The effect of adrenalectomy on ghrelin secretion and orexigenic action

Ghrelin is an orexigenic peptide made both in the periphery and in the central nervous system. Relatively little is known about the factors that regulate ghrelin secretion. Because both ghrelin and glucocorticoids are increased during fasting, we hypothesised that ghrelin secretion from the stomach is stimulated by glucocorticoids. Plasma ghrelin concentrations were determined by radioimmunoassay in fed and fasted adrenalectomised (ADX) and sham-operated rats. Fasting plasma ghrelin concentrations were significantly increased in ADX relative to sham rats and were normalised by glucocorticoid replacement. Several lines of evidence suggest that the orexigenic action of ghrelin is mediated through neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurones. Because ADX reduces the orexigenic actions of NPY and AgRP, we hypothesised that ADX would also reduce the orexigenic action of ghrelin. Food intake was assessed in ADX and sham rats following an intra-third-ventricular injection of either saline or ghrelin (1, 5 or 10 microg in 2 microl). ADX rats were equally sensitive to the orexigenic action of ghrelin compared to sham rats. Given that ghrelin has been shown to stimulate glucocorticoid secretion, the current data imply the existence of a regulatory feedback loop whereby glucocorticoids inhibit further ghrelin secretion. The results also suggest that, unlike the orexigenic effects of NPY and AgRP, the ability of ghrelin to stimulate food intake is maintained in ADX rats.     

Endogenous Opioids Modulate the Oxytocin Response to Insulin-Induced Hypoglycaemia and Partially Mediate the Inhibitory Effect of Ethanol in Man

The possible inhibition exerted by ethanol on the oxytocin (OT) response to insulin-induced hypoglycaemia was tested in man. Furthermore, the possibilities that endogenous opioids play a role in the control of hypoglycaemia and/or ethanol action on OT were examined. Insulin tolerance tests were performed in three groups of eight age- and weight-matched normal men treated with: 1) naloxone, group 1 1 mg bolus naloxone + 2.5 mg over 105 min, group 2 2 mg bolus naloxone + 5 mg over 105 min, group 3 4 mg bolus naloxone + 10 mg over 105 min; 2) ethanol (50 ml in 110ml of whiskey) to all the groups; 3) a combination of ethanol + naloxone; 4) normal saline. Furthermore, the effect of ethanol + naloxone (4+10mg) in the absence of insulin-induced hypoglycaemia was evaluated in seven additional subjects. During this latter test, the plasma levels of OT remained unchanged. Insulin-induced hypoglycaemia produced a 2.2-fold increment in plasma OT levels in the control experiments. This response was not changed by the treatment with the lowest dose of naloxone (1+2.5mg) in group 1, but it was significantly enhanced by administration of naloxone at higher doses (mean peak OT levels rose 2.8-fold in both group 2 and group 3). In all subjects the OT response to hypoglycaemia was completely abolished by ethanol. However, when ethanol was given together with naloxone, the hypoglycaemia-induced OT rise was only partially inhibited by ethanol. At all doses naloxone produced similar effects; in fact, in all groups OT rose 1.5-fold in response to hypoglycaemia during insulin tolerance test + ethanol + naloxone. Neither naloxone nor ethanol altered the basal secretion of OT, as tested during 45 min before the insulin tolerance test. These data demonstrate that the OT response to insulin-induced hypoglycaemia is inhibited by ethanol. Furthermore, the data indicate that endogenous opioids are involved in the control of hypoglycaemia-stimulated OT secretion and partially modulate ethanol inhibitory action.     

