EFFECTS OF MODULATION OF SULFATION AND GLUCURONIDATION ON CHLORPROPHAM METABOLISM AND CYTOTOXICITY IN ISOLATED RAT HEPATOCYTES

After modulation of sulphation and glucuronidation, the relationship b etween the changes in metabolism and cytotoxicity of chlorpropham (CIP C), a widely used herbicide, was investigated in isolated rat hepatocy te suspensions. Under physiological conditions, CIPC had a cytolytic e ffect, modified membrane permeability and reduced intracellular ATP le vel. CIPC was metabolized by hepatocytes mainly into 4-OH chlorpropham sulphate (37%) and glucuronide conjugates (18%). Inhibition of sulpha tion, by omitting sulphate from the isolation and incubation media, di d not affect the cytotoxicity of CIPC, since there was a 2.5-fold comp ensatory increase in 4-OH CIPC glucuronide. Inhibition of glucuronidat ion by adding 4 mM D-galactosamine in the incubation medium led to a 6 6% decrease of glucuronide conjugate and simultaneously to a 32% decre ase of sulphate conjugate. In that case, concentrations of free 4-OH C IPC in both hepatocytes and incubation medium were markedly increased, while those of 3-chloroaniline and 3-chloroacetanilide were slightly modified and remained low. This alteration of metabolism was accompani ed by modification of cell permeability and reduction in ATP synthesis . The cytolytic effect was due to CIPC itself, whereas the effect on e nergetic metabolism was attributed to a metabolite. Results demonstrat ed for the first time a partial inhibition of sulphation by D-galactos amine (4 mM), probably due to the effect of D-galactosamine on intrace llular ATP levels.