Diluted isoflurane as a suitable alternative for diethyl ether for rat anaesthesia in regular toxicology studies

Despite its explosive properties and toxicity to both animals and humans, diethyl ether is an agent long used in Japan in the anaesthesia jar method of rat anaesthetises. However, in response to a recent report from the Science Council of Japan condemning diethyl ether as acceptable practice, we searched for an alternative rat anaesthesia method that provided data continuous with pre-existing regular toxicology studies already conducted under diethyl ether anaesthesia. For this, we examined two candidates; 30% isoflurane diluted with propylene glycol and pentobarbitone. Whereas isoflurane is considered to be one of the representatives of modern volatile anaesthetics, the method of propylene glycol-diluted 30% isoflurane used in this study was our modification of a recently reported method revealed to have several advantages as an inhalation anaesthesia. Intraperitoneal pentobarbitone has long been accepted as a humane method in laboratory animal anaesthesiology. These 2 modalities were scrutinized in terms of consistency of haematology and blood chemistry with previous results using ether. We found that pentobarbitone required a much longer induction time than diethyl ether, which is suspected to be the cause of fluctuations in several haematological and blood chemical results. Conversely, only calcium ion concentration showed a slight difference from traditional results in the case of 30% isoflurane. Additionally, serum prolactin and corticosterone levels indicated that 30% isoflurane induced less stress than ether, confirming that 30% isoflurane can both provide results consistent with diethyl ether, while at the same time remove its disadvantages. As such 30% isoflurane appears to be a strong alternative anaesthetic agent for future regular toxicology studies in Japan.