Elsevier

Regulatory Peptides

Volume 92, Issues 1–3, 25 August 2000, Pages 17-24
Regulatory Peptides

Leptin effects on pulsatile gonadotropin releasing hormone secretion from the adult rat hypothalamus and interaction with cocaine and amphetamine regulated transcript peptide and neuropeptide Y

https://doi.org/10.1016/S0167-0115(00)00144-0Get rights and content

Abstract

Leptin may act as a negative feedback signal to the hypothalamic control of appetite through suppression of neuropeptide Y (NPY) secretion and stimulation of cocaine and amphetamine regulated transcript (CART). We aimed at studying the effects of leptin, CART and NPY on the hypothalamic control of the pituitary–gonadal system. Pulsatile gonadotropin-releasing hormone (GnRH) secretion was studied in vitro using retrochiasmatic hypothalamic explants from adult rats. In the female, GnRH pulse amplitude was significantly increased by leptin (10−7 M) and CART (10−6 M) irrespective of the estrus cycle phase while no such effects were seen in the male. The GnRH interpulse interval was not affected in both sexes. Passive immunoneutralization against CART caused a reduction in GnRH pulse amplitude in the female. A slight but significant increase in GnRH pulse amplitude was caused by NPY (10−7 M) in the female. However, GnRH pulse amplitude was not affected by a Y5-receptor antagonist (10−6 M) while the interpulse interval was significantly increased as shown previously in the male. The increase in GnRH pulse amplitude caused by leptin was totally prevented by coincubation with an anti-CART antiserum whereas it was not affected by coincubation with the NPY Y5-receptor antagonist (10−7 M). In conclusion, leptin and NPY show separate permissive effects on GnRH secretion in the adult rat hypothalamus. In both sexes, NPY is prominently involved in the control of the frequency of pulsatile GnRH secretion through the Y5 receptor subtype. Leptin causes a female-specific facilitatory effect on GnRH pulse amplitude which is mediated by CART and which occurs irrespective of the estrus cycle phase.

Introduction

Alteration in energy balance may influence reproductive function in many species. Food restriction can alter adult reproductive function [1], [2] and delay the timing of pubertal onset [3], [4] by suppression of luteinizing hormone (LH) secretion. Many studies showed that leptin, a key regulator of food intake and energy balance, may play a regulatory role in the hypothalamic–pituitary–gonadal axis. In female ob/ob mice, leptin administration increased basal LH levels and restored fertility [5], [6], [7]. Other experiments have demonstrated that intracerebroventricular (i.c.v.) injection of leptin antiserum led to a decrease in LH pulsatility and an impairment of reproductive function [8].

Neuropeptide (NPY) and, more recently, the cocaine and amphetamine regulated transcript (CART) were shown to be involved in the mechanisms of leptin action on food intake. The hypothalamic transcripts of NPY, a potent stimulator of food intake, were increased by food restriction [9] and reduced by i.c.v. administration of leptin [10], [11]. Leptin administration to obese (ob/ob) mice stimulated the mRNA expression of CART, a hypothalamic inhibitor of food intake [12]. Therefore, it appeared interesting to study whether NPY and CART could be involved in leptin effects on the hypothalamic–pituitary–gonadal system.

Discrepant stimulatory and inhibitory effects of NPY on sexual maturation and reproduction were observed depending on species, steroidal environment [13], site of NPY administration in the brain [14] and chronic [15], [16], [17] versus acute pattern of infusion [18]. CART effects on the reproductive axis were unknown till we reported very recently a study of pulsatile GnRH secretion from hypothalamic explants of prepubertal male and female rats [19]. The frequency of GnRH pulsatility was stimulated by leptin. CART was likely to mediate such an effect. Using the same paradigm, NPY was found to accelerate GnRH pulsatility through the Y5-receptor subtype which appeared to be not involved in mediation of leptin effects [20]. Here, we used hypothalamic explants from adult male rats and female rats at different phases of the estrus cycle. We aimed at studying the effects of leptin and the possible mediating role of NPY and CART in the regulation of frequency and amplitude of pulsatile GnRH secretion.

