MICROVESSEL DIAMETERS OF HUMAN COLON ADENOCARCINOMA DURING ACUTE TREATMENT WITH SEROTONIN

Modulation of tumor blood flow could be of clinical importance, especi ally when it is combined with radio- or chemotherapy. Serotonin (5-HT) , a naturally occurring agent, selectively reduces tumor blood flow an d consecutively inhibits the growth of many animal tumors. Therefore, we introduce a new preparation that allows the study of topically appl ied 5-HT (10(-8) to 10(-2) mol/l) in the microcirculation of a human c olon adenocarcinoma. This tumor has been xenotransplanted subcutaneous ly under the dorsal surface of the ear in athymic nude mice. 5-HT was also tested in the normal skin. The microvascular diameters of large a nd small arterioles (A(1-3)) and venules (V-1-4) as well as capillarie s were measured via closed-circuit videomicroscopy. Normal skin arteri oles and venules constricted at higher doses (> 10(-7) mol/l) of 5-HT. In human colon carcinoma, doses of 5-HT higher than 10(-7) mol/l caus ed constriction of these microvessels; yet, tumor arterioles constrict ed more than skin arterioles. Thus, 5-HT could selectively reduce bloo d flow of human colon adenocarcinoma. Based on these findings, we sugg est that 5-HT can inhibit growth of human tumors by selectively constr icting tumor arterioles.