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Calcium- and glucose- dependent pulsatility of LHRH release from the rat hypothalamus in vitro

We have recently shown the pulsatile pattern of LHRH release in vitro from the retrochiasmatic hypothalamus (RCH) of male rats and the increased frequency of these LHRH pulses before puberty (Endocrinology, May 1984). Additional experiments were carried out to evaluate the specificity of the in vitro observations. Single, unagitated RCH removed from pubertal rats were immediately incubated in 0.5 ml Dulbecco's Modified Eagle's Medium (DMEM) renewed every 7.5-min period. In these serial samples, the release of LHRH was determined using a highly sensitive RIA. A significant pulse was ≥ 6 pg/7.5 min (4 variation coefficients of the recovery of synthetic LHRH). In control conditions (DMEM with 1.25 mM Ca++ and 25 mM glucose), a depolarization by 20 or 50 μM veratridine (n=69) induced a marked increase (p < 0.001) in LHRH release (19.8 pg/7.5 min). The mean response to veratridine was significantly lowered to 5.7, 1.5 and 2.8 pg/7.5 min, in the presence of 5.6 mM 2-deoxyglucose (n=28), 20 mM EGTA (n=10) and 0.1 mM D-600, a calcium channel blocker (n=11) respectively. In control conditions, the mean frequency of spontaneous LHRH pulses was 2.8/2h. A significantly reduced frequency (1.1, 0.2 and 0.3 pulses/2 h) was observed with 2-deoxyglucose, EGTA and D-600. In conclusion, the availability of Ca++ and, to a lesser extent, glucose, may determine the occurrence of pulses in LHRH release from the RCH, either spontaneously or induced by a depolarization, in vitro.