A Comparison of the Effects of Repeated Anaesthesia with Ether or Isoflurane in Rats

Ether anaesthesia has been used in rodents for routine blood sampling in toxicological studies for many years. Because of the highly flammable nature of ether and the inability to control the depth of anaesthesia, more suitable alternatives are needed. This study was conducted to compare data obtained using ether or isoflurane. Groups of male and female Sprague–Dawley rats, 5 weeks of age, were maintained on a normal diet for up to 25 weeks. Body weights were recorded during the study. Blood was sampled from the retro-orbital sinus under the different anaesthetics from the animals at 8, 12, 21 and from females only at 25 weeks of age for the analysis of standard haematology and biochemical parameters. These animals were killed at 25 weeks of age for histological examination. Body weights were unaffected. The major biochemical and haematological parameters were similar at the various time points with both types of anaesthetic. Minor variations, such as an increase in potassium and a reduction in glucose with isoflurane were seen, but there was no consistent trend. Examination of the liver, kidneys, heart and lungs did not reveal any changes that were considered to be associated with either anaesthetic. Blood was taken for prolactin analysis from a subgroup of animals at 12 weeks of age anaesthetised with ether or isoflurane, and from tail-bled animals without anaesthesia, these animals being killed at 17 weeks of age for histological examination. The level of prolactin at 12 weeks of age was reduced in the isoflurane group particularly in the males. This is considered to indicate that there was less stress. Based on these results, isoflurane is proposed as a suitable alternative to ether.