Stratum comeum species differences

It must be stressed that both transdermal flux and Kp are not only chemical dependent but also tightly constrained by the membrane system studied as well as the method of topical application (neat compound, vehicle, length of experiment, etc.). The PC that is integral to Kp is the PC between the surface or applied vehicle and the stratum comeum. Different vehicles will thus result in different PCs. Similarly, skin from different species may result in different PCs due to differences in the stratum comeum lipids and intercellular path lengths. 

An additional variable that must be accounted for in derma absorption studies that may overshadow the difference between chemicals Is body site differences in absorption within a species. Regional variation in skin permeability at different body. sites may be related to skin thickne.ss, number of cell layers, cell size of the epidermis and stratum comeum, and di.stribution of hair follicles and sweat pores. Because of thick layers of stratum corneum, permeability in palmar and plantar skin is expected to be less than that in the scalp or forearm (Feldmann and Maibach, 1974). Data from several studies suggc.st that regional variation in vascular anatomy and blood flow should also be considered (Montciro-Rivicrc o/.. 1990 Qiao cf a/.. 1993). 

The stratum comeum cell layers may vary in thickness from one body site to another. An interregional analysis was conducted in nine species to assess the variability in thickness and blood flow between body sites as well as the effect histologic techniques have on these metrics (Table 1.1). Such regional differences... 

Although the basic structure of skin is similar in most terrestrial mammals, between- and within-species differences exist in the thickness of the epidermis and dermis in various regions of the body (Monteiro-Riviere, 1991 Chapter 1, this volume). For example, in the pig, epidermal and stratum comeum thickness is almost twice that in cattle and horses. Stratum comeum thickness in sheep is similar to that in cattle, yet the epidermis in sheep is only half as thick. Other investigators have speculated that transappendagial transport of dmgs across skin in cattle and sheep... 

---