The validity of anesthetic protocols for the surgical procedure of castration in rats

To achieve surgical anesthesia in animal experimentation, it is necessary to select the appropriate anesthetic protocol by considering its pharmacological properties and the surgical procedure to be performed. However, few studies have investigated the validity of anesthetic protocols under surgical conditions in small rodents. The present study aimed to clarify the pharmacological properties of 4 anesthetic protocols during the surgical procedure of castration in rats. Eight-week-old male Wistar rats were anesthetized with anesthetics, including the combination of ketamine and xylazine (K/X), the combination of medetomidine, midazolam, and butorphanol (M/M/B), isoflurane, and sevoflurane. Castration was performed under each anesthesia, and anesthetic depth and times were assessed, as were vital signs. The injectable anesthetics were investigated at standard and high doses. The concentration of inhalant anesthetics was adjusted to 1.5 minimum alveolar concentration (MAC). K/X at both doses demonstrated sufficient anesthetic depth with rapid induction and recovery. However, bradycardia and hypothermia were prominent in high-dose K/X, indicating that the standard-dose is more appropriate for surgical anesthesia in castration procedures. M/M/B demonstrated high anesthetic sensitivity variation in individual animals. In contrast to injectable anesthetics, inhalant anesthetics provided stable anesthetic depth with less cardiorespiratory influence. Sevoflurane did not lead to a significant decrease in rectal temperature during the anesthetic period. Results of the present study revealed the optimal dose and pharmacological features of several anesthetic protocols for castration, and may contribute to the standardization of surgical anesthesia in rats.