Actinomycin D peritonitis in rats: a tool for the study of early events in inflammation.

The injection of 50 microgram i.p. of actinomycin D produces, in rats, a biphasic inflammatory reaction. The first short lasting phase (approximately 24 h) is characterized by the decrease of the peritoneal cells number, by the increase of the levels of both cAMP and cGMP in the peritoneal cells and by the increased synthesis and release of lysosomal enzymes from these cells. The second long lasting phase (greater than 120 h) is characterized by the exudate formation, intense cellular immigration, continuous release of lysosomal enzymes, return to or below the normal values of the intracellular levels of cyclic nucleotides. The treatment of rats with a steroidal drug reduces the beta-glucuronidase release and, concomitantly, the intracellular cyclic nucleotides levels. Indomethacin is ineffective.