2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) ALTERS PANCREATIC MEMBRANETYROSINE PHOSPHORYLATION FOLLOWING ACUTE TREATMENT

To understand the basic mechanisms of TCDD's action to cause hypoinsul inemia in several experimental animals, we have studied TCDD-induced c hanges in various protein kinase activities in membrane preparations o f guinea pig pancreas. For this purpose, young male guinea pigs were t reated through a single intraperitoneal injection with 1 or 3 mug/kg o f TCDD in vivo, and, after given time periods, pancreas samples were o btained and membranes were isolated through homogenization and centrif ugation procedures. Several sets of incubation conditions were selecte d for protein kinase activity assay, each favoring a specific type of protein kinase. It was found that overall protein phosphorylation acti vities were higher in the preparation from TCDD-treated animals as com pared to those found in pair-fed controls and that this trend was more pronounced when he assay medium contained Mn2+ in place of Mg2+ and E GTA. These are the conditions that are known to favor protein tyrosine kinases. Other types of protein kinases from the treated animals did not show any significant differences from the pair-fed control animals , though that of protein kinase C in the treated preparation showed a modest increase. To establish that the type of protein kinases stimula ted by TCDD are protein tyrosine kinases, we have carried out phosphoa mino acid analyses, KOH digestion, and western blot analyses using an antibody to phosphotyrosine. All the results were consistent in suppor ting the idea that TCDD causes a rise in protein-tyrosine kinases in p ancreas at early stages of poisoning.