Effect of neurohumoral modulators on the morphine-induced hyperthermia in non-tolerant rats.
Parole chiave
Astratto
Wistar rats from one supplier have been shown to exhibit the atypical body temperature responses to morphine. In contrast to commonly used rats, in which morphine induced dose-dependent changes in body temperature, the initial administration of morphine (5, 10, 20, and 40 mg/kg, s.c.) to rats of this particular strain produced a consistent and prominent hyperthermia. This hyperthermia is mediated via an action on the typical morphine receptors since it was completely prevented by a specific narcotic antagonist, naloxone. Effects of neurohumoral modulators on the hyperthermia have been investigated in these rats. Pretreatment of animals with p-chlorophenylalanine, alpha-methyltyrosine, phenoxybenzamine or propranolol did not alter the hyperthermia. In contrast, the s.c. administration of 1 mg/kg of either tertiary or quaternary anticholinergic drug such as scopolamine, atrophine, methscopolamine and methylatropine significantly inhibited the hyperthermia. These results suggest that morphine causes hyperthermia in some strains of rats by a cholinergic mechanism and the involvement of an adrenergic or serotonergic mechanism in this case appears unlikely.