Effect of reserpine, phenoxybenzamine and cold stress on the neuropeptide Y content of the rat peripheral nervous system

Neuropeptide Y is a mediator of chronic vascular and metabolic maladaptations to stress and hypernutrition

Neuropeptide Y (NPY) is a central neuromodulator and peripheral sympathetic neurotransmitter that also has important regulatory roles in cardiovascular, neuroendocrine, immune and metabolic functions during stress. Focusing on the peripheral actions of the peptide in rodent models, we summarize recent studies from our laboratory demonstrating that stress-induced release of NPY mediates accelerated atherosclerosis/restenosis, obesity and metabolic-like syndrome, particularly when combined with a high fat, high sugar diet. In this review, we propose mechanisms of NPY's actions, its receptors and cellular substrates that increase the risk for cardiovascular and metabolic diseases when chronic stress is associated with pre-existing vascular injury and/or states of hypernutrition.

alpha2-Adrenoceptors control the release of noradrenaline but not neuropeptide Y from perivascular nerve terminals

Neuropeptide Y (NPY) and noradrenaline (NA) are co-transmitters at many sympathetic synapses, but it is not yet clear if their release is independently regulated. To address this question, we quantified the electrically evoked release of these co-transmitters from perivascular nerve terminals to the mesenteric circulation in control and drug-treated rats. 6-Hydroxydopamine reduced the tissue content and the electrically evoked release of ir-NPY and NA as well as the rise in perfusion pressure. A 0.001 mg/kg reserpine reduced the content of ir-NPY and NA, but did not modify their release nor altered the rise in perfusion pressure elicited by the electrical stimuli. However, 0.1mg/kg reserpine reduced both the content and release of NA but decreased only the content but not the release of ir-NPY; the rise in perfusion pressure was halved. Clonidine did not affect the release of ir-NPY while it lowered the outflow of NA, not altering the rise in perfusion pressure elicited by the electrical stimuli. Yohimbine, did not modify the release of ir-NPY but increased the NA outflow, it antagonized the clonidine effect. Therefore, presynaptic alpha2-adrenoceptors modulate the release of NA but not NPY, implying separate regulatory mechanisms.

Galanin/GMAP- and NPY-like immunoreactivities in locus coeruleus and noradrenergic nerve terminals in the hippocampal formation and cortex with notes on the galanin-R1 and -R2 receptors

By using immunofluorescence methodology, extensive galanin (GAL) and GAL message-associated peptide (GMAP)-positive terminal networks were observed in the hippocampal formation. The majority of the GAL/GMAP fibers were dopamine beta-hydroxylase- (DBH) positive, that is, they were noradrenergic. This finding was established with GAL/GMAP-DBH double-staining and with 6-hydroxy-dopamine treatment, which totally abolished all fibers in which GAL/GMAP and DBH coexisted. Also, reserpine treatment caused a marked depletion of GAL. No evidence for GAL/GMAP coexistence with 5-hydroxytryptamine was obtained. In the ventral hippocampus, GAL/GMAP-, DBH-negative fibers were seen in the stratum oriens, the anterior stratum radiatum, along the granule cell layer and in the strata oriens and alveus. In the locus coeruleus (LC), around 80% of the GMAP-positive neurons contained neuropeptide tyrosine (NPY), and about 40% of the NPY-positive neurons expressed GMAP. GAL-R1 receptor mRNA was expressed in Barrington's nucleus (close to the LC), but was not detected in the hippocampal formation/dorsal cortical areas. GAL-R2 receptor mRNA was found in the granule cell layer in the dentate gyrus. The present results show that most, but not all, immunohistochemically detectable GAL/GMAP in the hippocampal formation/dorsal cortex is present in noradrenergic nerve terminals originating in the LC, which has a robust GAL/GMAP synthesis. The functional role of GAL may be related to noradrenaline, possibly by a presynaptic action. However, the presence of GAL in other systems and of GAL-R2 receptor mRNA in granule cells also indicates other targets.

