Blood Microcirculation Under Photodynamic Process

Abstract

Changes in microcirculation and impairment of microvascular wall in the mesentery and the liver of white rats under photodynamic conditions have been investigated with the help of biomicroscopy and electron microscopy. Hematoporphyrin derivative, photosan II, photofrin II, and chlorine E₆ in concentrations from 0.01 to 50 mg/kg of animal body weight have been used as photosensitizers (PS). The total energy delivered was up to 100 J/cm². Under photodynamic conditions, thrombocyte aggregation is induced, which leads to periwall depositions. This process causes complete vessel occlusion and arrest of local bloodflow. The rate of thrombocyte aggregation was constant, and the level of photodynamic effect depended on the concentration of the injected photosensitizer and the dosage of light energy. Ultrastructural analysis demonstrated deep changes in both microvascular wall components and in blood cells, especially thrombocytes, at the peak of photodynamic therapy. These changes are similar to the effect produced on membrane structures by free radicals. The essence of the pathogenetic mechanism of the microvascular photoinjury lies in the formation of active oxygen forms affecting the components of microcirculation. This is supported by a definite localization of intensive thromboformation at the site of direct light irradiation and by the correlation between the process dynamics and the photosensitizer concentration and irradiation dosage.