Gonadotropin-releasing hormone radioimmunoassay and its measurement in normal human plasma, secondary amenorrhea, and postmenopausal syndrome

Advances and perspectives in the analytical technology for small peptide hormones analysis: A glimpse to gonadorelin

In the last twenty years, we have witnessed an important evolution of bioanalytical approaches moving from conventional lab bench instrumentation to simpler, easy-to-use techniques to deliver analytical responses on-site, with reduced analysis times and costs. In this frame, affinity reagents production has also jointly advanced from natural receptors to biomimetic, abiotic receptors, animal-free produced. Among biomimetic ones, aptamers, and molecular imprinted polymers (MIPs) play a leading role. Herein, our motivation is to provide insights into the evolution of conventional and innovative analytical approaches based on chromatography, immunochemistry, and affinity sensing referred to as peptide hormones. Indeed, the analysis of peptide hormones represents a current challenge for biomedical, pharmaceutical, and anti-doping analysis. Specifically, as a paradigmatic example, we report the case of gonadorelin, a neuropeptide that in recent years has drawn a lot of attention as a therapeutic drug misused in doping practices during sports competitions.

Changes in peripheral blood levels and pulse frequencies of GnRH in patients with hypopituitarism

Pituitary dysfunction occasionally results from brain tumors or the surgical resection of brain tumors. The authors examined two patients with hypogonadotropic secondary amenorrhea, who had undergone surgical removal of brain tumors. Changes in immunoreactive gonadotropin-releasing hormone (GnRH) secretion are of interest in patients with a gonadotropin and gonadal steroid deficit, because both steroid and pituitary feedback systems are altered by tumors or tumor resection. The authors thus measured GnRH, luteinizing hormone, and follicle-stimulating hormone levels every 15 minutes for 4 hours by radioimmunoassay and investigated qualitative and quantitative changes in the pulsatile patterns of these hormones in two hypogonadotropic hypogonadism patients. They also performed similar multiple measurements of GnRH in two normal cycle women in follicular phase and two postmenopausal women. The concentration of plasma GnRH in two hypopituitarism patients was compared with that in two normal cycle women and two postmenopausal women. The study showed that the peripheral blood level of GnRH was significantly lower in two hypopituitarism patients than in both normal cycle and postmenopausal women, and that the pulsatile frequency was not different among these three groups. These findings suggest that alteration of feedback systems results in a decrease in the blood level of GnRH, and that pulses of GnRH maintain normal fluctuation despite the alteration of the hormonal circumstances in two hypogonadotropic hypogonadism patients.

Estrogen induced enhancement of LHRH clearance in amenorrheic women

In order to assess the effect of estrogen administration on LHRH metabolism in human plasma, plasma LHRH levels were determined in six amenorrheic women following iv injection of 500 ng synthetic LHRH before and after im injection of 5 mg estradiol benzoate (EB) for 4 days. The plasma levels of LHRH reached a maximum 1.25 min after LHRH administration, and they rapidly decreased in both situations. The initial disappearance of LHRH after EB treatment (half-life = 1.87 +/- 0.15 min) was significantly (p less than 0.05) more rapid than that before treatment (half-life = 2.45 +/- 0.21 min). The mean basal levels of plasma estradiol significantly (p less than 0.05) increased from 15.2 pg/ml to 4,387 pg/ml after EB treatment. Gonadotropin response to LHRH after EB treatment were not different from those before treatment. These data suggest that exogenous estrogen may stimulate the clearance of LHRH from the plasma of amenorrheic women.

Plasma luteinizing hormone-releasing hormone levels in normal women and patients with amenorrhea

Plasma levels of immunoreactive luteinizing hormone-releasing hormone (LH-RH) in 89 women with normal menstrual cycles and 109 patients with amenorrhea of various etiologies were determined by specific radioimmunoassay after methanol extraction. The LH-RH levels in patients with hypergonadotropism and Sheehan's syndrome were more than 10 pg/ml, and were significantly higher than basal levels during normal cycles (4.2 +/- 0.3 pg/ml). The mean levels of LH-RH were low in all hypogonadotropic patients with amenorrhea, with the exception of a few patients who showed high LH-RH levels suggestive of a pituitary lesion. The LH-RH levels in patients with polycystic ovary syndrome were comparable with basal levels during normal cycles. It is concluded that, although there is considerable overlap of the plasma LH-RH levels in each group of amenorrheic patients divided according to gonadotropin level, determination of LH-RH levels may be useful for the differentiation of hypothalamic amenorrhea from pituitary amenorrhea.

The effect of gonadotropin-releasing hormone on blood glucose insulin, luteinizing hormone, and follicle-stimulating hormone levels

Sixteen women volunteers with menstrual irregularities were studied with an intravenous injection of 100 microgram of gonadotropin-releasing hormone (GNRH). Serial blood samples were obtained for 2 hours after the injection and assayed for their concentration of glucose, insulin, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). There was a significant increase in the levels of both gonadotropins following the injection, with the peak for LH occurring at 30 minutes and the peak for FSH occurring at 90 minutes. There was a slight decrease in the glucose level at 45 minutes and in the insulin levels at 60 and 120 minutes. Because GNRH causes only minor changes in these parameters of carbohydrate metabolism, it would appear to be safe to use in women with ovulatory abnormalities secondary to diabetes mellitus.