Neuroendocrinology · Hypothalamic Pituitary Axis
Schally AV et al., 1972 · Am J Obstet Gynecol
This article has been designed to review recent developments in the field of hypothalamic hormones involved in the control of reproductive functions. A brief resume of early physiologic and anatomic studies was presented initially to give a better understanding of the concept of hypothalamic regulation of the release of gonadotropic hormones from the pituitary gland. Recently, an advance was achieved with the isolation from porcine hypothalami of a decapeptide which has both FSH-releasing hormone (FSH-RH) activity and LH-releasing hormone (LH-RH) activity. Its amino acid sequence was determined to be (pyro) gluhis-trp-ser-tyr-gly-leu-arg-pro-gly-NH2. The decapeptide corresponding to this structure was synthesized and shown to stimulate the release of LH and of FSH in laboratory and domestic animals and human beings. Natural and synthetic FSH-RH/LH-RH also stimulated the synthesis of both gonadotropins in tissue cultures of rat pituitaries in vitro. It was postulated that this decapeptide represents the hypothalamic hormone which regulates the release of both LH and FSH from the anterior pituitary gland. Complex effects of sex steroids on the release of LH and FSH were reviewed briefly. It was suggested that the over-all control of secretion of FSH and LH is most likely mediated by the interaction of hypothalamic FSHand LH-releasing hormone with sex steroids. Clinical studies performed with natural and synthetic LH-RH/FSH-RH were reviewed. These studies, particularly induction of ovulation, suggest that LH-RH should find practical application in the treatment of sterility. Subsequent synthesis of LH-RH/FSH-RH by several laboratories and drug houses should provide enough material for large-scale clinical evaluation of this hormone. Some comments were made concerning probable clinical use of LH-RH. Finally, some speculations were offered about the possibility of developing new birth control methods based on LH-RH/FSH-RH, its analogues, or its derivatives.
Neuroendocrinology · Hypothalamic Pituitary Axis
Knobil E, 1990 · Am J Obstet Gynecol
The notion of an oscillator or signal generator in the central nervous system that controls the rhythmic release of GnRH and, thereby, the pulsatile secretion of the gonadotropic hormones, originated in the finding of strikingly abrupt and rhythmic fluctuations in the concentration of LH in the plasma of ovariectomized monkeys. These oscillations had a period of about one hour when blood samples were obtained at 10 to 20 minute intervals.I
These surprising observations were presaged by reports of seemingly random, major fluctuations in plasma gonadotropin concentrations in gonadectomized monkeys" and rats as well as in women.' In these earlier studies, the sampling intervals employed were never less than one hour and unable, therefore, to reveal the orderly, rhythmic events that occur with frequencies of one event per hour or more.
In the original study describing pulsatile LH secretion in ovariectomized monkeys the possibility was considered that the circhoral discharges of LH may be initiated by autoregulatory mechanisms involving long or short feedback loops, but the more likely view that these discharges were due to intermittent signals from the central nervous system unrelated to circulating LH levels that resulted in putative increments in GnRH release was favored. Nevertheless, the possible role of autoregulatory mechanisms in the control of pulsatile LH secretion was repeatedly considered,6 but finally laid to rest in the relatively recent past.7Conversely, the view that each pulse of LH released from the pituitary gland is the consequence of a bolus of GnRH secreted into the pituitary portal system has been unequivocally upheld by the demonstration of synchronous increments of GnRH assessed in the pituitary portal circulation and of LH measured in samples of peripheral blood obtained simultaneously.s, 9 In any case, the phenomenon of pulsatile gonadotropic hormone secretion was rapidly extended to most vertebrate species studied in this regard, including our own, and forms the basis of an increasingly voluminous, rapidly expanding literature.
Neuroendocrinology · Hypothalamic Pituitary Axis
Bonomi M et al., 2018 · European journal of endocrinology
Isolated hypogonadotropic hypogonadism (IHH) is a rare disorder with pubertal delay, normal (normoosmic-IHH, nIHH) or defective sense of smell (Kallmann syndrome, KS). Other reproductive and non-reproductive anomalies might be present although information on their frequency are scanty, particularly according to the age of presentation.
Observational cohort study carried out between January 2008 and June 2016 within a national network of academic or general hospitals.
We performed a detailed phenotyping of 503 IHH patients with: (1) manifestations of hypogonadism with low sex steroid hormone and low/normal gonadotropins; (2) absence of expansive hypothalamic/pituitary lesions or multiple pituitary hormone defects. Cohort was divided on IHH onset (PPO, pre-pubertal onset or AO, adult onset) and olfactory function: PPO-nIHH (n = 275), KS (n = 184), AO-nIHH (n = 36) and AO-doIHH (AO-IHH with defective olfaction, n = 8).
90% of patients were classified as PPO and 10% as AO. Typical midline and olfactory defects, bimanual synkinesis and familiarity for pubertal delay were also found among the AO-IHH. Mean age at diagnosis was significantly earlier and more frequently associated with congenital hypogonadism stigmata in patients with Kallmann's syndrome (KS). Synkinesis, renal and male genital tract anomalies were enriched in KS. Overweight/obesity are significantly associated with AO-IHH rather than PPO-IHH.
Patients with KS are more prone to develop a severe and complex phenotype than nIHH. The presence of typical extra-gonadal defects and familiarity for PPO-IHH among the AO-IHH patients indicates a common predisposition with variable clinical expression. Overall, these findings improve the understanding of IHH and may have a positive impact on the management of patients and their families.
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