In vitro release of hypothalamic beta-endorphin (beta E) by arginine vasopressin, corticotropin-releasing hormone and 5-hydroxytryptamine: evidence for release of opioid active and inactive beta E forms.

The aims of the present experiments were: 1) to test whether substances which modulate beta-endorphin-immunoreactive (beta E-ir) release from the pituitary gland might act similarly in hypothalamic tissue; and 2) to further characterize the beta E-ir forms which are released from hypothalamus. To address these questions, hypothalamic tissue was incubated in vitro for 10 min periods in either normal media (basal conditions) or in media containing 55 mM KCl or one of several other test substances (stimulation conditions) and release was estimated by measuring the beta E-ir concentrations in the media. Depolarizing concentrations of K+ increased beta E-ir release 2-3 fold over basal levels and this effect appeared to be Ca2(+)-dependent. Dose-dependent increases in beta E-ir release were elicited by nanonolar to micromolar concentrations of either corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), or 5-hydroxytryptamine (5-HT). Conversely, dopamine (1 microM) inhibited both the basal and K(+)-stimulated release of beta E-ir from hypothalamus. Gel filtration chromatography revealed that beta E1-31 and beta E1-27/beta E1-26 were the primary beta E-ir peptides released under either basal or CRH-stimulated conditions; the relative amounts of the beta E-ir peptides found in the media were nearly identical to those found in the hypothalamus itself. This result indicates that the release of different beta E-ir peptides into the media appears to be proportional to the relative amounts stored in tissue.(ABSTRACT TRUNCATED AT 250 WORDS)