Guanethidine-sensitive release of neuropeptide Y-like immunoreactivity in the cat spleen by sympathetic nerve stimulation

The role of adenosine A2A and A3 receptors on the differential modulation of norepinephrine and neuropeptide Y release from peripheral sympathetic nerve terminals

The pre-synaptic sympathetic modulator role of adenosine was assessed by studying transmitter release following electrical depolarization of nerve endings from the rat mesenteric artery. Mesentery perfusion with exogenous adenosine exclusively inhibited the release of norepinephrine (NA) but did not affect the overflow of neuropeptide Y (NPY), establishing the basis for a differential pre-synaptic modulator mechanism. Several adenosine structural analogs mimicked adenosine's effect on NA release and their relative order of potency was: 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride = 1-[2-chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-beta-d-ribofuranuronamide = 5'-(N-ethylcarboxamido)adenosine >> adenosine > N(6)-cyclopentyladenosine. The use of selective receptor subtype antagonists confirmed the involvement of A(2A) and A(3) adenosine receptors. The modulator role of adenosine is probably due to the activation of both receptors; co-application of 1 nM 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride plus 1 nM 1-[2-chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-beta-D-ribofuranuronamide caused additive reductions in NA released. Furthermore, while 1 nM of an A(2A) or A(3) receptor antagonist only partially reduced the inhibitory action of adenosine, the combined co-application of the two antagonists fully blocked the adenosine-induced inhibition. Only the simultaneous blockade of the adenosine A(2A) plus A(3) receptors with selective antagonists elicited a significant increase in NA overflow. H 89 reduced the release of both NA and NPY. We conclude that pre-synaptic A(2A) and A(3) adenosine receptor activation modulates sympathetic co-transmission by exclusively inhibiting the release of NA without affecting immunoreactive (ir)-NPY and we suggest separate mechanisms for vesicular release modulation.

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

Sympathetic activation of hepatic and splenic IL-1beta mRNA expression during oscillation stress in the rat

Interleukin (IL)-1beta mRNA expression in the liver and spleen was examined after subjection to oscillation stress in the rat. Thirty-minute subjection to oscillation stress increased IL-1beta mRNA expression in the both organs. Prior treatment of rats with gadolinium chloride, which eliminates macrophages, prevented the stress-induced IL-1beta expression. Either adrenalectomy or treatment of guanethidine, a blocker of norepinephrine release in the sympathetic nerve endings, partially attenuated the stress-induced response, but the combined treatment completely blocked it. Injection of beta-adrenergic antagonist (propranolol) also suppressed the stress-induced response. These results suggest that oscillation stress induces IL-1beta mRNA expression in the liver and spleen, probably in Kupffer cells and splenic macrophages, and that stress-induced IL-1beta expression is elicited by catecholamines released from sympathetic nerve terminals and the adrenal gland.

Neuropeptide Y actions and the distribution of Ca2+-dependent Cl- conductance in rat dorsal root ganglion neurons

Neuropeptide Y (NPY) increases the excitability of 'small', nociceptive, dorsal root ganglion (DRG) neurons. This effect, which may contribute to the etiology of 'neuropathic' pain, has been attributed to attenuation of Ca2+-sensitive K+ conductance(s) (gK,Ca) following suppression of Ca2+ entry via N-type Ca2+ channels. A problem arises with this conclusion because rat DRG neurons normally contain high intracellular Cl- and some of them express a Ca2+-dependent Cl- conductance (gCl,Ca). In this study, we find that in rat DRG neurons increasing intracellular Cl- does not attenuate the effect of 1 microM NPY because gCl,Ca is not found in 'small' DRG cells and the peptide failed to affect the gCl,Ca found in 'large' cells. Thus, the presence of gCl,Ca in a subpopulation of 'large' DRG neurons does not alter the conclusion that excitatory effects of NPY result from attenuation of gK,Ca.

Nerve injury increases an excitatory action of neuropeptide Y and Y2-agonists on dorsal root ganglion neurons

Damage to sensory nerves invokes the expression of neuropeptide Y in the cell bodies of sensory neurons in dorsal root ganglia. We therefore compared the action of this peptide on control dorsal root ganglia neurons with its action on neurons from animals in which the sciatic nerve had been cut. Neuropeptide Y (0.1-1.0 microM) increased the excitability of 24% of control neurons and its effect was stronger and more cells (56%) were affected after axotomy. Increased excitability was mediated via a Y2-receptor and resulted from attenuation of Ca2+-sensitive K+-conductance(s) secondary to suppression of N-type Ca2+ channel current. Y1-agonists potentiated L-type Ca2+ channel current in control neurons without altering excitability. This Y1-effect was attenuated whereas effects mediated via Y2-receptors were enhanced after axotomy. No evidence was found for involvement of Y4- or Y5-receptor subtypes in the actions of neuropeptide Y either on control or on axotomized dorsal root ganglion neurons. It is concluded that neuropeptide Y increases the excitability of sensory neurons by interacting with a Y2-receptor and thereby decreasing N-type Ca2+ channel current and Ca2+-sensitive K+-conductance(s). When peripheral nerves are damaged, dorsal root ganglion neurons start to express neuropeptide Y and its excitatory Y2-excitatory effects are enhanced. The peptide may therefore contribute to the generation of aberrant sensory activity and perhaps to the etiology of injury-induced neuropathic pain.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

Nociceptive inhibition of migrating myoelectric complex by nitric oxide and monoaminergic pathways in the rat

This study investigated the role of nitric oxide (NO) and adrenergic and dopaminergic mechanisms in reflex inhibition of the migrating myoelectric complex (MMC) after intraperitoneal administration of acid in rats. Acid instilled immediately after an activity front inhibited the migrating complex and prolonged the cycle length from 13.0 +/- 0.7 to 98.5 +/- 17.2 min (P < 0.001). Administration of N omega-nitro-L-arginine, reserpine, or guanetidine before acid decreased the prolonged cycle length to 18.1 +/- 2.8 (P < 0.001), 19.0 +/- 2.0 (P < 0.001), and 27.5 +/- 9.3 min (P < 0.001), respectively. Similarly, haloperidol given before acid shortened the prolonged cycle length to 46.7 +/- 5.2 min (P < 0.05). There was no effect of phentolamine in combination with propranolol or hexamethonium given alone. After intraperitoneal instillation of acid there was an increase in the plasma levels of somatostatin and a decrease of calcitonin gene-related peptide, but there was no change of neuropeptide Y, vasoactive intestinal peptide, substance P, neurokinin A, or neurotensin. The results indicate that NO and adrenergic, dopaminergic, and somatostatinergic mechanisms cooperate in inhibiting the MMC after nociceptive stimulation of the peritoneum.

Noradrenaline storing vesicles in sympathetic neurons and their role in neurotransmitter release: an historical overview of controversial issues

More than 25 years have passed since the original demonstration that proteins such as chromogranin A and dopamine-beta-hydroxylase, which are co-stored together with noradrenaline in large dense cored vesicles in adrenergic nerves, are released by exocytosis. Despite much evidence in favour, it was for a long time thought that large dense cored vesicles were not eminently involved in the release of noradrenaline. The present review attempts to demonstrate, making use of evidence from different approaches, that the release of noradrenaline from sympathetic neurons occurs ultimately from large dense cored vesicles. A model of the secretory cycle is proposed.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Novel neuropeptide Y receptor antagonists block vasoconstriction in the hamster cheek pouch microcirculation

We investigated the efficacy of novel neuropeptide Y (NPY) antagonists to inhibit the microcirculatory dynamics of NPY in the hamster cheek pouch microcirculation using intravital microscopy and computer-assisted image analysis. Changes in arteriolar diameter served as an index of vasomotor alterations. Fluorescein isothiocyanate-labeled Dextran 150 served as a tracer for measurements of macromolecular transport. GW 383 and GW 1229, two novel NPY receptor antagonists, were applied topically in separate experiments. Pretreatment with 10(-5), 10(-6) and 10(-7) M GW 383 and with 10(-6) and 10(-8) M GW 1229 attenuated the vasoconstriction induced by 10(-7) M NPY in a dose-dependent manner. Furthermore, pretreatment with 10(-7) and 10(-8) M GW 1229 significantly inhibited the 10(-9) M NPY-induced vasoconstriction. At these doses, the NPY antagonists did not alter microvascular permeability. Our results demonstrate that the novel NPY antagonists inhibit the vasoconstriction induced by NPY in the hamster check pouch microcirculation. We suggest that the inhibition is due to binding of antagonists to Y1-type NPY receptors.

