Biological actions of peptide YY: effects on endocrine pancreas, pituitary-adrenal axis, and plasma catecholamine concentrations in the dog

Appetite-regulating hormones cortisol and peptide YY are associated with disordered eating psychopathology, independent of body mass index

OBJECTIVE

Disordered eating occurs in women at both weight extremes of anorexia nervosa (AN) and obesity. Cortisol, peptide YY (PYY), leptin, and ghrelin are hormones involved in appetite and feeding behavior that vary with weight and body fat. Abnormal levels of these hormones have been reported in women with AN, functional hypothalamic amenorrhea (HA), and obesity. The relationship between appetite-regulating hormones and disordered eating psychopathology is unknown. We therefore studied the relationship between orexigenic and anorexigenic hormones and disordered eating psychopathology in women across a range of weights.

DESIGN

A cross-sectional study of 65 women, 18-45 years: 16 with AN, 12 normal-weight with HA, 17 overweight or obese, and 20 normal-weight in good health.

METHODS

Two validated measures of disordered eating psychopathology, the Eating Disorders Examination-Questionnaire (EDE-Q) and Eating Disorders Inventory-2 (EDI-2), were administered. Fasting PYY, leptin, and ghrelin levels were measured; cortisol levels were pooled from serum samples obtained every 20 min from 2000 to 0800 h.

RESULTS

Cortisol and PYY levels were positively associated with disordered eating psychopathology including restraint, eating concerns, and body image disturbance, independent of body mass index (BMI). Although leptin levels were negatively associated with disordered eating psychopathology, these relationships were not significant after controlling for BMI. Ghrelin levels were generally not associated with EDE-Q or EDI-2 scores.

CONCLUSIONS

Higher levels of cortisol and PYY are associated with disordered eating psychopathology independent of BMI in women across the weight spectrum, suggesting that abnormalities in appetite regulation may be associated with specific eating disorder pathologies.

Peptide YY in adolescent athletes with amenorrhea, eumenorrheic athletes and non-athletic controls

BACKGROUND

Bone mineral density (BMD) is lower in amenorrheic athletes (AA) compared with eumenorrheic athletes (EA). Decreased energy availability and altered levels of appetite regulating hormones (ghrelin and leptin) in AA contribute to hypogonadism, an important cause of low BMD. The role of other nutritionally regulated hormones such as peptide YY (PYY) and adiponectin in mediating gonadal status and bone metabolism remains to be determined.

OBJECTIVES

Our objective was to determine whether PYY and adiponectin are higher in AA compared with EA and contribute to hypogonadism and impaired bone metabolism in AA.

METHODS

We determined PYY and adiponectin in 16 AA, 15 EA and 16 non-athletic controls 12-18 years old, and other nutritionally dependent hormones including ghrelin, leptin and IGF-1. We also measured testosterone, estradiol, PINP and NTX (markers of bone formation and resorption) and BMD.

RESULTS

PYY was higher in AA than EA (111+/-52 vs. 61+/-29 pg/ml, p<0.05), whereas adiponectin did not differ between groups. Although activity scores did not differ, BMI was lower in AA than EA and a larger proportion (62.5% vs. 6.7%) reported disordered eating, indicating lower energy availability. PYY and adiponectin were independent predictors of testosterone in a regression model (p=0.01 and 0.04), but did not predict estradiol. PYY, but not adiponectin, was an independent and negative predictor of PINP (p=0.002) and lumbar bone mineral apparent density Z-scores (p=0.045) in this model.

CONCLUSION

High PYY levels (but not adiponectin) differentiate AA from EA, and may be an important factor contributing to low bone density in athletes.

Neuropeptide Y (NPY) actions on the corticotroph cell of the anterior pituitary gland are not mediated by a direct effect

