Increase of plasma neuropeptide Y-like immunoreactivity following chronic hypoxia in the rat

Increasing Catecholamine Secretion Through NPY in Pheochromocytomas With False-Negative 123 I-MIBG Scintigraphy

INTRODUCTION

123 I-MIBG has been well established as a functional imaging tool, and 131 I-MIBG therapy is being considered for catecholamine-secreting tumors. Tumors with the characteristics of a noradrenergic biochemical phenotype, small, malignant, metastatic, extra-adrenal, bilateral, and hereditary, especially SDHx -related tumors, are reported to correlate with reduced MIBG uptake. However, the potential molecular mechanisms influencing MIBG uptake have been poorly studied.

PATIENTS AND METHODS

To identify critical genes that may enhance MIBG accumulation in pheochromocytomas (PCCs), we performed RNA-seq analyses for 16 operated patients with PCCs (6 MIBG-negative and 10 MIBG-positive) combined with RT-qPCR for 27 PCCs (5 MIBG-negative and 22 MIBG-positive) and examined primary cultures of the surgical tissues.

RESULTS

In the present study, 6 adrenal nodules of 66 nodules surgically removed from 63 patients with PCCs (9%) were MIBG negative. MIBG, a guanethidine analog of norepinephrine, can enter chromaffin cells through active uptake via the cellular membrane, be deposited in chromaffin granules, and be released via Ca 2+ -triggered exocytosis from adrenal chromaffin cells. When we compared expression of several catecholamine biosynthesis and secretion-associated genes between MIBG-negative and MIBG-positive tumors using transcriptome analyses, we found that neuropeptide Y, which is contained in chromaffin granules, was significantly increased in MIBG-negative tumors. NPY stimulated norepinephrine secretion dose-dependently in primary cell culture derived from MIBG-positive PCC. In our study, MIBG-negative PCCs were all norepinephrine-hypersecreting tumors.

CONCLUSIONS

These data indicate that NPY upregulation in PCCs may stimulate chromaffin granule catecholamine secretion, which is associated with false-negative 123 I-MIBG scintigraphy.

Neuropeptide Y in the brain of Euphlyctis cyanophlyctis tadpoles responds to hypoxic stress

Neuropeptide Y (NPY) has emerged as a novel peptide to antagonize various physiological consequences of stress within a mammalian brain. Hypoxia induced neuropeptide Y release in mammalian systems is well established. However, the possible role of NPY in regulating the effects of oxygen variation in lower vertebrates has not been investigated. We have studied the distribution and neuro-anatomical expression of NPY in the brain of Euphlyctis cyanophlyctis tadpoles, exposed to normal and reduced oxygen levels using immunohistochemistry. Animals exposed to hypoxia (<2mg/ml) exhibited a significant amplification of NPY-immunoreactivity throughout the brain. Increased NPY-ir perikarya appeared in all the sub-divisions of pallium, septum and preoptic area of telencephalon; suprachiasmatic nucleus, central and lateral thalamus, infundibulum and habenular regions of diencephalon; and nucleus cerebella and medulla of rhombencephalon. Most of these regions form the stress and anxiety regulating centers of a vertebrate brain and some of the parallel regions also respond to respiratory reflexes in mammals. Hence, our results suggest NPY induced modulation of hypoxia in Euphlyctis cyanophlyctis tadpoles.

Lack of association between impaired glucose tolerance and appetite regulating hormones in patients with obstructive sleep apnea

STUDY OBJECTIVES

Understanding the etiologic mechanisms underlying impaired glucose tolerance in obstructive sleep apnea (OSA) would assist development of therapies against this comorbidity. We hypothesized that in patients with OSA impaired glucose tolerance (IGT) would be associated with elevated levels of hormones associated with appetite regulation (leptin, ghrelin, neuropeptide Y [NPY] and peptide tyrosine-tyrosine [PYY]).

METHOD

We studied 68 OSA patients (mean AHI 22 events/h) and 37 age and weight matched healthy controls recruited by advertisement. All participants received a standardized evening meal, attended polysomnography and an oral glucose tolerance test (OGTT) on waking. Hormones were measured in blood taken before sleep (22:30) and at the start of the OGTT.