Changes in expression of the genes for the leptin receptor and the growth hormone-releasing peptide/ghrelin receptor in the hypothalamic arcuate nucleus with long-term manipulation of adiposity by dietary means

Changes in leptin and ghrelin levels occur with alterations in adiposity, but signalling may be affected by levels of the relevant receptors. We measured expression of the leptin receptor (Ob-Rb) and the ghrelin/growth hormone releasing peptide receptor (GHS-R) in the arcuate nucleus of sheep held at either high or low levels of adiposity. Plasma growth hormone (GH) levels were lower in Fat animals and higher in Lean animals. Plasma insulin and leptin levels were higher in Fat animals and lower in Lean animals. Frozen hypothalamic sections of arcuate nucleus were extracted and mRNA levels measured for mRNA for Ob-Rb and GHS-R. Gene expression for both Ob-Rb and GHS-R was higher in Lean animals than in Fat animals, with no difference in expression between Fat and Normal animals. A second group of animals (n = 4 per group) was used for double-labelling immunohistochemistry to determine whether the increase in Ob-Rb gene expression was translated into Ob-Rb protein and to ascertain whether this effect is localised to the cells of the arcuate nucleus that produce either neuropeptide Y (NPY) and/or pro-opiomelanocortin-derived peptides. Lean animals displayed a 255% increase in immunoreactive NPY cells (P < 0.005), a 167% increase in cells with Ob-Rb (P < 0.037) protein and a 344% increase in cells that were staining for both NPY and Ob-Rb (P < 0.02). There was no difference between the Normal and Lean animals in the number of cells that were detected with an adrenocorticotrophic hormone (ACTH) antibody or the number of ACTH-immunoreactive cells that also stained for Ob-Rb. Finally, we measured plasma ghrelin levels in Normal, Fat and Lean ewes (n = 4/group); levels were higher (P < 0.05) in Fat animals than in Lean animals. We conclude that lowering body weight leads to increased expression of Ob-Rb, ghrelin/GHS-R expression and proportion of NPY cells that express Ob-Rb in the arcuate nucleus. This may be an adaptive mechanism to increase responsivity to both leptin and ghrelin.     

Intracerebroventricular Neuropeptide Y Acutely Influences Glucose Metabolism and Insulin Sensitivity in the Rat

Acute administration of neuropeptide Y(NPY) into the hypothalamus and third cerebral ventricle (ICV) increases respiratory quotient, reduces energy expenditure and increases circulating, insulin, glucagon and corticosterone. Therefore, it is likely that hypothalamic NPY has acute effects on the metabolism of fuels, such as glucose. To test this hypothesis, we determined if ICV infusion of NPY influences glucose metabolism and its sensitivity to insulin in conscious, unrestrained rats, not given access to food. Glucose turnover was 4.7±0.3  mg/min, 45–55  min after ICV NPY was administered at 3  μg/h vs 3.7±0.2 (P<0.05) for ICV saline. In a time course study, glucose turnover was significantly increased 30  min, and remained elevated at 50  min after starting a similar ICV NPY infusion. In neither study was plasma glucose, insulin, glucagon or corticosterone significantly affected by ICV NPY. During an hyperinsulinaemic euglycaemic clamp, the glucose infusion rate corrected for body weight and insulin concentration, M/I was 0.22±0.03 for NPY vs 0.36±0.05  mg  min⁻¹  kg⁻¹  μU⁻¹  ml (P<0.05) for saline. NPY treatment prevented the decline in glucose production rate but did not influence the rise in glucose disposal rate resulting from hyperinsulinaemia. It was concluded that ICV NPY rapidly stimulates glucose turnover by a mechanism that does not depend on changes in insulin, glucagon or corticosterone secretion. Furthermore, ICV NPY decreased insulin sensitivity by reducing the effect of insulin on glucose production but not on whole body glucose disposal.     

Dexamethasone differentially alters naltrexone effects on vasopressin and oxytocin release during tail electroshock

