Microcirculation of transplanted tumors.

A transparent chamber was implanted in the dorsal skin flap of 32 Syrian gold hamsters, 48 h after microsurgery, 4x10(4) cells of the amelanotic melanoma A-Mel-3 were transplanted s.c. in the area exposed for daily in vivo microscopy (16 animals). A platinum multiwire electrode and quantitative video-techniques were utilized for measurements of local pO2, microvascular morphology and measurements of local PO2, microvascular morphology and capillary hemodynamics. When compared to controls (16 animals), mean local PO2 on the tumor's surface decreased with tumor development. The density of erythrocyte perfused capillaries in the melanoma was elevated 4 days after humor transplantation indicating excessive neovascularization. Probably due to increased intratumor tissue pressure and thrombosis, capillary density decreased significantly until day 12, whereas mean capillary blood cell velocity did not change. Of microhemodynamic significance were huge platelet conglomerates consistently noted in short, dilated capillaries as the melanoma edge. As a result, the capillary filling time (15.7 s for melanoma capillaries, 3.2 s for control preparations) was prolonged suggesting an increase in capillary resistance. These findings might indicate that the efficacy of melanoma treatment is diminished by an enhanced capillary resistance. Intratumor tissue pressure and thrombosis with concomitant widening of intercapillary distances might significantly affect the therapy of melanomas.