neuropeptide-y and estradiol-3-benzoate

Overnutrition due to a high-fat diet (HFD) can increase the vulnerability of the metabolic system to maladjustments. Estradiol has an inhibitory role on food intake and this hormone has demonstrated to be a crucial organizer during brain development.. Our aim was to determine whether increased levels of estradiol in the early postnatal period modulate the alterations in metabolism and brain metabolic circuits produced by overnutrition.. Twenty-four male and 24 female Wistar rats were submitted to a HFD (34.9% fat) or a control diet (5% fat) from gestational day 6. From postnatal (P) 6 to P13, both control and HFD groups were administered a s.c. injection of vehicle or estradiol benzoate (0.4 mg/kg), resulting in eight experimental groups (n = 6 in each group). Body weight, food intake and subcutaneous, visceral, and brown fat pads were measured. Agouti-related peptide, neuropeptide Y, orexin, and proopiomelanocortin (POMC) were analyzed by quantitative real-time polymerase chain reaction assay and plasma estradiol levels were measured by ELISA.. Males fed a HFD showed an increase in body weight and the amount of visceral and subcutaneous fat, which was coincident with an increase in the number of kilocalories ingested. Neonatal estradiol treatment restored the body weight and subcutaneous fat of HFD males to control levels. Hypothalamic POMC mRNA levels in HFD females were increased with respect to control females. This increase was reverted with estradiol treatment during development.. HFD and estradiol treatment have different effects on males and females. Overnutrition affects physiological parameters, such as body weight, visceral, and subcutaneous fat content, in males, while females present alterations in hypothalamic POMC mRNA levels. Hence, the increase in estradiol levels during a period that is critical for the programing of the feeding system can modulate some of the alterations produced by the continuous intake of high-fat content food.

Topics: Adiposity; Animals; Body Weight; Diet; Diet, High-Fat; Disease Models, Animal; Estradiol; Female; Hypothalamus; Male; Neuropeptide Y; Orexins; Overnutrition; Pro-Opiomelanocortin; Rats; Rats, Wistar; Sex Factors

Feeding behavior in both animals and humans is modulated by estrogens, as shown by the increased adiposity observed in women and rats upon the drop of estradiol levels at menopause. Estradiol action on food intake is mediated through its cognate receptors within several hypothalamic nuclei, namely the arcuate nucleus (ARN). The ARN contains two neuronal populations expressing peptides that exert opposing effects on the central control of feeding: the orexigenic neuropeptide Y (NPY) and the anorexigenic α-melanocyte-stimulating hormone (α-MSH).. To understand the role played by estradiol in the modulation of food intake, we have used an animal model of cyclic 17β-estradiol benzoate (EB) administration and stereological methods to estimate the total number of neurons immunoreactive for NPY and α-MSH in the ARN of ovariectomized rats.. Present results show that the experimentally induced EB cyclicity prompted a decrease in food consumption and in body weight. Data also show that ovariectomy induced an increase in NPY expression and a decrease in α-MSH expression in the ARN that were reverted by EB administration. Conversely, EB blocked the expression of NPY and increased the synthesis of α-MSH in ARN neurons, without affecting the overall sum of NPY and α-MSH neurons.. These results suggest that estradiol affects food intake and, consequently, body weight gain, through an overriding mechanism superimposed in the physiological balance between both peptides in the ARN of female rats.

Topics: alpha-MSH; Analysis of Variance; Animals; Arcuate Nucleus of Hypothalamus; Cell Count; Contraceptive Agents; Eating; Estradiol; Female; Gene Expression Regulation; Neurons; Neuropeptide Y; Ovariectomy; Rats; Rats, Wistar; Stereotaxic Techniques; Time Factors