The origin of endogenous opioid peptides that inhibit release of vasopressin (VP) and oxytocin (OT) into the bloodstream after tail electroshock was investigated. We hypothesized that endogenous opioid peptides derived from the anterior pituitary reduced secretion of VP and OT during this stimulus. To test this hypothesis, dexamethasone (DEX) was used to preferentially suppress release of endorphins with ACTH from the anterior pituitary. We evaluated the effects of an opiate receptor antagonist, naltrexone, on the rise in plasma [VP] and [OT] after tail electroshock in male Sprague-Dawley rats given DEX either chronically or acutely before the shock. In the chronic study rats were injected SC daily with saline (3.2 ml/kg) or DEX (0.2 mg/kg) for 17 days. In the short term study, rats were injected IP with saline (5 ml/kg) or DEX (0.5 mg/kg) the day before and again 105 min prior to tail electroshock. Thirty min (chronic study) or 90 min (acute study) after saline or DEX was given on the last day, rats were injected SC with saline (1 ml/kg) or naltrexone (1 mg/kg). Fifteen min later, animals received tail electroshock (41 V, 30 sec) and were decapitated 15 sec after shock was completed. Control animals were treated similarly but not shocked. Amounts of VP and OT in plasma and the neurointermediate lobe were quantified by RIA. [VP] and [OT] were elevated in plasma of all rats given tail electroshock. Greater increases (p less than 0.05) in hormone concentrations were measured in plasma of shocked rats treated with DEX.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ghrelin-induced sleep responses in ad libitum fed and food-restricted rats

Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor and a well-characterized food intake regulatory peptide. Hypothalamic ghrelin-, neuropeptide Y (NPY)-, and orexin-containing neurons form a feeding regulatory circuit. Orexins and NPY are also implicated in sleep-wake regulation. Sleep responses and motor activity after central administration of 0.2, 1, or 5 microg ghrelin in free-feeding rats as well as in feeding-restricted rats (1 microg dose) were determined. Food and water intake and behavioral responses after the light onset injection of saline or 1 microg ghrelin were also recorded. Light onset injection of ghrelin suppressed non-rapid-eye-movement sleep (NREMS) and rapid-eye-movement sleep (REMS) for 2 h. In the first hour, ghrelin induced increases in behavioral activity including feeding, exploring, and grooming and stimulated food and water intake. Ghrelin administration at dark onset also elicited NREMS and REMS suppression in hours 1 and 2, but the effect was not as marked as that, which occurred in the light period. In hours 3-12, a secondary NREMS increase was observed after some doses of ghrelin. In the feeding-restricted rats, ghrelin suppressed NREMS in hours 1 and 2 and REMS in hours 3-12. Data are consistent with the notion that ghrelin has a role in the integration of feeding, metabolism, and sleep regulation.     

Glucose injection reduces neuropeptide Y and agouti-related protein expression in the arcuate nucleus: a possible physiological role in eating behavior

Evidence suggests that neuropeptide Y (NPY) and agouti-related protein (AgRP) in the arcuate nucleus (ARC) are modulated by glucoregulatory hormones and involved in maintaining normal eating patterns and glucose homeostasis in states of energy deficiency. This study investigated whether these peptides respond to glucose itself under conditions, e.g., before the nocturnal feeding cycle, when carbohydrate stores are low. After removal of food 3 h before dark onset, Sprague-Dawley rats were given a single, intraperitoneal (i.p.) injection of saline or 10% glucose (0.13 g/kg) and were sacrificed at different intervals, from 3.5 to 90 min later, for measurements of circulating hormones and metabolites or of NPY and AgRP mRNA in the ARC. With no change in insulin, leptin, or triglycerides, glucose injection produced a 1.8-mM rise in circulating glucose during the first 15 min, followed by a 30-60% reduction in NPY and AgRP mRNA at 30 and 60 min post-injection. A similar effect was observed with intraventricular administration of 5% glucose. At 90 min, however, this suppressive effect of i.p. glucose relative to saline was lost and actually reversed into a 50% increase in NPY and AgRP, possibly attributed to a decline in circulating glucose followed by a 50% rise in corticosterone at 60 min. These biphasic shifts over a 90-min period may reflect mechanisms underlying natural eating patterns at the onset of the nocturnal cycle, when spontaneous meals are approximately 90 min apart and rich in carbohydrate, glucose levels are low, and corticosterone and ARC peptides naturally peak.     

