Nitric Oxide Mediates Inhibitory Effect of Leptin on Insulin-Like Growth Factor I Augmentation of 17β-Estradiol Production in Human Granulosa Cells1

Alterations in Appetite-Regulating Hormones in Girls with Central Early or Precocious Puberty

The prevalence of central precocious puberty (CPP) in girls has increased worldwide and is often associated with obesity in childhood as well as high fat/high glycemic index diets. Evidence suggests that subjects with obesity present with alterations in appetite-regulating hormones. The arcuate and paraventricular nuclei of the hypothalamus are the centers of action of appetite hormones, as well as the location of gonadotropin-releasing hormone (GnRH) neurons, the activation of which results in the onset of puberty. This anatomical proximity raises the question of possible alterations in appetite-regulating hormones in patients with CPP. Furthermore, diet-induced hypothalamic inflammation constitutes a probable mechanism of the pathophysiology of CPP, as well as alterations in appetite-regulating hormones in young children. In this article, we summarize the evidence investigating whether girls with CPP present with alterations in appetite-regulating hormones. We present evidence that leptin concentrations are elevated in girls with CPP, ghrelin concentrations are lower in girls with CPP, nesfatin-1 and orexin-A concentrations are elevated among girls with premature thelarche, and insulin concentrations are increased in girls with early menarche.

Roles of Nitric Oxide in the Regulation of Reproduction: A Review

Nitric oxide (NO) has attracted significant attention as a stellar molecule. Presently, the study of NO has penetrated every field of life science, and NO is widely distributed in various tissues and organs. This review demonstrates the importance of NO in both male and female reproductive processes in numerous ways, such as in neuromodulation, follicular and oocyte maturation, ovulation, corpus luteum degeneration, fertilization, implantation, pregnancy maintenance, labor and menstrual cycle regulation, spermatogenesis, sperm maturation, and reproduction. However, the mechanism of action of some NO is still unknown, and understanding its mechanism may contribute to the clinical treatment of some reproductive diseases.

Effects of plane of nutrition and arginine on ovarian follicles in non-pregnant sheep: Cell proliferation, and expression of endothelial nitric oxide and its receptor

The aim of this study was to investigate the role of the nitric oxide (NO) system in ovarian function, by determining if arginine (Arg) supplementation impacts follicle number, cell proliferation, and expression of the NO system members in nutritionally compromised ewes. Ewes were randomly assigned into maintenance (C, 100% requirements), excess (O; 2xC), or restricted (U; 0.6xC) diets 8 weeks prior to Arg treatment. Ewes were individually fed twice daily with pelleted diets. Ewes from each nutritional group were randomly assigned to one of two treatments: saline or Arg, which was initiated on day 0 of the estrous cycle and administered 3 times per day. Ovaries were collected at the early-luteal, mid-luteal and late-luteal/follicular phases of the estrous cycle to determine 1) the number of surface follicles, 2) follicle cell proliferation marked by Ki67 protein expression, and 3) expression of endothelial nitric oxide (eNOS; NOS3) and soluble guanylyl cyclase beta (sGC; GUCY1B3) protein and mRNA in granulosa (G) and theca (T) layers using immunohistochemistry followed by image analysis and qPCR, respectively. During nutritional treatment, C maintained body weight, O gained 6±1.2 kg, and U lost 14±1.3 kg. Our data show that: 1) Ki67 was expressed in all ovarian compartments, eNOS protein was detected in blood vessels of T and stroma, and sGC protein was detected in T cells, and blood vessels of T layer and other ovarian compartments; 2) plane of nutrition affected the number of surface follicles, and thus folliculogenesis, cell proliferation in the T layer, eNOS and sGC protein expression in T, and NOS3 and GUCY1B3 mRNA expression in G; 3) Arg treatment affected cell proliferation in G and T, eNOS and sGC protein expression in T, mRNA expression of NOS3 in T in all groups, and GUCY1B3 in G depending on the stage of the estrous cycle; and 4) G and T cell proliferation, and expression of eNOS and sGC protein in T was affected by the stage of the estrous cycle. Our data demonstrated that plane of nutrition and Arg are involved in the regulation of follicular functions in non-pregnant sheep.

Progesterone secretion by ovine granulosa cells: effects of nitric oxide and plane of nutrition

The aim was to evaluate the effects of nutritional plane on in vitro progesterone (P4) secretion by granulosa (G) cells cultured in the presence or absence of effectors of the nitric oxide (NO) system. Ewes were randomly assigned into three nutritional groups: control (C), overfed (O; 2 × C), or underfed (U; 0.6 × C). Follicular development was induced by FSH injections. On day 15 of the estrous cycle, G cells were isolated and cultured with or without DETA-NONOate (NO donor), L-NAME (NO synthase [S] inhibitor), Arg and (or) LH for 8 h. DETA-NONOate decreased basal and LH-stimulated P4 secretion, and L-NAME increased basal P4 secretion in all groups. In U, Arg decreased LH-stimulated P4 secretion. These data demonstrate that (i) plane of nutrition affects basal P4 secretion by G cells, (ii) the NO donor decreases, NOS inhibitor increases but Arg does not affect basal P4 secretion, and (iii) effects of Arg on LH-stimulated P4 secretion are affected by plane of nutrition in FSH-treated sheep. Thus, plane of nutrition affects G cell function, and the NO system is involved in the regulation of basal and LH-stimulated P4 secretion. The mechanism of the NO system effects on secretory activity of G cells remains to be elucidated.