The ovarian steroid hormone, estradiol, is one of several peripheral metabolic signal modulators that are integrated at the level of the arcuate nucleus of the hypothalamus (ARH), and is implicated in the control of ARH neuropeptides that maintain energy balance, including neuropeptide Y (NPY) and proopiomelanocortin (POMC). The present studies utilized quantitative real-time RT-PCR techniques to examine the hypothesis that estradiol regulates ARH NPY, POMC, and cocaine- and amphetamine-related transcript (CART) gene expression during acute insulin-induced hypoglycemia (IIH) and that adaptive modifications in transcriptional reactivity during recurring exposure are steroid dependent. ARH tissue was obtained by micropunch dissection from estradiol benzoate- and oil-implanted ovariectomized (OVX) rats that were treated by subcutaneous injection of one or four doses of the intermediate insulin formulation, Humulin NPH, over as many days, or vehicle alone. Our data show that in OVX plus estradiol benzoate and OVX plus oil groups, a single injection of insulin did not modify gene expression profiles, with the exception of acute hypoglycemic reduction of ARH NPY transcripts in the presence of estrogen. Prior exposure to daily hypoglycemia significantly diminished basal NPY and POMC mRNA levels in estradiol benzoate-, but not oil-implanted OVX rats, but elevated baseline CART transcripts in oil-treated animals. Recurring IIH enhanced ARH NPY gene expression relative to baseline, irrespective of the estradiol manipulation, but net tissue levels were greater in the absence of estrogen. In contrast, reexposure to hypoglycemia decreased POMC and CART gene transcription in estradiol benzoate- and oil-implanted OVX animals, respectively, relative to the single-dose groups. These studies show that estrogen modulates the impact of precedent exposure to IIH on basal and/or hypoglycemia-associated patterns of expression of ARH neuropeptide genes of characterized significance for energy homeostasis. The novel evidence for transcriptional acclimation of NPY, POMC, and CART to recurring IIH supports the possibility that adaptation of compensatory behavioral and physiological responses to acute versus chronic exposure to this metabolic stress may reflect neural regulatory mechanisms involving one or more neurotransmitters encoded by these genes.

Topics: Animals; Arcuate Nucleus of Hypothalamus; Estradiol; Female; Gene Expression Regulation; Hypoglycemia; Insulin; Nerve Tissue Proteins; Neuropeptide Y; Ovariectomy; Pro-Opiomelanocortin; Rats; Rats, Sprague-Dawley; Transcription, Genetic

Of the various environmental factors influencing reproduction, food availability plays a particularly significant role, and an insufficient supply of oxidizable metabolic fuels inhibits reproduction in female mammals. When ovariectomized, steroid-primed hamsters are food deprived for 48 h, estrous behavior is suppressed. However, the specific neuroendocrine alterations that mediate the suppression of estrous behavior are unknown. Several conditions that inhibit female sexual behavior are thought to be associated with altered neuropeptide Y (NPY) activity in the brain. Intracerebroventricular (ICV) infusion of NPY inhibits estrous behavior in ovariectomized steroid-primed rats and hamsters. Furthermore, food-deprived rats have an increase in NPY mRNA in the arcuate nucleus (ARC) of the hypothalamus. Unlike rats, studies in Syrian hamsters have failed to detect any alterations in ARC NPY mRNA following food deprivation. Here we show that ARC NPY immunoreactivity and mRNA is increased in food-deprived hamsters but not in hamsters given other metabolic challenges that inhibit estrous behavior. These findings support the hypothesis that NPY contribute to, but not be critical for, the nutritional inhibition of sexual receptivity.

Topics: Animals; Antimetabolites; Arcuate Nucleus of Hypothalamus; Behavior, Animal; Body Weight; Cell Count; Cold Temperature; Cricetinae; Deoxyglucose; Eating; Epoxy Compounds; Estradiol; Estrus; Female; Food Deprivation; Hypoglycemic Agents; Immunohistochemistry; In Situ Hybridization; Mesocricetus; Neurons; Neuropeptide Y; Ovariectomy; Posture; Progesterone; Propionates; RNA, Messenger; Sexual Behavior, Animal

Studies in rats suggest that neuropeptide Y (NPY) plays a stimulatory role in the generation of the preovulatory luteinizing hormone (LH) surge, via the Y1 receptor. We have investigated this issue using the oestradiol benzoate (EB)-treated ovariectomized (OVX) ewe which is a model for the preovulatory LH surge. A Y1 receptor antagonist (BIBO3304) was infused (25 microg/h) into the third cerebral ventricle (III-V) from 2 h before EB injection for 24 h, and had no effect on the ensuing LH surge. Using in situ hybridization, we then examined expression of NPY mRNA in the arcuate nucleus during the luteal, follicular and oestrous phases of the oestrous cycle, and found that levels were greatest during the luteal phase. Thus, reduced NPY synthesis might be an integral factor in the events leading to the cyclic preovulatory LH surge. This was tested by infusion of NPY (25 microg/h) into the III-V (as above). The NPY infusion delayed the LH surge until the infusion was ceased. High levels of NPY expression during the luteal phase of the oestrous cycle may be caused by progesterone. Thus, we determined whether NPY cells possess progesterone receptors (PR) and whether progesterone treatment up-regulates NPY mRNA expression in the arcuate nucleus. Immunohistochemistry for NPY and PR was performed in OVX, oestrogen-treated ewes, but no NPY cells of the arcuate nucleus were seen to colocalize PR. In situ hybridization for NPY was performed in OVX and OVX ewes treated with progesterone. There was no significant effect of progesterone treatment on NPY mRNA expression in the arcuate nucleus. We conclude that chronically elevated levels of NPY block the preovulatory surge of gonadotropin-releasing hormone/LH secretion in sheep, but high levels of NPY mRNA expression in the luteal phase of the oestrous cycle cannot be explained by an action of progesterone.

