Melatonin and human reproduction: Shedding light on the darkness hormone

Melatonin, N-acetyl-5-methoxytryptamine, is a molecule with diverse physiological functions. This neuro-hormone affects reproductive performance in a wide variety of species. In most animals, but not exclusively all, melatonin has an antigonadotrophic effect. The seasonal changes in the number of hours per day that melatonin is secreted mediate the temporal coupling of reproductive activity to seasonal changes in day-length. These observations stimulated a search for a role for the pineal gland and melatonin in human reproduction. Clinical experience related to this issue has yielded inconclusive and sometimes conflicting results. This article reviews the current available evidence concerning the effects of melatonin on human reproductive processes (e.g., puberty, ovulation, pregnancy, and fertility). Possible reasons for the vagueness and elusiveness of the clinical effects are discussed.     

The role of the leptin in reproduction

PURPOSE OF REVIEW: Since its discovery in 1994, leptin has appeared to be a pleiotrophic hormone, governing energy homeostasis and affecting many tissues in the body. Numerous pieces of evidence have accumulated showing that leptin potentially plays an important role in the control of the reproductive function. RECENT FINDINGS: This review presents the major concepts for the role of leptin in the modulation of reproductive function. As a marker of the nutritional status, leptin affects the hypothalamo-pituitary-gonadal axis, regulating gonadotrophin-releasing hormone and luteinising hormone secretion, and appears to be a permissive factor in the onset of the puberty. This protein and its receptor have been found in the reproductive tissues, indicating that this system could be also implicated in several processes such as embryo development, implantation and pregnancy. Moreover, disorders of the leptin system have been related to some reproductive pathologies such as pre-eclampsia and polycystic ovary syndrome. However, controversy surrounds several aspects of the action of leptin in reproduction that require a deeper investigation of this system. SUMMARY: Results to date suggest that this system could be implicated in important reproductive processes such as embryonic development and implantation. Moreover, understanding the role of leptin might be useful for new treatments in reproductive pathologies.     

Vitamin D (soltriol), light, and reproduction

Evidence from autoradiographic studies with 1,25(OH)2-vitamin D3 (vitamin D, soltriol) labeled with tritium and from the literature indicates that the steroid hormone soltriol regulates and modulates reproductive processes in the female, as it does in the male. Nuclear receptors for soltriol have been discovered in the uterus, oviduct, ovary, mammary gland, placenta, and fetal membranes, as well as in the pituitary and hypothalamus. Soltriol is recognized as a transducer and hormonal messenger of sunlight, acting as a somatotropic activator and modulator of vital processes for the seasonal and estival adaptation of growth, development, and procreation. Its influence on calcium equilibrium is just one of its many functions to serve this goal. This article reviews experimental, clinical, and epidemiologic evidence that suggests the involvement of soltriol in the control of reproductive processes, noting its importance for the onset of puberty, fertility, pregnancy, lactation, and probably sexual behavior. Cooperative actions between soltriol and other steroid hormones, especially estradiol, are pointed out.     

Leptin and reproduction: a review

OBJECTIVE: To review recent advances in understanding the role of leptin in the physiology and pathophysiology of reproduction, with a focus on relevant clinical situations. DESIGN: A MEDLINE computer search was performed to identify relevant articles. RESULT(S): Leptin, an adipocyte hormone important in regulating energy homeostasis, interacts with the reproductive axis at multiple sites, with stimulatory effects at the hypothalamus and pituitary and inhibitory actions at the gonads. More recently, leptin has been shown to play a role in other target reproductive organs, such as the endometrium, placenta, and mammary gland, with corresponding influences on important physiologic processes such as menstruation, pregnancy, and lactation. As a marker of whether nutritional stores are adequate, leptin may act in concert with gonadotropins and the growth hormone axis to initiate the complex process of puberty. Conditions in which nutritional status is suboptimal, such as eating disorders, exercise-induced amenorrhea, and functional hypothalamic amenorrhea, are associated with low serum leptin levels; and conditions with excess energy stores or metabolic disturbances, such as obesity and polycystic ovarian syndrome, often have elevated serum or follicular fluid leptin levels, raising the possibility that relative leptin deficiency or resistance may be at least partly responsible for the reproductive abnormalities that occur with these conditions. CONCLUSION(S): Leptin may act as the critical link between adipose tissue and the reproductive system, indicating whether adequate energy reserves are present for normal reproductive function. Future interventional studies involving leptin administration are expected to further clarify this role of leptin and may provide new therapeutic options for the reproductive dysfunction associated with states of relative leptin deficiency or resistance.     

