Autonomous /3-endorphin secretion from the pituitary neurointermediate lobe: in vivo studies

The existence of independent control mechanisms of /3-endorphin (/3-EP) secretion from the anterior (AP) and intermediate (NIL) pituitary lobes is now ascertained. The aim of this study was to evaluate the effect of surgical separation from the hypothalamus of the two pituitary lobes on /3-EP secretion. Two experimental models of surgical hypothalamo-pituitary disconnection were used: 1) rats with ablation of the medial basal hypothalamus (MBH); 2) rats bearing two entire ectopic pituitaries or two anterior pituitaries (APs) only, transplanted under the kidney capsule. In rats with MBH-ablation plasma /3-EP levels were significantly higher than in sham-operated controls. Plasma /3-EP levels increased in rats transplanted with entire pituitaries 3 days after surgery and were still elevated after 1 week. In rats transplanted with APs only, no significant /3-EP changes in plasma were evident. In both experimental conditions no significant difference was present in /3-LPH plasma levels. Concentrations of /3-EP in the ectopic NILs decreased gradually after transplantation. In all these results indicate that the NIL but not the AP is capable, when is disconnected from the hypothalamus, of secreting autonomously /3-EP.