The Female Athlete Triad by Catherine M. Gordon & Meryl S. LeBoff

Author:Catherine M. Gordon & Meryl S. LeBoff
Language: eng
Format: epub
Publisher: Springer US, Boston, MA

Gonadotropin-Releasing Hormone

Gonadotropin-releasing hormone (GnRH) plays a key role in regulating reproductive functioning. It is released by the arcuate nucleus in the hypothalamus in pulses that occur every 60–90 min in the follicular phase and every 120–360 min in the luteal phase of the menstrual cycle, and the precise frequency and amplitude of GnRH pulses is critical for proper HPO axis functioning [6]. The pattern of GnRH pulses coordinates pulsatile release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary. LH and FSH subsequently induce production of a variety of hormones including estradiol, progesterone, androstenedione, testosterone, inhibin, activin, and insulin-like growth factor-I (IGF-I).

Aberrations in GnRH pulsatility disrupt secretion of LH and FSH. Abnormal GnRH pulse patterns in FHA include alterations in pulse frequency or amplitude, or both [7]. Many hormones and neurotransmitters can modulate GnRH secretion, indicating that the control of GnRH release patterns is complex. These include the gonadal steroids (with positive and negative feedback effects on GnRH pulsatility), as well as prolactin, corticotropin-releasing hormone (CRH), neuropeptide Y (NPY), catecholamines, and opiates. Some factors, such as CRH and NPY, not only act directly on the hypothalamic GnRH pulse generator, but also on areas that affect caloric consumption and appetite. In turn, appetite-regulating hormones such as leptin, ghrelin, and peptide YY (PYY) can impact GnRH pulsatility, as can hormones such as insulin and IGF-I [8]. Figure 6.1 is a schematic of some of the hormonal interactions in FHA.

Fig. 6.1Hormonal and other changes in patients with hypothalamic amenorrhea. In patients with hypothalamic amenorrhea, there are alterations of hormones and other factors that affect the secretion of gonadotropin-releasing hormone (GnRH), including low levels of leptin and high levels of both ghrelin and neuropeptide Y (NPY). Β-endorphin, corticotropin-releasing hormone (CRH), dopamine, and γ-aminobutyric acid (GABA) are factors that negatively influence GnRH secretion. Some of these factors may also serve as hunger signals from the peripheral to the central nervous system and as links between nutrition and reproduction. Hallmark findings in adolescents and young women with hypothalamic amenorrhea include overactivity of the hypothalamic–pituitary–adrenal axis, suppression of the hypothalamic–pituitary–adrenal axis, and alterations in thyroid hormone regulation. FSH follicle-stimulating hormone, LH luteinizing hormone, TSH thyrotropin, and T 3 triiodothyronine. (Reprinted from Gordon CM. Clinical practice. Functional hypothalamic amenorrhea. N Engl J Med. 2010;363(4):365–71, with permission from Massachusetts Medical Society)

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