Hyperprolactinemia: pathophysiology and therapeutic approach

Abstract

Prolactin (PRL) is a hormone, mainly secreted by lactotroph cells of the anterior pituitary gland. Recent studies have shown it may also be produced by many extrapituitary cells. Its well-recognized PRL plays an important role in lactation during pregnancy, but it is involved in other biological functions such as angiogenesis, immunoregulation and osmoregulation. Hyperprolactinemia is a typical condition producing reproductive dysfunction in both sexes, resulting in hypogonadism, infertility and galactorrhea. It may be also asymptomatic. Lactotroph adenomas (prolactinoma) is one of the most common cause of PRL excess, representing approximately 40% of all pituitary tumors. Several other conditions should be excluded before a clear diagnosis of hyperprolactinemia is made. Hyperprolactinemia may be secondary to pharmacological or pathological interruption of hypothalamic–pituitary dopaminergic pathways or idiopathic. Stress, renal failure or hypothyroidism are other frequent conditions to exclude in patients with hyperprolactinemia. We will review biochemical characteristics and physiological functions of that hormone. Clinical and pharmacological approach to hyperprolactinemia will also be discussed.     

KNDy神经元在女性生殖内分泌中的研究与应用

Kisspeptin/神经激肽B/强啡肽(kisspeptin/neurokinin B/dynorphin,KNDy)神经元是Kisspeptin神经元的一个亚组,是性激素负反馈的靶细胞,它产生神经激肽B(Neurokinin B,NKB)和强啡肽(Dynorphin A,Dyn),NKB起刺激作用,Dyn起抑制作用...     

Melatonin utility in neonates and children

Melatonin (N-acetyl-5-methoxytryptamine) is an endogenously produced indoleamine secreted by the pineal gland and the secretion is suppressed by light. Melatonin is a highly effective antioxidant, free radical scavenger, and has anti-inflammatory effect. Plenty of evidence supports the utility of melatonin in adults for cancer, neurodegenerative disorders, and aging. In children and neonates, melatonin has been used widely, including for respiratory distress syndrome, bronchopulmonary dysplasia, periventricular leukomalacia (PVL), hypoxia-ischemia encephalopathy and sepsis. In addition, melatonin can be used in childhood sleep and seizure disorders, and in neonates and children receiving surgery. This review article discusses the utility of melatonin in neonates and children.     

Leptin and reproduction

In the few years since leptin was identified as a satiety factor in rodents, it has been implicated in the regulation of various physiological processes. Leptin has been shown to promote sexual maturation in rodent species and a role in reproduction has been investigated at various sites within the hypothalamo-pituitary-gonadal axis. This review considers the evidence that leptin (or alteration in amount of body fat) can affect reproduction. There is evidence that leptin plays a permissive role in the onset of puberty, probably through action on the hypothalamus, where leptin receptors are found in cells that express appetite-regulating peptides. There is little evidence that leptin has a positive effect on the pituitary gonadotrophs and the gonads. There is also very little indication that leptin acts in an acute manner to regulate reproduction in the short term. It seems more likely that leptin is a 'barometer' of body condition that sends signals to the brain. Studies in vitro have shown negative effects on ovarian steroid production and there are no reports of effects on testicular function. Leptin concentrations in plasma increase in women during pregnancy, owing to production by the placenta but the functional significance of this is unknown. A number of factors that affect the production and action of leptin have yet to be studied in detail.     