Neuropeptide Y has been implicated in the activation of the hypothalamic-pituitary-adrenal (HPA) axis, the regulation of growth and sexual function, and is the most potent stimulant of feeding yet reported. The actions of NPY on the HPA axis are thought to be mediated via an activation of the corticotrophin releasing hormone (CRH) neurones within the paraventricular nucleus of the hypothalamus. The ability of NPY to directly influence the corticotroph cell is currently controversial. These studies investigated whether NPY could have a direct influence on anterior pituitary adrenocorticotrophic hormone (ACTH) release. In dispersed male rat anterior pituitary cells, NPY (1-1000 nM) had no effect on either basal or CRH (1 nM) stimulated ACTH release. Basal release, NPY (1000 nM) 111 +/- 6% vs. control 103 +/- 5%. CRH stimulated release, CRH (1 nM) with NPY (1000 nM) 226 +/- 23% vs. CRH (1 nM) alone 228 +/- 20%. In addition, NPY (1000 nM) had no effect on either basal or CRH (1 nM) stimulated ACTH release in the mouse corticotroph cell line, AtT-20. Thus, in two models of the anterior pituitary corticotroph NPY had no effect on ACTH release. NPY induced activation of the HPA axis is likely to be mediated via a modulation of hypothalamic CRH and not via a direct action at the level of the anterior pituitary.

Peptide YY in the mammalian pancreas: immunocytochemical localization and immunochemical characterization

Peptide YY (PYY) was demonstrated by immunochemical and/or immunocytochemical methods in endocrine cells in the pancreas of adult mice, rats, guinea-pigs, cats, dogs, pigs and cows. In the pancreas of mouse and rat, immunoreactive PYY was observed in a major subpopulation of the glucagon cells (splenic lobe of the pancreas); immunoreactive PYY also occurred in a subpopulation of the pancreatic polypeptide (PP) cells (duodenal lobe), and in a few extra-insular endocrine cells dispersed throughout the pancreatic parenchyma. In the pancreas of cat, dog and pig immunoreactive PYY was found to coexist with PP, but not with glucagon. Radioimmunoassay (RIA) revealed PYY-like material in extracts of pancreas (and colon) of all the species examined. The highest concentrations were found in the pancreas of cat and mouse; moderate amounts were found in the rat and only small amounts were detected in guinea-pig and pig. The concentrations in the pancreas were uniformly much lower than those in the colon. Analysis by high performance liquid chromatography (HPLC) showed that the PYY-immunoreactive material from pancreas (and rat colon) had an elution profile very similar to that of synthetic PYY, and distinct from that of PP and neuropeptide Y.

Low hepatic clearance of peptide YY (PYY) in the perfused rat liver

The hepatic clearance rate and secretion rate mainly determine peripheral plasma concentrations of regulatory peptides released from the gastrointestinal tract. In the present study hepatic extraction of peptide YY (PYY) during a single passage was investigated in the in situ perfused rat liver excluding modulating actions of circulating hormones. During perfusion of low amounts of PYY (50, 100, 500 pmol l-1), peptide concentrations in the portal vein (5.1 +/- 4.6, 98.1 +/- 2.6, 558 +/- 13.6 pmol l-1) and in the hepatic vein (50.2 +/- 1.4, 88.6 +/- 2.2, 503 +/- 18.1 pmol l-1 was only 22.1%. PYY had no influence on hepatic glucose and lactate production, portal flow as well as bile flow and bile acid secretion at these concentrations. PYY seems to traverse the liver almost intact and reaches the target organs without any significant hepatic extraction. Concomitant studies on metabolic and excretory functions of the liver showed no effect of PYY.

PYY-like material and its spatial relationship with NPY, CGRP and 5-HT in the lung of the Syrian golden hamster

We investigated the presence of peptide YY, neuropeptide Y, calcitonin gene-related peptide and serotonin in the hamster lung by radioimmunoassay, high performance liquid chromatography and immunocytochemistry. Lung-tissue concentrations of peptide YY and neuropeptide Y were 1.3 +/- 0.2 and 2.5 +/- 0.2 pmol/g wet weight, respectively. These two closely related pancreatic peptides were demonstrated in separate peaks with high performance liquid chromatography. The peptide YY appeared fragmented as immunoreactive peptide YY eluted primarily late in the gradient but showed additional peaks early in the gradient. Peptide YY-like immunoreactivity (PYY-LI) was predominantly observed in one or more cells of neuroepithelial bodies in all airways peripheral to bronchioles, and in solitary neuroendocrine cells primarily located in the same peripheral areas. Neuropeptide Y-LI was seen in individual, thin nerve fibers around arteries and veins, in the airway lamina propria, and in the airway epithelium; in the latter also immunopositive nerve terminals were located. This pattern did not appear to coincide with that of calcitonin gene-related peptide-LI in epithelial nerve fibers and terminals. Peptide YY-LI, calcitonin gene-related-LI and serotonin-LI were present in cells of one and the same neuroepithelial body. However, peptide YY-LI was never found to be co-localized with calcitonin gene-related-LI or serotonin-LI, but the latter two were co-localized as previously reported.

