[Stress responses of the ACTH-corticosterone and LH-testosterone systems in male rats given naloxone].

A single injection of naloxone (1 mg/kg s. c.) increased plasma baseline levels by 6 times for ACTH, 17 times for corticosterone, 3 times for LH and 2 times for testosterone. A concomitant ether-stress induced a further 6 fold increment in ACTH and an additional 2 fold increment in corticosterone, both hormones attaining their similar levels to those after ether-stress alone. On the other hand no further increment was observed for LH and testosterone, which actually were more stimulated by naloxone than by stress alone. The tonic inhibition exerted by endogenous opiates on ACTH and LH appears, therefore, to interfere with stress in a different way for the two neuroendocrine systems considered.