title: Ultrastructural and biochemical alterations induced by tryptophan pyrolysis products on rat hepatocytes in primary culture. I. Action on the transcriptional process.
abstract: Adult rat hepatocytes in primary culture were used to study the effect of tryptophan pyrolysis products on the transcriptional process. Hepatocytes were treated with 1, 5 and 10 micrograms/ml of 3-amino-1,4-dimethyl-5H-pyrido-[4,3-b]-indole (Trp-P-1) or 3-amino-1-methyl-5H-pyrido-[4,3-b]-indole (Trp-P-2) for 2 and 4 h. The ultrastructural study revealed the appearance of nucleolar microsegregation accompanied by a reduction in peri- and interchromatin fibrils and granules in hepatocytes exposed to 10 micrograms/ml of each pyrolysate for 1 or 2 h. Biochemical investigation showed that the incorporation of [3H]uridine into nuclear RNA of treated hepatocytes was strongly decreased. Time- and concentration-related inhibition have been established; however, the inhibitory effect of Trp-P-1 was always superior to that of Trp-P-2. The determination of Mg2+-dependent RNA polymerase activity in an in vitro system functioning with isolated rat liver nuclei incubated in the presence of Trp-P-1 or Trp-P-2 showed a 40% inhibition of this activity. After a 1-h exposure of hepatocytes to 5 and 10 micrograms/ml of Trp-P-1, the recovery of RNA synthesis capacity was complete by 2 h and that of normal ultrastructural aspect was achieved within 4 h. All these results indicated that Trp-P-1 and Try-P-2 acted at the nucleolar level by a blockade of pre-rRNA synthesis and at the extranucleolar by decreasing the ultrastructural RNP responsible for hnRNA synthesis.
mesh_terms: D000818:Animals; D002243:Carbolines / Q000494:pharmacology*; D002273:Carcinogens / Q000494:pharmacology*; D002478:Cells, Cultured; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D002243:Carbolines; D002273:Carcinogens; D007211:Indoles; C019133:3-amino-1-methyl-5H-pyrido(4,3-b)indole; D012321:DNA-Directed RNA Polymerases; C019132:3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole