Effect of in vivo pre-treatment with oestradiol and either GnRH, GnRH agonistic analog or GnRH antagonistic analog on GnRH-stimulated secretion of LH in vitro

In vivo treatment with GnRH or with GnRH agonistic analog (AG), but not with GnRH antagonistic analog (ANT), depleted the LH stores of the rat pituitary gland. This depletion was potentiated by oestradiol. Oestradiol augmented the in vitro LH response of the pituitary gland to GnRH. This augmenting effect of oestradiol became smaller with increasing rates of in vivo administration of GnRH or AG, but not with ANT. With respect to both depletion of the LH stores and suppression of the augmenting effect of oestradiol, AG ist about 20 times as potent as GnRH.     

Comparison of the time courses of luteinizing hormone (LH) secretion rates during continuous stimulation by LH-releasing hormone (LH-RH) in vivo and in vitro

Summary The patterns of LH secretion during constant stimulation of the pituitary glands of estradiol-treated ovariectomized rats with a maximally stimulating amount of LH-RH in vivo and in vitro correspond with each other qualitatively and quantitatively. In vitro the changes with time of the LH secretion rate are somewhat retarded, especially the occurrence of desensitization.