Effect of theophyllin and isoproterenol on cAMP level in melanotic and amelanotic hamster melanomas.

The level of cAMP was investigated in the following three types of hamster malignant melanomas: amelanotic, depigmented and melanotic. The amelanotic and depigmented tumors were undifferentiated, with high proliferative activity, and lacked tyrosinase. The melanotic one was slow growing, highly differentiated, and expressed tyrosinase activity. Among the melanomas investigated, the higher concentration of cAMP was found in undifferentiated tumors. The single treatment of the tumor-bearing animals with theophyllin or isoproterenol did not change the cAMP level in melanotic tumors, but significantly enhanced the cAMP content in amelanotic and especially depigmented melanomas. Multiple theophyllin treatment of tumor-bearing animals caused elevation of cAMP content in all tumors, but this effect was accompanied by enhancement of tyrosinase activity only in melanotic melanoma.