Growth hormone-releasing peptide-6 increases insulin-like growth factor-I mRNA levels and activates Akt in RCA-6 cells as a model of neuropeptide Y neurones

Chronic systemic administration of growth hormone (GH)-releasing peptide-6 (GHRP-6), an agonist for the ghrelin receptor, to normal adult rats increases insulin-like growth factor (IGF)-I mRNA and phosphorylated Akt (pAkt) levels in various brain regions, including the hypothalamus. Because neuropeptide Y (NPY) neurones of the arcuate nucleus express receptors for ghrelin, we investigated whether these neurones increase their IGF-I and p-Akt levels in response to this agonist. In control rats, immunoreactive pAkt was practically undetectable; however, GHRP-6 increased p-Akt immunoreactivity in the arcuate nucleus, with a subset of neurones also being immunoreactive for NPY. Immunoreactivity for IGF-I was detected in NPY neurones in both experimental groups. To determine if activation of this intracellular pathway is involved in modulation of NPY synthesis RCA-6 cells, an embryonic rat hypothalamic neuronal cell line that expresses NPY was used. We found that GHRP-6 stimulates NPY and IGF-I mRNA synthesis and activates Akt in this cell line. Furthermore, inhibition of Akt activation by LY294002 treatment did not inhibit GHRP-6 induction of NPY or IGF-I synthesis. These results suggest that some of the effects of GHRP-6 may involve stimulation of local IGF-I production and Akt activation in NPY neurones in the arcuate nucleus. However, GHRP-6 stimulation of NPY production does not involve this second messenger pathway.     

Neuropeptide Y and food intake in fasted rats: effect of naloxone and site of action

Central administration of neuropeptide Y (NPY) induces food intake in freely feeding animals and this effect is mediated by hypothalamic sites. Little is known, however, about the effect of NPY on food intake and site of action in food-deprived animals. To examine this further, 24-h fasted rats received injections of saline or NPY into the lateral cerebral ventricle (10 micrograms/10 microliters; n = 8) or into the lateral (LH) or ventromedial hypothalamus (VMH) (1 microgram/0.5 microliters; n = 44). In addition, intracerebroventricular (i.c.v.) injections of NPY were carried out with or without i.c.v. naloxone (25 micrograms), a specific opioid receptor antagonist. During the first 40 min food intake was not different with or without NPY. After 60 and 120 min, food intake was 5.9 +/- 0.4 g and 8.3 +/- 0.6 g with i.c.v. saline which was significantly augmented by i.c.v. NPY to 8.7 +/- 0.9 g and 14.4 +/- 1.5 g, respectively (P less than 0.05). This increase in food consumption was due to a prolongation of feeding time. The opioid receptor antagonist naloxone significantly augmented latency to feed, both in the absence and presence of NPY (8.0 vs 1.7 min or 14.7 vs 2.8 min, respectively) and abolished the NPY-induced increase in food intake. Following intrahypothalamic injection of NPY, an increase in food intake (greater than 20%) was observed in 50% of the histologically identified LH and VMH sites, but only in 15% of the injection sites outside the LH/VMH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Food deprivation-like effects of neuropeptide Y on heroin self-administration and reinstatement of heroin seeking in rats

Numerous findings suggest that drug seeking and ingestive behaviors share common neurobiological mechanisms, but the relevant pathways are unknown. Dietary manipulations result in changes in endocrine the and/or neuropeptide signals, such as the hormones leptin and ghrelin, which are dynamically linked to energy balance and the regulation of feeding behavior. We have recently demonstrated that food deprivation-induced reinstatement of heroin seeking can be blocked with leptin, and others have suggested a role for ghrelin in drug-related behaviors. The feeding-relevant effects of leptin and ghrelin involve the inhibition or activation, respectively, of neuropeptide Y/agouti-related peptide (NPY/AGRP) neurons in the hypothalamus. However, the effects of NPY, a highly potent orexigenic peptide, on drug-related behaviors have not been thoroughly studied. Here we examined the effect of acute NPY administration on the rate of heroin self-administration and the reinstatement of extinguished heroin-seeking behavior. Heroin intake (0.05mg/kg/infusion) was tested using a self-administration procedure (FR-1), 10-min post-NPY injections (0.0, 4.0, and 10mug/rat, ICV). In a different group of rats, NPY-induced reinstatement (0.0, 4.0, and 10mug/rat, ICV) of extinguished heroin seeking was assessed. NPY injections increased on-going heroin self-administration, and induced a reinstatement of extinguished heroin-seeking behavior. These findings suggest that NPY can modulate the rewarding and conditioned reinforcing effects of drugs of abuse.     

