Effects of tumour cells on angiogenesis and vasoconstrictor responses in sponge implants in mice

The effects of tumour cells (Colon 26) on the development and response of new blood vessels to different vasoconstrictors (platelet activating factor; PAF, endothelin-1, angiotensin II, adrenalin and 5-hydroxytryptamine) have been investigated. Sponge implants in mice were used to host tumour cells while washout of 133Xe was employed to assess local blood flow in the implanted sponges. By 14 days after implantation the response of vessels in tumour-bearing implants to the various vasoconstrictors generally was decreased compared to that obtained in control sponge implants or adjacent normal skin. Thus at this time point the t1/2 for 133Xe washout from control sponges treated with adrenalin (0.5 micrograms) was 30 +/- 4 min whereas in tumour-bearing sponges it was 5 +/- 1 min. This decreased sensitivity in tumour vessels was probably not due to a complete lack of contractile elements since actin was demonstrated by immunohistochemistry around blood vessels in both types of implant. The results of the present study have shown that the pharmacological responses of blood vessels in a growing tumour, Colon 26, differed from the responses of vessels of a similar age in non-neoplastic tissue. These results appear to suggest that the different angiogenic stimuli released from tumour tissue may markedly influence pharmacological reactivity of newly formed blood vessels.