Caroline Jane Small

Ghrelin increases food intake in obese as well as lean subjects

OBJECTIVE:To investigate whether effects on food intake are seen in obese subjects receiving exogenous administration of ghrelin.DESIGN:Randomised, double-blind, placebo-controlled study of intravenous ghrelin at doses 1 pmol/kg/min and 5 pmol/kg/min.SUBJECTS:In all, 12 healthy lean subjects (mean body mass index (BMI) 20.5±0.17 kg/m2) and 12 healthy overweight and obese subjects (mean BMI 31.9±1.02 kg/m2).MEASUREMENTS:Food intake, appetite and palatability of food, ghrelin and other obesity-related hormones, growth hormone.RESULTS:Low-dose infusion of ghrelin increased ad libitum energy intake at a buffet meal in the obese group only (mean increase 36.6±9.4%, P<0.01.) High-dose ghrelin infusion increased energy intake in both groups (mean increase 20.1±10.6% in the lean and 70.1±15.5% in the obese, P<0.01 in both cases.) Ghrelin infusion increased palatability of food in the obese group.CONCLUSION:Ghrelin increases food intake in obese as well as lean subjects. Obese people are sensitive to the appetite-stimulating effects of ghrelin and inhibition of circulating ghrelin may be a useful therapeutic target in the treatment of obesity.

Oxyntomodulin increases energy expenditure in addition to decreasing energy intake in overweight and obese humans: a randomised controlled trial

Background:Oxyntomodulin has recently been found to decrease body-weight in obese humans and may be a potential anti-obesity therapy.Objective:To determine whether oxyntomodulin alters energy expenditure, in addition to reducing energy intake, in ‘free-living’ overweight and obese volunteers.Design:Randomized double-blind controlled cross-over trial.Setting:Community and hospital-based.Participants:Fifteen healthy overweight and obese men and women (age: 23–49 years, BMI: 25.1–39.0 kg/m2). All volunteers completed the study protocol.Interventions:Four-day subcutaneous self-administration of pre-prandial oxyntomodulin, three times daily. Participants were advised to maintain their normal dietary and exercise regimen.Measurements:(1) Energy expenditure, measured by indirect calorimetry and combined heart rate and movement monitoring; (2) energy intake, measured during a study meal.Results:Oxyntomodulin administration reduced energy intake at the study meal by 128±29 kcal (P=0.0006) or 17.3±5.5% (P=0.0071), with no change in meal palatability. Oxyntomodulin did not alter resting energy expenditure; but increased activity-related energy expenditure by 143±109 kcal/day or 26.2±9.9% (P=0.0221); total energy expenditure by 9.4±4.8% (P=0.0454) and physical activity level by 9.5±4.6% (P=0.0495). A reduction in body weight of 0.5±0.2% was observed during the oxyntomodulin administration period (P=0.0232).Conclusion:Oxyntomodulin increases energy expenditure while reducing energy intake resulting in negative energy balance. This data supports the role of oxyntomodulin as a potential anti-obesity therapy.

The central melanocortin system affects the hypothalamo-pituitary thyroid axis and may mediate the effect of leptin.

Prolonged fasting is associated with a downregulation of the hypothalamo-pituitary thyroid (H-P-T) axis, which is reversed by administration of leptin. The hypothalamic melanocortin system regulates energy balance and mediates a number of central effects of leptin. In this study, we show that hypothalamic melanocortins can stimulate the thyroid axis and that their antagonist, agouti-related peptide (Agrp), can inhibit it. Intracerebroventricular (ICV) administration of Agrp (83-132) decreased plasma thyroid stimulating hormone (TSH) in fed male rats. Intraparaventricular nuclear administration of Agrp (83-132) produced a long-lasting suppression of plasma TSH, and plasma T4. ICV administration of a stable alpha-MSH analogue increased plasma TSH in 24-hour-fasted rats. In vitro, alpha-MSH increased thyrotropin releasing hormone (TRH) release from hypothalamic explants. Agrp (83-132) alone caused no change in TRH release but antagonized the effect of alpha-MSH on TRH release. Leptin increased TRH release from hypothalami harvested from 48-hour-fasted rats. Agrp (83-132) blocked this effect. These data suggest a role for the hypothalamic melanocortin system in the fasting-induced suppression of the H-P-T axis.