Focal administration of neuropeptide Y into the S2 somatosensory cortex maximally suppresses absence seizures in a genetic rat model

Purpose: Neuropeptide Y (NPY) is an inhibitory neurotransmitter that suppresses focal and generalized seizures in animal models. In this study, we investigated the sites within the thalamocortical circuit that NPY acts to suppress seizures in genetic absence epilepsy rats from Strasbourg (GAERS). Methods: In conscious freely moving GAERS, NPY was administered via intracerebral microcannulae implanted bilaterally into one of the following regions: primary somatosensory cortex (S1), secondary somatosensory cortex (S2), the primary motor cortex (M1), caudal nucleus reticular thalamus (nRT), or ventrobasal thalamus (VB). Animals received vehicle and up to three doses of NPY, in a randomized order. Electroencephalography (EEG) recordings were carried out for 30 min prior to injection and 90 min after the injection of NPY or vehicle. Key Findings: Focal microinjections of NPY into the S2 cortex suppressed seizures in a dose‐dependent manner, with the response being significantly different at the highest dose (1.5 mm ) compared to vehicle for total time in seizures postinjection (7.2 ± 3.0% of saline, p < 0.01) and average number of seizures (9.4 ± 4.9% of saline, p < 0.05). In contrast NPY microinjections into the VB resulted in an aggravation of seizures. Significance: NPY produces contrasting effects on absence‐like seizures in GAERS depending on the site of injection within the thalamocortical circuit. The S2 is the site at which NPY most potently acts to suppress absence‐like seizures in GAERS, whereas seizure‐aggravating effects are seen in the VB. These results provide further evidence to support the proposition that these electroclinically “generalized” seizures are being driven by a topographically restricted region within the somatosensory cortex.     

Effects of intravenous infusion of substance P on arginine vasopressin and oxytocin secretion in normal men.

In order to establish possible stimulatory effects of increasing plasma concentrations of substance P (SP) on the arginine vasopressin (AVP) and/or oxytocin (OT) secretion, successively increasing doses of SP(0.5, 1 and 1.5 pmol/kg-1/min-1; each dose for 20 min) were infused in 7 normal men. Plasma AVP and OT levels were measured before infusion and every 20 min, just before increasing the infusion dose of SP. During tests, SP infusion did not produce untoward side effects or changes in blood osmolality and/or pressure. Plasma OT levels did not change during SP infusion. Plasma AVP concentrations were not modified by the infusion of the lowest dose of SP, whereas they were significantly increased in a dose response fashion when higher amounts of SP were given. These findings demonstrate for the first time in humans that the systemic administration of SP exerts stimulatory effects on AVP, but not on OT secretion.     

Enhanced Neurohypophyseal Vasopressin Release is Associated with Increased Opioid Inhibition of Oxytocin Release