RESULTS

Impaired glucose tolerance was present in 54% of patients and 32% of controls (p = 0.05). The only differences between groups was that leptin was significantly higher at 22:30 in OSA patients compared to controls (9.6 ng/L vs 7.9 ng/L, p = 0.05). OSA patients had marginally elevated plasma NPY levels at 22:30 (56.6 [52, 67] pmol/L vs 51.1[47.3, 61] pmol/L; p = 0.04). No differences in ghrelin, PYY or NPY were observed between patients with IGT and those without. However OSA patients with IGT had significantly higher value of leptin at both 22:30 (10.9 [7.7, 15.9] ng/mL vs 7.4 [5.6, 12.3] ng/mL, p = 0.02) and 07:00 (11.6 [7.6, 16.2] ng/mL vs 6.9 [5.4, 12.6] ng/mL, p = 0.024) than those without. In multivariate analysis the only major association of leptin was body mass index.

CONCLUSION

Clinically significant abnormalities of appetite regulating hormones are not present in OSA. Appetite regulating hormones did not differ in OSA patients with and without impaired glucose tolerance.

Chronic stress induces adrenal hyperplasia and hypertrophy in a subregion-specific manner

The adrenal gland is an essential stress-responsive organ that is part of both the hypothalamic-pituitary-adrenal axis and the sympatho-adrenomedullary system. Chronic stress exposure commonly increases adrenal weight, but it is not known to what extent this growth is due to cellular hyperplasia or hypertrophy and whether it is subregion specific. Moreover, it is not clear whether increased production of adrenal glucocorticoid after chronic stress is due to increased sensitivity to adrenocorticotropic hormone (ACTH) vs. increased maximal output. The present studies use a 14-day chronic variable stress (CVS) paradigm in adult male rats to assess the effects of chronic stress on adrenal growth and corticosterone steroidogenesis. Exogenous ACTH administration (0-895 ng/100 g body wt) to dexamethasone-blocked rats demonstrated that CVS increased maximal plasma and adrenal corticosterone responses to ACTH without affecting sensitivity. This enhanced function was associated with increased adrenal weight, DNA and RNA content, and RNA/DNA ratio after CVS, suggesting that both cellular hyperplasia and hypertrophy occurred. Unbiased stereological counting of cells labeled for Ki67 (cell division marker) or 4,6-diamidino-2-phenylindole (nuclear marker), combined with zone specific markers, showed that CVS induced hyperplasia in the outer zona fasciculata, hypertrophy in the inner zona fasciculata and medulla, and reduced cell size in the zona glomerulosa. Collectively, these results demonstrate that increased adrenal weight after CVS is due to hyperplasia and hypertrophy that occur in specific adrenal subregions and is associated with increased maximal corticosterone responses to ACTH. These chronic stress-induced changes in adrenal growth and function may have implications for patients with stress-related disorders.

The role of neuropeptide Y in the ovine fetal cardiovascular response to reduced oxygenation

This study investigated the role of neuropeptide Y (NPY) in mediating cardiovascular responses to reduced oxygenation in the late gestation ovine fetus by: (1) comparing the effects on the cardiovascular system of an exogenous infusion of NPY with those elicited by moderate or severe reductions in fetal oxygenation; and (2) determining the effect of fetal I.V. treatment with a selective NPY-Y(1) receptor antagonist on the fetal cardiovascular responses to acute moderate hypoxaemia. Under general anaesthesia, 14 sheep fetuses (0.8-0.9 of gestation) were surgically prepared with vascular and amniotic catheters. In 5 of these fetuses, a Transonic flow probe was also implanted around a femoral artery. Following at least 5 days of recovery, one group of fetuses (n = 9) was subjected to a 30 min treatment period with exogenous NPY (17 microg kg(-1) bolus plus 0.85 microg kg(-1) min(-1) infusion). In this group, fetal blood pressure and heart rate were monitored continuously and the distribution of the fetal combined ventricular output was assessed via injection of radiolabelled microspheres before and during treatment. The second group of fetuses instrumented with the femoral flow probe (n = 5) were subjected to a 3 h experiment consisting of 1 h of normoxia, 1 h of hypoxaemia, and 1 h of recovery during a slow I.V. infusion of vehicle. One or two days later, the acute hypoxaemia protocol was repeated during fetal I.V. treatment with a selective NPY-Y(1) receptor antagonist (50 microg kg(-1) bolus + 1.5 microg kg(-1) min(-1) infusion). In these fetuses, fetal arterial blood pressure, heart rate and femoral vascular resistance were recorded continuously. The results show that fetal treatment with exogenous NPY mimics the fetal cardiovascular responses to asphyxia, and that treatment of the sheep fetus with a selective NPY-Y(1) receptor antagonist does not affect the fetal cardiovascular response to acute moderate hypoxaemia. These results support a greater role for NPY in mediating the fetal cardiovascular responses to acute asphyxia than to acute moderate hypoxaemia.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Neuropeptide Y blocks anxiogenic-like behavioral action of corticotropin-releasing factor in an operant conflict test and elevated plus maze

