INDUCTION OF ALKOXYRESORUFIN O-DEALKYLASES AND UDP-GLUCURONOSYL TRANSFERASE BY PHENOBARBITAL AND 3-METHYLCHOLANTHRENE IN PRIMARY CULTURES OF PORCINE CILIARY EPITHELIAL-CELLS

Our previous studies have shown that drug-metabolizing activities in the eye are highest in the ciliary body, a tissue responsible for aqueous humor production. In this work, we have separated nonpigmented epithelial (NPE) cells and pigmented epithelial (PE) cells from porcine ciliary body and determined basal and induced activities of 7-ethoxyresorufin (ER) O-dealkylase, 7-pentoxyresorufin (PR) O-dealkylase, and UDP-glucuronosyl transferase (UDP-GT) using primary cultures of separated cells. ER and PR activities were associated primarily with NPE cells and were very low in PE cells. Treatment of NPE cells with phenobarbital (PB) for 48 hr resulted in about a 4-fold increase in PR O-dealkylase activity but only a 1.3-fold rise in ER O-dealkylase activity. Conversely, 3-methylcholanthrene (MC) treatment augumented the ER O-dealkylase activity of NPE cells 6 times over the basal activity in 48 hr but had little effect on PR O-dealkylase activity. Both NPE and PE cells had low basal UDP-GT activities. UDP-GT activity increased about 5-fold in PB-treated PE cells and about 4-fold in PB-treated NPE cells in 48 hr. The results of MC treatment were similar to those of PB treatment; enhancement of UDP-GT was more pronounced in PE cells than in NPE cells. Induction by PB and MC of ER O-dealkylase, PR O-dealkylase and UDP-GT activities in ciliary NPE and PE cells was inhibited almost completely by 3.5-mu-M cyclohexamide and 40nM actinomycin D. The heterogeneous distribution of these enzymes suggests that a harmonious interplay between NPE and PE cells is important for metabolic detoxification of blood plasma prior to aqueous humor formation.