Neuropeptide Y Induced Feeding in the Rat Is Mediated by a Novel Receptor1

There are now six recognized neuropeptide Y (NPY) receptor subtypes (Y1-Y4 and two recently cloned distinct receptors labeled Y5), of which Y1 and one of the Y5s have been suggested could mediate the effect of NPY on feeding. The fragments NPY(2-36) and NPY(3-36), which bind Y1 only poorly, were injected intracerebroventricularly (icv) and found to have similar dose-response relationships to NPY in the stimulation of feeding. However NPY (13-36), which stimulates both Y2 and Y5, caused no increase in food intake, even at high doses. Maximal stimulation with the classical Y1 agonist [Pro34]-NPY produced only 50% of the maximum effect of NPY itself despite fully inhibiting adenylyl cyclase activity in vitro in a Y1 system. The novel fragment [Pro34]-NPY(3-36) is as effective at stimulating food intake as the classical Y1 analogue [Pro34]-NPY but bound to the Y1 receptor with only 1/20th of the affinity of NPY and failed to inhibit adenylyl cyclase through this receptor. [Pro34]-NPY(3-36) is therefore a relatively appetite-selective ligand. Coadministration of high dose NPY(13-36) and [Pro34]NPY did not enhance feeding compared with [Pro34]-NPY alone. In addition, the NPY Y1 receptor antagonist BIBP-3226, which does not bind Y2, Y4, or Y5 receptors, significantly reduced NPY induced feeding. These results indicate that the feeding effect of icv NPY involves a novel receptor and that it is functionally distinct from the recognized receptor subtypes.There are now six recognized neuropeptide Y (NPY) receptor subtypes (Y1–Y4 and two recently cloned distinct receptors labeled Y5), of which Y1 and one of the Y5’s have been suggested could mediate the effect of NPY on feeding. The fragments NPY(2–36) and NPY(3–36), which bind Y1 only poorly, were injected intracerebroventricularly (icv) and found to have similar dose-response relationships to NPY in the stimulation of feeding. However NPY(13–36), which stimulates both Y2 and Y5, caused no increase in food intake, even at high doses. Maximal stimulation with the classical Y1 agonist[ Pro34]-NPY produced only 50% of the maximum effect of NPY itself despite fully inhibiting adenylyl cyclase activity in vitro in a Y1 system. The novel fragment[ Pro34]-NPY(3–36) is as effective at stimulating food intake as the classical Y1 analogue [Pro34]-NPY but bound to the Y1 receptor with only 1/20th of the affinity of NPY and failed to inhibit adenylyl cyclase through this receptor.[ Pro34]-NPY(3–36) is therefore a rela...

The Central Effects of Orexin‐A in the Hypothalamic‐Pituitary‐Adrenal Axis In Vivo and In Vitro in Male Rats

Orexin‐A is synthesized in the posterolateral hypothalamus and immunoreactive fibres project to many central nervous system structures, including the paraventricular nucleus, which is rich in corticotropin releasing factor (CRF) neurones and neuropeptide Y (NPY) innervation. We investigated the central effects of orexin‐A on the hypothalamic‐pituitary‐adrenal (HPA) axis by measuring plasma concentrations of corticosterone and adrenocorticotropic hormone (ACTH) in vivo. We explored the potential neuropeptide pathways involved by investigating the effects of orexin‐A on CRF, NPY, arginine vasopressin (AVP) and noradrenaline release from hypothalamic explants in vitro. Intracerebroventricular (i.c.v.) injection of orexin‐A (3 nmol) in male rats stimulated increases in plasma concentrations of corticosterone between 10 and 40 min after injection, and of plasma ACTH at 20 and 90 min after injection. Orexin‐A significantly stimulated CRF and NPY release from hypothalamic explants in vitro. Orexin‐A did not stimulate CRF release in the presence of the selective NPY Y1 receptor antagonist, BIBP3226. BIBP3226 alone did not alter CRF release from hypothalamic explants. Orexin‐A had no effect in vitro on the release of other neuropeptides, AVP and noradrenaline, involved in the central regulation of the HPA axis. These results suggest that orexin‐A is involved in activation of the HPA axis, and that these effects could be mediated via the release of NPY.