Growth hormone deficiency as the only identifiable cause for primary amenorrhea

Background: There is much evidence that growth hormone plays an important role in the development and function of the reproductive system of both males and females. Growth hormone exerts its effects on the ovarian follicular cycle directly or by local production of insulin-like growth factor 1 (IGF-1). It is known that growth hormone deficiency during childhood may delay pubertal development, but there is limited data about primary amenorrhea in GH-deficient girls with sufficient stimulated gonadotropin levels.Methods: Case series.Results: In the evaluation of primary amenorrhea and delayed puberty, 3 cases of adolescent females aged 17-19 years were identified as isolated GH-deficiency. Among the 3 patients, 2 had history of intracranial surgery due to hydrocephalus (shunt operation) or prolactin-secreting pituitary macro-adenoma (transphenoidal surgery, one year before). 17-year-old patient with shunted hydrocephalus and 19-year-old patient with primary amenorrhea showed short statue (< 5%) and delayed bone maturation. The patient undertaken transphenoidal surgery for prolactinoma showed normal height and bone maturation. There was no familial history of delayed puberty. On physical examination, 3 patients showed variable degree of breast development from Tanner stage II to IV without sex-steroid replacement. In sella MRI, small pituitary gland were identified in 2 patients with short statue and delayed bone maturation. All of the 3 patients underwent combined pituitary function test. After insulin-induced hypoglycemia, peak growth hormone levels of the 3 patients were 0.08, 1.4 and 1.4 ng/ml and were compatible with growth hormone deficiency. Peak LH after intravenous gonadrelin (FACTREL) were 19.0 to 56.1 mIU/ml and LH % responses were 217 to 1100% and were hence defined as not being gonadotropin deficiency. Other anterior pituitary functions were normal in all of the 3 patients.Conclusions: We found isolated growth hormone deficiency as the only identifiable cause for primary amenorrhea in three patients with sufficient gonadotropins secretion. These findings suggest a complementary role of GH to gonadotropins in the occurrence of menarche.     

Leptin and its influence on the main gynecoobstetric diseases

Leptin is a protein hormone synthesized and secreted by adipose tissue and also probably in other organs and systems in human body. It has multiple functions such as to regulate feed intake and energy balance, gonadal regulation, action in the hypothalamo-pituitary-gonadal axis, regulates the metabolism of the fetal-placental unit in the pregnancy, fertility and reproductive systems, actions in the endometrium, mammary gland with corresponding influences on important physiologic processes such as menstruation, pregnancy and lactation. In the gynecologic surgery the serum leptin concentration is also modified. The knowledge of serum leptin concentration in the oncological diseases is going-up. Leptin is modified in the choriocarcinoma, Meigs' syndrome and other tumors. A better understanding of regulatory mechanisms will have direct clinical significance, as leptin has been proposed to impact on those causes of human perinatal morbidity and mortality that are associated with abnormalities of fetal maturity and development, general concept growth, trophoblast endocrinology, and placental sufficiency. Further investigations in this area will be necessary to improve new knowledge and a better understanding of the actions about this hormone.     

Does mode of delivery affect neonate oxidative stress in parturition? Review of literature

Purpose

The production of reactive oxygen substances plays an important regulatory role in many physiologic reproductive processes. Excessive production may lead to oxidative stress (OS), and bring about pregnancy disorders. Growing evidence indicates that OS plays a major role in the pathophysiology of complications such as early pregnancy loss, placental insufficiency, preeclampsia, fetal growth restriction, and neonatal complications. Whether parturition induces oxidative stress is in dispute. In this review, we elaborate the influence of mode of delivery (vaginal delivery or cesarean delivery) on oxidative stress of neonates.

Methods

A review of old and recent literature was done. The studies were divided according to the impact of mode of delivery on oxidative stress in the newborn.

Results

There is a divergence in the oxidative stress production according to the mode of delivery.

Conclusions

In view of neonatal oxidative stress measures, no major difference was found between uncomplicated vaginal delivery and elective cesarean section.     

Paracrine/autocrine control of female reproduction

Neuropeptides, growth factors and cytokines are expressed in reproductive organs and tissues, where they interact with afferent endocrine messages to modulate cell proliferation and differentiation, local hormone secretion and vascular function. These events regulate complex processes such as gonadotropin pulsatility, ovulation, implantation and parturition.

During reproductive life, a number of neuropeptides produced within the hypothalamus play a modulatory role in the control of gonadotropin-releasing hormone (GnRH) release, hence characterizing a hypothalamic paracrine system. The pituitary gland is a source and target of inhibin-related proteins, and these typical ‘gonadal’ products, once secreted by the pituitary cells, acquire the function of paracrine modulators of follicle-stimulating hormone (FSH) secretion. In the ovary, the effect of gonadotropins is locally modulated by growth factors acting in an autocrine/paracrine manner, although their precise role in folliculogenesis remains uncertain. Numerous local factors are involved in the control of endometrial growth, differentiation, receptivity and menstruation. Alterations in the paracrine endometrial system may underlie pathological processes such as infertility or endometrial neoplasia. The human placenta and its related membranes produce cytokines, hormones and growth factors that participate in the control of gestational development as well as in the maternal–fetal adaptation to gestational diseases.

