Effects of corticosterone and testosterone on pituitary gonadotropin content, secretion, bioactivity and messenger RNA levels in the presence or absence of GnRH in male rats

Gut microbiome combined with metabolomics reveals biomarkers and pathways in central precocious puberty

BACKGROUND

Central precocious puberty (CPP) is a common disease in prepubertal children and results mainly from disorders in the endocrine system. Emerging evidence has highlighted the involvement of gut microbes in hormone secretion, but their roles and downstream metabolic pathways in CPP remain unknown.

METHODS

To explore the gut microbes and metabolism alterations in CPP, we performed the 16S rRNA sequencing and untargeted metabolomics profiling for 91 CPP patients and 59 healthy controls. Bioinformatics and statistical analyses, including the comparisons of alpha and beta diversity, abundances of microbes, were undertaken on the 16S rRNA gene sequences and metabolism profiling. Classifiers were constructed based on the microorganisms and metabolites. Functional and pathway enrichment analyses were performed for identification of the altered microorganisms and metabolites in CPP.

RESULTS

We integrated a multi-omics approach to investigate the alterations and functional characteristics of gut microbes and metabolites in CPP patients. The fecal microbiome profiles and fecal and blood metabolite profiles for 91 CPP patients and 59 healthy controls were generated and compared. We identified the altered microorganisms and metabolites during the development of CPP and constructed a machine learning-based classifier for distinguishing CPP. The Area Under Curves (AUCs) of the classifies were ranged from 0.832 to 1.00. In addition, functional analysis of the gut microbiota revealed that the nitric oxide synthesis was closely associated with the progression of CPP. Finally, we investigated the metabolic potential of gut microbes and discovered the genus Streptococcus could be a candidate molecular marker for CPP treatment.

CONCLUSIONS

Overall, we utilized multi-omics data from microorganisms and metabolites to build a classifier for discriminating CPP patients from the common populations and recognized potential therapeutic molecular markers for CPP through comprehensive analyses.

Glucocorticoid repression of the reproductive axis: effects on GnRH and gonadotropin subunit mRNA levels

Activation of the stress axis by glucocorticoids suppresses reproductive function in many species. Here, we performed studies to determine whether these effects are mediated at the level of the hypothalamus or pituitary or both, and to dissect the underlying molecular mechanisms, using two established rodent models. Rats were treated either chronically or acutely with glucocorticoids, and circulating gonadotropins, GnRH mRNA levels, and gonadotropin subunit mRNAs levels were measured. In model I, chronic treatment for 6 days with corticosterone (CORT) was used in adult intact male rats. CORT caused a significant decrease in serum LH but not FSH secretion compared to vehicle. Whereas pituitary LHbeta and FSHbeta mRNA levels were not affected by CORT treatment, hypothalamic GnRH mRNA was significantly decreased by 35-40%. In model II, acute blockade of the estradiol (E(2))-induced gonadotropin surge by dexamethasone (DEX) was used in 28-day-old female rats. DEX treatment resulted in substantially lower serum LH and FSH concentrations compared to vehicle, although DEX had no effect on GnRH mRNA and LHbeta mRNA levels. By contrast, FSHbeta mRNA levels were about 14-fold lower in DEX-treated females. Taken together, these results indicate that suppression of gonadotropin levels by chronic elevations in glucocorticoids/stress may be accounted for in part by suppression of GnRH mRNA levels, whereas short-term glucocorticoid treatment to block the gonadotropin surge appears to involve other mechanisms including decreased FSHbeta mRNA levels.

Effects of perinatal maternal food restriction on pituitary-gonadal axis and plasma leptin level in rat pup at birth and weaning and on timing of puberty

The effects of maternal 50% food restriction (FR) during the last week of gestation and/or lactation on pituitary-gonadal axis (at birth and weaning), on circulating levels of leptin (at weaning), and on the onset of puberty have been determined in rats at birth and at weaning. Maternal FR during pregnancy has no effect at term on the litter size, on the basal level of testosterone in male pups, and on the drastic surge of circulating testosterone that occurs 2 h after birth. At weaning, similar retardation of body growth is observed in male and female pups from mothers exposed to FR. This undernutrition induces the most drastic effects when it is performed during both gestation and lactation or during lactation alone. Drastic retardation of testicle growth with reduction of cross-sectional area and intratubular lumen of the seminiferous tubules is observed in male pups from mothers exposed to undernutrition during both gestation and lactation or during lactation alone. Maternal FR during the perinatal period reduces circulating levels of FSH in male pups without affecting LH and testosterone concentrations. Maternal FR does not affect circulating levels of LH, estradiol, and progesterone in female pups. Female pups from mothers exposed to FR during both gestation and lactation show a significant increase of plasma FSH as well as a drastic retardation of ovarian growth. The follicular population was also altered. The number of antral follicles of small size (vesicular follicles) was increased, although the number of antral follicles of large size (graafian follicles) was reduced. Maternal FR occurring during both late gestation and lactation (male and female pups), during lactation alone (male and female pups), or during late gestation (female pups) induces a drastic reduction of plasma leptin and fat mass in pups at weaning. The onset of puberty is delayed in pups of both sexes from mothers exposed to FR during lactation and during both gestation and lactation. In conclusion, these data demonstrate that a perinatal growth retardation induced by maternal FR has long-term consequences on both size and histology of the genitals, on plasma gonadotropins and leptin levels, on fat stores at weaning, and on the onset of puberty.

Dexamethasone or triamcinolone increases follicular development in immature female rats

We have previously reported that dexamethasone increased follicle-stimulating hormone (FSH) secretion via suppression of inhibin in immature female rats. In the present study, we investigated the effects of dexamethasone or triamcinolone on follicular development and ovarian functions (estradiol and inhibin secretion) in equine chorionic gonadotropin (eCG)-primed immature female rats. Dexamethasone significantly increased the number of ovulated oocytes in immature female rats treated with 5 i.u. eCG. Serum concentration of FSH in eCG-treated female rats was increased by administration of dexamethasone or triamcinolone, showing the peak value at 9 h after its administration, although the levels of inhibin markedly decreased at that time. Serum concentrations of inhibin and estradiol in eCG-treated female rats increased at 24 h after administration of dexamethasone or triamcinolone. These results demonstrate that dexamethasone or triamcinolone increases FSH secretion, and the excess amount of FSH strongly stimulates follicular development cooperating with exogenous eCG.

Dexamethasone increases follicle-stimulating hormone secretion via suppression of inhibin in rats

In the present study, the effects of dexamethasone on follicle-stimulating hormone (FSH) secretion in immature female rats were investigated. Dexamethasone increased the selective secretion of FSH and decreased plasma concentrations of inhibin in immature female rats. The effects of dexamethasone on FSH secretion were not confirmed in rats treated with ovariectomy or immunoneutralization against inhibin. In addition to the direct effect of dexamethasone on FSH synthesis in gonadotrophs, the present study has clearly demonstrated that the increased level of FSH in dexamethasone-treated rats is mediated by suppression of ovarian function, especially by the inhibition of inhibin secretion.

The 1994 Stevenson Award Lecture. Follicle-stimulating hormone and luteinizing hormone: a tale of two gonadotropins

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.