Variation in mRNA expression of alpha-adrenergic, neurokinin and muscarinic receptors amongst four arteries of the rat

Different mechanisms mediate constriction and dilation in different vascular beds. We have used reverse transcription-polymerase chain reaction to investigate whether specific patterns of receptor gene expression may underlie these variable responses. Total RNA, from the basilar, pulmonary, mesenteric and tail arteries of anaesthetised adult Wistar rats, was reverse transcribed and amplified using primers specific for the molecular subtypes of the alpha 1(A, B, D)- and alpha 2(A, B, C)-adrenergic, neurokinin (NK1-NK3) and muscarinic (m1-m5), receptors. Results showed that the pattern of gene expression was variable with no two arteries having the same receptor profile. Messenger RNA for the alpha 1A, alpha 1B, alpha 2B, NK1, NK3, m3 and m5 receptor subtypes were detected in all vessels studied while the remaining subtypes showed a variable expression amongst the arteries. This is the first description of mRNA for the m5 muscarinic receptor in peripheral tissue. The NK3 receptor was the major neurokinin receptor expressed in all vessels except the pulmonary artery, in which the NK1 receptor was also strongly expressed. We conclude that each artery expressed a specific receptor array which may permit some unique neural and hormonal controls.

Neuropeptide Y release and contractile properties: differences between canine veins and arteries

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.

Pressor effect of the putative M1 muscarinic receptor agonist MCN-A-343 in the conscious rat

The putative M1 muscarinic receptor agonist McN-A-343 evoked a dose-dependent increase in mean arterial pressure (MAP) when administered intravenously to conscious freely-moving rats pretreated with the ganglionic nicotinic receptor antagonist pentolinium. A tachycardia accompanied the increase in MAP which was blocked by the beta-adrenergic receptor antagonist propranolol. The increase in MAP was attenuated by the alpha 1-adrenergic receptor antagonist prazosin combined with the alpha 2-adrenergic receptor antagonist yohimbine. Adding propranolol to alpha-adrenergic receptor blockade uncovered a latent pressor response. Replacing prazosin with benextramine (which blocks NPY in addition to alpha-adrenergic receptors) attenuated the pressor response unmasked by propranolol. This attenuation was comparable to that provided by benextramine of the pressor response to intravenous administration of NPY. Adrenal demedullation only slightly attenuated the pressor response while having no effect on the tachycardia. The catecholamine depletor guanethidine greatly attenuated the McN-A-343-evoked increase in MAP and heart rate. The combination of adrenal demedullation and guanethidine did not further attenuate the increase in MAP but did provide better attenuation of the tachycardia than guanethidine alone. These results show that McN-A-343-evokes an increase in MAP and heart rate of conscious freely-moving rats primarily by causing the release of catecholamines, and possibly NPY, from sympathetic neurons with the adrenal glands playing a minor role.

SR 120107A antagonizes neuropeptide Y Y1 receptor mediated sympathetic vasoconstriction in pigs in vivo

The effects of the neuropeptide Y Y1 receptor antagonist SR 120107A (1-[2-[2-(2-naphtylsulfamoyl)-3-phenylpropionamido]-3-[4-[N- [4- (dimethylaminomethyl)-cis-cyclohexylmethyl]amidino]phenyl]propiony l] pyrrolidine, (S,R) stereoisomer) on sympathetic non-adrenergic vasoconstriction in a variety, of vascular beds were studied in reserpinized anesthetized pigs in vivo. The rapid vasoconstrictor response evoked by single impulse stimulation, in hind limb and nasal mucosa, was not affected by SR 120107A (1.5 mg kg-1 i.v.). In contrast, SR 120107A potently inhibited the long-lasting phase of vasoconstriction evoked by high frequency (60 impulses at 20 Hz) sympathetic nerve stimulation, in the main and deep femoral, the saphenous and the internal maxillary arteries, leaving merely the initial rapid peak of vasoconstriction in these vessels. Furthermore, the vasoconstrictor response was nearly abolished in the kidney and was attenuated in the spleen and main femoral artery, despite maintained neuropeptide Y overflow. The vasoconstrictor response evoked in the kidney by peptide YY, a neuropeptide Y Y1 and Y2 receptor agonist, was also nearly abolished in the presence of SR 120107A. This inhibitory effect on the response to exogenous agonist correlated well with the long-lasting inhibition of the response to nerve stimulation in the same tissue. The peptide YY-evoked vasoconstriction in the spleen was not altered by SR 120107A, in accordance with the view that the neuropeptide Y receptor population in this organ consists mainly of neuropeptide Y Y2 receptors. SR 120107A did not influence the vasoconstrictor effects of alpha, beta-methylene ATP (mATP) or phenylephrine in any of the tissues studied. We conclude that SR 120107A is a potent neuropeptide Y Y1 receptor antagonist with long duration of action in vivo. Endogenous neuropeptide Y acting on the neuropeptide Y Y1 receptor is likely to account for the long-lasting component of the reserpine-resistant sympathetic vasoconstriction upon high frequency stimulation in hind limb and nasal mucosa. Furthermore, the peak vasoconstriction in kidney, and to some extent in spleen, is also neuropeptide Y Y1 receptor mediated.

Circulating neuropeptide Y in humans: relation to changes in catecholamine levels and changes in hemodynamics

Neuropeptide-Y (NPY) is a sympathetic cotransmitter, which causes vasoconstriction, decreases coronary blood flow and decreases cardiac output. Circulating immunoreactive NPY (ir-NPY) levels increase with exercise, in patients admitted to the coronary care unit, and during thoracic surgery, and may play a role in postoperative hemodynamics. We studied changes in ir-NPY, epinephrine (E) and norepinephrine (NE) arterial plasma levels, and their correlation to simultaneous hemodynamic measurements at 8 perioperative time points in 13 patients undergoing open heart surgery. Changes in circulating ir-NPY negatively correlated with changes in systemic vascular resistance index (SVRI), mean arterial pressure (MAP) and mean pulmonary arterial pressure (MPAP) (P < 0.05), suggesting that the hemodynamic changes were the cause of the changes in ir-NPY levels, inducing overflow of NPY into the circulation via sympathetic activation. Changes in NE and E levels positively correlated with changes in heart rate (HR), SVRI and MPAP. Changes in E levels also positively correlated with changes in stroke volume index (SVI), central venous pressure (CVP) and cardiac index (CI). NE levels correlated well with E levels, but catecholamine levels did not correlate with ir-NPY levels. These results suggest, that the elevation in circulating NPY levels previously noted in patients with heart failure and acute myocardial infarction may reflect changes in NPY overflow and/or clearance secondary to increased sympathetic activity and to hemodynamic changes.

