Differential cell photosensitivity in photodynamic therapy of the rat endometrium

The purpose of this study was to determine the optical dose needed for both lasting endometrial destruction and prevention of implantation by photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) as a photosensitizer. Three hours after topical drug administration 74 female Sprague-Dawley received varying optical doses of 630 nm light delivered by an intrauterine cylindrical light diffusing fiber. Histologic evaluation of the endometrium 1 and 21 days after PDT as well as the number of implantation sacs after mating were assessed. Irreversible endometrial destruction was determined measuring the thickness of the endometrial layer 3 weeks after treatment. An in situ dose of 64 J/cm 2 was required to eradicate endometrial glands and prevent regeneration. In contrast, a 43 J/cm 2 in situ dose visibly damaged the endometrial stroma and myometrium but the endometrial glands survived and the endometrium regenerated to its full thickness within 21 days. However, implantation potential was significantly reduced at these low light levels. Due to differential cell photosensitivity, the optical threshold for lasting endometrial destruction is higher than for functional damage. For lasting endometrial destruction the endometrial glands must be destroyed, whereas for reproductive impairment, damage to the endometrial stroma seems to be sufficient