Serum Levels of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) in Subjects Accidentally Exposed to 192Ir Gamma rays
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Serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay in 6 subjects who had been exposed accidentally to 192Ir gamma rays. All subjects showed normal levels of LH and FSH shortly after the irradiation. From 100 to 150 days post-irradiation, however, serum FSH levels increased in subjects who received 12.2 rad or more, a finding in agreement with the decrease in sperm concentration below 10 millions/ml, while in the other 2 subjects who received 9.8 and 10.9 rad, it remained within normal range. The elevation in serum FSH levels in one of the severely exposed subjects (Y. S.) was noted as late as 413 days after the exposure, while the hormone levels in the all other cases declined toward normal level.Keywords:
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Luteinizing hormone-releasing hormone (LHRH) induces two Ca2+ responses in single gonadotropes: a Ca2+ spike/plateau or oscillation. Similar receptor-mediated Ca2+ signals have been reported in many cell types but their functional significance is obscure. Accordingly, we have determined the concentration-response properties of LHRH-induced luteinizing hormone (LH) release at the single cell level. We demonstrate a critical single cell LHRH threshold for LH release. Each gonadotrope had a particular LHRH threshold value and a range of different single cell thresholds was distributed in the gonadotrope population. The physiological significance of the threshold was demonstrated by a striking reduction (delta ED50 = 153 nM) of the LHRH threshold immediately before the preovulatory surge of LH release. The metestrous phenotype of secretion resembled a quantal process in contrast with the graded process of the proestrous phenotype. That is, the quantity of hormone secreted per metestrous gonadotrope was independent of LHRH concentration and more all-or-none than graded. The LHRH threshold and the quantal secretion process of metestrous gonadotropes was further studied by measuring cytosolic Ca2+ using fura-2 and digital imaging microscopy. We provide evidence suggesting that the Ca2+ spike/plateau and oscillation are the respective responses to subthreshold and suprathreshold concentrations of LHRH. It is proposed therefore that the Ca2+ oscillation and spike/plateau response form a binary intracellular signaling code that functions as an on-off switch. It is further proposed that this potential code unraveled here for the regulation of hormone secretion may also regulate other gonadotrope functions. Thus, while the Ca2+ spike/plateau response is strongly associated with LH release, it may be associated with reduced levels of LH-beta mRNA, and reduced numbers of LHRH receptors. Conversely, while the Ca2+ oscillation appears to be unrelated to LH release, it may be associated with increased levels of LH-beta mRNA, and increased numbers of LHRH receptors. This model may explain in molecular terms the long-standing observation that an invariant, albeit pulsatile, pattern of LHRH release is sufficient to support the preovulatory surge of LH release.
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A combined radioimmunoassay (RIA) for the measurement of the anterior pituitary proteins luteinizing hormone (LH) and prolactin (PRL) is described and compared with individual RIAs for these hormones. The standard curves and the sample values for LH and PRL were identical when determined in a combined or in an individual RIA. This technique may prove useful to a number of laboratories where it is desirable to determine levels of more than one hormone in limited sample volumes.
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A sensitive and specific radioimmunoassay technique for quantitating human luteinizing hormone (LH) is described. Purified human pituitary LH is used for the development of antibodies, for radioiodination and for standards. A good correlation was seen between biological and immunological potency estimates of a number of pituitary extracts varying greatly in their LH and FSH contents. This method, when applied to serum, revealed differences in levels between normal adults and postmenopausal women. Cyclic variation was noted in the normally menstruating woman and the presence of LH in the serum of prepubertal children was also confirmed.
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The gonadotropin extracts of 24-hr samples of urine of a postmenopausal woman were assayed by a general gonadotropin assay and by assays for follicle stimulating and luteinizing activity. By each of the 3 assay systems it was found that there was a 2-fold fluctuation in the amount of gonadotropin excreted from day to day.
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Recent studies of luteinizing hormone-releasing hormone (LH-RH) are reviewed. A decapeptide isolated from porcine hypothalami was synthesized and shown to have LH-RH activity identical to that of the natural hormone. The hormone also had follicle stimulating hormone (FSH)-releasing activity and it was proposed that this hormone is the hypothalamic control for release of both LH and FSH from the anterior pituitary. Different plasma levels of LH and FSH were then investigated as a function of the interaction between LH-RH and the sex steroids. Clinical studies indicate that the hormone may be used to induce ovulation. Research done on LH-RH analogues is also reviewed.(AUTHORS MODIFIED)
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Although most gonadotropes synthesize both luteinizing hormone and follicle-stimulating hormone, the transcription, content, and secretion rates of the two gonadotropins can be separated. The signals external to the gonadotropic cells that appear to be important in the differential regulation are gonadotropin-releasing hormone pulse frequency (high pulse frequency favors luteinizing hormone), steroid feedback (works on both but induces a more powerful negative feedback on luteinizing hormone), and gonadal peptide feedback (activin increases follicle-stimulating hormone; inhibin and follistatin decrease it). We know very little about the pathways within the gonadotropes that favor one gonadotropin rather than another. It is expected that the cloning of the genes for both gonadotropins and the use of specific cell lines and transfections will lead to elucidation of these pathways.Key words: luteinizing hormone, follicle-stimulating hormone, gonadotropin-releasing hormone, inhibin, anterior pituitary, gonads.
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