Content and formation of prostaglandins and distribution of prostaglandin-related enzyme activities in the rat ocular system

Abstract

The steady-state levels of prostaglandin D 2, E 2 and F 2α in the rat eye were 0.5, 0.1 and 1.0 ng/g, respectively, which increased differently among the prostaglandins after a 40-min incubation of the homogenate at 37° C (to 23, 12 and 14 ng/g, respectively). When the eye was dissected into anterior uveal, scleral, and retinal complexes, prostaglandin D 2 was formed in the highest degree in all the complexes, whereas prostaglandin E 2 and F 2α formation was specific to given ocular regions. Three prostaglandin synthetase activities with similar K m values (20–40 μM) were found in the 10000 × g supernatant of these tissues i.e., GSH-independent and soluble D, GSH-dependent and membrane-bound E, and soluble F synthetase activities. These enzyme activities correlated well with the prostaglandin formation in each tissue, D synthetase activity being highest in all the tissues (11–25 nmol/min per g). Three types of prostaglandincatabolizing enzyme activities were detected in the 100000 × g supernatant of the tissues i.e., type II 15-hydroxy dehydrogenase ( K m = 10–30 μM), 9-keto (500 μM) and 11-keto reductase (2.5 mM). The activity of the dehydrogenase was low even in the retina, the tissue with the highest levels (0.51, 0.35 and 0.15 nmol/min per g for prostaglandin E 2, F 2α and D 2, respectively).