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Development of the hypothalamic-pituitary-ovarian axis
1Department of Obstetrics & Gynecology, Helsinki University, Finland.
Insights
Puberty onset involves increased hypothalamic gonadotropin-releasing hormone (GnRH) activity, leading to higher luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. This process gradually shifts from sleep-entrained patterns to daytime pulsatility, activating ovarian steroidogenesis.
Area of Science:
- Reproductive Endocrinology
- Neuroendocrinology
- Pediatric Endocrinology
Background:
- Puberty onset is a complex, centrally regulated process with incompletely understood mechanisms.
- It involves activation of the hypothalamic GnRH pulse generator, leading to increased pituitary LH and FSH secretion.
- LH pulsatility is present in mid-childhood, particularly during sleep, and changes significantly at puberty.
Purpose of the Study:
- To elucidate the detailed mechanisms underlying the onset of puberty.
- To describe the changes in pulsatile secretion of gonadotropins (LH and FSH) during pubertal development.
- To understand the hormonal events, including steroidogenesis and ovarian function, during early puberty.
Main Methods:
- Observational study analyzing hormonal profiles (GnRH, LH, FSH, estradiol, androgens).
- Assessment of pulsatile secretion patterns of LH and FSH, including amplitude and frequency.
- Correlation of hormonal changes with pubertal progression and ovarian activity.
Main Results:
- Puberty onset is characterized by increased GnRH pulse generator activity, resulting in greater LH and FSH secretion, with amplitude increasing more than frequency.
- A shift occurs from sleep-entrained LH pulsatility to increased daytime pulsatility.
- Ovarian steroidogenesis is activated by increased LH, leading to elevated androgens and estrogens, with initial menstrual cycles often being anovulatory and luteal phase insufficiency common.
Conclusions:
- The onset of puberty is a dynamic neuroendocrine process involving significant alterations in gonadotropin pulsatility and ovarian function.
- Early pubertal development is marked by hormonal shifts that lead to initial reproductive acyclicity and potential luteal phase defects.
- Further research is needed to fully delineate the central mechanisms governing pubertal initiation.
Abstract:
The onset of puberty is a centrally driven process, the detailed mechanisms of which are not known. It is translated into an increased activity of the hypothalamic GnRH pulse generator. This in turn is seen as increased pituitary pulsatile secretion of LH and FSH. LH pulses are observed even in midchildhood, particularly after the onset of sleep. Onset of puberty is associated with a greater increase in LH pulse amplitude than frequency and a much greater increase in LH and FSH. A progressive increase in daytime pulsatility occurs, with a gradual reduction of sleep-entrained amplification. Prepubertal FSH concentrations are relatively high in girls, and continous ovarian follicular growth and atresia take place, with estradiol concentrations being higher than in boys. Only after the steep early pubertal increase in LH, ovarian steroidogenesis is activated, with increases in androgen and estrogen secretion. Under further FSH stimulation, follicular growth and maturation proceed. The first menstrual cycles are mostly anovulatory for 1 to 2 years. Luteal phase insufficiency is common the first five years after menarche.