Interspecies and Interregional Analysis of the Comparative Histologic Thickness and Laser Doppler Blood Flow Measurements at Five Cutaneous Sites in Nine Species

Studies in dermatology, cutaneous pharmacology, and toxicology utilize skin from different animal species and body sites. However, regional differences exist in topical chemical percutaneous absorption studies in man and in animals. The objective of this study was to compare epidermal thickness and number of cell layers across species and body sites using both formalin-fixed paraffin and frozen sections. Cutaneous blood flow determined by laser Doppler velocimetry (LDV)was compared to histologic data. Six animals of each of the following species were used: monkeys, pigs, dogs, cats, cows, horses, rabbits, rats, and mice. Cutaneous blood flow was determined and 6-mm skin biopsies were taken directly from the following sites: buttocks, ear, humeroscapular joint, thoracolumbar junction, and abdominal area. When the two histologic methods were compared across all species and body sites, the thickness of the epidermis was significantly greater, and the thickness of the stratum corneum significantly less, in paraffin sections versus frozen sections (p < 0.05). There were no differences in the number of viable cell layers determined by both methods. The values for LDV-determined blood flow did not significantly correlate (p > 0.05) to epidermal or stratum corneum thickness. However, regional and species differences were noted in all these parameters. In conclusion, these data indicate that thickness and LDV blood flow are independent and must be evaluated separately when comparisons are made between species and body sites. This work provides a data base for future comparative studies in which a knowledge of skin thickness or blood flow might be important variables.