Impact of maternal malnutrition during the periconceptional period on mammalian preimplantation embryo development

During episodes of undernutrition and overnutrition the mammalian preimplantation embryo undergoes molecular and metabolic adaptations to cope with nutrient deficits or excesses. Maternal adaptations also take place to keep a nutritional microenvironment favorable for oocyte development and embryo formation. This maternal-embryo communication takes place via several nutritional mediators. Although adaptive responses to malnutrition by both the mother and the embryo may ensure blastocyst formation, the resultant quality of the embryo can be compromised, leading to early pregnancy failure. Still, studies have shown that, although early embryonic mortality can be induced during malnutrition, the preimplantation embryo possesses an enormous plasticity that allows it to implant and achieve a full-term pregnancy under nutritional stress, even in extreme cases of malnutrition. This developmental strategy, however, may come with a price, as shown by the adverse developmental programming induced by even subtle nutritional challenges exerted exclusively during folliculogenesis and the preimplantation period, resulting in offspring with a higher risk of developing deleterious phenotypes in adulthood. Overall, current evidence indicates that malnutrition during the periconceptional period can induce cellular and molecular alterations in preimplantation embryos with repercussions for fertility and postnatal health.

Leptin and queen ovary: new insights about ovulation

Leptin has been proven to be crucial in the ovulatory process. Aims of this study are to assess the expression of leptin receptor (Ob-R) in the ovaries of queens at estrus and to evaluate the capability of leptin in modulating ovarian contractility in vitro. Right ovaries underwent immunoblot analysis. Left ovaries were mounted in an organ bath under physiological condition and exposed to murine leptin (10(-6) M). Immunoblot analysis showed that the queen ovary expresses leptin receptor at estrus. Leptin at the dose of 10(-6) M significantly reduced the contractile activity of the ovary. The presence of ovarian Ob-R and leptin inhibitory effects on ovarian contractility suggest leptin implication in the modulation of ovarian activity, as well as in ovulatory disorders.

In vivo oocyte developmental competence is reduced in lean but not in obese superovulated dairy cows after intraovarian administration of IGF1

The present study investigated the role of IGF1 in lactating lean and non-lactating obese dairy cows by injecting 1 μg IGF1 into the ovaries prior to superovulation. This amount of IGF1 has been linked with pregnancy loss in women with the polycystic ovary syndrome (PCOS) and was associated with impaired bovine oocyte competence in vitro. Transcript abundance and protein expression of selected genes involved in apoptosis, glucose metabolism, and the IGF system were analyzed. Plasma concentrations of IGF1 and leptin, and IGF1 in uterine luminal fluid (ULF), were also measured. IGF1 treatment decreased embryo viability in lean cows to the levels observed in obese cows. Obese cows were not affected by IGF1 treatment and showed elevated levels of IGF1 (in both plasma and ULF) and leptin. Blastocysts from lean cows treated with IGF1 showed a higher abundance of SLC2A1 and IGFBP3 transcripts. IGF1 treatment reduced protein expression of tumor protein 53 in blastocysts of lean cows, whereas the opposite was observed in obese cows. IGF1 in plasma and ULF was correlated only in the control groups. Blastocyst transcript abundance of IGF1 receptor and IGFBP3 correlated positively with IGF1 concentrations in both plasma and ULF in lean cows. The detrimental microenvironment created by IGF1 injection in lean cows and the lack of effect in obese cows resemble to a certain extent the situation observed in PCOS patients, where IGF1 bioavailability is increased in normal-weight women but reduced in obese women, suggesting that this bovine model could be useful for studying IGF1 involvement in PCOS.

Expression of adipokines in preimplantation rabbit and mice embryos

Recent studies point to a role for adipokines in reproduction. Leptin is involved in embryo metabolism and may participate in embryo-maternal crosstalk. Little is known about potential roles of other adipokines in reproduction. We therefore studied the expression of adiponectin and pathway members during the pre- and periimplantation period in rabbits and mice. Adiponectin protein is localized in glandular epithelium of the rabbit endometrium on day 6 and 8 p.c. and in mouse endometrium on day 3.5 and 5 p.c. Rabbit, but not mice blastocysts express adiponectin mRNA. Adiponectin receptors one and two, adiponectin paralogues and PPARs were found in both species. Both, trophoblast and embryoblast were adiponectin positive. Real time PCR for adipoR1 and adipoR2 in rabbit blastocysts of different gastrulation stages at day 6 p.c. revealed a specific switch in expression: Expression was high in the trophoblast in early stages and in the embryoblast shortly prior to implantation. In conclusion, during the pre- and periimplantation period, members of the adiponectin pathway are expressed in endometrium and blastocysts, with a specific expression pattern in the embryonic disk of the gastrulating rabbit blastocyst, giving support to a role of the adipokine network in blastocyst differentiation and embryo-maternal interactions.

