Modification of tumour blood flow--a review.

Tumour vascularization is based on two types of vessels, incorporated normal host tissue vessels and newly formed vessels, and is characterized by a wide heterogeneity. No adrenergic innervation has been related to newly formed tumour vessels but may still be found in incorporated normal vessels. In most studies vasoconstricting drugs were found to decrease tumour blood flow, while vasodilating drugs had no significant influence on tumour blood flow. From this it was concluded that the tumour vascular bed is normally in a state close to maximal dilatation, and this is supported by observations of hypoxia and local acidosis in tumour tissue. Some conflicting results have been reported with an increased tumour blood flow after administration of, for example, calcium channel blockers. Tumour blood modification is of interest in radiotherapy but also in tumour hyperthermia, where circulatory disturbances are explained on a multifactorial basis. Based on conflicting observations, with results varying with tumour-host systems studied and techniques for flow recording, it seems reasonable to concentrate further on methodological studies to develop clinically relevant techniques for tumour blood flow recording.