Topics: Animals; Arcuate Nucleus of Hypothalamus; Arginine; Cross-Over Studies; Down-Regulation; Estradiol; Estrus; Female; Gonadotropin-Releasing Hormone; In Situ Hybridization; Luteinizing Hormone; Neuropeptide Y; Ovariectomy; Ovulation; Progesterone; Receptors, Neuropeptide Y; Receptors, Progesterone; RNA, Messenger; Sheep

To clarify the role of neuropeptide Y (NPY) in the regulation of the reproductive axis, these experiments evaluated the extent to which reproductive hormone secretions may be compromised in the absence of NPY expression. In NPY knockout (NPY-KO) and wild-type (WT) mice, hormone secretions were analyzed under conditions of basal release, following ovariectomy (OVX), in proestrus, after estrogen treatments which induce gonadotropin surges and after injection of gonadotropin-releasing hormone (GnRH). Radioimmunoassays of serum from metestrous females revealed that basal luteinizing hormone (LH), follicular-stimulating hormone (FSH), estrogen and progesterone levels, as well as hypothalamic GnRH tissue concentrations, were not different between the two genotypes. The LH and FSH levels and GnRH tissue concentrations were likewise similar in WT and NPY-KO mice 5 and 10 days following OVX. Significant differences in LH levels were observed however when animals were exposed to pheromone stimulation (male mouse urine) to induce preovulatory LH surges. In proestrous animals, mean LH levels at 18.30-19.00 h were reduced by about 66% in NPY-KO versus WT mice (4.33 +/- 1.12 ng/ml in the WT mice vs. 1.47 +/- 0.42 ng/ml in the NPY-KO mice, p = 0.028). Despite diminishment of LH surges in NPY-KO mice, corpora lutea were equally abundant in the ovaries of NPY-KO and WT mice. In an additional experiment, a surge-inducing regimen of estradiol-17-beta (E2) and estradiol benzoate (E2B) was administered to OVX animals. The LH surges in the NPY-KO animals treated in this manner were again diminished by approximately 50% compared to corresponding values in WT animals (WT mice 7.33 +/- 0.97 ng/ml, NPY-KO mice 3.58 +/- 0.74 ng/ml; p = 0.0063). To assess the contribution of altered pituitary responsiveness to the diminishment of LH surges, LH responses to a GnRH challenge (200 ng/kg subcutaneously) were determined; NPY-KO animals exhibited LH responses that were significantly reduced compared to values in WT mice (WT mice 4.88 +/- 0.56 ng/ml, NPY-KO mice 3.00 +/- 0.41 ng/ml; p = 0.013). Taken together, these observations do not support the idea that NPY plays a major role in the regulation of basal gonadotropin secretion or in mediating negative feedback actions of gonadal hormones. They demonstrate however that preovulatory NPY release is required for normal amplification of the LH surge that occurs on proestrus. Involvement of NPY in the generation of normal LH surges is partiall

Topics: Animals; Estradiol; Female; Gonadotropin-Releasing Hormone; Luteinizing Hormone; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neuropeptide Y; Ovariectomy; Pheromones; Pregnancy; Proestrus; Reproduction

