CHARACTERIZATION OF TUMOR BLOOD-FLOW USING A TISSUE-ISOLATED PREPARATION

Tumour blood flow was characterised in a 'tissue-isolated' rat tumour model, in which the vascular supply is derived from a single artery an d vein. Tumours were perfused in situ and blood flow was calculated fr om simultaneous measurement of (1) venous outflow from the tumour and (2) uptake into the tumour of radiolabelled iodo-antipyrine (IAP). Com parison of results from the two measurements enabled assessment of the amount of blood 'shunted' through the rumours with minimal exchange b etween blood and tissue. Kinetics of IAP uptake were also used to dete rmine the apparent volume of distribution (VDapp) for the tracer and t he equilibrium tissue-blood partition coefficient (lambda). lambda was also measured by in vitro techniques and checks were made for binding and metabolism of IAP using high-pressure liquid chromatography. VDap p and 1 were used to calculate the perfused fraction (alpha) of the tu mours. Tumour blood flow, as measured by IAP (TBFIAP), was 94.8 +/- 4. 4% of the blood Bow as measured by venous outflow, indicating only a s mall amount of non-exchanging flow. This level of shunting is lower th an some previous estimates in which the percentage tumour entrapment o f microspheres was used. The unperfused fraction ranged from 0 to 20% of the tumour volume in the majority of tumours. This could be due to tumour necrosis and/or acutely ischaemic tumour regions. For practical purposes, measurement of the total venous outflow of tumours is a rea sonable measure of exchangeable tumour blood flow in this system and a llows for on-line measurements. Tracer methods can be used to obtain a dditional information on the distribution of blood flow within tumours .