Prejunctional regulation of reserpine-resistant sympathetic vasoconstriction and release of neuropeptide Y in the pig

The prejunctional regulation of non-adrenergic sympathetic vasoconstriction and release of neuropeptide Y (NPY) was investigated in vivo. In reserpinized pigs (with depleted noradrenaline (NA)), it was demonstrated that brief sympathetic nerve stimulation (2 pulses of 20 Hz) of the spleen, kidney and hind limb in the presence of the alpha 2-adrenoceptor agonist UK 14,304 (1 micrograms/kg per min i.v.) evoked reproducible vasoconstrictor responses which were reduced by 40-80% in comparison to that in the absence of UK 14,304. In addition, the splenic overflow of NPY-like immunoreactivity (-LI) was reduced. After cessation of the UK 14,304 infusion all these effects were reversed by addition of the alpha 2-adrenoceptor antagonist yohimbine (0.2 mg/kg i.v.). Also the Y2 receptor agonist NPY(13-36) reduced the splenic overflow of NPY-LI. Splenic vasoconstriction per se was evoked by another Y2 receptor agonist N-acetyl[Leu28Leu31]NPY(24-36), while no vascular effects in the kidney or hind limb were observed. Both Y2 agonists displaced [125I]NPY binding to splenic membranes with higher potency than the Y1-receptor agonist [Leu31Pro34]NPY(1-36). No evidence was obtained for angiotensin II mechanisms being important for the enhanced NPY release after reserpine in spite of elevated renin release. The present results show that in the absence of NA, repetition of brief sympathetic nerve stimulation evokes vascular effects and NPY-LI release which are repeatable and these effects are efficiently modulated via alpha 2-adrenoceptors. Furthermore, the Y2 receptors may mediate both prejunctional inhibition of NPY release, as well as postjunctional vasoconstrictor effects in the pig spleen.

Neuropeptide Y is a vasoconstrictor and adrenergic modulator in the hamster microcirculation by acting on neuropeptide Y1 and Y2 receptors

The microvascular effects of neuropeptide Y, and two analogs with preferential affinity for different neuropeptide Y receptor subtypes, were assessed by intravital microscopy on the hamster cheek pouch. The interaction of neuropeptide Y and its analogs with noradrenaline was also studied. Superfusion with 0.1-300 nM neuropeptide Y caused a concentration-dependent reduction in microvascular conductance that was paralleled by reductions in arteriolar and venular diameters. These effects of neuropeptide Y were equipotent with noradrenaline, but slower to develop and longer-lasting than that of noradrenaline. Neuropeptide Y did not affect permeability to macromolecules, as measured by extravasation of fluorescent dextran. The neuropeptide Y Y1 receptor agonist, [Leu31,Pro34]neuropeptide Y, mimicked neuropeptide Y with similar potency but shorter duration, while neuropeptide Y-(13-36), a neuropeptide Y Y2 receptor agonist, was at least 10-fold less potent than neuropeptide Y to induce a delayed and prolonged reduction in microvascular conductance. The joint superfusion of 1 nM neuropeptide Y plus 0.1 mu M noradrenaline did not cause synergism, nor even summation of effects, but reduced the contractile effect of noradrenaline. No synergism was observed after a 10 min priming with 1 nM neuropeptide Y, followed by its joint application with 0.1 mu M noradrenaline, but a significant vasodilation and hyperemia ensued upon stopping noradrenaline application. Priming with 1 nM [Leu31,Pro34]neuropeptide Y prolonged noradrenaline vasoconstriction without evidence of hyperemia. In contrast, priming with 1 nM neuropeptide Y-(13-36) significantly antagonized noradrenaline vasoconstriction. These findings indicate that both neuropeptide Y receptor subtypes are present in arterioles and venules of the hamster, and suggest that their activation with neuropeptide Y induces a rapid (Y1 receptor subtype activation) and a delayed (Y2 receptor subtype activation) vasocontractile response. The interaction with noradrenaline is complex, without evidence for synergism, but neuropeptide Y Y2 receptor activation seems to antagonize noradrenaline and/or to facilitate auto-regulatory vasodilation after the catecholamine-induced vasoconstriction.

Inhibition of vagally induced gastric contractions by sympathetic stimulation, neuropeptide Y and galanin

The effects on vagally-induced gastric contractions of local electrical stimulation of the gastric sympathetic nerves were investigated in anaesthetised cats. Sympathetic stimulation caused an inhibition of vagally mediated gastric contractions which survived beta-adrenoceptor blockade and could not be mimicked by the alpha-adrenoceptor agonist phenylephrine. We therefore concluded that the inhibition was not predominantly dependent upon activation of alpha or beta adrenoceptors, although some effect attributable to noradrenaline could not be entirely excluded. In an attempt to determine the mechanism of this phenomenon, we administered exogenous neuropeptide Y (NPY) and galanin (GAL), both of which are known to occur as cotransmitters in some sympathetic nerves in the cat. Both NPY and GAL were able to mimic the effect of sympathetic stimulation on vagally-induced gastric contractions but their effects were variable.

Beta-adrenoceptor stimulation increases neuropeptide Y release from sympathetic nerves in intact rats

This study was undertaken to assess in conscious normotensive rats the effects of beta-adrenoceptor stimulation on plasma neuropeptide Y (NPY) levels. Wistar rats were subjected to adrenal demedullation on the right side and were either adrenalectomized or sham-operated on the left side. Eleven days later, the conscious rats were infused i.v. for 30 min with either isoproterenol (10 ng/min) or its vehicle. Plasma NPY levels were significantly lower (23.8 +/- 2.6 pM, means +/- S.E.M., n = 12, P < 0.01) in vehicle-treated medullectomized rats than in corresponding sham-operated controls (36.7 +/- 4.1 pM, n = 12). The medullectomized rats infused with isoproterenol showed plasma NPY levels (36.7 +/- 3.3 pM, n = 11) comparable to those of sham-operated rats having received the vehicle. These data therefore demonstrate that plasma NPY levels are lower in rats without adrenal medulla and that in these animals isoproterenol increases NPY release, most likely by activating pre-synaptic beta-adrenoceptors.

Evidence against differential release of noradrenaline, neuropeptide Y, and dopamine-beta-hydroxylase from adrenergic nerves in the isolated perfused sheep spleen

The subcellular storage and release of noradrenaline (NA), dopamine-beta-hydroxylase (D beta H), and neuropeptide Y (NPY) was studied in the isolated perfused sheep spleen. Subcellular distribution studies showed a bimodal distribution for NA which was well reflected by D beta H and indicated the occurrence of two types of NA storage vesicles. The most dense, presumably large dense-cored vesicles (LDV), contain both membrane-bound and soluble D beta H; the less dense presumably corresponds to small dense-cored vesicles (SDV) and at least does not contain soluble D beta H. The distribution of NPY is extended but shows a peak only at the position of LDV, indicating that LDV contain NPY. Continuous electrical stimulation of the splenic nerve at 2 Hz, 5 Hz, 10 Hz, and 20 Hz or at 20 hz with bursts induced the release of NA, NPY, and D beta H. The ratio among these components was constant. The fractional release of D beta H and NA was comparable at all frequencies used; that of NPY was 10-20 times lower, suggesting the occurrence of a large nonreleasable NPY pool. The present data argue against a high frequency stimulation or intermittent stimulation-induced preferential release of NPY from adrenergic neurons and question the concept of frequency-dependent chemical coding of sympathetic transmission in general. The simplest interpretation of our data is that NA and NPY are released at all frequencies from a single pool. The present finding might signify that only large dense-cored vesicles are involved in the sympathetic stimulation-evoked secretion of catecholamines from adrenergic nerve terminals of the isolated sheep spleen.

