sincalide and 2-6-dichloro-4-nitrophenol

Brain phenolsulfotransferase (PST) is involved in the sulfation of simple phenols like dopamine and of precursors of biologically active peptides like cholecystokinin octapeptide (CCK-8). Therefore, inhibition of brain PST would provide a new approach to studying the sulfation of CCK-8 and other sulfated compounds. Since 2,6-dichloro-4-nitrophenol (DCNP) produces a prolonged and selective inhibition of the sulfoconjugation of exogenous phenols by the liver, we decided to examine the applicability of DCNP to studies of sulfation of CCK-8 and other compounds by brain. DCNP was capable of completely inhibiting PST activity in rat brain homogenates incubated with p-nitrophenol, phenol or dopamine as substrates. The IC50 values for p-nitrophenol and dopamine were 12 and 14 microM respectively. The concentrations of DCNP in brain cortex and plasma were measured by high pressure liquid chromatography (HPLC) after a dose of 100 mumoles/kg, i.p. Peak concentrations of 380 microM in plasma and 25 mumoles/kg in brain were achieved 30 min after injection. Subsequently, DCNP concentrations decreased with half-lives of 8 and 6 hr in plasma and brain cortex, respectively. To establish if DCNP can inhibit CCK sulfation in vivo, rats were injected with 100 micromoles/kg, i.p., of the drug 30 min before injection of 35SO4(2-) into the cerebral cortex and were killed 4.5 hr later. DCNP caused a 55% inhibition of [35S]CCK-8-SO4 formation as measured by HPLC. No change in the content of endogenous CCK-8-SO4 was detectable, however, in the brain cortex of rats treated with DCNP for up to 4 days, indicating that the PST which remained active was capable of maintaining CCK-8 content at steady state.

Topics: Animals; Arylsulfotransferase; Brain; In Vitro Techniques; Kinetics; Male; Nitrophenols; Peptides; Phenols; Rats; Rats, Inbred Strains; Sincalide; Sulfurtransferases