Reduction of acute inflammation in rats by diazepam: role of peripheral benzodiazepine receptors and corticosterone.

Carrageenin causes a reproducible inflammatory reaction and remains the standard irritant for examining acute inflammation and anti-inflammatory drugs. High doses of diazepam (10.0-20.0 mg/Kg) were shown to reduce the volume of acute inflammatory paw edema in rats as a response to carrageenin administration. The present experiment was undertaken to investigate the possible roles of peripheral-type benzodiazepine receptors (PBRs) and corticosterone on the anti-inflammatory effects of diazepam. Five experiments were conducted to assess the effects of a single dose (10.0 mg/Kg) of diazepam on carrageenin-induced paw edema (CIPE), pleurisy and increase in vascular permeability in rats. Results showed that: 1. diazepam or Ro5-4864 (a PBR agonist) treatment reduced CIPE values; 2. prior treatment with PK11195 (a non-benzodiazepine PBR antagonist) suppressed the effects of either diazepam or Ro5-4864 on CIPE; 3. diazepam reduced the volume of the pleural exudate in carrageenin-injected rats, as well as its leukocyte count; 4. diazepam treatment reduced the magnitude of the increase in vascular permeability caused by carrageenin; 5. adrenalectomy suppressed the effects of diazepam on CIPE; and 6. diazepam treatment increased the serum concentration of corticosterone. These results suggest a relevant role of PBR and corticosterone on diazepam-induced changes in inflammation. They are discussed in the light of a possible activation of mitochondrial PBRs within the adrenal gland cells by diazepam, thereby increasing the serum levels of corticosterone and thus reducing CIPE.