New insights into the local regulation of blood flow by perivascular nerves and endothelium

Blood flow, particularly in the skin, is essential for the success of plastic surgical operations. This review describes recent studies of the perivascular nerves and vascular endothelial cells which regulate blood flow. Perivascular nerves, once considered simply adrenergic or cholinergic, release many types of neurotransmitters, including peptides, purines and nitric oxide. Cotransmission (synthesis, storage and release of more than one transmitter by a single nerve) commonly takes place. Some afferent nerves have an efferent (motor) function and axon reflex control of vascular tone by these "sensory-motor" nerves is more widespread than once thought. Endothelial cells mediate both vasodilatation and vasoconstriction. The endothelial cells can store and release vasoactive substances such as acetylcholine (vasodilator) and endothelin (vasoconstrictor). The origins and functions of such vasoactive substances are discussed. Endothelial vasoactive substances may be of greater significance in the response of blood vessels to local changes while perivascular nerves may be concerned with integration of blood flow in the whole organism. The dual regulation of vascular tone by perivascular nerves and endothelial cells is altered by aging and conditions such as hypertension, as well as by trauma and surgery. Studies of vascular tone in disease and after denervation or mechanical injury suggest possible trophic interactions between perivascular nerves and endothelial cells. Such trophic interactions may be important for growth and development of the two control systems, particularly in the microvasculature where neural-endothelial separation is small.

Roles of noradrenaline and ATP in sympathetic vasoconstriction of the guinea-pig main ear artery

This study has investigated the roles of noradrenaline (NA) and adenosine 5'-triphosphate (ATP) in sympathetic vasoconstriction of the main ear artery from guinea-pigs. A range of agents which interact with adrenoceptors or purinoceptors was tested on contractions produced by exogenous NA or ATP, and on contractions produced by transmural stimulation of sympathetic axons. Contractions produced by NA were antagonized competitively by prazosin (Schild plot slope 0.88 +/- 0.13, not significantly different from 1.0). Dihydroergotamine (10 microM) produced significant depression of contractions produced by all concentrations of NA. Yohimbine (1 microM) caused a small rightward shift in the NA concentration-response curves (0.34 log units), whereas propranolol had no effect. alpha,beta,m-ATP (6 microM) enhanced contractions produced by low concentrations of NA (0.1-1 microM), whereas suramin (30 microM) produced a slight depression in the maximum NA-induced contraction in all experiments. Contractions produced by ATP (0.1 mM) were greatly reduced by suramin (30 microM; 59% reduction) and by alpha,beta,m-ATP (6 microM); 96% reduction), and were slightly depressed by dihydroergotamine (10 microM; 12% reduction). Transmural electrical stimulation with trains of 200-300 pulses produced contractions which were rapid in onset and recovery, and sometimes were biphasic. Contractions at both 5 Hz and 20 Hz were reduced by 50-70% after treatment with prazosin (0.1-1 microM). The remaining contractions were enhanced significantly by yohimbine (1 microM), were reduced very slightly by dihydroergotamine, and were largely abolished by guanethidine (1 microM). alpha,beta,m-ATP (1-100 microM) alone often enhanced neurogenic contractions (by 100-200%), whereas suramin (30 microM) alone reduced contractions by 48%.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated renal and splenic sympathetic nerve stimulation in anaesthetized pigs: maintained overflow of neuropeptide Y in controls but not after reserpine

The overflow and the arterial vascular effects of neuropeptide Y (NPY) in response to repeated sympathetic nerve stimulation of kidney and spleen were investigated in anaesthetized pigs. The responses under control conditions were compared to those evoked in pigs with tissue stores of noradrenaline (NA) selectively depleted by reserpine pretreatment combined with sympathetic nerve transection. The renal and splenic sympathetic nerves were repeatedly stimulated at 1 h intervals with one 5 Hz stimulation for 48 s and transmitter overflow determined. Between these stimulations, 5 min stimulations with bursts of 20 Hz (for 1 s every 10 s) were given in order to induce a depletion of nerve transmitter. In the control group, overflow of NPY and NA and vasoconstrictor responses were almost identical for the 5 consecutive stimulations in the kidney, whereas in the spleen the parameters showed a slight tendency to be reduced. In the reserpine-treated group, the initial evoked overflow of NPY was increased 8-fold and 3-fold in the kidney and spleen, respectively, compared to the control group. Upon each subsequent stimulation the overflow decreased gradually, in parallel with the evoked vasoconstrictor response. After a 2 h recovery period no change in evoked overflow of NPY compared to the amount released by the previous stimulation was observed. The present study illustrates, the high capacity of maintenance of not only NA but also NPY overflow and vascular responses in control conditions, whereas the enhanced release of NPY in the absence of NA cannot be maintained. It is therefore possible that the NA-mediated prejunctional feedback mechanism is important for the maintenance of a constant NPY release in situations of high sympathetic activation.

Molecular cloning of NPY-Y1 receptor cDNA from rat splenic lymphocytes: evidence of low levels of mRNA expression and [125I]NPY binding sites

The present study addressed the question of whether the effects of neuropeptide Y (NPY) on parameters of cellular immune activity are mediated by the direct action of this neuropeptide on lymphocyte NPY receptors. A partial cDNA corresponding to bp 3-585 of the NPY-Y1 receptor coding sequence was cloned from rat splenic lymphocytes and found to have 100% nucleotide sequence homology with that segment of the NPY-Y1 receptor in brain. Basal levels of NPY-Y1 mRNA expression and [125I]NPY binding sites of rat splenic lymphocytes were markedly lower than in frontal cortex. These data provide the first direct evidence that cells of the immune system possess NPY receptors, and suggest that further study will be necessary to determine their physiological significance.

Heterogeneity of alpha 1-adrenoceptor subtypes involved in adrenergic contractions of dog blood vessels

1. We determined the alpha 1-adrenoceptor subtypes involved in adrenergic contractions of eight different blood vessels isolated from the dog. 2. Noradrenaline produced concentration-dependent contractions in all the blood vessels tested, which were competitively inhibited by prazosin, WB4101, HV723 and 5-methylurapidil. However, there was considerable difference between the vessels with regard to the pKB values for all the antagonists. The alpha 1-adrenoceptors of dog vertebral and carotid arteries had high affinity for prazosin (pKB > 9.0) but low affinity for WB4101 (< 8.5), 5-methylurapidil (< 7.5) and HV723 (< or = 8.5). By contrast, HV723 had higher affinity (> 9.0) than prazosin (< 8.3), WB4101 (< 8.7) and 5-methylurapidil (< 8.2) in the portal vein, mesenteric artery and vein, and renal artery. In the femoral artery and vein, however, the four antagonists showed pKB values in the range 8.0-8.7. 3. Chloroethylclonidine (10 microM) produced a remarkable reduction of the contractile responses to noradrenaline in the vertebral and carotid arteries as compared with those in the other vessels. Nifedipine inhibited the responses to noradrenaline in all the tissues tested, and had marked effects in the portal vein. 4. Sympathetic adrenergic contractions induced by transmural electrical stimulation were also inhibited by prazosin and HV723 at different potencies among tissues. The relative potencies of both the antagonists paralleled the relationship in inhibiting the responses to exogenous noradrenaline in each vessel. 5. According to recent alpha l-adrenoceptor subclassification, the present results suggest that the contractions of blood vessels induced by endogenous and exogenous noradrenaline are mediated through different alpha l-adrenoceptor subtypes heterogeneously distributed in each vessel; presumably, the alpha 1 B subtype in the carotid and vertebral arteries, the alpha IN subtype in the visceral region and the alpha IL subtype in the femoral region. Regionally different expression of alpha 1-adrenoceptor subtypes may be in part associated with the regional heterogeneity of sympathetic responses in the blood vessels.

Vascular responses to neuropeptide Y in the rat: effect of age

Neuropeptide Y (NPY) is co-released with norepinephrine (NE) from sympathetic neurons, which innervate blood vessels, and acts to potentiate NE-induced smooth muscle contraction. This study sought to determine if vascular levels of NPY-like immunoreactivity or the contractile effects of NPY are altered by age in segments of isolated blood vessels from Fischer 344 and Brown Norway-F344-F-1 rats. Tissue extracts of femoral and tail arteries of Fischer 344 rats, aged 6, 12, 20, and 24 months, were analyzed for NPY content by radioimmunoassay. Neither blood vessel showed a significant age-related difference in NPY content. Contractile responses of the tail artery to adrenergic transmural nerve stimulation (TNS) were compared in the same age groups. No significant age-related differences in contractile responses to TNS were observed in either rat strain. NPY, at concentrations of 1 and 10 nM, both potentiated and prolonged the contractile response to TNS; 6-month-old F-344 rats were significantly less responsive to the effects of NPY. However, advancing age from 12 to 24 months did not alter the responses to NPY in either rat strain. We conclude that an age-dependent increase in the contractile responses to NPY occurs from age 6 to 12 months, and this responsiveness to NPY is maintained through senescence.

