ABSTRACT
It is well established that release of posterior pituitary hormones is also regulated at the level of the neurohypophysis (1 ,2). Many endogenous substances are involved in this regulation. The release of oxytocin is under inhibitory control of endogenous opioids (3). Furthermore, the opioid-binding sites in the nerve terminals are predominantly K, and substances interfering with K-receptors (i.e., dynorphin and some selective K-receptor agonists) inhibit the evoked release of oxytocin and vasopressin from the isolated neurohypophysis and from isolated nerve terminals (4,5), indicating the presence of functional K-receptors on terminals of oxytocin and vasopressin neurons.