Central administration of neuropeptide Y (NPY) produces anxiolytic-like behavioral effects in rat models of anxiety. Because previous evidence has suggested a relationship between NPY and corticotropin-releasing factor (CRF) in the brain, we have focused on the interaction of these neuropeptide systems in emotional responsiveness to stressful stimuli. Intracerebroventricular administration of CRF produced a marked response suppression in an operant incremental shock conflict paradigm. NPY [(1 microg, intracerebroventricularly (i.c.v.)] significantly antagonized the response-suppressing effects of CRF (0.75 microg, i.c.v.) on punished responding in the conflict test at doses that produced little or no behavioral effect when administered alone. Central administration of the CRF antagonist [D-Phe(12), Nle(21,38),C(alpha) MeLeu(37)]CRF (D-Phe CRF(12-41)) alone did not alter punished or unpunished responding in the conflict test. However, pretreatment with the CRF antagonist before a subthreshold dose of NPY (1 microg, i.c.v.) produced a significant potentiation of the release of punished responding relative to NPY alone and untreated controls. NPY also antagonized the "anxiogenic-like" behavioral effects of CRF in the elevated plus maze. These findings support the hypothesis that NPY and CRF may reciprocally modulate an animal's behavioral response to stressful stimuli.

Cardiovascular actions of neuropeptide Y and social stress

The role of central neuropeptide Y (NPY) in the cardiovascular response to social stress was evaluated in freely moving rats using telemetry. In unstressed rats, intracerebroventricular (ICV) administration of NPY and the selective Y1 receptor agonist [Leu31, Pro34]-NPY decreased blood pressure and heart rate, while the selective Y2 agonist NPY13-36 transiently raised blood pressure. NPY and [Leu31, Pro34]-NPY blunted elevations in blood pressure and pulse rate following exposure to the resident-intruder procedure, an established social stress paradigm. In contrast, the Y2 agonist significantly augmented stress-induced pressor effects. These observations indicate that the hypotensive effects of ICV NPY appear to be mediated by the Y1 receptor subtype and the NPY receptor subtypes may mediate opposing cardiovascular actions in response to stressful stimuli.

Attenuated response of renal mechanoreceptors to volume expansion in chronically hypoxic rats

Multifiber renal afferent nerve activity responds to volume expansion in sea level rats but not in chronically hypoxic (high altitude) rats. We performed single-unit recordings of renal afferent nerve activity to characterize renal sensory receptors and their responses to volume expansion in these animals. Hypoxia was induced by placing Wistar rats in an altitude chamber (380 Torr, 5,500 m) for 4 wk. Spontaneously firing renal R2 chemoreceptor and arterial, ureteropelvic, and venous mechanoreceptors were identified. The basal activity of each receptor was similar among these rats. In response to specific stimulus, the increasing impulse of R2 chemoreceptor was similar between two groups of rats, but the increasing activity of each mechanoreceptor was less in hypoxic rats. When challenged with saline load, R2 chemoreceptor activity decreased, but all mechanoreceptors activated in all rats. Despite similar increases of arterial, renal ureteropelvic, and venous pressure during saline load, the increasing activity of each mechanoreceptor was significantly less in hypoxic rats. These results indicated chronic hypoxia attenuates the sensitivity of renal mechanoreceptors in response to the stimulation of saline load.

