Selective accumulation of meso-tetra(hydroxyphenyl)chlorin in steroid-synthesizing cells of the rat adrenal gland

Rat adrenal glands fluoresce intensely after systemic application of meso-tetra(hydroxyphenyl)chlorin (mTHPC). We investigated which parts of the adrenal gland accumulate mTHPC. Furthermore we examined the time course of adrenal mTHPC-accumulation. Ten male Wistar rats each were given 0.5 or 0.7 mg mTHPC kg-1 iv. Each two animals were perfused with normal saline and Zamboni fixative 6, 12, 24, 48 and 72 hours after photosensitization. Untreated animals served as controls. Fluorescence was quantified on 20 micrometer frozen sections with CCD-camera and appropriate software. Immunohistochemistry identified specific cell types with antibodies to steroid-synthesizing enzymes. The cortex exhibited an intense fluorescence, with weaker fluorescence of corticocytes in the zona glomerulosa compared to the other zones. Besides intensely fluorescing singly lying scattered cells, the medulla showed a faint mTHPC-induced fluorescence. Immunohistochemistry revealed that intramedullary cells with intense fluorescence were corticocytes, showing a positive reaction to the 21-(beta) -hydroxylase antibody. Peak accumulation of mTHPC was always observed after 24 hours. Our results indicate for the first time that only steroid synthesizing cells of the adrenal gland exhibit an intense photosensitizer-induced fluorescence. Thus mTHPC-application is an uncomplicated method to identify steroid-synthesizing cells, possibly also in other organs.

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