Expression of catecholamine-synthesizing enzymes, peptidylglycine alpha-amidating monooxygenase, and neuropeptide Y mRNA in the rat adrenal medulla after acute systemic nicotine

The expression of catecholamine-synthesizing enzymes in the adrenal medulla is upregulated in parallel by stress and pharmacological treatments. In this study we examined whether a neuropeptide and its processing enzyme are regulated in parallel with catecholamine enzyme genes after drug treatment. Because the main effect of stress on the adrenal medulla is via splanchnic nerve stimulation of nicotinic receptors, we used nicotine to stimulate the medulla and visualized expression of catecholamine enzyme genes, the medullary peptide neuropeptide Y (NPY), and the neuropeptide-processing enzyme peptidylglycine alpha-amidating monooxygenase (PAM) by in situ hybridization quantified by image analysis of autoradiographic images. Rats received a single injection of nicotine (0, 1, or 5 mg/kg sc). Six hours later, rats were transcardially perfused. Free-floating adrenal gland sections were hybridized with 35S-labeled cDNA probes for tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), PAM, and NPY. Nicotine treatment upregulated the expression of TH, PNMT, and NPY genes in a dose-dependent fashion. Small but nonsignificant increases were observed in DBH and PAM mRNA levels. These results suggest that common transcriptional activation mechanisms may upregulate both catecholamine and neuropeptide synthesis in the adrenal medulla after nicotinic stimulation.

Neuronal markers, peptides and enzymes in nerves and chromaffin cells in the rat adrenal medulla during postnatal development

Neuronal markers, peptides and enzymes were analyzed in the rat adrenal medulla during the postnatal period, i.e., when the 'functional' splanchnic innervation is assumed to 'mature'. Nerve fibers were present on day 2 as indicated by neurofilament 10 (NF10)- and growth associated protein 43 (GAP43)-like immunoreactivities (LIs). Acetylcholinesterase (AChE)- and enkephalin (ENK)-immunoreactive (IR) fibers, presumably of preganglionic nature, increased in number and intensity during the postnatal period. In contrast, calcitonin gene-related peptide (CGRP)- and galanin (GAL)-IR fibers were almost fully developed on day 2. Thus, the presumably sensory innervation of the adrenal gland seems to precede the development of the autonomic nerves. The AChE- and ENK-IR fibers may exert a suppressive effect on ENK-, CGRP- and neurotensin (NT)-LIs in chromaffin cells, since the levels of these peptides were high in the early postnatal period and then decreased. On the other hand, GAL-LI in chromaffin cells was low also in young rats, while GAP43-IR cells were observed at all stages. Neuropeptide tyrosine (NPY) was expressed in many chromaffin cells at all stages and its turnover rate seemed to decrease towards the adult stage. The expression of the catecholamine synthezising enzymes changed only marginally during development. These results indicate that the preganglionic fibers, but not the sensory axons, in the splanchnic nerve are involved in the developmental control of expression of some, but not all, peptides in the chromaffin cells and that these changes thus may reflect the maturation of a 'functional' transmission.

Neuropeptide Y immunoreactivity in the mammalian liver: pattern of innervation and coexistence with tyrosine hydroxylase immunoreactivity

