Abstract
The effect of an anesthetic, ketamine, on the serum prolactin level was examined in wild-originating female cynomolgus monkeys (Macaca fascicularis) imported from South East Asia. Serum prolactin levels were measured by the homologous radioimmunoassay system which was developed for human prolactin. The validity was confirmed by using an extract of pituitary gland from a female cynomolgus monkey as well as serum and amniotic fluid from a pregnant monkey. Additionally, serum luteinizing hormone (LH) levels were determined by the radioreceptorassay system developed in our laboratory using Leydig cells collected from rat's testes as a receptor fraction. The experiment was repeated three times at one-month interval, using twenty animals that were divided into three groups consisting of 5, 7 and 8 monkeys each. In the first experiment, the first group was injected with physiological saline and the second and third groups were intramuscularily given ketamine at a dose level of 5 mg/kg B. W, and 15 mg/kg B. W., respectively. In the second experiment, the first and second groups were given ketamine at a dose of 5 mg/kg B. W. and of 15 mg/kg B. W., respectively, and the third group was served as control injected with saline. In the third experiment, the first and third groups were administered with 15 mg/ kg and 5 mg/kg of ketamine and the second group was injected with saline. In short, all of the twenty monkeys received the three different treatments for two months. The serum prolactin level showed a marked increase after the administration of ketamine. However, this increase was observed only in half of the twenty monkeys and no change was observed in the remaining half. In contrast with the prolactin level, no effect was produced on the LH level by the administration of ketamine in all of the animals used. The effect of ketamine on prolactin secretion from pituitary gland in cynomolgus monkeys varied with every individuals. That is, the secretion of prolactin was significantly stimulated in some animals and was not in some other. The reason why this difference was existing among individuals is not clear as yet. However, the present study suggests that such an individual difference my explain a cause of discrepancy among the results of previous reports.