Neuropeptides in the internal anal sphincter in neurogenic faecal incontinence

The internal anal sphincter has both an intrinsic and extrinsic innervation which modulates its activity. While the nature of the extrinsic innervation has been well characterised, the same is not true of the intrinsic innervation. Although a variety of neurotransmitters have been identified in the human internal anal sphincter, their physiological role in health, and possible involvement in disease processes, have received little attention. Using immunohistochemistry we have studied the distribution and nerve fibre densities of a range of neuropeptides in the internal anal sphincter from 12 cancer patients (controls) and from 16 patients with neurogenic faecal incontinence. We have also studied the in vitro effect of vasoactive intestinal peptide, neuropeptide tyrosine, and galanin on isolated preparations of the internal anal sphincter from 11 cancer controls and 5 patients with neurogenic faecal incontinence. There was no difference in either the distribution or density of the neuropeptides between the 2 groups of patients, and there was no qualitative difference in the in vitro responses of the sphincter to the neuropeptides. These findings suggest that these neuropeptide components of the intrinsic innervation of the internal anal sphincter are unaffected in patients with neurogenic faecal incontinence.

Comparison of the acute influence of neuropeptide Y and sympathetic stimulation on the composition of blood cells in the splenic vein in vivo

The acute influence of exogenous transmitters and sympathetic nerve stimulation on the composition of blood cells in the splenic vein in relation to the splenic vascular effects was investigated in anaesthetized pigs. Intra arterial bolus injections of 720 pmol neuropeptide Y (NPY), 4.9 nmol noradrenaline (NA) and 20 nmol alpha,beta-methylene adenosine triphosphate (mATP) in the spleen were given and these doses caused arterial vasoconstriction in the same range, and increase in splenic venous haematocrit. NPY administration evoked a decrease in splenic venous blood flow and an unchanged leukocyte outflow from the spleen. mATP and NA, on the other hand, evoked increases in splenic venous blood flow and leukocyte outflow. Sympathetic nerve stimulation caused increases in haematocrit and leukocyte outflow in control pigs as well as in pigs with reserpine-induced depletion of tissue NA, although these effects, as well as the vascular effects, were significantly reduced after reserpine treatment. For comparison, the vasodilator calcitonin gene-related peptide increased leukocyte outflow without change in haematocrit. It is concluded that haematocrit and leukocyte concentration in the splenic venous blood are acutely modulated in different ways by vascular changes evoked by different sympathetic mediators. Furthermore, the capacitance function seems to be regulated by adrenergic and possibly purinergic transmission, whereas the non-adrenergic mediator NPY seems to be involved mainly in splenic arterial vasoconstriction.

Pharmacological separation of cardio-accelerator and vagal inhibitory capacities of sympathetic nerves

Prolonged attenuation of vagal action at the heart, proposed to be due to release of the sympathetic cotransmitter neuropeptide Y (NPY), follows stimulation of cardiac sympathetic nerves. It has been shown that pretreatment with reserpine depletes cardiac and neuronal stores of both noradrenaline and NPY, while combined pretreatment with reserpine and the ganglion blocking agent chlorisondamine reduces depletion of NPY, while still depleting noradrenaline. The effects of reserpine pretreatment and combined chlorisondamine and reserpine pretreatment on the inhibition of cardiac vagal action evoked by cardiac sympathetic nerve stimulation (16 Hz, 2 min) were compared in anaesthetised dogs. In dogs with no pretreatment (n = 6), sympathetic stimulation evoked an immediate cardio-acceleration, and a prolonged inhibition of cardiac vagal action, with a maximum percent inhibition (MPI) and time to half-recovery (T50) of 78 +/- 6% and 16 +/- 2 min respectively. In dogs pretreated with reserpine (n = 6, 1 mg/kg, 24 h), the immediate cardio-acceleration (ANOVA, P < 0.01), and the magnitude (MPI = 31.8%, ANOVA, P < 0.001) and duration (T50 = 6 +/- 1 min, ANOVA, P < 0.05) of inhibition of cardiac vagal action following sympathetic stimulation were significantly attenuated. In dogs with combined chlorisondamine (n = 5, 2 mg/kg, 48 and 24 h) and reserpine pretreatment, there was again significantly reduced cardio-acceleration (ANOVA, P < 0.01), but the inhibition of cardiac vagal action following sympathetic stimulation did not significantly differ from untreated animals (MPI = 79 +/- 8%, T50 = 21 +/- 6 min). Intravenous injections of NPY (25-50 micrograms/kg) evoked prolonged inhibition of cardiac vagal action in untreated and both groups of pretreated animals. These experiments indicate that the cardio-accelerator and vagal inhibitory capacities of sympathetic nerve stimulation can be separated, and are consistent with the sympathetic vagal inhibitory factor being NPY.

Inhibition of cardiac vagal action by galanin but not neuropeptide Y in the brush-tailed possum Trichosurus vulpecula

1. Stimulation of the right cardiac sympathetic nerve for 2 min at 16 Hz in the presence of either beta- or alpha- and beta-adrenoceptor blockade evoked attenuation of cardiac vagal action in eight possums: 31.3 +/- 10.3% maximum inhibition of cardiac vagal action on prolonging pulse interval, with a time to half-recovery of 4.9 +/- 1.1 min. 2. Intravenous injection of galanin (2-3.5 nmol kg-1) evoked similar inhibition of cardiac vagal action: 41.3 +/- 4.1% maximum inhibition of cardiac vagal action on pulse interval, with a time to half-recovery of 13.4 +/- 2.3 min. 3. Intravenous injection of neuropeptide Y (NPY) at greater molar doses (6.5-10 nmol kg-1) caused no inhibition of cardiac vagal action. 4. The galanin injections caused a powerful pressor response: 57.1 +/- 4.9 mmHg increase in systolic blood pressure. NPY caused a smaller pressor response, despite administration of higher molar doses: 36.7 +/- 3.0 mmHg increase in systolic blood pressure. 5. In the possum, galanin but not NPY can mimic the effects of cardiac sympathetic nerve stimulation on vagal action. Galanin also causes large pressor effects.

Neuropeptide Y and differential sympathetic control of splenic blood flow and capacitance function in the pig and dog

The roles of different mediators in the sympathetic regulation of the pig and dog spleens were investigated using a preparation with intact vascular perfusion in vivo. Sympathetic nerve stimulation caused overflow of neuropeptide Y-like immunoreactivity (NPY-LI) and noradrenaline (NA), arterial vasoconstriction, increase in venous blood flow and haematocrit. The dog spleen responded to single impulse stimulation, whereas more prolonged stimulation was required to elicit vascular responses in the pig spleen. Furthermore, the maximal splenic capacitance response was about 10 times larger in the dog than in the pig. After depletion of neuronal NA content by reserpine combined with preganglionic denervation, about 70% of the splenic arterial vasoconstrictor responses in the dog and pig still remained at 5 Hz stimulation. Fifty per cent of the capacitance response evoked by nerve stimulation still remained in the pig while in the dog spleen the capacitance response was virtually abolished after reserpine. The stimulation-evoked overflow of NPY-LI in pig spleen was increased several fold after reserpine treatment as compared to controls reaching levels in the venous effluent where exogenous NPY evokes vasoconstriction. In the dog spleen, overflow of NPY-LI was only observed after reserpine. Administration of NA caused arterial vasoconstriction with an initial increase in venous blood flow while NPY mainly reduced arterial blood flow. It is concluded that NA is involved in both the splenic arterial vasoconstriction and the capacitance responses while a non-adrenergic splenic vasoconstriction at least in the pig may be mediated by NPY.

