Naloxone effects on a nociceptive response of hypophysectomized and adrenalectomized mice

Naloxone (1 and 3 mg/kg) or saline was administered to adrenalectomized, sham-adrenalectomized, hypophysectomized, and sham-hypophysectomized mice prior to placing them on a 55° C hot plate. Naloxone reduced the jump latency of the adrenalectomized, sham-adrenalectomized, and sham-hypophysectomized mice, but did not reduce the jump latency of hypophysectomized mice. Hypophysectomy and adrenalectomy $\text{per se}$ did not significantly affect the jump latency. These results indicate that the pituitary is necessary for naloxone to reduce the escape latency of mice on the hot plate. The possibility of a hyperalgesic factor is suggested.