Penetration of radionuclides across skin barriers of animal skin models in vitro

In this paper: (i) the time dependence of permeation of 137Cs+, 60Co2+, and 147Pm3+ from aqueous solution through animal skin model has been studied, (ii) the biologic structure mostly responsible for the barrier effect was selected and proved, (iii) the relative importance of the main diffusion pathways for 137Cs+, 60Co2+ and 147Pm3+ (the diffusion across the intact skin and the diffusion through the hair channels) was assessed. All experiments were done using radioactive tracers. Experimental arrangement consisted of Franz-type vertical permeation cells used with fresh skin from abdominal region of 5 day old rats (5DR) of Wistar strain (Breeding Farm Dobra Voda, SK) and 9 day old rats (9DR), respectively. 5DR are still hairless, and 9DR are just short haired. The 5DR skin was used in full form (intact), and then with decreasing thickness of horny layer after the skin had been stripped with Scotch type (3M) 5-20 times respectively, or the skin was splitted under 60 degC hot water so that the whole epidermis was removed. The penetrated amounts of ions were found to be proportional to the time at least in the first 7 hours. The permeation resistance of the skin is proportional to the thickness of the horny layer, the principal barrier mostly restricting the flux of ions. The more the skin is stripped, the more enhanced is the penetration of ions. This corroborates the fact that stratum corneum represents the most important barrier function of the whole skin (of rats). The additional diffusion through channels along hairs (follicules) can be of important value also in case of human skin where hair density is many times lower than in the case of the animal models used