Regulation of immunoreactive beta-endorphin release from rat pituitary cell culture

The release of immunoreactive beta-endorphin from rat anterior pituitary cells in culture was studied by radioimmunoassay and gel-filtration chromatography. Two forms of immunoreactivity were detected corresponding to beta-lipotrophin (beta-LPH) and beta-endorphin. Cells were found to release beta-endorphin-like immunoreactivity (beta-endorphin LIR) into the culture medium for up to 10 days with a trough in release occurring between days 2-4. The ratio of beta-LPH to beta-endorphin released remained constant during the course of culture. After 4 days in culture beta-endorphin LIR release was constant and responsive to modulation. Incubation with lysine-vasopressin (0.1 units/ml) produced a two- to threefold increase in release and dexamethasone (10 (-6) mol/l) suppressed release to 33% of controls. Neither stimulation nor suppression resulted in a change in the ratio of beta-LPH to beta-endorphin released. Dexamethasone suppression was not overcome by removal of dexamethasone or addition of vasopressin.