CIRCADIAN VARIATIONS OF PITUITARY ?-ENDORPHIN-LIKE IMMUNOREACTIVITY AND ITS RELATIONSHIP TO THE PAIN THRESHOLD IN RATS / 解剖学报

ABSTRACT

Immunohistochemical method, immuno-electron microscopic technique and radioimmunoassay (RIA) were used for the demonstration of ?-endorphin-like immunoreactivity (?-EP-IR) and of the circadian variation of the ?-EP-IR level in rat pituitary. ?-ER-IR was located in all cells of the pituitary intermediate lobe. A few ?-ER-IR-positive cells were scattered in the anterior lobe, and no positive immunoreactivity was found in the posterior lobe. The controls were negative. Under electron microscope, ?-ER-IR-positive dense particles were mostly located in the secretion granules, and a few of them were scattered freely in the cytoplasm of the intermediate lobe cells. Both pituitary ?-EP-IR concentration and the basal pain threshold in rat showed circadian variations in the experiment done at 4-hr intervals over a 24-hr period (P