Co-release of neuropeptide Y (NPY) and noradrenaline from the sympathetic nerve terminals supplying the rat vas deferens; influence of calcium and the stimulation intensity

Epididymal (E) and prostatic (P) segments of the rat vas deferens were incubated with tritium-labeled noradrenaline (NA); upon transmural electrical stimulation for 20 or 60 s (70 V, 1 ms, 3-35 Hz), the outflow of immunoreactive neuropeptide Y (ir-NPY) and NA was detected in the superfusion media. Ir-NPY was detected only following trains of 35 Hz for 60 s in both E and P. In contrast, tritium was released in a graded fashion following trains of 3, 15 or 35 Hz stimulation for 60 s in E, whereas in P it reached a plateau at frequencies larger than 15 Hz. The outflow of tritium, under present conditions, was dependent on the duration of the stimuli, while the release of ir-NPY was only evoked with stimuli of 60 s duration. In the absence of external Ca2+, neurotransmission was blocked and co-release of ir-NPY and NA was prevented.

An opioid peptide inhibits capsaicin-sensitive vasodilatation in the pig's skin

Microcirculatory effects of electrical stimulation of nerves through a pair of needle electrodes in the skin of anaesthetized pigs were studied by using the laser Doppler flowmetric method. Electrical stimulation (0.3-30 Hz) evoked a short-lasting decrease in capillary blood flux (vasoconstriction) followed by an increase (vasodilatation), of longer duration. Vasoconstriction was inhibited by local guanethidine, but not by capsaicin pretreatment, whereas vasodilatation was blocked by local capsaicin, but not by guanethidine. Both phases of the response were suppressed by local application of tetrodotoxin. Thus, vasoconstriction due to electrical stimulation seems to be of sympathetic origin, while vasodilatation is a result of a release of vasoactive substances from capsaicin-sensitive nerve endings. Vasodilatation due to electrical stimulation was strongly and dose-dependently inhibited by the opioid peptide [D-Met2,Pro5] enkephalinamide, while vasoconstriction remained apparently unchanged. At both doses of the opioid peptide tested (0.03 and 0.15 mumol/kg i.m.) inhibition of vasodilatation was larger at lower than at higher frequencies of stimulation. Guanethidine pretreatment did not influence the inhibitory action of [D-Met2,Pro5] enkephalinamide. Naloxone (1.5 mumol/kg i.m.) reversed or prevented the inhibitory action of the opioid peptide; naloxone on its own did not influence responses due to 0.3-30 Hz stimulation. [D-Met2,Pro5] enkephalinamide (0.15 mumol/kg i.m.) did not influence basal blood flux in the skin, mean arterial blood pressure, respiratory minute volume or respiratory frequency. It was concluded that stimulation of opioid receptors by [D-Met2,Pro5] enkephalinamide is likely to inhibit stimulation-evoked vasodilatation by reducing the release of vasoactive substances from capsaicin-sensitive afferent neurons, an effect that does not depend on functional integrity of sympathetic nerves. Endogenous opioids probably do not modulate the capsaicin-sensitive vasodilatation.

A sensitive and specific two-site, sandwich-amplified enzyme immunoassay for neuropeptide Y

The development of a new enzyme immunoassay for neuropeptide Y (NPY) is reported. Two monoclonal antibodies directed against distinct epitopes of NPY are used, one as a capture antibody (NPY02) and the other one as an indicator antibody (NPY05), this latter antibody being labeled with alkaline phosphatase. The assay calibration curve was performed over concentrations of 1 to 250 pM in a NPY-free plasma. The intra-assay coefficient of variation (CV) ranged from 0.025 to 11.9%, whereas the interassay CV was comprised between 5 and 12%. The limit of detection of this assay was 1 pM (100 amol/well). Neuropeptide Y levels are related to sampling conditions; basal concentrations of NPY with low SEM are found when less than 1.2 ml of blood is taken in EDTA tubes, the sample is centrifuged at 4 degrees C, and immediately frozen. Unanesthetized spontaneously hypertensive rats exhibited higher NPY plasma concentrations than normotensive Wistar-Kyoto controls (53 +/- 7 pM and 25 +/- 2 pM, respectively, mean +/- SEM, p < 0.01). Plasma NPY levels are similar in 16- and 36-week-old animals. In conclusion, this technique makes it possible to assay a large number of samples within 24 h without requiring radioactivity.

Neuropeptide Y in the primate model of subarachnoid hemorrhage

The cause of cerebral vasospasm after subarachnoid hemorrhage (SAH) remains unknown. Recently, an association between the potent vasoconstricting peptide, neuropeptide Y, and delayed cerebral vasospasm after SAH has been postulated. This was based on the findings of increased neuropeptide Y levels in the cerebrospinal fluid (CSF) and plasma after SAH in animals and humans. For this study, the primate model of SAH was used to assess the possible role of neuropeptide Y in delayed vasospasm after SAH. Fifteen cynomolgus monkeys underwent placement of a clot of either whole blood or red blood cells in the subarachnoid space around the middle cerebral artery (MCA). Sequential arteriography for assessment of MCA diameter and sampling of blood and CSF for neuropeptide Y were performed: before SAH (Day 0); 7 days after SAH, when signs of delayed cerebral vasospasm peak in this model and in humans; 12 days after SAH; and 28 days after SAH. Subarachnoid hemorrhage did not evoke changes in CSF or plasma levels of neuropeptide Y. Nine monkeys had arteriographic evidence of vasospasm on Day 7, but no change in neuropeptide Y levels occurred in plasma or CSF. In addition, neuropeptide Y levels did not change, even after resolution of vasospasm on Day 12 or Day 28. Neuropeptide Y levels were substantially higher in CSF than in arterial plasma (p less than 0.003 at each interval). No correlation was found between neuropeptide Y levels in CSF and in plasma. These results do not confirm a relationship between neuropeptide Y levels in the CSF or peripheral plasma and delayed cerebral vasospasm in SAH.

Comparison of locations and peptide content of postganglionic neurons innervating veins and arteries of the rat hindlimb

The ganglionic location of hindlimb vasoconstrictor sympathetic neurons in several species is known but the locations of neurons innervating limb arteries or veins, specifically, have not been compared and neurochemical differences between them have not been examined in detail. This study was designed to determine whether neurons innervating arteries and veins are organized as distinct populations and whether neurons innervating arteries, veins or footpads contain the same peptides. Retrograde transport of fluorescent dyes was used to identify, separately, paravertebral postganglionic neurons in the 13th thoracic to 6th lumbar (T13-L6) chain ganglia that innervate the femoral arteries, femoral veins and footpads of the rat hindlimb. The proportions of venous and arterial vasomotor neurons and footpad neurons containing neuropeptide Y- and vasoactive intestinal polypeptide-immunoreactivity (NPY-Ir, VIP-Ir) were then compared. Venous vasomotor neurons were found mostly (62%) in the L1 and L2 ganglia. The majority of arterial vasomotor neurons (81%) were distributed slightly more caudally in L1-L3. Veins and arteries were not innervated by the same cells. Footpad neurons were located mostly in L4-L6. NPY-Ir was identified in 17% of the venomotor neurons, in 94% of arterial neurons and in 24% of footpad neurons. VIP-Ir was found in 3% of the venomotor neurons, 8% of the arterial neurons and in 44% of the footpad neurons. In conclusion, hindlimb venous and arterial vasomotor neurons are anatomically distinct, are mixed randomly within the chain ganglia and differ markedly in their content of NPY, consistent with reported differences in neuromuscular transmission to arteries and veins. The most likely hindlimb postganglionic neurons to contain VIP were those innervating footpads, probably controlling sweat gland function.