A large body of evidence indicates that neuropeptide Y (NPY) is involved in stimulation of basal and cyclic release of hypothalamic LHRH and pituitary LH. To identify the NPY receptor subtypes that mediate the excitatory effects of NPY in these two modalities of LH release, we studied the effects of 1229U91, a selective Y1 receptor antagonist and Y4 receptor agonist, in two experimental paradigms that reproduce the two modalities of LH secretion in steroid-primed ovariectomized (OVX) rats. Rats were ovariectomized and implanted with a permanent cannula into the lateral cerebroventricle. In the first experiment, rats received estradiol benzoate (EB, 30 microg/rat) on day 5, followed 2 days later with progesterone (2 mg/rat) at 1000 h to induce an afternoon LH surge. 1229U91 (30 microg/3 microl) or vehicle (control) was injected intracerebroventricularly into these rats either once at 1300 h or twice (15 microg/injection) at 1100 and 1200 h. Blood samples were collected before progesterone injection at 1000 h and at hourly intervals from 1300 -1800 h via an intrajugular cannula implanted on the previous day. In control rats, serum LH levels rose significantly at 1400 h, and these high levels were maintained until 1700 h. After two injections of 1229U91, LH levels displayed a tendency to rise at 1300-1400 h, as in controls, but thereafter, decreased rapidly below the control range. In the second experiment, the acute effect of 1229U91 on LH release was evaluated in OVX rats pretreated with EB alone. Saline alone or saline containing 1, 3, 10, or 30 microg 1229U91 was injected intracerebroventricularly at 1000 h, and the effects on LH release were analyzed at 10, 20, 30, and 60 min. 1229U91 elicited a dose-dependent stimulation of LH release, with maximal response (950% of basal levels) occurring at 10 min after the 30-microg dose; elevated levels were maintained for 1 h. Because 1229U91 is a potent Y4 agonist with some affinity for Y5 receptors, these results raised the possibility that activation of Y4/Y5 receptors by 1229U91 may augment LH release. Therefore, we examined the effects of icv administration of rat pancreatic polypeptide, a Y4-selective agonist, and [D-Trp32]-NPY, a Y5 agonist on LH release in EB-primed rats. Rat pancreatic polypeptide (0.5-2 microg/rat) stimulated LH release in a dose-related manner, and peak levels (280% of basal levels) were seen at 10-20 min; the response evoked by a higher dose (10 microg) was smaller than that induced by

Topics: Amino Acid Sequence; Animals; Estradiol; Female; Luteinizing Hormone; Molecular Sequence Data; Neuropeptide Y; Ovariectomy; Pancreatic Polypeptide; Peptides, Cyclic; Pituitary Gland; Progesterone; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide Y

In previous studies we have shown that the pulsatility of LH-releasing hormone (LHRH) release in gonadectomized monkeys is modulated by input from neuropeptide-Y (NPY) neurons: 1) the endogenous release of NPY in the stalk-median eminence (S-ME) was pulsatile; 2) NPY pulses were temporally correlated with LHRH pulses, with NPY pulses preceding LHRH pulses by approximately 5 min; and 3) infusion of NPY into the S-ME stimulated LHRH release, whereas 4) infusion of antiserum to NPY suppressed endogenous LHRH pulses. It is not known, however, whether ovarian steroid hormones alter the pulsatility of NPY and LHRH release or whether the temporal correlation of NPY and LHRH pulses is maintained during the LH surge. In the present study we examined the changes in pulsatile release of NPY and LHRH in ovariectomized monkeys treated with estradiol benzoate (EB) followed by progesterone or oil. Using push-pull perfusion, perfusate samples from S-ME were collected at 10-min intervals for 15 h. NPY and LHRH concentrations in the perfusates were measured by RIA. Circulating LH levels were also monitored by periodic blood sampling and RIA. Injection of progesterone (sc) after EB induced an LH surge with a peak latency of 7.3 +/- 1.3 h (mean +/- SE) in seven of seven monkeys, whereas oil injection after EB elicited an LH surge in none of seven monkeys. The progesterone-induced LH surge was associated with an increase in LHRH release; the mean, pulse amplitude, and pulse frequency increased significantly (for all, P < 0.05) 4-8 h after progesterone. NPY pulse frequency also increased significantly (P < 0.05) 4-8 h after progesterone treatment, whereas mean release and pulse amplitude did not change in response to progesterone. Oil treatment after EB administration did not alter any parameter of LHRH and NPY pulses. Interestingly, the NPY and LHRH pulses were highly correlated (P < 0.001) in monkeys treated with either EB-progesterone or EB-oil, and NPY pulses preceded LHRH pulses by 4.8 +/- 0.7 and 5.1 +/- 0.6 min, respectively. In summary, 1) an episode of increased LHRH release occurs before and during the progesterone-induced LH surge; 2) acceleration of LHRH pulse frequency and the increase in LHRH pulse amplitude after progesterone are accompanied by acceleration of NPY pulse frequency; and 3) ovarian steroids do not affect the temporal correlation between NPY and LHRH pulses.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Animals; Estradiol; Estrogens; Female; Gonadotropin-Releasing Hormone; Luteinizing Hormone; Macaca mulatta; Neuropeptide Y; Progesterone; Pulsatile Flow; Radioimmunoassay; Time Factors