In the central role of GnRH in the regulation of reproductive functions: mechanism of action and practical results.

The regulation of reproductive functions is influenced by several hormones. The hypothalamic hormone GnRH has a central role in reproduction. Several superactive and inhibitory analogs of GnRH synthesized in our laboratory showed use in animal breeding. GnRH was suggested to be degraded by the hypothalamus itself and also by the pituitary. We have used cultured fetal hypothalamic cells, and cultured pituitary cells to study the storage, the release and the action of this neuropeptide. It was found that neither the cultured hypothalamic nor the pituitary cells degrade GnRH, and pretreatment of these cultured cells with steroids do not induce GnRH degradation. The basal GnRH secretion from the cultured hypothalamic cells was increased by steroid pretreatment while the neurotransmitter induced GnRH release did not change. At the pituitary level it was found that GnRH regulates its own effect by priming or desensitizing gonadotropin release depending on the pretreatment time or the concentration of GnRH. The self-regulatory action of GnRH follows a similar pattern for both LH and FSH release.