Sites at which neuropeptide Y modulates parasympathetic control of heart rate in guinea pigs and rats

Immunohistological evidence indicates that neuropeptide Y (NPY) is present in the cardiac innervation of numerous species. The present experiments determined if NPY influences in vivo parasympathetic control of heart rate in guinea pigs and rats by either pre- or postganglionic mechanisms or by an interaction at muscarinic receptors at the sino-atrial node. Urethane-anesthetized animals were prepared with arterial and venous catheters, and ECG leads. The cervical vagi were sectioned and propranolol was administered to minimize reflex changes in heart rate. Methacholine injection, carbachol injection, or electrical stimulation of the peripheral end of the vagus nerve was performed to activate the neuroeffector site, intracardiac ganglion cells, or preganglionic neurons, respectively. All three trials were performed before, during, and after NPY infusion. No differences in methacholine- or carbachol-induced bradycardia were observed between control and NPY groups in either species. NPY infusion inhibited vagal-mediated bradycardia in guinea pigs and in rats. However, NPY inhibited vagal-mediated bradycardia at a lower dose in guinea pigs (1 microgram/kg/min) than in rats (4 micrograms/kg/min). These data indicate that NPY modulates cardiac vagal preganglionic, but not postganglionic nerve function or neuroeffector sites at the sino-atrial node, in guinea pigs and rats. Furthermore, due to the different effective dosages, NPY may play a greater modulatory role in guinea pigs than in rats.

Neuropeptide Y interaction with the adrenergic transmission line: a study of its effect on alpha-2 adrenergic receptors

Neuropeptide Y (NPY), first isolated in 1982, is widely distributed among the neurons of the central and peripheral nervous systems, often in close association with catecholamines. Because of its wide distribution and concentrations in selected areas of the brain, NPY is considered a putative neurotransmitter with several possible physiological effects including modulation of blood pressure, food intake and pituitary hormone release at a central level. Peripherally, the peptide seems to be involved, via direct and indirect mechanisms, in noradrenaline (NA)-mediated vasoconstriction. The ability of NPY to interact with the catecholamine transmission line may underly a possible modulatory influence of NPY on catecholamine receptor characteristics. We recently observed interaction between alpha-2 adrenergic receptors and those for NPY at the presynaptic level. Additional data from our studies in spontaneously hypertensive rats suggest that impairment of these interactions may contribute to the hypertension in this strain.

Tyrosine hydroxylase and neuropeptide Y are increased in ciliary ganglia of sympathectomized rats

We have examined the expression of tyrosine hydroxylase and neuropeptide Y in ciliary ganglia of normal adult rats and of adult rats in which the environment of these neurons was altered by sympathectomy at birth. Following neonatal 6-hydroxydopamine treatment, the proportion of tyrosine hydroxylase-immunoreactive and neuropeptide Y-immunoreactive neurons in ciliary ganglia was significantly increased. In ciliary neurons of both control and sympathectomized rats, neuropeptide Y immunoreactivity was preferentially co-localized with tyrosine hydroxylase. Immunoblot analysis confirmed the presence of tyrosine hydroxylase and its increase following sympathectomy. In situ hybridization studies revealed that many ciliary neurons contain mRNA for tyrosine hydroxylase and for neuropeptide Y. Like tyrosine hydroxylase immunoreactivity, the number of ciliary neurons containing tyrosine hydroxylase mRNA and the amount of mRNA per cell were increased in 6-hydroxydopamine-treated rats. In contrast, neuropeptide Y mRNA levels were the same in control and 6-hydroxydopamine-treated rats. Nerve growth factor is a candidate for mediating the effects of sympathectomy and most ciliary neurons in control and sympathectomized rats expressed immunoreactivity for the low-affinity nerve growth factor receptor. In addition, ciliary neurons from 6-hydroxydopamine-treated animals possessed increased nerve growth factor receptor immunoreactivity. These studies indicate that both tyrosine hydroxylase and neuropeptide Y in the ciliary ganglion are regulated by alterations in their environment. Their expression was enhanced by chemical sympathectomy which does not affect ciliary neurons directly but, rather, removes sympathetic innervation of shared targets, including the iris. In situ hybridization analysis suggests that the increased tyrosine hydroxylase and neuropeptide Y levels result from different mechanisms and provides evidence that neuropeptide levels can be regulated without changes in mRNA levels.

Inhibitory effect of neuropeptide Y on stimulated renin secretion of awake rats

1. (1-36)-NPY is a vasoconstrictor peptide widely distributed in sympathetic nerve terminals. This peptide exerts an inhibitory action on renin release induced by various stimuli. Post-synaptic neuropeptide Y (NPY) receptors show a high affinity for (1-36)-NPY as well as for the agonist (Pro34)-NPY, while presynaptic receptors bind preferentially (13-36)-NPY. 2. This study was undertaken to assess whether the NPY induced renin suppression in awake normotensive rats infused with the beta-adrenoceptor stimulant isoproterenol is mediated by activation of pre- or post-synaptic receptors. 3. Non-pressor doses of (1-36)-NPY and (Pro34)-NPY markedly attenuated the renin secretion triggered by isoproterenol whereas (13-36)-NPY had no effect. This suggests that the effect of NPY on renin release is due to the stimulation of post-synaptic receptors. However it remains unknown whether NPY acts directly on juxtaglomerular cells or indirectly by modifying intraglomerular haemodynamics.

Diminished contractile responses to neuropeptide Y of arteries from diabetic rabbits

The vascular smooth muscle contractile response to neuropeptide Y (NPY), potassium, noradrenaline, histamine and serotonin was studied in circular segments of isolated vessels in vitro from rabbits with alloxan-induced diabetes mellitus. The injection of alloxan resulted in a marked and maintained increase in serum glucose as early as 1 week after treatment. Four vessel types were examined: abdominal aorta, and renal, left anterior descending coronary and middle cerebral arteries. There was no difference in the contractile response to histamine or serotonin between control and diabetic vessels. However, in the cerebral artery the contractile response to noradrenaline was reduced in the diabetic group, while in the aorta and the renal artery no significant differences were seen. Noradrenaline failed to evoke any contractile response in the coronary arteries in either group. NPY induced strong, concentration-dependent contractions of coronary and cerebral arteries, but did not have any contractile effect per se in aorta or renal arteries, either in control or in alloxan-treated rabbits. The maximal contractile effect and the sensitivity to NPY was significantly less in diabetic coronary and cerebral vessels as compared to control. There was no difference in dilator effect of acetylcholine and substance P between the diabetic animals and the control group in any of the vessel types, indicating that the changed vascular responses to NPY and noradrenaline were not endothelium-dependent. In conclusion, the present study has shown that the postjunctional effects of NPY and noradrenaline in the peripheral sympathetic nervous system are selectively attenuated in this model of chronic diabetes.

Nerve-induced tachykinin-mediated vasodilation in skeletal muscle is dependent on nitric oxide formation

Nerve-induced vasodilatation was studied by intravital microscopy of the rabbit tenuissimus muscle, pretreated with pancuronium, phentolamine, and guanethidine. Nerve stimulation of the tenuissimus nerve induced a vasodilatation which was frequency and pulse duration-dependent and insensitive to atropine and propanolol but abolished by tetrodotoxin. The nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 100 microM), but not its enantiomer, D-NAME, markedly inhibited the vasodilation induced by nerve stimulation or by exogenous substance P or neurokinin A. Vasodilatation due to calcitonin gene-related peptide, prostaglandin E2 or nitroprusside was unaffected. The substance P antagonist, spantide (30 microM), significantly attenuated nerve-induced vasodilatation, in parallel with L-NAME. Our results indicate that nerve-induced vasodilatation in skeletal muscle can be attributed to the release of substance P and/or other tachykinins and that nitric oxide subsequently mediates the response to endogenous tachykinins released from nerves.

