Pulsatile beta-endorphin release from the human pituitary in vitro

An in vitro perifusion system was used to characterize spontaneous immunoreactive beta-endorphin (i beta-END) release from 10 human fetal (20-23 weeks gestation) and 2 human adult anterior pituitaries. Spontaneous i beta-END release from fetal anterior pituitaries was pulsatile, with a mean (+/- SE) pulse interval of 9.1 +/- 0.5 minutes, pulse amplitude of 120.8 +/- 46.1 pg with nadir to peak increment of 106.0 +/- 32.9%, and overall release rate of 209.7 +/- 65.0 pg/2 minutes. Blockade of calcium activity with 10 microM verapamil and 4 mM EGTA suppressed the frequency and amplitude of the spontaneous pulsatile i beta-endorphin release (n = 2). Administration of 2 nM human CRF for 20 minutes at the end of 2 perfusions induced 205 and 883% increases of i beta-END release over the preceding basal levels. Administration of 2 nM CRF for 50 minutes at the end of another perifusion led to a greater and prolonged increase (maximum 4620% relative to the immediately preceding basal level) in i beta-END release. Addition of 56 mM KCl during the last 20 minutes of this prolonged CRF stimulation further increased i beta-END release (to 7680% relative to the baseline preceding the CRF stimulation). Each of 4 quarters of adult anterior pituitaries (2 quarters each from 1 male and 1 female) also released i beta-END in a pulsatile fashion, with a pulse interval of 11.8 +/- 2.0 minutes, pulse amplitude of 7.4 +/- 0.8 ng with nadir to peak increment of 51.4 +/- 15.3%, and overall release rate of 21.7 +/- 2.9 ng/2 minutes. These studies demonstrate that i beta-END release from the isolated human anterior pituitary in vitro is characterized by high-frequency pulses, independent of hypothalamic stimulation. This spontaneous calcium-dependent pulsatile i beta-END release apparently reflects the activity of an intrapituitary pulse-generating mechanism.