There is increasing evidence that paracrine signaling plays a fundamental role in all spheres of female reproductive function, and future research will concentrate on clarifying which of these local mechanisms play a decisive role in both physiology and disease, thus giving rise to new therapeutic strategies.     

Paracrine/autocrine control of female reproduction.

Neuropeptides, growth factors and cytokines are expressed in reproductive organs and tissues, where they interact with afferent endocrine messages to modulate cell proliferation and differentiation, local hormone secretion and vascular function. These events regulate complex processes such as gonadotropin pulsatility, ovulation, implantation and parturition. During reproductive life, a number of neuropeptides produced within the hypothalamus play a modulatory role in the control of gonadotropin-releasing hormone (GnRH) release, hence characterizing a hypothalamic paracrine system. The pituitary gland is a source and target of inhibin-related proteins, and these typical 'gonadal' products, once secreted by the pituitary cells, acquire the function of paracrine modulators of follicle-stimulating hormone (FSH) secretion. In the ovary, the effect of gonadotropins is locally modulated by growth factors acting in an autocrine/paracrine manner, although their precise role in folliculogenesis remains uncertain. Numerous local factors are involved in the control of endometrial growth, differentiation, receptivity and menstruation. Alterations in the paracrine endometrial system may underlie pathological processes such as infertility or endometrial neoplasia. The human placenta and its related membranes produce cytokines, hormones and growth factors that participate in the control of gestational development as well as in the maternal-fetal adaptation to gestational diseases. There is increasing evidence that paracrine signaling plays a fundamental role in all spheres of female reproductive function, and future research will concentrate on clarifying which of these local mechanisms play a decisive role in both physiology and disease, thus giving rise to new therapeutic strategies.     

Melatonin levels in maternal plasma before and during delivery, and in fetal and neonatal plasma

In the present study, in order to clarify the diurnal changes in pregnant women, fetuses and neonates, pineal hormone (melatonin) was analyzed with a RIA Kit. Results: 1. The venous melatonin concentration at night was higher than during the day in healthy women and full term pregnant women without labor. 2. Melatonin concentrations in maternal venous blood (MV) (67.44 pg/ml) were significantly higher than in umbilical venous blood (UV) (37.78 pg/ml). 3. A distinct midnight peak of melatonin was observed in MV, and UV at delivery. 4. Significant correlations were observed between MV, UV or umbilical arterial blood (UA), but those were non linear. 5. In neonates on the first to fourth day after birth, no midnight peak was able to be clearly observed, but fluctuations were observed. These result indicate that there is a diurnal change in melatonin in full term pregnant women without labor and women in labor. And we suggest that the pineal gland of early neonates secretes melatonin, but no diurnal change in melatonin is established up to 4th day after birth.     

The female rat as a model describing patterns of pulsatile LH secretion during puberty and their control by melatonin

A characteristic of the advent of final stages of sexual maturation in the rat, the equivalent of puberty in the human, is the development of a specific pattern of pulsatile GnRH secretion, reflected by an equivalent pattern of LH secretion. Many hypotheses have been put forward to explain these last changes, including a change at the hypothalamic level and a modification of the ovary. These models are developed to include melatonin, an indoleamine produced by the pineal gland, which appears to play a role in the establishment of the final pattern of LH secretion, thus affecting both vaginal opening and subsequent estrous cycles. Prior to first ovulation, pulsatile release of LH acquires at least two types of patterns, one with low-amplitude, high-frequency pulses, announcing a pattern observed in the follicular phase of primates, and one with high-amplitude, low-frequency pulses, mimicking what is seen in the luteal phase of primates. From the results presented, it is postulated that chronic melatonin administration increases the number of patterns typical of luteal phases, and reduces those of the follicular type, resulting in a decrease frequency of LH pulses and longer intervals between estrous cycles.     

The female rat as a model describing patterns of pulsatile LH secretion during puberty and their control by melatonin

A characteristic of the advent of final stages of sexual maturation in the rat, the equivalent of puberty in the human, is the development of a specific pattern of pulsatile GnRH secretion, reflected by an equivalent pattern of LH secretion. Many hypotheses have been put forward to explain these last changes, including a change at the hypothalamic level and a modification of the ovary. These models are developed to include melatonin, an indoleamine produced by the pineal gland, which appears to play a role in the establishment of the final pattern of LH secretion, thus affecting both vaginal opening and subsequent estrous cycles. Prior to first ovulation, pulsatile release of LH acquires at least two types of patterns, one with low-amplitude, high-frequency pulses, announcing a pattern observed in the follicular phase of primates, and one with high-amplitude, low-frequency pulses, mimicking what is seen in the luteal phase of primates. From the results presented, it is postulated that chronic melatonin administration increases the number of patterns typical of luteal phases, and reduces those of the follicular type, resulting in a decrease frequency of LH pulses and longer intervals between estrous cycles.     

