neuropeptide-y and Hemorrhage

The primary purpose of this investigation was to determine whether ApoE(-/-) mice, when subjected to chronic stress, exhibit lesions characteristic of human vulnerable plaque and, if so, to determine the time course of such changes. We found that the lesions were remarkably similar to human vulnerable plaque, and that the time course of lesion progression raised interesting insights into the process of plaque development. Lard-fed mixed-background ApoE(-/-) mice exposed to chronic stress develop lesions with large necrotic core, thin fibrous cap and a high degree of inflammation. Neovascularization and intraplaque hemorrhage are observed in over 80% of stressed animals at 20 weeks of age. Previously described models report a prevalence of only 13% for neovascularization observed at a much later time point, between 36 and 60 weeks of age. Thus, our new stress-induced model of advanced atherosclerotic plaque provides an improvement over what is currently available. This model offers a tool to further investigate progression of plaque phenotype to a more vulnerable phenotype in humans. Our findings also suggest a possible use of this stress-induced model to determine whether therapeutic interventions have effects not only on plaque burden, but also, and importantly, on plaque vulnerability.

Topics: Animals; Atherosclerosis; Blood Pressure; Cholesterol; Coronary Stenosis; Corticosterone; Disease Models, Animal; Hemorrhage; Humans; Inflammation; Mice; Mice, Inbred C57BL; Necrosis; Neovascularization, Pathologic; Neuropeptide Y; Plaque, Atherosclerotic; Stress, Psychological

The ventrolateral medulla (VLM) has three functionally defined regions that contain catecholamine-synthesising neurons (rostral C1, caudal C1 and A1 regions). Many neuromessengers can alter cardiovascular functions in the VLM. The aims of this study were, first to validate the utility of real-time RT-PCR SYBR Green assay for quantitation of mRNA expression levels of neuromessengers in small site-specific neuronal populations in the VLM, and second to compare the basal mRNA levels of the adrenaline-synthesizing enzyme phenylethanolamine-N-methyltransferase (PNMT), neuropeptide Y (NPY) and preproenkephalin (ENK) in the three regions and third to examine the effects of haemorrhage on the expression of these three genes. Rats were anaesthetised with sodium pentobarbital and divided into three groups: perfused, sham-operated and haemorrhaged. A 15% haemorrhage was carried out on the haemorrhaged group. It was found that there are regional differences in the level of mRNA expression for all the three genes: with, in general, decreases from the rostral to caudal regions of VLM. A 15% haemorrhage significantly induced expression of PNMT in the rostral C1 region and NPY in the caudal C1 and A1 regions but had no effect on ENK at any sites, suggesting a differential regulation on the expression of these three genes in the VLM. Our results also demonstrate that real-time RT-PCR is a sensitive and accurate method for quantitative studies on neurotransmitter gene expressions in restricted brain regions.

Topics: Animals; Benzothiazoles; Blood Pressure; Diamines; Enkephalins; Fluorescent Dyes; Gene Expression; Glyceraldehyde-3-Phosphate Dehydrogenases; Hemorrhage; Male; Medulla Oblongata; Neuropeptide Y; Organic Chemicals; Phenylethanolamine N-Methyltransferase; Protein Precursors; Quinolines; Rats; Rats, Sprague-Dawley; Reproducibility of Results; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Considering the coexistence of neuropeptide Y (NPY) and norepinephrine in perivascular sympathetic nerves and the known vasoconstrictor cooperation of NPY with norepinephrine, we investigated the involvement of NPY in long-term control of cardiovascular functions using NPY transgenic (NPY-tg) rats. These rats were developed by injection of the rat (Sprague-Dawley) pronuclei with a 14.5-kb clone of the rat structural NPY gene. When compared with nontransgenic littermates, NPY concentrations were significantly increased in a number of cardiovascular tissues of NPY-tg hemizygotes. Direct basal mean arterial pressure and heart rate were not changed, but calculated total vascular resistance was significantly increased in NPY-tg subjects. Arterial pressure increases, in response to norepinephrine injection, were greater in the NPY-tg rats. Also, the hypotension and bradycardia in response to hemorrhage were significantly reduced in NPY-tg subjects. These results indicate that NPY, when expressed in increased amounts, potentiates the pressor effects of norepinephrine and contributes to maintaining blood pressure during hemorrhage, but it does not alter resting blood pressure. These transgenic rats will facilitate studies of the role of NPY signaling in cardiovascular regulation, particularly regarding its functional cooperation with norepinephrine.

