CLEARANCE OF GLUTATHIONE DISULFIDE FROM RAT MESENTERIC VASCULATURE

Organs of the digestive tract, including pancreas, small intestine, an d colon, have mechanisms to modulate plasma thioldisulfide balance. Be cause plasma glutathione disulfide (GSSG) concentration may be elevate d from <1 mu M in control rats to over 25 mu M during oxidative stress , we examined whether GSSG was cleared from rat mesenteric vasculature . When 100 mu M GSSG was perfused through the gut via the superior mes enteric artery, an average of 45% was lost in a single pass. Results s howed that gamma-glutamyltransferase (gamma-GT)-dependent and -indepen dent mechanisms were involved in GSSG loss. Acivicin (AT125) treatment inhibited gamma-GT activity in the mesenteric vasculature by 94% and attenuated the loss of GSSG equivalents by 44%. These results supporte d a role for gamma-GT in GSSG loss from the mesenteric vasculature but indicated that still other mechanisms were involved in GSSG clearance . Elevations of portal levels of glutathione (GSH) and the mixed disul fide of cysteine and GSH (CySSG) also occurred with vascular GSSG perf usion and could account for about 40% of GSSG equivalents lost. Becaus e portal elevations of GSH and CySSG were not inhibited by AT125, they were formed by a gamma-GT-independent mechanism(s). Given that cystei ne was present in the mesenteric vasculature, the most likely mechanis m to explain GSH and CySSG formation was via nonenzymatic thiol-disulf ide exchange between GSSG and cysteine. Uptake of vascular GSSG by pan creas, small intestine (jejunum and ileum), or colon apparently did no t occur as tissue contents of GSSG or GSH were not elevated, except fo r a small elevation of GSH in pancreas when mesenteric gamma-GT was in hibited with AT125. Additionally, GSSG was not transported from mesent eric vasculature into the small intestinal lumen because luminal level s of GSSG or GSH were not elevated. Further, total cysteine equivalent s in lumen were unchanged indicating that GSSG was not transported to lumen and degraded to cystine by gamma-GT and dipeptidases localized t o the intestinal brush-border. These results indicate that GSSG presen t in mesenteric vasculature is metabolized in the vascular compartment by gamma-GT-dependent and -independent reactions; together, these acc ount for over 80% of lost GSSG equivalents. They also suggest that org ans of the mesentery may play a quantitatively important role in plasm a GSSG clearance and modulation of vascular thiol-disulfide balance. ( C) 1994 Academic Press, Inc.