Junctional and compound pigmented nevi induced by 9, 10-dimethyl-1,2-benzanthracene in skin of albino guinea pigs.

Seventy albino guinea pigs were used in the experiment to investigate the influence of 9,10-dimethyl-1,2-benzanthracene on amelanotic melanocytes. A field 5 sq cm was marked on the flank of each animal. Hairs from these fields were clipped twice a week and painted for 20 consecutive weeks with 0.3 ml of 1% 9,10-dimethyl-1,2-benzanthracene in acetone. During the 1-year observation period, pigmented sports appeared in 40 animals. Biopsies were taken under local anesthesia, and sections were prepared for light and electron microscopic observations. Melanin formation of unknown mechanism took place in the epidermal melanocytes and in the melanocytes from the outer root sheath. These melanocytes also formed junctional and compound nevi; serial sections revealed various stages of pigmented nevi development. Schwann cells did not participate in the formation of nevi. Evidence is presented that 9,10-dimethyl-1,2-benzanthracene can convert amelanotic melanocytes into melanin-producing cells in the albino guinea pig skin. In addition, this system produces an animal model for the development of junctional and compound nevi.