Cl− concentrations of bovine, porcine and ovine aqueous humor are higher than in plasma

Aqueous humor (AH) Cl− levels were measured from live cows and pigs to confirm the Cl−-secretory activities found across the ciliary bodies of these species in in vitro experiments. The values obtained were compared to those of the electrolyte in plasma (PL). In addition, Na+ and K+ concentrations were also measured in AH and PL. For analogy, the same measurements were made in sheep and rabbit. The results indicate that the Cl− AH-to-PL ratios of the bovine, porcine and ovine species, but not that of rabbit, are comparable to published values for humans. Thus, the transport activities of the ciliary epithelia of the former animals may be more adequate as a representative model for human than the commonly used rabbit, which exhibits strikingly different transport properties with a ciliary epithelium that is primarily a bicarbonate-transporting tissue.