The distribution of nerve fibers displaying neuropeptide Y immunoreactivity in relationship to the catecholaminergic innervation of rat, guinea pig, and rabbit liver was investigated by single- and double-label immunofluorescence methods. In all three species, neuropeptide Y-immunoreactive fibers are prominent in association with the vasculature, biliary pathway, and stromal compartment. The neuropeptide Y innervation of the parenchyma, on the other hand, differs among the three species in term of density. It is quite sparse in the rat and rabbit, particularly in the former species. In the guinea pig liver, numerous single, varicose neuropeptide Y-containing nerve fibers innervate the hepatic parenchyma; often, thin processes surround single hepatocytes and lie close to sinusoids. The immunoreactive pattern of tyrosine hydroxylase, a marker for catecholaminergic neurons and fibers, is comparable to that of neuropeptide Y. Most neuropeptide Y-containing nerve fibers also contain tyrosine hydroxylase immunoreactivity, in all three species, with the exception of the rabbit parenchyma, where a substantial proportion of catecholaminergic fibers lack immunoreactivity for neuropeptide Y. Finally, systemic administration of the sympathetic neurotoxin, 6-hydroxydopamine, in rats and guinea pigs resulted in virtually complete elimination of both neuropeptide Y- and tyrosine hydroxylase-immunoreactive fibers. These findings are consistent with the hypothesis that neuropeptide Y-containing nerve fibers form a subpopulation of the sympathetic innervation of the mammalian liver, which is likely to originate from prevertebral sympathetic ganglia.

Neuropeptide Y mRNA regulation in rat sympathetic ganglia: effect of reserpine

To study the mechanism underlying trans-synaptic neuropeptide regulation, mRNA levels of neuropeptide Y were examined in the rat stellate and superior cervical ganglia using a specific neuropeptide Y cRNA probe. Basal levels of neuropeptide Y mRNA were detectable in total RNA extracts from single ganglia. Reserpine induced a large rise in ganglion neuropeptide Y mRNA. Decentralization prevented the increase of neuropeptide Y mRNA content in the ganglia. This suggests that the reserpine induced increase in neuropeptide Y mRNA was dependent on transsynaptic stimulation. Consequently, neuropeptide mRNA levels in sympathetic ganglia may be under the control of preganglionic impulse flow.

Neuropeptide Y and catecholamine synthesizing enzymes and their mRNAs in rat sympathetic neurons and adrenal glands: studies on expression, synthesis and axonal transport after pharmacological and experimental manipulations using hybridization techniques and radioimmunoassay

The effects of reserpine treatment (10 mg/kg, i.p.) on the content of neuropeptide Y-like immunoreactivity and catecholamines were compared with the levels of mRNA coding for neuropeptide Y, tyrosine hydroxylase and phenylethanolamine N-methyltransferase in rat sympathetic neurons and adrenal gland. A reversible depletion of neuropeptide Y-like immunoreactivity was observed in the right atrium of the heart, kidney and masseter muscle, while the immunoreactive neuropeptide Y content in the stellate and lumbar sympathetic ganglia and its axonal transport in the sciatic nerve increased following reserpine. The increase in the stellate ganglion was maximal at 48 h and absent 9 days after reserpine treatment. The expression of neuropeptide Y mRNA and tyrosine hydroxylase mRNA in both the stellate and the superior cervical ganglion increased earlier than the neuropeptide Y content, with a clear cut two-fold elevation at 24 h after reserpine. The increase in both mRNAs in the superior cervical ganglion and the depletion of neuropeptide Y, but not of noradrenaline, in terminal areas was prevented after pretreatment both with a nicotinic receptor antagonist (chlorisondamine) and with surgical preganglionic denervation. A marked (75-90%) depletion of neuropeptide Y-like immunoreactivity and adrenaline in the adrenal gland, concomitant with 3-4-fold increases in neuropeptide Y mRNA and tyrosine hydroxylase mRNA expression, was present at 24 h after reserpine treatment. Also in the adrenal gland, there was a reversal of the reserpine-induced increase in neuropeptide Y mRNA and tyrosine hydroxylase mRNA and depletion of neuropeptide Y and adrenaline following splanchnic denervation. Pharmacological, ganglionic blockade prevented the depletion of neuropeptide Y and the increased expression of neuropeptide Y mRNA, but not fully, the tyrosine hydroxylase mRNA elevation. In addition, a marked decrease in phenylethanolamine N-methyltransferase mRNA levels was noted after reserpine. This decrease was reversed by denervation and by ganglionic blockade. Denervation alone led to a small but significant decrease in all mRNAs examined both in the superior cervical ganglion and the adrenal medulla. The present data suggest that the depletion of neuropeptide Y-like immunoreactivity in sympathetic nerves and in the adrenal gland after reserpine is associated with a compensatory increase in neuropeptide Y synthesis and axonal transport, most likely due to increased nicotinic receptor stimulation. Whereas the reserpine depletion of neuropeptide Y in both sympathetic nerves and adrenal gland is related to neuronal activation, adrenal but not nerve terminal depletion of catecholamines can be prevented by the ganglionic blocker chlorisondamine.4+e difference in effect of pharmacological ganglionic

