ALPHA-2-ADRENOCEPTORS AND VIGILANCE IN CATS - ANTAGONISM OF MEDETOMIDINE SEDATION BY ATIPAMEZOLE

In order to evaluate the effect of a specific alpha2-adrenoceptor anta gonist, atipamezole, on vigilance, adult cats with implanted electrode s for polygraphy were tested in a double-blind Latin square design. Th e standard clinical dose (0.1 mg/kg i.m.) of the specific alpha2-adren oceptor agonist, medetomidine, promptly induced stuporous sedation. At ipamezole, given 30 min later at 0.2, 0.4 or 0.8 mg/kg i.m., reversed the sedation within 3 min, resulting in complete awareness of the anim al. After the small dose of atipamezole, arousal with some motor excit ation continued for 6 h, whereas after the larger doses, the physiolog ical sleep-wake cycle returned earlier. Used alone, the preferred dose , 0.4 mg/kg atipamezole i.m., allowed physiological sleep within 33 +/ - 9 min, compared to 22 +/- 3 min after saline. Atipamezole thus prove d to be a most effective antagonist to sedation with alpha2-adrenocept or agonist drugs, without disturbing excitatory effects. Specific alph a2-adrenoceptor modulating drugs have evident clinical application, as antidotes to overdosage of alpha2-adrenoceptor agonists, or to termin ate their effect after surgical procedures.