Use of Medetomidine for Sedation in the Laboratory Rat (Rattus norvegicus)

Abstract

Hauptman K., Jekl V. Jr., Knotek Z.: Use of Medetomidine for Sedation in the Laboratory Rats (Rattus norvegicus). Acta Vet. Brno 2003, 72: 583-591. Sixty-three rats (Rattus norvegicus) assigned to ten groups of six to seven animals were evaluated for depth and quality of sedation induced by intramuscular medetomidine. The first group received a dose of 50 µg/kg of medetomidine and the dosages in the other groups were 150 µg/kg, 200 µg/kg, 250 µg/kg, 300 µg/kg, 350 µg/kg, 400 µg/kg, 450 µg/kg and 500 µg/kg respectively. Respiratory rate, peripheral pulse, blood oxygen saturation, and disappearance and recovery of reflexes were evaluated at 5-minute intervals for the period of 60 minutes from the medetomidine injection. Disappearance of the lateral reflex was observed within 15 minutes in the 3 rd group and within 10 minutes in the 4 th to 10 th group. The peak of the sedation of the rat population was located between minute 10 and minute 20. All groups showed a drop in pulse rate, namely by 26% on average in the 2 nd group, by 18% in the 3 rd group, and by over 30% in groups 4 to 10. In groups 2 and 4, the maximum drop in pulse rate in minute 60 compared with minute 5 was by 30%; the drop was by 63% in group 10. Statistical evaluation of blood oxygen saturation did not reveal any statistically significant differences between the individual groups. The average blood oxygen saturation was 90.9 ± 4.34%. Recovery of reflexes after the atipamezole injection was monitored at 1-minute intervals. All reflexes under evaluation were recovered within 5 minutes. Our recommendation regarding rat sedation is to apply medetomidine from 150 to 250 µg/kg. Higher dosages induce a relatively strong respiratory depression.