Inhibitory effects of adrenomedullary hormone on the induction and growth of fibrosarcoma by methylcholanthrene.

Objective: Effects of adrenomedullary hormone(s) on the induction and growth of fibrosarcoma by methylcholanthrene (MC) were examined.

Methods: At 28 days of age, male Wistar rats were divided into four groups: 1) control, 2) bilateral adrenomedullectomy (Bil. AMX), 3) right AMX + left adrenomedullary autotransplantation (AMX + AMT), 4) Bil. AMX + epinephrine injection (Bil. AMX + E) groups. 14 days after surgery, MC crystals were inserted underneath the dorsal skin, and in the Bil. AMX + E group, epinephrine was injected subcutaneously, twice every week.

Results: The incidence of tumor at 90 days after the MC injection was 8 per 35 cases (22.9%) in the control group, 12 per 36 cases (33.3%) in the AMX + AMT group, 8 per 28 cases (28.6%) in the Bil. AMX + E group, and each value was lower compared with that of the Bil. AMX group, 24 per 34 cases (70.6 %), (P<0.001, P<0.002, P<0.005). Such differences among groups were not seen at 165 days after the injection of MC.

Discussion: The mechanisms of effects of AMX, AMT and/or epinephrine on the tumor incidence have been discussed with reference to tumor promotion, vascular neoplasia, etc. Since norepinephrine remaining in the blood of AMX rats was ineffective, at least it is likely that this inhibitory effect of epinephrine is mediated via the beta2-receptor.

Conclusion: The results suggest that adrenomedullary hormone, probably epinephrine, has inhibitory effects on the induction and growth of fibrosarcoma by MC, particularly in the early stage.