Dynamics of circulating concentrations of gonadotropins and ovarian hormones throughout the menstrual cycle in the bonnet monkey: role of inhibin A in the regulation of follicle-stimulating hormone secretion

Assessment of ovarian follicular dynamics and folliculogenesis associated endocrine profiles following gonadotropin stimulation in the bonnet monkey

We evaluated ovarian follicular dynamics in bonnet monkeys by employing trans-abdominal ultrasonography. Following the administration of human follicle stimulating hormone (hFSH) and/or human menopausal gonadotropin (hMG), multiple follicular development was assessed and their numbers, size and growth profiles were monitored. The ultrasonograms showed that the follicular antrum appeared distinctly anechoic with well-defined hyperechoic borders. Depending on the type, quantity (12.5-25IU), and duration (6-9days) of hormones administered, the number of developing follicles was 2-12 per ovary with their lowest diameter being 2mm. With continued hormone administration, their numbers and diameters increased; which were more pronounced in animals administered with hFSH than with hMG, with follicles of 6-8mm. Interestingly, human chorionic gonadotropin (hCG) injection (2000-3000IU), when follicles acquiring >6-8mm sizes, induced the maximum expansion of antral follicles with sizes reaching up to 14mm. On days 3-5 post-hCG, the ultrasonograms showed loosely demarcated multiple hypoechoic structures and well-demarcated hyperechoic structures with anechoic/hypoechoic cores corresponding to unruptured luteinized follicles and corpora lutea, respectively. On day 4 post-hCG, there was a substantial reduction in the number of antral follicles. In stimulated animals, follicular growth, ovulation, and formation of luteal structures were accompanied by corresponding physiological changes in the serum estradiol and progesterone profiles. These findings, for the first time, showed that ultrasonographic imaging approach is useful for precise monitoring of temporal changes in follicular developmental dynamics and to time the hCG induced ovulation in the bonnet monkey.

Studies on reactivation of regressing bonnet monkey corpus luteum on day 1 of menses: a pilot study

Studies on functional characteristics of the regressing primate corpus luteum (CL) to luteotrophic stimulus on day 1 of the non-fertile menstrual cycle are scarce. Recombinant human luteinizing hormone (rhLH) (20 IU/Kg BW; n = 10) or human chorionic gonadotropin (hCG) (180 IU; n = 6) were administered intravenously to female bonnet monkeys on day 1 of menses. Exogenous treatment of rhLH or hCG caused a significant increase in circulating progesterone (P(4)) levels 2-4 hours post treatment (P < 0.05). Lutectomy prior to onset of menses confirmed that CL is the site of the increased P(4) concentrations. Increased levels of phosphorylated P44/42 MAPK, MKK3/6 activation and concomitant histological changes were observed within 4 hours in CL of monkeys receiving hCG treatment. The results from this study demonstrate the acute progesterone synthesizing capacity of regressing monkey CL after LH or hCG challenge. This has potential implications for interpreting the steroidogenic response after gonadotropin stimulation tests in the early follicular phase of the normal ovulatory and anovulatory women undergoing controlled ovarian stimulation protocols as part of assisted reproductive technology (ART) and in women with polycystic ovarian syndrome.

Luteinizing hormone regulates inhibin-α subunit expression through multiple signaling pathways involving steroidogenic factor-1 and beta-catenin in the macaque corpus luteum

We employed different experimental model systems to define the role of GATA4, beta-catenin, and steroidogenic factor (SF-1) transcriptional factors in the regulation of monkey luteal inhibin secretion. Reverse transcription polymerase chain reactions and western blotting analyses show high expression of inhibin-α, GATA4, and beta-catenin in corpus luteum (CL) of the mid-luteal phase. Gonadotropin-releasing hormone receptor antagonist-induced luteolysis model suggested the significance of luteinizing hormone (LH) in regulating these transcriptional factors. Inducible cyclic AMP early repressor mRNA expression was detected in the CL and no change was observed in different stages of CL. Following amino acid sequence analysis, interaction between SF-1 and beta-catenin in mid-stage CL was verified by reciprocal co-immunoprecipitation experiments coupled to immunoblot analysis. Electrophoretic mobility shift analysis support the role of SF-1 in regulating luteal inhibin-α expression. Our results suggest a possible multiple crosstalk of Wnt, cAMP, and SF-1 in the regulation of luteal inhibin secretion.

The effect of progesterone replacement on gene expression in the corpus luteum during induced regression and late luteal phase in the bonnet monkey (Macaca radiata)

BACKGROUND

In higher primates, although LH/CG play a critical role in the control of corpus luteum (CL) function, the direct effects of progesterone (P4) in the maintenance of CL structure and function are unclear. Several experiments were conducted in the bonnet monkey to examine direct effects of P4 on gene expression changes in the CL, during induced luteolysis and the late luteal phase of natural cycles.

METHODS

To identify differentially expressed genes encoding PR, PR binding factors, cofactors and PR downstream signaling target genes, the genome-wide analysis data generated in CL of monkeys after LH/P4 depletion and LH replacement were mined and validated by real-time RT-PCR analysis. Initially, expression of these P4 related genes were determined in CL during different stages of luteal phase. The recently reported model system of induced luteolysis, yet capable of responsive to tropic support, afforded an ideal situation to examine direct effects of P4 on structure and function of CL. For this purpose, P4 was infused via ALZET pumps into monkeys 24 h after LH/P4 depletion to maintain mid luteal phase circulating P4 concentration (P4 replacement). In another experiment, exogenous P4 was supplemented during late luteal phase to mimic early pregnancy.

RESULTS

Based on the published microarray data, 45 genes were identified to be commonly regulated by LH and P4. From these 19 genes belonging to PR signaling were selected to determine their expression in LH/P4 depletion and P4 replacement experiments. These 19 genes when analyzed revealed 8 genes to be directly responsive to P4, whereas the other genes to be regulated by both LH and P4. Progesterone supplementation for 24 h during the late luteal phase also showed changes in expression of 17 out of 19 genes examined.

CONCLUSION

These results taken together suggest that P4 regulates, directly or indirectly, expression of a number of genes involved in the CL structure and function.

New targets for old hormones: inhibins clinical role revisited

Inhibins are gonadal peptide hormones belonging to the transforming growth factor-β (TGF-β) superfamily that regulate the pituitary follicle stimulating hormone (FSH) secretion by negative feedback mechanisms. It is evident that the understanding of inhibins function in the hypothalamic-pituitary-gonadal axis will provide insights into physiology and pathology of the gonadal function. In recent years, a great deal of attention has been focussed on clinical relevance of measuring circulating inhibins in normal and disease state. The past few years also have witnessed the emergence and discovery of extra pituitary action of inhibins that might provide further insights into the underlying diseases like cancer especially in the reproductive axis and various other new endocrine target organs. In this review after systematic analysis of literature, we discuss briefly the known and recent advances in function of these hormones highlighting also its structure, production and mechanisms of signal transduction. Also this review discusses about the physiological relevance of inhibin association in the normal function to the development of reproductive cancers. Finally, we describe evidence from various emerging studies that inhibins make an important contribution to other physiological functions apart from reproduction which reveals new endocrine target organs of inhibins. The emerging view is inhibin participates in multiple ways to regulate the function in different cell types and still complete repertoire of its actions is under investigation.