We tested the hypothesis of a cross-inhibition of oxytocin (OT) release by endogenous opioid peptides co-released with vasopressin (VP). This opioid cross-inhibition resulted in a selective block of OT release and hence in preferential release of VP. The effects of the opiate receptor antagonist naloxone were tested on neurohypophyseal VP release during dehydration, ethanol administration and sulphated cholecystokinin octapeptide (CCK-8S) application, assuming that the inhibition of pituitary OT release by endogenous opioids increases as neurohypophyseal VP output increases. A high VP output was found to coincide with increased inhibition of OT release: Subcutaneous injection of graded doses of naloxone (30 min prior to decapitation), augmented OT plasma levels significantly more in 24 h water-deprived male rats than in normally hydrated rats. Naloxone had no effect on VP release. Ethanol (10% in saline) administered intragastrically 50 min prior to decapitation and 20 min before subcutaneous naloxone (5 mg/kg) resulted in the inhibition of VP output. The ethanol treatment resulted in a rise in plasma OT levels that was additional to the effect of naloxone. These features were present in normally hydrated as well as in 24 h water-deprived animals, but were more pronounced in the latter group. Peripheral CCK-8S administration induces an abrupt and selective secretion of OT. Blocking the opioid inhibition of OT release with naloxone resulted in a significant rise of OT compared to that with CCK-8S alone. The magnitude of the opioid inhibition coincided with the activity of the VP system, and a higher dose of naloxone was needed to potentiate the CCK-8S effect on OT release in the water-deprived group than in euhydrated rats. No effect of CCK-8S and/or naloxone was found on VP plasma levels. The data indicate that opioid peptides co-released with VP (like dynorphin) may be responsible for cross-inhibition of OT release during dehydration. This suggests that dynorphin acts in a paracrine way, making it a strong candidate for this role.     

Plasma leptin, neuropeptide Y, ghrelin, and adiponectin levels and carotid artery intima media thickness in epileptic children treated with valproate

Background

Weight gain is a common side effect of valproate (VPA) treatment, although the mechanism is not clear. Abnormal weight gain and obesity are associated with dyslipidemia, hypertension, and atherosclerosis. Measurement of the common carotid artery intima media thickness (CAIMT) gives a picture of early arterial wall alterations and, currently, is considered a noninvasive marker of premature atherosclerosis. The aim of the present study was to evaluate plasma insulin, leptin, neuropeptide Y (NPY), ghrelin, and adiponectin levels in children with epilepsy treated with VPA and to evaluate these parameters for early atherosclerosis.

Material and methods

Twenty prepubertal children with idiopathic epilepsy treated with VPA were enrolled in this study. Body mass index (BMI) and fasting insulin glucose ratio (FIGR) were calculated, and the plasma insulin, leptin, NPY, ghrelin, and adiponectin levels; the lipid profiles; and CAIMT were measured for all subjects before the treatment and after a follow-up period of 6 and 12?months.

Results

When pretreatment values were compared with those at the end of 6 and 12?months, the mean BMI values, plasma insulin, leptin, NPY levels, and FIGR were increased, whereas the plasma ghrelin and adiponectin levels, lipid profiles, and CAIMT did not change significantly at the end of 6 and 12?months.

Conclusion

These results suggest that weight gain during VPA treatment may be related to increases in insulin, leptin, and NPY levels. Additionally, in this study, no increase in the risk for early atherosclerosis was determined by CAIMT in children with epilepsy treated with VPA.     

Estradiol decreases the orexigenic effect of neuropeptide Y, but not agouti-related protein, in ovariectomized rats

Available data suggest that estradiol exerts an inhibitory effect on food intake by modulating the actions of multiple gut- and brain-derived peptides implicated in the control of food intake. For example, recent studies have shown that estradiol decreases the orexigenic effects of ghrelin and melanin-concentrating hormone. In the present study, we examined estradiol's ability to decrease the actions of two additional orexigenic peptides, neuropeptide Y (NPY) and agouti-related protein (AgRP). Food intake was monitored following lateral ventricular infusions of 5 microg NPY, 10 microg AgRP, or saline vehicle in ovariectomized rats treated with either 1 microg estradiol or sesame oil vehicle. NPY increased food intake for 2h in both oil- and estradiol-treated ovariectomized rats. During this interval, the orexigenic effect of NPY was significantly greater in oil-treated rats, relative to estradiol-treated rats. In contrast to the short-term action of NPY, a single injection of AgRP increased food intake for 3 days in oil- and estradiol-treated rats. Meal pattern analysis revealed that the orexigenic effect of AgRP is mediated by an increase in meal size, not meal number. Unlike that observed following NPY treatment, estradiol failed to modulate the magnitude by which AgRP increased food intake and meal size. We conclude that a physiological regimen of estradiol treatment decreases the orexigenic effect of NPY, but not AgRP, in ovariectomized rats.     

