODS
  Full-thickness or stripped hairless rat skin was set in a Franz-type diffusion cell, and a solution of compound was applied on the epidermis or dermis side to determine the in vitro skin permeability.
  
  
  RESULTS
  Although the stripped skin permeability of pentyl paraben (PeP) with extremely high logK(o/w) was lower than full-thickness skin permeabilities, the addition of 3% ethanol resulted in the expected permeation order. Epidermis-to-dermis permeation of PeP through full-thickness skin was higher than dermis-to-epidermis permeation. Epidermis-to-dermis permeations of fluorescein isothiocyanate dextran (FD-4) and isosorbide 5-mononitrate with negative logK(o/w) were also higher than those in the opposite direction.
  
  
  CONCLUSIONS
  Morphological observation of skin after FD-4 permeation suggested that a conically shaped trans-follicular permeation pathway model could be advocated to explain the difference between the epidermis-to-dermis permeation and that in the opposite direction.
authors.affiliation: Faculty of Pharmaceutical Sciences, Josai University, 1-1 Keyakidai, Sakado, Saitama 350-0295, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Oshizaka
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Todo
authors.forename: Kenji
authors.initials: K
authors.lastname: Sugibayashi
mesh_terms: D000818:Animals; D008297:Male; D010539:Permeability; D010599:Pharmacokinetics; D051381:Rats; D054772:Rats, Hairless; D012867:Skin / Q000378:metabolism*