Leptin in embryos from control and diabetic rats during organogenesis: a modulator of nitric oxide production and lipid homeostasis

BACKGROUND

Leptin is involved in many metabolic and reproductive events and its levels are altered by the diabetic pathology. In this study, leptin concentrations and leptin effects on both nitric oxide (NO) and lipid concentrations were investigated in embryos from control and diabetic rats.

METHODS

Diabetes was induced by neonatal streptozotocin administration (90 mg/kg). Embryos from control and diabetic rats were obtained on days 10.5 and 13.5 of gestation, corresponding to early organogenesis and post-placentation periods respectively. Leptin was analysed by enzyme immunoanalysis and immunohistochemistry. Nitrates and nitrites were assessed as an index of NO production. Lipid concentrations were analysed by thin layer chromatography.

RESULTS

Leptin concentrations were decreased in embryos obtained from diabetic rats on days 10.5 and 13.5 of gestation when compared to controls. NO concentrations, elevated in diabetic embryopathy, were diminished in the presence of leptin in the embryos obtained from control and diabetic animals both during early organogenesis and after placentation. Leptin additions reduced phospholipid, cholesterol and cholesteryl ester concentrations in embryos obtained from diabetic rats during early organogenesis, although no leptin effects on lipid concentrations were observed in control embryos at this developmental stage. In embryos obtained on day 13.5 of gestation leptin additions reduced cholesteryl ester concentrations in controls, and diminished cholesteryl ester, triglycerides and phospholipids in embryos from diabetic rats.

CONCLUSIONS

We demonstrated that leptin plays a role in the regulation of NO concentrations and lipid homeostasis during embryo organogenesis and that the diabetic environment causes a reduction of leptin concentrations in rat embryos.

Inhibitory effect of leptin on the rat ovary during the ovulatory process

The aims of this study were to investigate the negative action of leptin on some intraovarian ovulatory mediators during the ovulatory process and to assess whether leptin is able to alter the expression of its ovarian receptors. Immature rats primed with gonadotrophins were used to induce ovulation. Serum leptin concentration was diminished 4 h after human chorionic gonadotrophin (hCG) administration, whereas the ovarian expression of leptin receptors, measured by western blot, was increased by the gonadotrophin treatment. Serum progesterone level, ovulation rate and ovarian prostaglandin E (PGE) content were reduced in rats primed with equine chorionic gonadotrophin (eCG)/hCG and treated with acute doses of leptin (five doses of 5 mug each). These inhibitory effects were confirmed by in vitro studies, where the presence of leptin reduced the concentrations of progesterone, PGE and nitrites in the media of both ovarian explants and preovulatory follicle cultures. We also investigated whether these negative effects were mediated by changes in the expression of the ovarian leptin receptors. Since leptin treatment did not alter the expression of ovarian leptin receptor, the inhibitory effect of leptin on the ovulatory process may not be mediated by changes in the expression of its receptors at ovarian level, at least at the concentrations assayed. In summary, the ovulatory process was significantly inhibited in response to an acute treatment with leptin, and this effect may be due, at least in part, to the direct or indirect impairment of some ovarian factors, such as prostaglandins and nitric oxide.

Relationship of serum leptin concentration with age, gender, and biomedical parameters in healthy, non-obese subjects

It is known that the circulating levels of leptin, the adipocyte hormone implicated in the control of energy balance, are correlated with fat body mass (FBM), although the influences of other physiological conditions are not fully understood. We investigated the relationships of serum leptin concentration with age, gender, and 36 hormone-metabolic parameters in a sample of a well defined healthy population (n=246; age range 20-93 years), and in subgroups of lean individuals according to their body mass index (BMI), within similar age range and gender distribution. Only insulin secretion (positively) and testosteronemia (negatively, in males) show direct correlations. The other relationships are not significant but throughout collaborating variables, such as serum lipids, especially through FBM, lean body mass (LBM) through insulin secretion, and gender through FBM. In males, LBM correlates with insulin secretions, s-IGF-1 and with s-testosterone. The relationship between insulin secretion and LBM persists up to advanced age. From the present study it may be concluded that the positive relationship of leptin with insulin secretion and the negative one with testosterone, indicate direct implications of leptin in insulin signaling, as well as in male sexual development. Finally, the fact that the amount of secreted insulin depends on LBM and the latter on testosterone and IGF-1, indicates the importance of muscle mass in the control of insulin secretion.

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.