Section snippets

Animals

Male and female Wistar rats were used. They were housed in temperature and light-controlled conditions (22°C, lights on between 07:00 and 19:00) with water and standard rat pellet ad libitum. The protocols were approved by the University Committee on animal research.

Hypothalamic explants incubation

The animals were sacrificed by decapitation between 10:00 and 11:00 for all experiments except during the estrous cycle when some experiments were started in the afternoon around 16:00. The retrochiasmatic hypothalamus was rapidly

Pulsatile GnRH secretion at different phases of the estrus cycle

Using hypothalamic explants of adult female rats obtained in the morning as well as in the afternoon (Table 1), the mean GnRH interpulse interval was around 40 min and did not change throughout the estrus cycle. Using explants obtained in the morning, the mean GnRH pulse amplitude did not change significantly throughout the cycle. Using explants obtained in the afternoon, when the preovulatory LH surge is known to occur on proestrus, a significantly increased pulse amplitude was seen on

Discussion

The preovulatory LH surge was known to take place during the afternoon of proestrus [27], [28], [29]. In this study, using explants obtained in the afternoon of the different cycle phases, we showed that the frequency of GnRH pulsatility did not change whereas the amplitude showed about a two fold increase on the afternoon of proestrus. Several in vivo studies showed that GnRH secretion in pituitary stalk plasma was markedly increased at the time of the preovulatory LH surge [30], [31], [32].

Acknowledgements

We would like to thank Dr. Peter Kristensen, Novo Nordisk (Bagsvaerd, Denmark) for the generous gift of purified CART protein and CART antibody. We are grateful to Dr. Graeme Semple, Ferring Research Institute (Chilworth, UK) for synthesis of the Novartis non peptidic Y5- receptor antagonist and Dr. V.D. Ramirez for the generous supply of the anti-GnRH antiserum. This study was supported by the Belgian Fonds de la Recherche Scientifique Médicale (grant 3.4529.97), the Faculty of Medecine at the

References (51)

  • T.M. Badger et al.

    Effects of fasting on luteinizing hormone dynamics in the male rat

    J. Nutr.

    (1985)
  • F.R.A. Cagampang et al.

    Effect of food deprivation on the pulsatile LH release in the cycling and ovariectomized female rat

    Horm Metab Res

    (1990)
  • D.L. Foster et al.

    Effect of restricted nutrition on puberty in the lamb: patterns of tonic luteinizing hormone (LH) secretion and competency of the LH surge system

    Endocrinology

    (1985)
  • G.C. Kennedy et al.

    Body weight and food intake as initiating factors for puberty in the rat

    J Physiol

    (1963)
  • I.A. Barash et al.

    Leptin is a metabolic signal to the reproductive system

    Endocrinology

    (1996)
  • F.F. Chehab et al.

    Correction of the sterility defect in homozygous obese female mice by treatment with the human recombinant leptin

    Nat Genet

    (1996)
  • K. Mounzih et al.

    Leptin treatment rescues the sterility of genetically obese ob/ob males

    Endocrinology

    (1997)
  • E. Carro et al.

    Influence of endogenous leptin tone on the estrous cycle and luteinizing hormone pulsatility in female rats

    Neuroendocrinology

    (1997)
  • S. Dryden et al.

    Neuropeptide Y and energy balance: one way ahead for the treatment of obesity?

    Eur J Clin Invest

    (1994)
  • I. Cusin et al.

    The weight reducing effects of an intracerebroventricular injection of leptin in genetically obese fa/fa rats: reduced sensitivity compared with lean animals

    Diabetes

    (1996)
  • M.W. Schwartz et al.

    Identification of targets of leptin action in rat hypothalamus

    J Clin Invest

    (1996)
  • P. Kristensen et al.

    Hypothalamic CART is a new anorectic peptide regulated by leptin

    Nature

    (1998)
  • O. Khorram et al.

    Bimodal effects of neuropeptide Y on hypothalamic release of gonadotrophin hormone in conscious rabbits

    Neuroendocrinology

    (1987)
  • K.Y.F. Pau et al.