Topics: Adrenergic alpha-Agonists; Animals; Animals, Genetically Modified; Blood Pressure; Dose-Response Relationship, Drug; Female; Heart Rate; Hemorrhage; Male; Neuropeptide Y; Norepinephrine; Rats; Rats, Sprague-Dawley; Time Factors; Vascular Resistance

Hypotensive haemorrhage induces nuclear Fos expression and upregulates tyrosine hydroxylase (TH) mRNA in catecholamine-containing cell groups of the rat medulla oblongata. To shed light on the significance of the coexistence of neuropeptide Y (NPY) in aminergic neurons, the impact of graded levels of haemorrhage on temporal changes in the expression of TH and NPY mRNAs was compared; concurrent staining for Fos permitted comparisons between cells that ostensibly were and were not targeted by the stimulus. A 15% haemorrhage provoked increased NPY expression in all medullary catecholamine cell groups except the A2; these changes were detected predominantly in Fos-immunoreactive neurons (Fos-ir) at later (2-4 h) time points. Upregulation of TH and NPY mRNAs in Fos-ir neurons followed distinct time courses, with NPY responses peaking more rapidly, particularly in the C1 and C2 cell groups. Adrenergic cell groups displayed greater maximal increases in NPY expression than the A1 noradrenergic cell group while the converse was true of TH mRNA response. Increasing the severity of haemorrhage resulted in more pronounced increases in both mRNA responses in each aminergic region. These findings indicate that haemorrhage differentially affects TH and NPY expression in medullary catecholamine cell groups that participate in the maintenance of cardiovascular homeostasis. The differential nature of these responses suggests them not to be a simple consequence of metabolic alterations pursuant to increased synaptic activity. The prompt and robust NPY mRNA responses in adrenergic neurons suggests a mechanism by which peptide content of these cell groups' terminal projections is defended.

Topics: Animals; Blood Volume; Catecholamines; Cerebrovascular Circulation; Gene Expression Regulation, Enzymologic; Hemorrhage; In Situ Hybridization; Male; Medulla Oblongata; Neurons; Neuropeptide Y; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; RNA, Messenger; Time Factors; Tyrosine 3-Monooxygenase

During intense sympathetic activation, as occurs during hemorrhage, veins constrict to a greater degree than do arteries. This study determined if differences in the amounts or actions of the sympathetic cotransmitter neuropeptide Y released from perivascular nerves could contribute to these differences. Strips of canine mesenteric and popliteal arteries and of saphenous and portal veins were superfused, and the releases of noradrenaline and neuropeptide Y evoked by transmural stimulation were assessed. Both compounds were released in greater amounts in the veins than in the arteries. In other experiments rings of each vessel were mounted in organ chambers for isometric-tension recording. Neuropeptide Y (up to 10(-4) M) did not contract any vessel; however, at 3 x 10(-7) M it shifted the frequency-response and concentration-response curves to noradrenaline in the arteries only. In the veins neuropeptide Y had no postsynaptic effect on strong contractions. These results suggest that neuropeptide Y functions locally to affect vasoconstriction of the arteries studied, and may have a different role in the veins. Further, processes involving neuropeptide Y do not appear to account for the differences in responsiveness of these arteries as compared to the veins during intense sympathetic stimulation.

Topics: Analysis of Variance; Animals; Dogs; Dose-Response Relationship, Drug; Female; Hemorrhage; Male; Mesenteric Arteries; Neuropeptide Y; Norepinephrine; Popliteal Artery; Portal Vein; Saphenous Vein; Sympathetic Nervous System; Vasoconstriction

The possible involvement of prejunctional alpha 2-adrenergic autoinhibition in hypertension is still controversial. The aim of this study was to determine the functional integrity of this regulatory mechanism in conscious DOCA-salt hypertensive rats, a model characterized by an increased sympathetic tone and reactivity. Basal and hemorrhage-induced increases in catecholamine and immunoreactive neuropeptide Y (NPY) levels were compared between control and yohimbine (alpha 2-adrenergic receptor antagonist) pretreated normotensive and DOCA-salt hypertensive rats. DOCA-salt hypertensive rats had higher basal norepinephrine levels (NE), as well as increased NE and epinephrine (EPI) responses to a 15-mL/kg hemorrhage as compared to control normotensive rats. In normotensive animals, yohimbine (0.5 mg/kg, intravenous [iv]) doubled plasma NE, EPI, and NPY levels in basal conditions and in response to the hemorrhage. In contrast, the same treatment had smaller or no effect on basal NE levels and on the hemorrhage-induced responses in DOCA-salt hypertensive rats, although basal EPI levels were increased in this group. These results therefore suggest a decreased function of the prejunctional alpha 2-adrenergic autoinhibitory mechanism at the level of sympathetic nerve terminals and adrenal medulla during sympathetic hyperactivity in DOCA-salt hypertension. This dysfunction could in part explain the hyperactivity and hyperreactivity of the sympathetic nervous system observed in this model, and thus contribute to the elevation of blood pressure in DOCA-salt hypertension.