Subcutaneous administration of ghrelin stimulates energy intake in healthy lean human volunteers.

Background:The gastric hormone ghrelin appears a useful agent to stimulate food intake in people with anorexia of illness. The loss of ghrelins acyl group renders it inactive, thus it has been thought that subcutaneous administration may be problematic.Objective:To investigate whether human subjects are sensitive to the effects of ghrelin administered by single subcutaneous injection.Study design:Randomized, double-blind, placebo-controlled trial.Subjects:Sixteen healthy lean volunteers (eight men and eight women).Protocol:Fasted subjects received subcutaneous injections of ghrelin (3.6 nmol/kg) or saline. After 30 min, a buffet breakfast was served.Results:Ghrelin injection increased energy intake by 27% (ghrelin 5076±691 kJ versus saline 4230±607 kJ, P=0.04). Ghrelin appeared to enhance the perceived palatability of the food offered (palatability score: ghrelin 81.1±3.6 versus saline 70.0±4.4; P=0.03).Conclusions:These results suggest that subcutaneous ghrelin is effective at stimulating energy intake and improving palatability and may be of direct use in the treatment of appetite loss.

Effects of acute and chronic relaxin-3 on food intake and energy expenditure in rats

The effects of acute and repeated intraparaventricular (iPVN) administration of human relaxin-3 (H3) were examined on food intake, energy expenditure, and the hypothalamo-pituitary thyroid axis in male Wistar rats. An acute high dose iPVN injection of H3 significantly increased food intake 1 h post-administration [0.4+/-0.1 g (vehicle) vs 1.6+/-0.5 g (180 pmol H3), 2.4+/-0.5 g (540 pmol H3) and 2.2+/-0.5 g (1,620 pmol H3), p<0.05 for all doses vs vehicle]. Repeated iPVN H3 injection (180 pmol/twice a day for 7 days) significantly increased cumulative food intake in ad libitum fed animals compared with vehicle [211.8+/-7.1 g (vehicle) vs 261.6+/-6.7 g (ad libitum fed H3), p<0.05]. Plasma leptin was increased in the H3 ad libitum fed group. Plasma thyroid stimulating hormone was significantly decreased after acute and repeated administration of H3. These data suggest H3 may play a role in long-term control of food intake.

Investigation of the feeding effects of melanin concentrating hormone on food intake — action independent of galanin and the melanocortin receptors

Melanin concentrating hormone (MCH) is recognised as a hypothalamic appetite stimulant. The mechanism of action of MCH is undetermined largely due to lack of identification of hypothalamic MCH receptors. We designed in vivo and in vitro studies to further characterise the feeding effects of MCH in the rat. MCH was injected directly into the paraventricular nucleus (PVN) at the beginning of the light phase. PVN MCH (0.5 microg) produced an increase in 2 h food intake of 272+/-60% vs. saline control (0.7+/-0.2 g), p<0.05. The time course of the effect of intracerebroventricular (i.c.v.) administration of 5 microg MCH on food intake was investigated. An increase in feeding was observed within 15 min from the time of injection and was not sustained beyond half an hour following administration. To investigate a possible interaction with galanin, 5 microg of MCH was injected i.c.v. with or without 10 microg of galanin. The two peptides together increased 1 h feeding above that of either peptide alone, 768+/-62% (compared with the saline group, 0.47+/-0.2 g), p<0.05 vs. 585+/-36%, galanin alone and 317+/-72%, MCH alone. Finally, to investigate if MCH bound to the brain melanocortin receptors, receptor autoradiography was performed on rat brain sections with the stable analogue of alpha MSH, [125I] Nle(4), D-Phe(7)-alphaMSH and unlabeled MCH. MCH did not compete with [125I] Nle(4), D-Phe(7)-alphaMSH binding. Results demonstrate that MCH stimulates feeding via the PVN, has a short onset and duration of action and activates feeding by mechanisms independent to galanin and the melanocortin receptors.

