Response of rat conjunctival mast cells to multiple versus single applications of compound 48/80

A single application of the mast cell secretagogue compound 48/80 to the surface of the rat eye induces significant histologic changes. Ocular anaphylaxis is usually the result of repeated, not single, exposures to allergenic substances. The response of conjunctival mast cells to repeated daily applications of compound 48/80 was, therefore, evaluated. Ninety rats received one dose of compound 48/80 or phosphate-buffered saline almost daily for 17 days. The frequency and degree of mast cell degranulation and the number of mast cells and other inflammatory cells in the subepithelial conjunctiva were determined histologically. The clinical response was most marked after one application of compound 48/80; repeated daily applications markedly reduced the clinical response. In eyes treated with multiple applications, 75% fewer mast cells were observable in the conjunctiva by light microscopy compared with phosphate-buffered saline treated eyes. Most mast cells were granulated; a few showed mild to moderate degranulation. Except for epithelial damage, no tissue injury was associated with multiple applications of compound 48/80. In contrast to conjunctivae subjected to a single application of compound 48/80, conjunctivae receiving multiple applications resembled that of phosphate-buffered saline controls.