Sympathetic and nonsympathetic neuropeptide Y-containing nerves in the rat myocardium and coronary arteries

We have examined the neuropeptide Y-containing intrinsic nerves of the heart in young (6-week-old) and adult (4-month-old) rats to determine whether they project to the coronary arteries or are capable of doing so if the neuropeptide Y-containing extrinsic nerves are removed. Chronic treatment of neonates with guanethidine was used to permanently destroy the sympathetic nerves. In the young treated animals, 33-54% of the neuropeptide Y remained in the heart despite a 90-99% reduction in norepinephrine; these proportions did not change in the animals that were allowed to develop to adulthood. The level of neuropeptide Y in the right atrium of young animals was unexpectedly high (252 +/- 28.7 pmol/g) compared with adults (75.4 +/- 18.8 pmol/g). The coronary arteries in the control rats received a moderately dense supply of neuropeptide Y-containing nerves; after guanethidine, all neuropeptide Y-containing nerves innervating the large coronary arteries disappeared, but some were still seen in association with small resistance vessels. No compensatory proliferation of the intrinsic neuropeptide Y-containing neurons occurred in the adult sympathectomized animals, and the intrinsic nerves did not reinnervate the large coronary arteries. These results are discussed in relation to the clinical syndrome of coronary artery spasm.

Are NPY and enkephalins costored in the same noradrenergic neurons and vesicles?

Separate studies show that NPY and enkephalins are widely distributed in peripheral noradrenergic neurons. In the present study, the subcellular costorage and release in response to intense sympathetic stimulation and reserpine at near therapeutic doses (0.05 mg/kg every other day) were examined. In young pig arteries and vas deferens, enkephalin and D beta H immunofluorescence show consistent but not total overlap. Also NPY is colocalized with D beta H in many fibers but with VIP (nonnoradrenergic) in others. Ultrastructural immunogold labeling indicates that individual terminals contain large dense cored vesicles (LDVs) which store either NPY or enkephalins, even though costorage of both peptides occurs. Some LDVs costore NPY and VIP, especially in the middle cerebral artery and in the lamina propria of vas deferens. Acute CNS ischemia depletes enkephalins and norepinephrine in all tissues analyzed without parallel loss of NPY. Reserpine depletes norepinephrine 70-85% but does not deplete NPY or enkephalins. The latter is in contrast to commonly used high doses known to produce nonspecific, detergent-like effects. In fact, low doses of reserpine induce a time-dependent new synthesis and processing of NPY precursor peptides in vas deferns. Contrasting effects of reserpine on NPY and enkephalin contents, new synthesis and apparent processing, and a differential response to acute CNS ischemia were found in every tissue studied. Activation of precursor neuropeptide processing occurred immediately upon intense sympathetic stimulation in most tissues. Dual localization of NPY in noradrenergic and nonnoradrenergic fibers and differences in subcellular LDV storage help explain why enkephalin correlates better than NPY with norepinephrine loss in response to acute CNS ischemia. Furthermore, the costorage of NPY and enkephalins in distinct subpopulations of noradrenergic fibers, which varies according to tissue, is likely to be under separate CNS control.

