Identification and Measurement of LH-RH in Biological Fluids by Radioimmunoassay
Zeitschrift für Naturforschung C - A Journal of Biosciences
Abstracts In terms of percentage of the basal value, LH in crement was more in the pre-pubertal (54 fold) than seen in the adults (32 fold), whereas the FSH in crement was just opposite, being 2.5 fold for the pre-pubertal and 4.2 fold for the mature animals. Prior treatment of the animals with sex steroids and gonadotropins upset the steroid-gonadotropin feed back mechanism, and great divurgence emerged be tween immature and mature animals when LH-RH was infused in them. The significance of
... s dif ference in the observed response during mammalian sexual maturation is discussed. Kindly supported by DFG (Gu 109/9). Feedback control involves regulation predominant ly by circulating levels of hormones. There are stimulatory and inhibitory as well as internal and external forms of feedback. In the classic external feedback the controlling signals are the hormones produced by the peripheral target glands. The re ceptors which respond to changes in circulating steroid levels by initiating a change in the secretion of gonadotropins are located in the basal medial hypothalamus, anterior hypothalamus and preoptic area as well as the anterior pituitary. The stimula tory effects of gonadal steroids which are thought to bring about ovulation in the normal animal are presumably mediated in the suprachiasmatic region and preoptic area. It is postulated that a noradrener gic synapse mediates the stimulatory effects of estrogen and progesterone on the ovulatory release of gonadotropins (cyclic release center). The ar cuate nucleus-median eminence dopaminergic tract may be involved in the so-called tonic discharge of gonadotropins and in the negative feedback action of gonadal steroids. Sex steroids also affect the response to natural and synthetic LRH. Complex interaction of sex steroids both in the hypothalamus and pituitary may evoke differential release of LH and FSH thus indicating the possible existence of separate con trol mechanisms for LH and FSH. There is recent evidence for short feedback loops, also referred to as auto or internal feedback. Short systems are involved in the regulation of LH and FSH secretion. LH via an effect on the basal median eminence seems to inhibit its on secretion. Inhibitory as well as stimulatory short feedback mechanisms have been described for the control of FSH secretion. This positive short feedback appears to be peculiar for immature animals and may play a role at the time of puberty. Finally, a third type described as ultrashort feed back has been found for the control of the gonado tropin releasing hormone on its own production. There are data indicating that hypothalamic LRH content is increased following small doses of chroni cally applied synthetic LRH in rodents under con ditions which do not alter circulating gonadotropins or pituitary sensitivity to LRH. Control systems concepts have become wide spread among reproductive neuro-endocrinologists. No sufficiently reliable data exist today which could be used to successfully apply the systems analysis approach. A radioimmunoassay for LH-RH has been de veloped using the following reagents: Synthetic LH-RH decapeptide (Hoechst) as standard; an anti serum raised in a rat to the des-glu1, his2-octapeptide of LH-RH conjugated to albumin; [12oI]labelled LH-RH decapeptide; ethanol precipitation is used to separate free and bound fractions. The assay is highly specific for LH-RH and parti cularly for the C-terminus of the molecule; lack of the C-terminal amide group results in a complete loss of immunoreactivity. The sensitivity of the as say is 0.5 pg of LH-RH. Assay of hypothalamic extracts after gel filtra tion, thin-layer chromatography and ion-exchange chromatography has shown that synthetic LH-RH and mammalian and avian LH-RH are immunochemically and chromatographically identical.