Topics: Adrenal Medulla; Animals; Blood Pressure; Body Weight; Desoxycorticosterone; Epinephrine; Hemorrhage; Hypertension; Male; Neuropeptide Y; Norepinephrine; Rats; Rats, Sprague-Dawley; Receptors, Adrenergic, alpha-2; Sodium Chloride; Sympathetic Nervous System; Yohimbine

Haemodynamic and humoral responses to two subsequent hypotensive haemorrhages, separated by 3 hours and each followed by retransfusion, were studied in unanaesthetized sheep. Haemorrhage was induced by removal of blood from a jugular vein at a rate of 0.7 ml kg-1 min-1 until the mean systemic arterial pressure suddenly decreased by 35 mmHg or more. In addition to the mean systemic arterial pressure, the cardiac output, the mean pulmonary arterial pressure, the central venous pressure and the pulmonary capillary wedge pressure decreased in response to each haemorrhage. The recovery of the systemic and pulmonary arterial pressure was slower and/or less efficient after the second haemorrhage, due to a less pronounced increase of the vascular resistance. Relative bradycardia, in association with the abrupt fall of the mean systemic arterial pressure, was more apparent during the first haemorrhage. The plasma levels of vasopressin, renin activity and angiotensin II were increased by each blood removal, but the vasopressin response to the second haemorrhage was significantly reduced. The plasma noradrenaline concentration was slightly and transiently elevated only in response to the second haemorrhage. The concentration of neuropeptide Y-like immunoreactivity in plasma was unaffected by both haemorrhages. It is suggested that the reduced and delayed increase in the systemic vascular resistance, accompanied by impaired recovery of the arterial pressure, and the relative absence of 'bleeding bradycardia', during the second haemorrhage, were due to the diminished vasopressin response.

Topics: Animals; Arginine Vasopressin; Blood Pressure; Blood Volume; Female; Heart Rate; Hemodynamics; Hemorrhage; Hypotension; Neuropeptide Y; Norepinephrine; Renin-Angiotensin System; Sheep

The acute effects of oxymetazoline, an alpha 2-adrenoceptor agonist, and idazoxan, an alpha 2-adrenoceptor antagonist, on the release of neuropeptide Y were evaluated during haemorrhage in pentobarbital-anaesthetized dogs. Plasma concentrations of neuropeptide Y and catecholamines (adrenaline, noradrenaline, and dopamine) were determined in samples simultaneously collected from aorta, portal vein, and adrenal veins. In control dogs, adrenal catecholamine output, aortic concentrations neuropeptide Y and catecholamines markedly increased during the hypotension period. However, adrenal neuropeptide Y output decreased significantly during this period. Portal venous noradrenaline and neuropeptide Y concentrations increased significantly. In dogs treated with idazoxan, catecholamine output from the adrenals increased to an extent similar to that observed in control dogs. However, the increase in noradrenaline and neuropeptide Y in aortic or portal venous blood during haemorrhage was significantly potentiated in the presence of idazoxan. Administration of oxymetazoline abolished this increase, but did not alter adrenal catecholamine or neuropeptide Y output. The present study demonstrates that neuropeptide Y is co-released with noradrenaline from sympathetic nerve fibers during haemorrhage. Since the release of neuropeptide Y appeared to follow a similar time course to that of noradrenaline release, the present observations suggest that haemorrhagic hypotension enhances both neuropeptide Y and noradrenaline release presumably through a common releasing mechanism. These results also indicate that, in peripheral sympathetic nerves but not in the adrenal gland, neuropeptide Y release is also modulated presynaptically by the inhibitory alpha 2-adrenoceptors in conjunction with the noradrenaline release.

