dynorphins and Cholestasis

Increased endogenous opioid activity has been implicated in cholestatic pruritus. In the present study, we have further defined the involvement of opioids in cholestasis. Rats underwent either bile duct ligation or a sham operation. Five days after surgery, brains were removed and agonist-stimulated [35S]GTPgammaS binding was measured in ten brain regions. Serum endomorphin-2, leu-enkephalin and dynorphin A levels were measured using ELISA on day five. Microdialysis to the dorsal hypothalamic area was conducted in the same animal before and after cholestasis. Dialysate endomorphin-1, leu-enkephalin and dynorphin A levels also were measured. Delta- and kappa-stimulated binding was significantly decreased in cholestasic animals compared to controls in the dorsal hypothalamic area. The serum dynorphin A level was lower in the cholestasic group than in controls (2.56+/-0.09 and 3.29+/-0.22 ng/ml, respectively, P<0.01). We propose that pruritus in cholestasis may result from an impaired balance between mu- and kappa-opioid systems.

Topics: Animals; Binding, Competitive; Brain; Cholestasis; Dialysis Solutions; Disease Models, Animal; Dynorphins; Enkephalin, Leucine; Guanosine 5'-O-(3-Thiotriphosphate); Hypothalamus; Male; Microdialysis; Oligopeptides; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Sulfur Radioisotopes

Cholestatic liver disease is associated with clinical and experimental findings consistent with increased opioidergic neuromodulation, increased plasma total opioid activity, and elevated plasma enkephalin concentrations. In contrast to the normal adult rat liver, preproenkephalin mRNA was detected by Northern blotting in livers of adult rats with cholestasis due to bile duct resection and not in the sham-resected controls. Preprodynorphin mRNA was not detected in livers of either group, while preproopiomelanocortin mRNA was found in very low levels in both groups. Preproenkephalin mRNA was not expressed in the livers of rats with acute hepatocellular necrosis induced by thioacetamide. Hybridization histochemistry of cholestatic livers demonstrated the presence of preproenkephalin mRNA primarily over cells in the periportal areas, some of which appeared to be proliferating bile ductular cells. Immunohistochemical staining of cholestatic liver indicated the production of at least Met-enkephalin in association with preproenkephalin gene expression. These findings suggest that the liver itself, by synthesizing enkephalins, contributes directly to the abnormalities of the opioid system reported in cholestasis.

Topics: Animals; Cholestasis; Dynorphins; Enkephalins; Histocytochemistry; Immunohistochemistry; Liver; Male; Necrosis; Nucleic Acid Hybridization; Pro-Opiomelanocortin; Protein Precursors; Rats; Rats, Sprague-Dawley; RNA, Messenger; Tissue Distribution