[Role of tricyclic antidepressants in the central regulation of hyperalgesia and stress analgesia].

The effect of hypophysectomy (HE) on pain thresholds was studied in female noninbred rats. Hyperalgesia was observed after HE since the first till the sixth day of the observation period. Droperidol (1 mg/kg i.p.) and amitryptyline (5 mg/kg i.p.) produced hyperalgesia in sham-operated rats, which was potentiated in hypophysectomized animals. In rats taken into the experiment 3 days after operation, no increase in the pain threshold was recordable during the 30-minute painful stress, and poststress autoanalgesia did not develop subsequently. The opposing data were obtained in sham-operated animals. On intraperitoneal administration of phentanyl (25 micrograms/kg) after the 30-minute painful stress hypophysectomized rats did not manifest any potentiation of its analgesic effect in contradistinction to sham-operated animals. Simultaneous administration of phentanyl at the same dose and melipramine (5 mg/kg i.p.) produced considerable potentiation of analgesia if administered after stress. In hypophysectomized rats, that effect was somewhat reduced.