Interstitial fluid pressure and hemodynamics in a sarcoma implanted in the rat tail

To investigate the influence on tumor blood flow of changes in interstitial fluid pressure (IFP) and tumor perfusion pressure, 0.1 ml of sarcoma cell suspension containing 10(6) cells obtained from ascites fluid was injected in the tail of Lister rats. Experiments were performed 10-35 days after implantation in tumors weighing 0.25-1.5 g. The hydrogen gas washout technique was used for flow measurements in tumor and normal tail tissue, while IFP was measured with the wick-in-needle technique. Control tumor blood flow averaged 0.18 ml/min . g (SD 0.15, N = 21), which was similar to tail skin. The corresponding tumor IFP was 26.6 mm Hg (SD 11.5, N = 21). Interstitial fluid pressure was increased by inflating a cuff at the tail root to 30 and 55 mm Hg and/or by plasma volume expansion by a 5% solution of bovine serum albumin, the latter resulting in a two- to threefold increase in tumor and tail skin blood flow. When the tail cuff was inflated to 55 mm Hg in control rats, mean IFP in tumor rose to 37.6 mm Hg and blood flow in tumor and tail skin fell by 45-70%. Inflating the cuff to 55 mm Hg in plasma volume expanded rats resulted in a rise in mean tumor IFP to 50.5 mm Hg and a reduction of tumor and tail skin blood flow by 40-56%. No change in tumor blood flow was observed after reduction of tail arterial pressure by 25 mm Hg. The experiments show that a high interstitial fluid pressure does not seem to affect tumor perfusion more than the host organ.