Differential effects of naloxone on the release of neurohypophysial hormones in normotensive and spontaneously hypertensive rats

The hypothalamo-neurohypophysial system is altered in the spontaneously hypertensive rat (SHR). We hypothesized that an aberrant regulation of vasopressin (VP) and oxytocin (OT) release by endogenous opioid peptides alters this neuroendocrine system in the SHR. Concentrations of the neurohypophysial hormones in plasma and the pituitary were measured in 17-week-old SHRs and two strains of normotensive controls. Wistar Kyoto (WKY) and Sprague-Dawley rats. Animals were decapitated 20 min after s.c. injection of saline (1 ml/kg) or naloxone hydrochloride (1 or 10 mg/kg). In addition, neurohypophysial hormones excreted during the day (08.00-17.30 h) and night (17.30-08.00 h) were determined in urine from 16-week-old animals kept in metabolic cages for 5 days. VP at extrahypothalamic sites was also measured as [VP] in acid extracts of the subfornical organ area, hippocampal commissure-fornix and choroid plexus. Hormones were quantified by radioimmunoassay. The pituitary content, plasma concentration, and urinary excretion of OT were reduced (P less than 0.05) in SHRs, whereas VP content was increased (P less than 0.05) in the pituitary and plasma, but unchanged in urine, of hypertensive animals. In extrahypothalamic tissues, [VP] in the hippocampal commissure-fornix was increased in the SHR. Naloxone elevated (P less than 0.05) the plasma concentration of OT in WKY animals and VP in SHRs. Neither [VP] nor [OT] in plasma was changed by naloxone in Sprague-Dawley rats. Pituitary stores of the neurohypophysial hormones were not altered by naloxone in either hypertensive or normotensive rats. In conclusion, endogenous opioid peptides tonically inhibit OT release in WKY rats, whereas VP release is decreased by opioid peptides in SHRs, 16-17 weeks of age. The neuromodulatory role of opioid peptides in the release of neurohypophysial hormones appears to be altered in the SHR such that VP release is suppressed and OT release is augmented.     

Effects of adrenomedullin on adrenocorticotropic hormone (ACTH) release in pituitary cell cultures and on ACTH and oxytocin responses to shaker stress in conscious rat

Adrenomedullin (AM) is a potent vasodilator peptide, which is initially isolated from tissue of human pheochromocytoma. In addition to the effect on cardiovascular system, previous studies suggest that AM plays some roles as a neuropeptide in the brain. In the present study, we examined the effect of AM on in vitro adrenocorticotropic hormone (ACTH) secretion stimulated by corticotropin-releasing hormone (CRH), vasopressin (VP) or oxytocin (OT) in cultured rat corticotrophs and on the response of plasma ACTH, corticosterone (B) and OT to shaker stress in vivo. In contrast to the previous report, basal or CRH (10(-9) M)-stimulated ACTH secretion was not affected by coincubation with AM. Either of VP (10(-8) M) or OT (10(-8) M) significantly increased ACTH secretion in cultured rat anterior pituitary cells (156.7+/-24.9 in basal incubation vs. 267.8+/-15.0 in VP-stimulation, P<0.05, and 308.6+/-41.3 pg/ml in OT-stimulation, P<0.05). AM (10(-10) M) significantly inhibited OT-stimulated ACTH secretion. AM tended to inhibit VP-stimulated ACTH secretion, although the inhibitory effect was not statistically significant. Thus, it is likely that AM attenuates OT-stimulated ACTH secretion in corticotrophs. In vivo study, male Wistar rats were prepared with a guide cannula in the lateral ventricle and a catheter in femoral artery for blood sampling. AM (0.5, 1.0 microg in 5 microl) or normal saline (5 microl, control) was intracerebroventricularly (i.c.v.) injected in conscious rats. Shaker stress (110 cycles/min for 5 min) produced a significant increase of plasma ACTH (baseline: 106.4+/-48.6; vs. just after stress: 388.9+/-56.1 pg/ml, P<0.05) and B (baseline: 198.6+/-46.8 vs. 15 min after stress: 378.5+/-13.6 ng/ml, P<0.05) in the control group. Plasma OT tended to increase after stress, although the change was not significantly different (baseline: 29.8+/-6.5; just after stress: 65.6+/-18.2 pg/ml). I.c.v. injection of AM at 3 min before the stress did not significantly affect stress-induced changes of plasma ACTH, B and OT. These results suggest that AM has an inhibitory effect on OT-induced ACTH release in vitro and the inhibitory effect may be overwhelmed in ACTH and B response to shaker stress.     