Topics: Adrenergic alpha-Antagonists; Animals; Cardiovascular System; Catecholamines; Dioxanes; Dogs; Hemorrhage; Hypotension; Idazoxan; Neuropeptide Y; Oxymetazoline; Receptors, Adrenergic, alpha

Neuropeptide Y (NPY), a putative sympathetic neurotransmitter and neuromodulator, is released during sympathetic nerve stimulation and causes vasoconstriction and cardiodepression. Whether the release of NPY contributes to stress-induced cardiovascular responses was assessed by studying i) plasma levels of circulating NPY-immunoreactivity (NPY-ir) during various stress paradigms and ii) mechanisms of action of NPY in the cardiovascular system of the rat. Plasma NPY-ir was increased by all stress situations, such as transfer to a new environment (by 52%), exposure to cold water (4 degrees C) (by 117%) and hemorrhage (4 ml/300 g body weight) (by 231%). The cold water, stress-induced, maximal increase in circulating plasma NPY-ir was delayed in relation to the peak pressor response by 10-20 min. Administration of NPY caused dose-dependent pressor responses that were greater in pithed rats--which have all centrally mediated circulatory reflexes removed--than in conscious rats. Infusion of a low pressor (8.5 +/- 1.5 mm Hg) dose of norepinephrine into conscious rats potentiated NPY-mediated pressor responses 2-fold and also tended to increase bradycardic effect of a higher dose of NPY (by 19%). Thus hypertensive and bradycardiac actions of NPY appear to depend on the level of adrenergic activity and on the interactions at the level of vascular smooth muscle, heart, and baroreceptor reflexes. During a hyperadrenergic state such as stress, cardiovascular effects of NPY may be greatly accentuated. NPY may enhance and prolong the stress-induced hypertensive responses while antagonizing adrenergic cardiostimulation.

Topics: Animals; Blood Pressure; Cold Temperature; Decerebrate State; Female; Handling, Psychological; Heart Rate; Hemorrhage; Male; Models, Biological; Neuropeptide Y; Norepinephrine; Pressoreceptors; Rats; Rats, Inbred Strains; Reference Values; Stress, Physiological; Stress, Psychological

Most peripheral noradrenergic nerves have been shown to contain the coexisting peptide, neuropeptide Y (NPY). The aim of this study was to determine whether NPY is released together with catecholamines during activation of the sympathoadrenal system by hemorrhagic stress in conscious rats. Plasma NPY rose from a baseline value of 7.7 +/- 1.2 to 14.4 +/- 2.7 and 14.9 +/- 2.3 ng/ml (mean +/- SEM, n = 8) 10 and 30 min after hemorrhage, respectively. Plasma norepinephrine (NE) and epinephrine concentrations rose immediately after hemorrhage and at 30 min were increased twofold and ninefold, respectively. To determine the source of the increase in circulating NPY after hemorrhage, rats were subjected to adrenalectomy or to chemical sympathectomy with intravenous (i.v.) 6-hydroxydopamine (6-OHDA). 6-OHDA-treated rats had no significant increase in plasma NPY after hemorrhage, whereas adrenalectomized rats had an enhanced NPY response to hemorrhage. These results suggest that the sympathetic nerves make the major contribution to the increase in plasma NPY concentrations after activation of the sympathoadrenal system by hemorrhagic stress.

Topics: Adrenal Medulla; Adrenalectomy; Animals; Consciousness; Epinephrine; Hemorrhage; Male; Neuropeptide Y; Norepinephrine; Osmolar Concentration; Rats; Rats, Inbred Strains; Sympathectomy, Chemical; Sympathetic Nervous System

The possibility that neuropeptide Y (NPY) exerts organizational effects on central noradrenergic systems was investigated by treating newborn rats with subcutaneous injections of a specific NPY-antiserum. Three months later, neuroendocrine function was determined by measuring plasma vasopressin following haemorrhage, since this response is known to be regulated by ascending noradrenergic pathways. Basal mean arterial pressure, heart rate and plasma vasopressin were similar in both control (normal rabbit serum-treated) and NPY-antiserum-treated rats. Treatment with this antiserum resulted in an impaired vasopressin response to haemorrhage, although the haemodynamic changes observed after this hypovolaemic challenge were similar to control rats. NPY and noradrenaline content in the hypothalamus and brainstem were examined at the end of these experiments. NPY-like immunoreactivity was similar in both groups of animals. However, electrochemical detection of noradrenaline after HPLC revealed significantly higher levels in the hypothalamus, but not brainstem, of NPY-antiserum-treated rats. The presence of enduring changes in noradrenaline levels and neurohypophyseal function following neonatal treatment with NPY-antiserum suggests a role for NPY in postnatal organization of the rat hypothalamus.

Topics: Animals; Animals, Newborn; Blood Pressure; Brain Stem; Heart Rate; Hemorrhage; Hypothalamus; Immune Sera; Male; Neuropeptide Y; Norepinephrine; Rats; Rats, Inbred Strains; Vasopressins