Glucagon-like peptide-1 stimulates luteinizing hormone-releasing hormone secretion in a rodent hypothalamic neuronal cell line.

To examine the influence of the putative satiety factor (GLP-1) on the hypothalamo-pituitary-gonadal axis, we used GT1-7 cells as a model of neuronal luteinizing hormone- releasing hormone (LHRH) release. GLP-1 caused a concentration-dependent increase in LHRH release from GT1-7 cells. Specific, saturable GLP-1 binding sites were demonstrated on these cells. The binding of [125I]GLP-1 was time-dependent and consistent with a single binding site (Kd = 0.07+/-0.016 nM; binding capacity = 160+/-11 fmol/mg protein). The specific GLP-1 receptor agonists, exendin-3 and exendin-4, also showed high affinity (Ki = 0.3+/-0.05 and 0.32+/-0.06 nM, respectively) as did the antagonist exendin-(9-39) (Ki = 0.98+/-0.24 nM). At concentrations that increased LHRH release, GLP-1 (0.5-10 nM) also caused an increase in intracellular cAMP in GT1-7 cells (10 nM GLP-1: 7.66+/-0.4 vs. control: 0.23+/-0.02 nmol/mg protein; P < 0.001). Intracerebroventricular injection of GLP-1 at a single concentration (10 microg) produced a prompt increase in the plasma luteinizing hormone concentration in male rats (GLP-1: 1.09+/-0.11 vs. saline: 0.69+/-0.06 ng/ml; P < 0.005). GLP-1 levels in the hypothalami of 48-h-fasted male rats showed a decrease, indicating a possible association of the satiety factor with the low luteinizing hormone levels in animals with a negative energy balance.

Central administration of orexin A suppresses basal and domperidone stimulated plasma prolactin.

Orexin immunoreactive fibres are abundant in the hypothalamus suggesting a neuroendocrine regulatory role. Intracerebroventricular (ICV) administration of orexin A suppressed plasma prolactin in male rats by 71% at 20 min post‐injection and 83% at 90 min post‐injection (P < 0.005 vs saline at both time points). To investigate whether this effect was through the tuberoinfundibular dopaminergic (TIDA) system, a supra‐maximal dose of domperidone, a dopamine receptor antagonist, was injected intraperitoneally (i.p.) prior to ICV injection of orexin A. ICV orexin A significantly suppressed domperidone (9 mg/kg)‐stimulated plasma prolactin levels, by up to 40% (i.p. domperidone + ICV orexin A 3 nmol 34.5 ± 7.4 ng/ml and i.p. domperidone + ICV orexin A 20 nmol 43.5 ± 4.3 ng/ml, both P < 0.005 vs i.p. domperidone + ICV saline 57.9 ± 2.7 ng/ml). Orexin A, 100 nM, significantly stimulated release of neurotensin, vasoactive intestinal polypeptide, somatostatin, corticotropin releasing factor and luteinizing hormone releasing hormone, but had no effect on release of dopamine, thyrotropin releasing hormone (TRH), vasopressin or melanin‐concentrating hormone from hypothalamic explants in vitro. Orexin A did not alter basal or TRH stimulated prolactin release in dispersed pituitary cells harvested from male rats. The data suggest that ICV administration of orexin A suppresses plasma prolactin in part through a pathway independent of the dopaminergic system.