Antiinflammatory and antinociceptive effects of 1,8-cineole a terpenoid oxide present in many plant essential oils

The formalin test in mice is a valid and reliable model of nociception and is sensitive for various classes of analgesic drugs. The noxious stimulus is an injection of dilute formalin (1% in saline) under the skin of the dorsal surface of the right hindpaw. The response is the amount of time the animals spend licking the injected paw. Two distinct periods of high licking activity can be identified, an early phase lasting the first 5 min and a late phase lasting from 20 to 30 min after the injection of formalin. In order to elucidate the involvement of inflammatory processes in the two phases, we tested different classes of drugs in the two phases independently. Morphine, codeine, nefopam, and orphenadrine, as examples of centrally acting analgesics, were antinociceptive in both phases. In contrast, the non-steroid anti-inflammatory drugs indomethacin and naproxen and the steroids dexamethasone and hydrocortisone inhibited only the late phase, while acetylsalicylic acid (ASA) and paracetamol were antinociceptive in both phases. The results demonstrate that the two phases in the formalin test may have different nociceptive mechanisms. It is suggested that the early phase is due to a direct effect on nociceptors and that prostaglandins do not play an important role during this phase. The late phase seems to be an inflammatory response with inflammatory pain that can be inhibited by anti-inflammatory drugs. ASA and paracetamol seem to have actions independent of their inhibition of prostaglandin synthesis and they also have effects on non-inflammatory pain.

Menthol and other aromatic vapours have been widely used in the symptomatic treatment of upper respiratory tract infections, although there is little objective evidence as to their benefit. We have investigated the action of aromatic vapours on the cough reflex in conscious guinea-pigs. Animals (n = 13) were pretreated with air or test vapours for 5 min at a rate of 1 l/min. One minute later the animal was challenged with aerosolized citric acid for 2 min. Control responses to air pretreatment were not significantly different throughout the procedures. Three concentrations of each aromatic vapour were used (3, 10 and 30 micrograms/l menthol, 50, 133 and 500 micrograms/l camphor and 0.8, 2.7 and 8 mg/l cineole). Menthol proved the most effective antitussive--10 and 30 micrograms/l produced a significant 28 and 56% reduction in cough frequency--500 micrograms/l camphor gave a significant 33% reduction, while cineole, at the concentrations used, had no significant effect. An increase in cough latency coincided with a reduction in cough frequency. These results demonstrate the efficacy of aromatic vapours as antitussives in chemically induced cough.