EFFECTS OF SINGLE AND MULTIPLE INJECTIONS OF KETAMINE-HYDROCHLORIDE ON SERUM HORMONE CONCENTRATIONS IN MALE CYNOMOLGUS MONKEYS

Using simulated short- and long-term effect studies, we evaluated the effect of ketamine anesthesia on serum cortisol, testosterone, and imm unoreactive luteinizing hormone (ILH) and bioactive LH (BioLH) concent rations in adult male cynomolgus monkeys. Cortisol, testosterone, and ILH were measured by use of radioimmunoassay, and BioLH was measured b y use of a radioreceptor assay method, For the acute effect, the first group (eight monkeys) was given four successive intramuscular injecti ons of ketamine (10, 5, 5, and 5 mg/kg of body weight at 0, 30, 60, an d 110 min respectively), Blood samples were taken at 0, 15, 30, 45, 60 , and 120 min. For the long-term effect, the second group (10 monkeys) was given a single injection of ketamine (10 mg/kg) once a week for 4 consecutive weeks. Blood samples were taken 5 to 10 min after each in jection, then were used to determine the variation in hormone concentr ations among the monkeys (inter-individual variation) and within each monkey (intra-individual variation), There were no statistically signi ficant differences in serum cortisol, testosterone, ILH, and BioLH val ues between the first blood sample (before the ketamine injection) and sequential blood samples in monkeys of the first group. Although intr a-individual variation in the hormones (i.e., hormonal change within e ach monkey) was not statistically significant, inter-individual variat ion (among the monkeys) was significantly (0.00001 < P < 0.033) differ ent in monkeys of the second group. These results indicate that an ade quate number of animals must be used to minimize animal-to-animal vari ability. Our results confirm that ketamine is a suitable anesthetic ag ent to immobilize male cynomolgus monkeys in experimental studies (sho rt- and long-term studies) aimed at elucidating hormonal changes.