Topical prostaglandin F2alpha treatment reduces collagen types I, III, and IV in the monkey uveoscleral outflow pathway.

ABSTRACT

BACKGROUND: Topical prostaglandin F2alpha isopropyl ester increases uveoscleral outflow in monkeys and humans. OBJECTIVE: To investigate the effects of prostaglandin F2alpha isopropyl ester with topical administration on collagen types I, III, and IV within the anterior segment tissue of monkey eyes. METHODS: Eight eyes of 4 cynomolgus monkeys were evaluated. One eye of each monkey was treated with 2 microg of prostaglandin F2alpha isopropyl ester twice daily for 5 days, and intraocular pressure reduction was confirmed. These eyes were fixed in methacarn, and paraffin sections were immunostained using antibodies to collagen types I, II, or IV. To measure staining intensity, optical density (OD) was determined using 2-dimensional imaging densitometry. Mean OD scores along line segments placed over the ciliary muscle were determined. RESULTS: Mean+/-SD OD scores for collagen types I, III, and IV were less in the ciliary muscle of prostaglandin-treated eyes than in vehicle-treated eyes by 52%+/-7%, 45%+/-6%, and 45%+/-5%, respectively. In the sclera adjacent to the ciliary body, mean OD scores for collagen types I and III were less in prostaglandin-treated eyes, by 43%+/-32% and 45%+/-13%, respectively. The scleral stroma was minimally immunoreactive for collagen type IV. All differences were significant by the paired Student t test (P<.05). CONCLUSIONS: This study shows reduced collagen types I, III, and IV immunoreactivity in the ciliary muscle and adjacent sclera following topical prostaglandin F2alpha isopropyl ester treatment. These reductions may contribute to the increased uveoscleral outflow observed with topical prostaglandin treatment. CLINICAL RELEVANCE The cellular mechanism by which certain prostaglandins lower intraocular pressure is not known. The present study provides immunohistochemical data demonstrating that intraocular pressure reduction that occurs with topical prostaglandin F2alpha is associated with a reduction of collagens within the uveoscleral outflow pathway.