Photodynamic activity of protoporphyrin IX in Harderian glands of Wistar rats: Monitoring by gland fluorescence

This paper presents results on Wistar rat Harderian glands photodegradation experimental study under visible light. Tests were conducted on 20 rats and a 632.8 nm He–Ne laser light was utilized for gland irradiation. The tissue degradation was evaluated by the microphotograph analysis, which demonstrated progressive disappearance of the acinus architecture and a increase in number of nuclei in the pyknotic form, characteristic for the cell degradation. At the same time, the intensities of initial fluorescence peaks at 636.2 nm and 705.8 nm, were diminished with increase in irradiation time and formation of a new peak with a maximum at 680 nm was observed. The systematic observation of the Harderian gland fluorescence spectrum evolutions in comparison with its tissue degradation factor demonstrated high occurrence of the result repetition for different animals even at very low light fluencies. This fact makes it possible to evaluate the tissue photodegradation level via monitoring of its fluorescence spectra as a function of the irradiation time and suggests that the Harderian glands provide an excellent experimental model for the study of the photodynamic process in vivo. Analysis of the Harderian gland fluorescence spectra evolution under light irradiation in comparison with that of protoporphyrin IX in solutions demonstrated that it is protoporphyrin IX responsible for gland fluorescence and photodynamic degradation. The formation of singlet oxygen under light irradiation of protoporphyrin IX solutions demonstrated that the principal mechanism of gland photodegradation is the Type II photodynamic.