Microvascular pressures in DMBA-induced rat mammary tumours.

Microvascular pressures have been measured in the superficial layers of DMBA-induced mammary tumours in rats. The vessels were punctured with glass micropipettes (tip diameter 1-3 micron), and pressure measured with a modified Wiederhielm servo-controlled counter-pressure technique. After measurement the microvascular tree in some tumours was visualized by silicone rubber injections. The mean arteriolar pressures were 44.5 and 38.9 mmHg in arterioles with diameters of 46-80 and 15-45 micron respectively. Mean capillary pressure was 23.8 mmHg, while mean pressures of 13.3 and 9.7 mmHg were obtained in vennules of 15-45 and 46-100 micron respectively. The 'local perfusion pressure' (arteriolar pressure minus venous pressure, where the local venous pressure almost equals the tissue pressure) in central areas of tumours of more than 5.5 g can be calculated to be maximally one half of that in skin. This may well contribute to tumour hypoxia and subsequent necrosis.