Suppression of testicular function by chronic stress in macaque monkeys.

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Five sexually mature, male Japanese monkeys (Macaca fuscata fuscata), at least 8 yrs old were used. They were housed in an each outdoor social group cage with some females at the Primate Research Institute, Kyoto University, Japan. After two weeks of blood sampling, they were isolated from a social group to an indoor air-conditioned individual cage in the mid breeding season. After two weeks these males were returned to their home cages. Blood samples were obtained following both the removal and the return two weeks later. Plasma concentrations of luteinizing hormone(LH), testosterone, cortisol, prolactin, and inhibin were determined by specific radioimmunoassays. Plasma concentrations of testosterone were significantly increased after the isolation, whereas cortisol levels were decreased. Following after return to their home cage, these changes were recovered. The absence of a stress response to separation in adult males is in contrast to the presence of a stress response observed in infants, juveniles, and adult females and possibly is due to the differences of environmental temperature.In the next bleeding season, same monkeys were isolated from a social group to an outdoor individual cage. After two weeks isolation, they were returned to their home cages. Blood samples were obtained in the same manner. Plasma testosterone were significantly increased immediately after both isolation and return, but decreased within the isolation period. In contrast with the previous study, plasma cortisol were elevated immediately after both isolation and return. Plasma LH, prolactin, and inhibin were not changed before and after the isolation. These results showed that the isolation was influenced these males as a stressor. Furthermore, the return to the social group did induce a psychosocial stress response in the males and the degree of the stress.