Evidence for noradrenergic-purinergic cotransmission in the hepatic artery of the rabbit

1. Transmural electrical field stimulation produced a transient contraction of the isolated hepatic artery of the rabbit that was frequency-dependent up to 64 Hz. A contraction was rarely evoked at a stimulation frequency of less than 8 Hz and never at 4 Hz or less. All contractions were abolished in the presence of tetrodotoxin. 2. Neurogenic contractions were partially inhibited by prazosin. After desensitization of the P2X-purinoceptor with alpha, beta-methylene ATP, contractions in response to electrical stimulation were significantly reduced at all frequencies tested (4-64 Hz). In most cases, contractions were abolished by a combination of both drugs. 3. In vessels treated with 6-hydroxydopamine, no nerve-mediated contractile responses were observed. 4. In arteries from reserpine-treated rabbits, nerve stimulation evoked contractions that were resistant to prazosin. After desentization of the P2X-purinoceptor with alpha,beta-methylene ATP, no neurogenic contractile response remained. 5. The tissue contracted to exogenously applied noradrenaline and alpha,beta-methylene ATP. There was an increase in sensitivity to noradrenaline in 6-hydroxydopamine-treated vessels compared with control vessels, but no difference in potency to alpha,beta-methylene ATP was detected. The potency of noradrenaline and alpha,beta-methylene ATP was not significantly affected by reserpine treatment. 6. In control tissues, fluorescence histochemistry demonstrated the presence of noradrenergic nerve fibres. Noradrenaline-containing nerves were not observed in 6-hydroxydopamine-treated or reserpine-treated vessels. 7. It is concluded that noradrenaline and ATP are cotransmitters in the sympathetic nerves supplying the hepatic artery of the rabbit. In contrast to other vessels, the hepatic artery requires a relatively high frequency of stimulation to evoke contractions and the purinergic component is not frequency-dependent. The significance of this finding in terms of the physiological demands of blood flow to the liver are discussed.

Changes in cardiac neuropeptide Y after experimental myocardial infarction in rat

We have investigated the hypothesis that neuropeptide Y (NPY) is released from noradrenergic sympathetic nerves during experimentally induced myocardial infarction. A left thoracotomy was performed, the left main coronary artery ligated, and the animals sacrificed 4 or 48 h later. NPY levels in heart tissue from these rats and sham-operated controls were measured with radioimmunoassay. Levels of NPY in the right atrium were greater than other regions of the rat heart. After ligation of the left coronary artery, the concentration of NPY in the infarcted area of the left ventricle was reduced at 4 and 48 h when compared to a similar area in sham-operated rats. NPY levels in the septum were unchanged. The results suggest that during myocardial infarction, NPY is released from nerves in the infarcted region and may deleteriously affect increased collateral blood flow surrounding the infarcted tissue.

Coexistence and gene expression of phenylethanolamine N-methyltransferase, tyrosine hydroxylase, and neuropeptide tyrosine in the rat and bovine adrenal gland: effects of reserpine

Expression and regulation of the catecholamine-synthesizing enzymes phenylethanolamine N-methyltransferase (PNMTase; S-adenosyl-L-methionine:phenylethanolamine N-methyltransferase, EC 2.1.1.28) and tyrosine hydroxylase [TyrOHase; tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] and the coexisting neuropeptide tyrosine (NPY) were studied in rat and bovine adrenal medulla. By using both immunohistochemistry and in situ hybridization, PNMTase- and NPY-positive cells exhibited a close overlap in bovine medulla and were preferentially localized in the outer two-thirds of the medulla. Although TyrOHase and its mRNA were observed in virtually all medullary gland cells, TyrOHase mRNA levels were much higher in the PNMTase- and NPY-positive cells. After administration of the catecholamine-depleting drug reserpine to rats, a brief increase, followed by a dramatic decrease, in the level of PNMTase mRNA was observed in the adrenal medulla. In contrast, mRNA for both TyrOHase and NPY only exhibited an increase, whereby the TyrOHase mRNA peak preceded that of NPY mRNA. Different regulatory mechanisms may thus operate for these three compounds coexisting in the adrenal medulla.

