Effect of intermittent versus continuous infusion of progesterone on LHRH release in vivo from the rat mediobasal hypothalamus.
1989
Kim K.G.
Present study examined the effect of intermittent versus continuous infusion of progesterone (P) on LHRH release in vivo from the mediobasal hypothalamus of ovariectomized, estradiol-primed adult rats bearing push-pull cannulae. Three experimental groups were studied: 1) control (perfusion medium only), 2) intermittent perfusion of P (10-min on, 20-min off), and 3) continuous perfusion of P. P (10 ng/ml) was directly infused into the MBH following a 3 hr basal collection. Perfusates were collected at 10 min intervals on ice and LHRH release was measured by LHRH radioimmunoassay. Cycle detector analysis revealed that the spontaneous LHRH output in the control group was pulsatile over a 7 hr push-pull perfusion period. The mean basal LHRH release, pulse amplitude and pulse period were 0.68 +- 0.03 pg/10 min, 1.15 +- 0.08 pg and 60 +- 9 min, respectively. Intermittent perfusion of P clearly stimulated the mean LHRH release (pre-P vs post-P: 1.14 +- 0.18 vs 1.99 +- 0.53 pg) without changes in LHRH pulse frequency. In contrast to intermittent infusion of P, continuous administration of P failed to modify LHRH release, since the mean LHRH release and pulse amplitude between pre-P and post-P perfusion were similar. The in vivo study clearly showed that intermittent, but not continuous administration of P is effective in stimulating LHRH release. Therefore, it appears that rhythmic secretion of P may be the effective signal for activating the neural LHRH apparatus.
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