Pharmacological effects of melatonin on reproductive activity: experimental bioimplants with sustained-release polymeric systems

A vast literature documents the role of melatonin in human reproductive function including: a) the relation between melatonin and the menstrual cycle in relation to the peak time of luteinizing hormone in the middle of the cycle; b) the varying concentrations of melatonin in the control of puberty; c) the fewer conceptions in some artic populations where melatonin is connected significantly to seasonal photoperiodicity during the months of the polar nights. The aim of this paper is to report our findings on the pharmacological action of this molecule on reproduction in which gonadal activity is clearly connected to photoperiodicity. We used polymer bioimplants programmed for the sustained release of melatonin for experimental gynecologic protocols. These implants had beneficial results with respect to the use of progestinics because melatonin allowed ovarian activity to be induced for at least two to three consecutive cycles with one single bioimplant. We thought it indispensable to use pharmacological systems with a sustained release because different preliminary tests showed that the half-life of melatonin is limited at maximum to two to three hours and, consequently, any other tested modalities of administration would not provide any appreciable results for our study. As a model for our research we used goats to administer melatonin via targeted programs since these animals clearly respond (even against the rule of the light/dark relation) in contrast to humans in whom response is less evident. For controls, after inserting bioimplants in the animals, we tested their efficiency in vitro and subsequently in vivo, evaluating blood parameters and pharmacological effects of melatonin occurring during the treatment. The final results proved to be interesting in relation to reproductive activity in that regular and programmed births were achieved.     

Mechanisms of progesterone action in inhibiting prematurity

Progesterone is a steroid hormone that plays an integral role in each step of human pregnancy. In early pregnancy, progesterone produced by the corpus luteum is critical to the maintenance of early pregnancy until the placenta takes over this function at 7 to 9 weeks of gestation, hence its name (pro-gestational steroid hormone). The role of progesterone in later pregnancy, however, is less clear. It has been proposed that progesterone may be important in maintaining uterine quiescence in the latter half of pregnancy by limiting the production of stimulatory prostaglandins and inhabiting the expression of contraction-associated protein genes within the myometrium. Although systemic progesterone withdrawl may not correlate directly with the onset of labour in humans, there is increasing evidence to suggest that progesterone exerts its influence indirectly via a ‘functional’ withdrawl at the level of the uterus. The molecular mechanisms by which progesterone is able to maintain uterine quiescence and prevent preterm birth in some high-risk women are not clear. Six putative mechanisms have been proposed in the literature by both US and other investigators and are explored in this review.     

Mechanisms of progesterone action in inhibiting prematurity.

Progesterone is a steroid hormone that plays an integral role in each step of human pregnancy. In early pregnancy, progesterone produced by the corpus luteum is critical to the maintenance of early pregnancy until the placenta takes over this function at 7 to 9 weeks of gestation, hence its name (pro-gestational steroid hormone). The role of progesterone in later pregnancy, however, is less clear. It has been proposed that progesterone may be important in maintaining uterine quiescence in the latter half of pregnancy by limiting the production of stimulatory prostaglandins and inhabiting the expression of contraction-associated protein genes within the myometrium. Although systemic progesterone withdrawl may not correlate directly with the onset of labour in humans, there is increasing evidence to suggest that progesterone exerts its influence indirectly via a 'functional' withdrawl at the level of the uterus. The molecular mechanisms by which progesterone is able to maintain uterine quiescence and prevent preterm birth in some high-risk women are not clear. Six putative mechanisms have been proposed in the literature by both US and other investigators and are explored in this review.     

Gender differences in leptin levels and physiology: a role for leptin in human reproduction

Leptin, an adipocyte-derived hormone known to play an important role in body-weight regulation, has been shown to be expressed differentially in men and women. These observations are potentially important for the understanding of differences between men and women in regulation of food intake, weight gain, and body fat distribution. Leptin is also involved in female fertility, especially in pubertal development. It may well be the triggering signal for the onset of puberty in girls. Although the exact mechanisms and interactions with sex steroids are not yet fully established, it is clear that leptin plays a role as an endocrine mediator in sexual development and reproduction.