    Hypothalamic site-dependent effects of neuropeptide Y on gonadotropin-releasing hormone secretion in rhesus macaques

    J Neuroendocrinol

    (1995)
  • N.M. Cruaz et al.

    Evidence that neuropeptide Y could represent a neuroendocrine inhibitor of sexual maturation in unfavorable metabolic conditions in the rat

    Endocrinology

    (1993)
  • D.D. Pierroz et al.

    Chronic administration of neuropeptide Y into the lateral ventricle starting at 30 days of life delays sexual maturation in the female rat

    Neuroendocrinology

    (1995)
  • D.D. Pierroz et al.

    Chronic administration of Neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insulin-like growth factor 1 secretion in intact adult male rats

    Endocrinology

    (1996)
  • S. Minami et al.

    Central administration of neuropeptide Y induces precocious puberty in female rats

    Neuroendocrinology

    (1992)
  • M.C. Lebrethon et al.

    Cocaine-and amphetamine-regulated transcript (CART)-peptide mediation of leptin stimulatory effect on the rat gonadotrophin-releasing hormone pulse generator in vitro

    J Neuroendocrinol

    (2000)
  • M.C. Lebrethon et al.

    In vitro stimulation of the prepubertal rat gonadotrophin-releasing hormone pulse generator by leptin and neuropeptide Y through distinct mechanisms

    Endocrinology

    (2000)
  • J.P. Bourguignon et al.

    Direct activation of GnRH secretion through different receptors to neuroexitatory amino acids

    Neuroendocrinology

    (1989)
  • J.P. Bourguignon et al.

    Pulsatile release of Gonadotrophin-releasing hormone from hypothalamic explants is restrained by blockade of N-methyl-d,l-aspartate receptors

    Endocrinology

    (1989)
  • G. Purnelle et al.

    Pulsatile secretion of gonadotrophin-releasing hormone by rat hypothalamic explants without cell bodies of GnRH neurons

    Neuroendocrinology

    (1997)
  • D.E. Hartter et al.

    Responsiveness of immature versus adult male rat hypothalami to dibutyryl cyclic AMP-and Forskolin-induced LHRH release in vitro

    Neuroendocrinology

    (1985)
  • Ruëger H., Schmidlin T., Rigollier P., Yamaguchi Y., Tintelnot-Blomley M., Schilling W., Criscione L., Mah R. Receptor...
  • Cited by (93)

    • The effect of CART on pituitary hormones release from cultured pituitary cells harvested from fasted and fed ad libitum male rats

      2017, Peptides
      Citation Excerpt :

      Secondly, CART is able to change GnRH generator activity, as a group of Lebrethon revealed that CART caused a reduction of GnRH interpulse interval [30]. Moreover, leptin effects on pulsatile GnRH secretion are mediated by CART [37]. Finally, the findings of Brunetti and co-workers confirmed that CART coexists with gonadotrophins, LH and FSH, in the secretory granules of gonadotrophic cells [9].

    • Physiology of the Adult Gonadotropin-Releasing Hormone Neuronal Network

      2015, Knobil and Neill's Physiology of Reproduction: Two-Volume Set
    • Chemical identity of hypothalamic neurons engaged by leptin in reproductive control

      2014, Journal of Chemical Neuroanatomy
      Citation Excerpt :

      However, LepRb signaling via neural targets alone is sufficient for reproductive function. Dense LepRb expression in the hypothalamus along with leptin’s role in increasing frequency of LH pulses initially suggested that leptin acted directly on gonadotropin-releasing hormone (GnRH) neurons (Yu et al., 1997; Lebrethon et al., 2000; Parent et al., 2000; Wojcik-Gladysz et al., 2009). However, virtually no LepRb has been detected in GnRH neurons and the deletion of the Lepr gene from GnRH cells produces no reproductive deficit (Quennell et al., 2009; Donato et al., 2011a; Louis et al., 2011).

    View all citing articles on Scopus
    View full text