Postprandial ghrelin release in anorectic patients before and after weight gain

The appetite-modulating hormone ghrelin transmits changes in food intake to the central nervous system. In patients with anorexia nervosa, weight gain reduces elevated fasting ghrelin levels to normal, however, less is known about the effects on postprandial ghrelin levels. In 20 female anorectic in-patients (25.6 +/- 1.0 years; body mass index (BMI) 15.1 +/- 0.3 kg/m2) a standardized test with 250 ml fluid meal (250 kcal: 9.4 g protein, 34.4 g carbohydrates, and 8.3 g fat) was performed at three different times (at admission, after partial weight gain of at least 2 kg, and at discharge) and compared to healthy controls (n = 6; BMI 21.1 +/- 0.7 kg/m2). Plasma ghrelin levels were measured preprandially as well as 20 and 60 min postprandially by a commercially available radioimmunoassay (Phoenix Pharmaceuticals, USA). At admission plasma ghrelin levels significantly decreased postprandially (from 871.9 +/- 124 to 620.3 +/- 80 pg/ml 60 min after meal; P < 0.005). After partial weight gain (2.8 +/- 0.1 kg; BMI 16.1 +/- 0.3 kg/m2) postprandial ghrelin concentrations decreased from 597.0 +/- 79 to 414.7 +/- 39 pg/ml (P < 0.0001), at discharge (weight gain: 7.6 +/- 0.5 kg; BMI 17.9 +/- 0.4 kg/m2) from 570.4 +/- 78 to 395.4 +/- 44 pg/ml (P < 0.0001). Mean postprandial ghrelin decrease was not significantly different between the three tests (29, 25, and 26%, respectively) or to controls (20%). In anorectic patients mean postprandial ghrelin decrease did not change during weight gain. These findings indicate that in anorexia nervosa the suppression of ghrelin release by acute changes of energy balance (feeding) is not disturbed and that it is independent from chronic changes in energy balance (weight gain).     

Differential effects of neuropeptide Y and the mu-agonist DAMGO on 'palatability' vs. 'energy'.

Differential effects of neuropeptide Y (NPY) and mu-opioid DAMGO on 'palatability' vs. 'energy'. A variety of studies suggest that NPY is an important manager of energy metabolism. In contrast, the opioid peptides appear to influence the 'rewarding' aspects of feeding. In the current study, we stimulated feeding by injecting NPY (110 pmol) or the mu-opioid agonist DAMGO (2 nmol) into the paraventricular nucleus of rats. Following injection, rats were given free access to laboratory chow and a 10% sucrose solution. Animals injected with saline derived 10% of their kilocalories from the chow and 90% from the sucrose solution (total kcal/4 h=12.2+/-1. 0). Those rats injected with NPY derived 48% of their energy from chow and 52% from the sucrose solution (total kcal/4 h=24.8+/-1.7). The DAMGO-injected rats derived only 15% of their kilocalories from chow and the remainder from the sucrose solution (total kcal/4 h=23. 0+/-2.3). Thus, while NPY and DAMGO both stimulated energy intake compared to saline controls (P<0.0001), the effect on intake of a palatable dilute energy solution (0.4 kcal/g) vs. a 'bland' laboratory chow (3.95 kcal/g) was different. The results of this study reinforce the notion that NPY has a major effect on energy needs, whereas opioids influence the 'rewarding' characteristics of foods.