Renal sympathetic nerve activation in relation to reserpine-induced depletion of neuropeptide Y in the kidney of the rat

The effect of reserpine treatment on renal sympathetic nerve activity and tissue levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) were studied in rats. Injection of reserpine (1 mg kg-1 i.v.) caused a clear-cut (about 50%) increase in rectified activity of the post-ganglionic sympathetic nerves to the kidney within 15 min in chloralose-anaesthetized rats compared to a saline-treated control group. This increase in nerve activity was still maintained 120 min after the reserpine injection. The renal nerve activation was accompanied by a progressive fall in mean arterial blood pressure and an initial tachycardia. In a separate group of conscious rats, the levels of NPY-LI (1.3 +/- 0.06 pmol g-1) and NA (1.6 +/- 0.07 nmol g-1) in the kidney were significantly reduced (by 74 and 83%, respectively) 24 h after reserpine treatment (1 mg kg-1 i.v.). The reserpine-induced depletion of NPY-LI, but not that of NA, was inhibited by pretreatment with the ganglionic blocking agent chlorisondamine or the alpha 2-adrenoceptor agonist clonidine, both of which are known to decrease renal sympathetic nerve activity. The tissue content of NPY-LI in the right atrium (16.3 +/- 0.7 pmol g-1) was not reduced by reserpine. Arterial plasma NPY-LI in the rat was high (222 +/- 5 pmol l-1), and this value did not change after pretreatment with reserpine, chlorisondamine or clonidine, indicating that, in the rat, circulating NPY-LI is not a good indicator of sympatho-adrenal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y and reserpine-resistant vasoconstriction evoked by sympathetic nerve stimulation in the dog skeletal muscle

1. The effects of sympathetic nerve stimulation (evoked by recordings of authentic irregular vasoconstrictor nerve fibre discharge with average frequencies of 0.59, 2.0 and 6.9 Hz) on the perfusion pressure and the overflow of noradrenaline (NA) and neuropeptide Y-like immunoreactivity (NPY-LI) were investigated in the blood-perfused gracilis muscle of the dog in situ. 2. Nerve stimulation in the untreated control group evoked a frequency-dependent increase in perfusion pressure and overflow of NA. A significant overflow of NPY-LI was found at the highest frequency only. 3. In a separate group of animals, the sympathetic supply was unilaterally interrupted by preganglionic decentralization before the administration of reserpine (1 mgkg-1 i.v.) 24 h before the experiment. Reserpine reduced the NA content of the intact and decentralized gracilis and gastrocnemius muscle by 98-99%. Reserpine also induced a marked (80%) reduction of the muscular content of NPY-LI. The depletion of NPY-LI was, in contrast to that of NA, prevented by the decentralization, suggesting that nerve impulse activity was of primary importance for the reserpine-induced depletion of NPY-LI. 4. A slowly developing and long-lasting perfusion pressure increase was evoked by nerve stimulation, at 2.0 and 6.9 Hz after reserpine treatment. These responses were larger in the decentralized, as compared to the intact gracilis muscle and correlated with the nerve stimulation evoked overflow of NPY-LI (r = 0.79, P less than 0.001). Stimulation at 0.59 Hz caused vasoconstriction in the decentralized but not in the intact gracilis. 5. Administration of alpha,beta,-methylene adenosine triphosphate did not evoke an increase in perfusion pressure in the gracilis muscle of reserpine-treated animals. 6. In conclusion, a large perfusion pressure increase to sympathetic nerve stimulation occurs in the reserpine-pretreated skeletal muscle vasculature of the dog in vivo, providing that preganglionic decentralization has been performed. It is suggested that the released NPY-LI may mediate this vasoconstrictor response.

