ARGININE-VASOPRESSIN TRANSPORT AND METABOLISM IN THE PIGMENTED RABBITCONJUNCTIVA

The purpose of this study was to evaluate the transepithelial transpor t and metabolism of arginine vasopressin (AVP) in the pigmented rabbit conjunctiva, both in the absence and presence of protease inhibitors. The apparent permeability coefficient, P-app, for H-3-AVP was determi ned in the modified Ussing chamber, and AVP metabolites were monitored by reversed phase HPLC using a C-18 column. At 50 nM donor H-3-AVP, t he P-app in the mucosal-to-serosal (ms) direction was about five times higher than that in the opposite direction. Excess (0.1 mM) AVP decre ased the P-app for labelled AVP in the mucosal-to-serosal (ms) directi on by about 50%. However, intact AVP transport showed neither concentr ation nor direction dependence. HPLC analysis revealed two subspecies of H-3-AVP in the receiver fluid and virtually no degradation products in the donor fluid following 3 h flux experiments. H-3-AVP transporte d in the ms direction underwent extensive hydrolysis (73%), which was decreased by 33% with mucosal application of 2 mM camostat mesylate (a n aminopeptidase inhibitor) or by 27% with 0.5 mM leupeptin (a serine protease inhibitor). By contrast, H-3-AVP transported in the serosal-t o-mucosal (sm) direction resulted in only 37% hydrolysis, and mucosal application of either inhibitor did not significantly affect the P-app for intact AVP. These data suggest that intact AVP transport in the c onjunctiva may be mediated mostly by passive diffusion and enzymatic d egradation of AVP may be mediated by proteolytic enzymes present on th e mucosal side of the conjunctiva. (C) 1998 Elsevier Science B.V.