Prostaglandins and transepithelial ionic transport.

Given the complexity of the preparation and the fact that the measured potential difference and SCC result from the algebraic contribution of several apparent ionic components (as well as unidentified ones) in the various cell membranes of the preparation, the effect of PGF2 alpha on the SCC requires further elucidation, for example, by determination of the effects of this PG on H14CO3- fluxes. However, experiments already completed suggest that PGF2 alpha can effectively stimulate the SCC of the ciliary epithelium. Since stimulation of the SCC can be expected to reflect enhanced fluid secretion, the effect of PGF2 alpha on the ciliary epithelium, at least in rabbits, can be regarded as a potentially beneficial one, providing increased production of aqueous humor. It remains to be seen whether PGF2 alpha has a similar stimulatory effect on ciliary epithelium transport function in primates whose aqueous humor, in contrast to rabbits, is deficient in HCO3- as compared to blood plasma. The possibility that PGF2 alpha does stimulate aqueous humor secretion in the human eye is suggested by the fact that PGF2 alpha-1-isopropylester applied topically to the human eye in doses greater than the minimal dose required to cause ocular hypotension yields an initial increase in intraocular pressure (see Alm and Villumsen, 1989) and a small increase in rate of aqueous production was detected in the PGF2 alpha treated eyes of cynomolgus monkeys (Nilsson et al., 1989). These considerations suggest that the effects of PGs on the transport function of the mammalian ciliary epithelium deserves further attention.