Intrinsic pulsatility of luteinizing hormone release from the human pituitary in vitro

An in vitro perifusion system was used to investigate the spontaneous luteinizing hormone (LH) release from 10 human fetal (21-23 weeks of gestation) and 1 adult female pituitaries. The pattern of LH release from fetal pituitaries (n = 6) exhibited a remarkable pulsatile character with a mean (+/- SE) pulse interval of 12.7 +/- 1.7 min. The mean pulse amplitude was 5.2 +/- 0.9 mIU with a nadir to peak increment of 69.5 +/- 6.4%. The mean LH release rate was 12.3 +/- 3.3 mIU/2 min. Blockade of calcium activity with 0.1 mM verapamil and 4 mM EGTA suppressed the frequency (from 1 pulse/12-20 min to 1 pulse/50-100 min) and amplitude (from 5.4-5.7 mIU to 1.4-2.1 mIU) of this spontaneous pulsatile LH release (n = 2). Administration of 8 nM gonadotropin-releasing hormone induced 255 and 954% increases in LH secretion (n = 2). Each quarter of an adult human pituitary also secreted LH in a pulsatile fashion, with a pulse interval of 15.2 +/- 5.6 min, a pulse amplitude of 5.4 +/- 0.6 mIU, a nadir to peak increment of 67.5 +/- 5.2%, and an overall release rate of 14.8 +/- 0.9 mIU/2 min. These studies demonstrate that LH release from the isolated human pituitary in vitro is characterized by high-frequency/low-amplitude pulses, independent of hypothalamic stimulation. Accordingly, this spontaneous calcium-mediated pulsatile LH release apparently reflects the activity of an intrinsic intrapituitary pulse-generating mechanism.