Hydrolysis of 4-methylumbelliferyl sulfate in periportal and pericentral areas of the liver lobule

Abstract

4-Methylumbelliferyl sulfate was used to characterize sulfatase activity in periportal and pericentral regions of the liver lobule in the perfused rat liver. Following infusion of 1.5 mM of this organic sulfatester, free 4-methylumbelliferone and 4-methylumbelliferyl glucuronide were formed at rates of 13 and 9 μmoles/g/h, respectively, in livers from fasted, phenobarbital-treated rats. 5-Pregnen-3β-ol, 20-one sulfate inhibited hydrolysis and metabolite production completely, whereas perfusion with nitrogen-saturated perfusate or FCCP decreased total metabolite formation by only 30%. 4-Methylumbelliferone formed from the hydrolysis of 4-methylumbelliferyl sulfate was monitored with micro-light guides placed on periportal and pericentral areas of the liver lobule. Detection of the desulfated product was always greater in the downstream region, i.e., infusion of 4-methylumbelliferyl sulfate produced a higher fluorescence signal in pericentral areas when perfusion was in the anterograde direction, while periportal areas demonstrated higher activity during perfusion in the retrograde direction. Perfusion with nitrogen-saturated perfusate abolished these differences. Taken together, these data suggest that uptake of organic sulfateesters is partially energy dependent, follows the hepatic oxygen gradient inversely, and is a major rate determinant for sulfatase activity in the liver.