The study of cardiac output (CO) distribution to tumors and metastases is of interest for a better understanding of tumor biology and for pharmacological approaches. A radioactive microsphere method was developed to assess CO distribution in C57BL/6J mice bearing syngeneic 3LL or BALB/c mice with JWS. At the initial stages of cancer growth, the CO relative fractions per g of tissue (%CO/g) to 3LL and JWS were similar to those in surrounding tissues. In both tumors a positive, significant correlation was found between tumor weight and tumor CO fraction, but %CO/g was lower in 3LL 2 and 3 weeks after transplantation, whereas it did not change in JWS. Indeed, much larger necrotic areas developed in 3LL than in JWS. The %CO/g to the lungs increased in both models when metastases were not yet visible; subsequently, the appearance of lung nodules was accompanied by a decrease of %CO/g in JWS and a further increase in 3LL. This corresponded to the much higher ratio of metastatic to intact lung tissue in JWS than in 3LL. In fact, isolated lung metastases had a significantly lower blood supply than the surrounding tissue. This might be due to a different vascularization pattern and/or smaller amounts of vasodilator substances being produced by metastatic nodules; the latter is suggested by lower generation of prostacyclin activity in isolated lung metastases than in intact pulmonary tissue.
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