The tissue reactions to foreign materials varied depending on the quality and quantity of materials deposited, the anatomical sites injected, and the animal species used. Three different patterns of tissue reaction to foreign materials introduced into the dermis have been described. Inert substances remained in the connective tissue or were partly deposited in the regional lymph nodes. Irritating substances caused acute inflammation or chronic granulomatous reaction. The third reaction to foreign substances in the upper dermis was transepithelial elimination.
Several investigators have reported granulomatous tissue reactions to sodium stearate, sodium
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palmitate and silica introduced into the human skin, and transepithelial elimination to charcoal introduc-
ed into the skin of guinea pigs.
This study was undertaken to evaluate, both gross and histologically, the sequential changes of tissue reactions to foreign materials in the skin in rabbits. Ten adult rabbits were used in this experiment. The left back skin of each epilated rabbit was injected with a 0.2 M sodium palmitate suspension and the right back skin was injected with a 0.25% charcoal intradermally.
The results are as follows ;
A. Clinical observations;
1. The injection sites of sodium palmitate showed whitish hard nodules with centrally attached crust after the 3rd day. From some of the injection sites a whitish soapy material was expelled through a slightly dilated follicle without crust formation.
2. Blue macules persisted at the sites of charcoal injection during the entire period of this experiment up to 3 weeks.
B. Histopathologic observations;
1. Sodium palmitate injection group,
1) Early tissue reaction from the 6th hour through the 2nd day was capillary dilatation and marked infiltration of neutrophils around the sodium palmitate deposits.
2) Foreign body granuloma was observed initially in some of the rabbits on the 3rd day at the periphery of the aggregates of the degenerated neutrophils and sodium palmitate deposits and in half of the rabbits on the 4th day, and in all the rabbits on the 8th day.
3) Transepithelial elimination through the hyperplastic follicular epithelium was evident on the 3rd
day in some of the rabbits, in half of the rabbits on the 7th day, and in all the rabbits on the 12th day.
4) After the completion of transepithelial elimination, the dermis was replaced by granulation tissue and overlying epidermis was hyperplastic.
2. Activated charcoal injection group;
1) Early tissue reaction from the 6th hour through the 1st day was capillary dilatation and a moderate infiltration of neutrophils around the charcoal deposits.
2) On the 3rd and 4th days, macrophages phagocytizing charcoal were predominant cells, which remained unchanged during the remainder of the observation period.
3) Some of the charcoal particles phagocytized by macrophages seemed to be eliminated through the vascular system.
In conclusion, tissue reactions to sodium palmitate in rabbits consisted of foreign body granuloma and transepithelial elimination, and most of the charcoal remained in the connective tissue of the rabbit´s skin. These results suggest that tissue reactions in rabbits to foreign materials differ from those previously observed in other experimental animals. It appears that the rabbit could be used as an animal model for the investigation of dermatosis showing transepithelial elimination or granuloma.
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