Neuropeptide tyrosine in the rat adrenal gland--immunohistochemical and in situ hybridization studies

The adrenal gland of the rat was analysed with immunohistochemistry and antisera to neuropeptide tyrosine, to the catecholamine-synthesizing enzymes tyrosine hydroxylase, phenyl-ethanolamine-N-methyltransferase, and to acetylcholinesterase and with in situ hybridization using a nick-translated 280 base pair deoxyribonucleic acid probe coding for exon 2 of the rat neuropeptide tyrosine gene. Neuropeptide tyrosine-like immunoreactivity was observed in three structures: chromaffin cells, medullary ganglion cells and nerve fibers. The chromaffin cells were of both the noradrenaline- and adrenaline-type. The ganglion cells did not seem to contain any catecholamine-synthesizing enzymes but exhibited a strong immunoreaction for acetylcholinesterase. They were thus in all probability cholinergic neurons. In situ hybridization using the nick-translated deoxyribonucleic acid probe to rat neuropeptide tyrosine messenger ribonucleic acid revealed a very high-grain density over the ganglion cells, a moderate density over the chromaffin cells and a low background over cortex, in agreement with the immuno-histochemical demonstration of neuropeptide tyrosine-like immunoreactivity both in chromaffin and ganglion cells. The intense neuropeptide tyrosine-like immunoreactivity and low content of neuropeptide tyrosine messenger ribonucleic acid suggest that the chromaffin cells have fairly large peptide stores but that the peptide turnover is low. In contrast, the ganglion cell bodies seem to contain low amounts of neuropeptide tyrosine-like immunoreactivity but exhibit a high neuropeptide tyrosine synthesis rate. Preliminary studies with the amine-depleting drug reserpine revealed an increase in messenger ribonucleic acid both in ganglion cells and medullary cells. In the chromaffin cells the highest activity was seen 3 and 4 days after injection, and the levels were down to normal after 8 days. The present findings demonstrate neuropeptide tyrosine synthesis and storage in two cell populations in the adrenal medulla. In situ hybridization with its cellular resolution can provide information on possible differential effects of drugs and experimental procedures on these two neuropeptide tyrosine stores.

Stress-induced changes of circulating neuropeptide Y in the rat: comparison with catecholamines

Circulating concentrations of neuropeptide Y-like immunoreactivity (NPY), noradrenaline (NA) and adrenaline (AD) were measured in conscious, chronically catheterized rats submitted to various stress protocols. Basal plasma levels of NPY, NA and AD (194 +/- 52 fmol/ml, 0.90 +/- 0.11 pmol/ml and 0.52 +/- 0.07 pmol/ml) were increased by handling (+132%, +76% and +629%, respectively) and rose further during electric shock treatment. Adrenalectomy resulted in the complete disappearance of circulating adrenaline but did not alter either control or stress values of noradrenaline. In comparison circulating levels of NPY were reduced, but not significantly in adrenalectomized animals. Insulin stress induced a large increase in plasma AD levels and cold stress induced an increase in plasma NA levels, without any parallel change in NPY concentrations. These results demonstrate that NPY, which is colocalized with catecholamines in the peripheral nervous systems, is also released during stress responses and that its release parallels more closely changes in circulating NA than AD. Furthermore, stress-induced changes in circulating NPY-like immunoreactivity do not originate from the adrenal gland but mainly from the peripheral nervous system, and the release of NPY is dependent upon the nature of the stimulus.

Peptides in the mammalian cardiovascular system

Ample immunocytochemical evidence is now available demonstrating that several peptides are present in the mammalian cardiovascular system where they are localised to nerve fibres and myocardial cells. The neuropeptides (neuropeptide Y, calcitonin gene-related peptide, tachykinins and vasoactive intestinal polypeptide) are localised to large secretory vesicles in subpopulations of afferent or efferent nerves supplying the heart and vasculature of several mammals, including man. Although they often exert potent pharmacological effects on the tissues in which they occur their physiological significance has still to be established. They may act directly via specific receptors and/or indirectly by influencing the release and action of other cardiovascular transmitters. In marked contrast, atrial natriuretic peptide is produced by cardiac myocytes and considered to act as a circulating hormone.