Alteration in central and peripheral substance P- and neuropeptide Y-like immunoreactivity after chronic hypoxia in the rat

The influence of long-term hypoxia on substance P (SP) and neuropeptide Y (NPY)-like immunoreactivity (LI) in discrete brain areas and peripheral structures was assessed by radioimmunoassay. Rats were exposed to normobaric hypoxia (10% O2 in nitrogen) for 14 days. In the carotid bodies of hypoxic animals, NPY-LI was significantly increased (56% vs. normoxic controls) while SP-LI was unchanged. In the brain, NPY-LI was increased in the ventrolateral medulla oblongata (23%) and in the striatum (53%); however, SP-LI was unaltered in these two regions. In the anterior pituitary, NPY-LI was increased (99%), while SP-LI was decreased (37%). No significant alteration in NPY-LI and SP-LI was observed in other discrete brain areas or peripheral structures studied. These results show that, in the rat, long-term hypoxia induces changes in NPY-LI or SP-LI in a few central and peripheral structures; these biochemical alterations may be linked to adaptative mechanisms involving morphological changes in carotid bodies or alterations in sympathetic control and neuroendocrine function.

Renal kallikrein in chronic hypoxic rats

1. We have studied the role of kallikrein (KK) in the maintenance of renal function in chronic hypoxic rats (high altitude; HA), compared with control rats kept at sea level (SL). Hypoxia was induced by placing female Wistar rats (198-290 g) in an altitude chamber (5500 m) 15 h/day for 4 weeks. Experiments were also conducted to study the interaction of KK with renal nerve activity and endothelin (ET), two parameters previously shown to be altered in this model. 2. It was found that renal cortex tissue KK activity (TKA) was not significantly different in 10 SL and 10 HA rats. However, the urinary KK activity (UKA) was reduced nearly to half (from 35.2 +/- 4.6 to 18.5 +/- 1.7 pkat/min) in HA rats after 4 weeks of chronic hypoxia. 3. Acute renal denervated diuresis was accompanied by a significant increase in UKA (from 9 +/- 2 to 14 +/- 2 pkat/min in HA and denervated HA rats, respectively; P < 0.05) in HA rats. Intrarenal arterial pretreatment of aprotinin reduced the denervated diuresis. 4. Endothelin (600 ng/kg per h) reduced urine flow, sodium and potassium excretion in the ipsilateral kidney in another 10 SL and 10 HA rats. The extent of the drop of these parameters was significantly less in HA rats. Urinary KK activity was correlated significantly with the measured renal functional parameters (r ranging from 0.472 to 0.612) in SL rats, but was insignificant in HA rats (r ranging from 0.032 to 0.192). 5. We have demonstrated that chronic exposure to hypoxia decreases urinary KK excretion and that KK is involved in acute renal denervated diuresis generated in these animals. The present study suggests that KK plays a partial role in the maintenance of renal function in chronic hypoxic rats.

Inhibitory effect of propofol on sympathetic neurotransmission results in changes of plasma neuropeptide Y in rats

1. The effects of propofol on sympathetic neurotransmission and changes of plasma level of neuropeptide Y-like immunoreactivity (NPY-ir) were investigated in rats. 2. Intraperitoneal injection of propofol into rats lowered the systemic blood pressure and plasma NPY-ir in a dose-dependent manner. 3. Decrease of plasma NPY-ir induced by propofol was not modified in adrenalectomized rats. In the activation of adrenergic neurotransmission by a ganglionic nicotinic agonist, elevation of plasma NPY-ir was also reduced by propofol indicating the direct effect on peripheral adrenergic nerve terminals. 4. Plasma level of NPY-ir reversed in parallel with the recovery of anaesthesia induced by propofol. After an intracerebroventricular injection of propofol into the rats, both the lowering of plasma NPY-ir and the induction of anaesthesia were observed. Thus, a central nervous system effect of propofol can also be considered in its effect on plasma NPY-ir. 5. The data suggest that propofol has the ability to lower plasma NPY-ir in rats through an inhibition of adrenergic neurotransmission via central nervous pathway and/or peripheral nerve terminal blockade.

Vasoconstrictive action of neuropeptide Y in bone. The porcine tibia perfused in vivo

The hemodynamic effects of neuropeptide Y (NPY) and norepinephrine (NE) in bone were studied by infusion into the nutrient artery of an in vivo and in situ perfused tibia in 19 pigs. NPY and NE caused elevation of the perfusion pressure and decline in intraosseous pressure, which was evidence of intraosseous vasoconstriction. The study suggests that NPY, along with NE, acts as a sympathetic neurotransmitter in the control of vascular tone in bone.