Brain neuropeptide Y in the control of adrenocorticotropic hormone secretion in the dog

An immunoneutralization technique with specific antibodies was used to explore the role of endogenous neuropeptide Y (NPY) in the adrenocorticotropic hormone (ACTH) release after hypoglycemic stress in the dog. Dogs received injections of rabbit antihuman NPY gamma-globulin (anti-NPY) or normal gamma-globulin (NGG) into the third cerebral ventricle, which was followed by i.v. injection of insulin. Hypoglycemia of a 40% fall in systemic glucose levels occurred in anti-NPY-treated dogs as well as NGG-treated animals. An intraventricular administration of anti-NPY significantly inhibited the ACTH and cortisol release to hypoglycemia, but had no effect on the pancreatic polypeptide (PP) response. These findings suggest involvement by endogenous NPY in the ACTH secretion induced by hypoglycemia.

Physiological antagonism between prostaglandin E2 and neuropeptide Y on thermoregulation in the dog

These experiments were undertaken to determine whether neuropeptide Y (NPY) could suppress a prostaglandin hyperthermia in conscious dogs. Prostaglandin E2 (PGE2) (5 micrograms), injected into the lateral cerebral ventricle (ILV), evoked a hyperthermia of approximately 1 degrees C. Addition of ILV NPY (5 micrograms) significantly attenuated the PGE2-induced hyperthermia, whereas pancreatic polypeptide (PP), another member of the PP family peptide, did not. These results provide evidence for a role of NPY on thermoregulation in the dog.

Effect of neuropeptide Y on the hypothalamic-pituitary-adrenal axis in the dog

There is increasing evidence that neuropeptide Y (NPY) affects the release of pituitary hormones, including adrenocorticotropic hormone (ACTH). The present study was designed to clarify the mechanism by which NPY activates the hypothalamic-pituitary-adrenal (HPA) axis in the dog. Mongrel dogs were equipped with a chronic cannula allowing intra-third (i.t.v.) or intra-lateral (i.l.v.) cerebroventricular administration. A 1.19 nmol, i.t.v. dose of NPY produced as great an ACTH and cortisol response as did equimolar ovine corticotropin releasing factor (CRF). This action of NPY was dose-dependent and shared by peptide YY (PYY) and pancreatic polypeptide (PP), other members of the PP family peptide. Intravenously (i.v.) administered NPY (1.19-11.9 nmol) was much less potent than i.v. CRF in stimulating ACTH and cortisol secretion. However, i.v. NPY significantly increased plasma ACTH and cortisol concentrations, raising the possibility that NPY may modulate the activity of corticotrophs. We have next investigated the possible relationship between NPY and CRF on the HPA axis. Pretreatment with a novel CRF antagonist, alpha-helical CRF9-41 (130.9 nmol i.t.v. or 261.8 nmol i.v.), partly but significantly attenuated the ACTH and cortisol responses to i.t.v. NPY (1.19 nmol). Furthermore, adding a subthreshold dose of i.t.v. NPY (0.119 nmol) to i.t.v. CRF (1.19 nmol) or i.v. NPY (2.38 nmol) to i.v. CRF (0.595 nmol) resulted in the potentiation of CRF-induced ACTH secretion. These results indicate that NPY may activate the HPA axis in concert with CRF probably at hypothalamic and/or pituitary levels. The present findings that NPY evokes ACTH secretion and potentiates the effectiveness of CRF as a secretagogue, together with high concentrations of NPY in the hypothalamus and pituitary portal blood, suggest that NPY is involved in the multihormonal control of ACTH release.

Peptide YY receptors in the brain

Radiolabelled ligand binding studies demonstrated that specific receptors for peptide YY are present in the porcine as well as the canine brains. Peptide YY was bound to brain tissue membranes via high-affinity (dissociation constant, 1.39 X 10(-10)M) and low-affinity (dissociation constant, 3.72 X 10(-8)M) components. The binding sites showed a high specificity for peptide YY and neuropeptide Y, but not for pancreatic polypeptide or structurally unrelated peptides. The specific activity of peptide YY binding was highest in the hippocampus, followed by the pituitary gland, the hypothalamus, and the amygdala of the porcine brain, this pattern being similarly observed in the canine brain. The results suggest that peptide YY and neuropeptide Y may regulate the function of these regions of the brain through interaction with a common receptor site.