Sympathetic nerve stimulation influences mucociliary activity in the rabbit maxillary sinus

The effect of preganglionic sympathetic nerve stimulation on mucociliary activity in the rabbit maxillary sinus was investigated in vivo. Response to nerve stimulation was recorded photoelectrically and expressed as a percentage of the basal mucociliary activity prior to stimulation. Nerve stimulation (15 V, 5 ms) for 60 s at 2, 10 and 20 Hz stimulated mucociliary activity, the maximum increase being 21.1 +/- 1.3% at 20 Hz, an increase that pretreatment with the cholinergic antagonist atropine reduced to 14.5 +/- 2.4%, suggesting that part of the response involves cholinergic mechanisms. Nerve stimulation (10 Hz) of animals pretreated with the beta-adrenoceptor antagonist propranolol reversed the mucociliary response from an increase to a decrease (-10.6 +/- 1.6%), indicating the involvement of beta-receptors in the nerve-evoked increase. Pretreatment with the alpha-adrenoceptor antagonist phentolamine had no effect on response to nerve stimulation. Rabbits given a combined atropine, propranolol and phentolamine blockade manifested decreased mucociliary activity in response to nerve stimulation (-10.6 +/- 2.1%). Guanethidine pretreatment blocked the effect of nerve stimulation on mucociliary activity, including the observed decrease after combined blockade, indicating the effect to be mediated via sympathetic nerve fibres. The decrease in mucociliary activity in response to nerve stimulation after combined cholinergic-, beta-, and alpha-adrenoceptor blockade suggests the presence of a nonadrenergic, non-cholinergic inhibitory mechanism. It is possible that this effect is mediated by release of neuropeptide Y, as intraarterial injections of neuropeptide Y reduce mucociliary activity in the rabbit maxillary sinus, and as neuropeptide Y is released in the upper airways upon sympathetic nerve stimulation.

D-myo-inositol-1,2,6-trisphosphate is a selective antagonist of neuropeptide Y-induced pressor responses in the pithed rat

The antagonistic effects of a new inositol phosphate derivative, D-myoinositol-1,2,6-trisphosphate (PP56), on pressor responses to preganglionic sympathetic nerve stimulation and exogenously administered phenylephrine or neuropeptide Y (NPY) were investigated in vivo in the pithed rat. In this model an intravenous (i.v.) bolus administration of PP56 (1-50 mg/kg) dose dependently inhibited the increase in mean arterial blood pressure (MAP) induced by a continuous infusion of NPY (2 micrograms/kg per min for 10 min). PP56 in a dose of 5 mg/kg i.v. bolus reduced the entire NPY dose-response curve (0.4-8 microgram/kg per min 10 min infusion) without any shift to the right indicating a non-competitive interaction. Furthermore, PP56 (10-50 mg/kg i.v.) was found to inhibit the pressor response to preganglionic sympathetic nerve stimulation and i.v. bolus injection of the alpha 1-adrenoceptor agonist, phenylephrine. The dose-response curves for increasing doses of phenylephrine and incremental preganglionic sympathetic nerve stimulation were not significantly altered by a lower dose of PP56 (5 mg/kg i.v. bolus). We conclude that PP56, representing a new class of synthetic drugs, can antagonize the actions of exogenous and endogenous NPY in vivo, an action which is specific for NPY within a limited dose range.

Evidence for two neuropeptide Y receptors mediating vasoconstriction

The presence of receptor subtypes mediating the vascular and prejunctional effects of neuropeptide Y (NPY) was investigated using the Y2 receptor agonist, NPY-(13-36), and the Y1 agonist, [Leu31,Pro34]NPY. NPY-(1-36) and [Leu31,Pro34]NPY administered i.v. to anesthetized pigs evoked dose-dependent increases in mean arterial blood pressure and splenic and renal vascular resistance, and a decrease in heart rate. The potency of [Leu31,Pro34]NPY was 10-30% that of NPY-(1-36). In the spleen, NPY-(13-36) evoked vasoconstriction similar to that evoked by [Leu31,Pro34]NPY, but did not significantly increase renal vascular resistance or mean arterial blood pressure. Local intra-arterial administration of [Leu31,Pro34]NPY caused an increase in nasal mucosal vascular resistance with a potency similar to that of NPY-(13-36) evoked only a minor (17%) increase in nasal mucosal vascular resistance. The NPY analogues were further characterized in receptor binding studies on pig spleen membranes. Compared to NPY-(1-36), 800 times higher concentrations of [Leu31,Pro34]NPY, and 7 times higher concentrations of NPY-(13-36) were required to achieve the same 50% displacement of [125I]NPY-(1-36). Electrically evoked contractions in rat vas deferens were inhibited by 50% by 0.05 microM NPY-(1-36) and 0.3 microM NPY-(13-36), while [Leu31,Pro34]NPY only slightly attenuated the contractions (by 24% at 1 microM). The present data suggest the existence of subtypes of NPY receptors mediating vasoconstriction. Thus, the splenic vascular bed of the pig contains both Y1 and Y2 receptors while the Y1 subtype predominates in the kidney, nasal mucosa and for blood pressure control. The prejunctional receptor in rat vas deferens seems to be of the Y2 subtype.

Neuropeptide Y and sigma ligand (JO 1784) act through a Gi protein to block the psychological stress and corticotropin-releasing factor-induced colonic motor activation in rats

The effects of neuropeptide Y and sigma ligands (d-NANM and JO 1784) on corticotropin-releasing factor (CRF) and psychological stress-stimulated caecal and colonic motility were evaluated by electromyography in rats equipped with chronically implanted electrodes on the caecum and proximal colon and a small catheter into the right lateral ventricle of the brain. Exposure to a psychological stress for 30 min increased significantly (P less than 0.05) the frequency of caecal and colonic spike bursts, an effect which was mimicked by intracerebroventricular administration of CRF (300 ng/kg). Injected intracerebroventricularly, 30 min prior to the psychological stress or intracerebroventricular administration of CRF, neuropeptide Y (150 ng/kg) abolished the excitatory effect on caeco-colonic motility. Similarly, prior administration of d-NANM (100 ng/kg) and JO 1784 (50 ng/kg) abolished the caeco-colonic hypermotility induced by psychological stress and intracerebroventricular injection of CRF. Four days after intracerebroventricular administration of pertussis toxin (150 ng/kg), both neuropeptide Y and JO 1784, when administered centrally, were unable to antagonize the stress-induced hyperkinesia. It is concluded that central administration of neuropeptide Y and sigma ligands abolish the stimulatory effects of psychological stress on caeco-colonic motility by blocking the pathways by which CRF activates the motility, through a common mechanism involving a pertussis toxin-sensitive Gi protein.

Modulation of sympathetic activity by brain neuropeptide Y in cardiac hypertrophy

Several observations now support the view that the sympathetic system actively participates in the development of cardiac hypertrophy. Since norepinephrine (NE)-containing neurons involved in cardiovascular regulation in the brain are known to coexist with neuropeptide Y (NPY), it is possible that a functional interaction between NPY and NE exists centrally. In an effort to clarify whether or not central catecholamine systems are modulated by NPY soon after imposing an increased pressure overload on the heart, male Sprague-Dawley rats underwent aortic constriction and were examined 14 days later. Rats were anesthetized and subjected to microdialysis sampling by stereotaxically implanting a probe into the caudal ventrolateral medulla (A1). Perfusate was collected after a 1-hour stabilization period, purified, and analyzed for interstitial concentrations of NE and other catecholamines using high-performance liquid chromatography with an electrochemical detector. Extracellular NE concentrations in the A1 area were found to be decreased. These results were associated with increased rate of change in the specific activity of NE (NE turnover) in heart, indicating increased sympathetic activity and an increased left ventricular weight. Also, infusion of NPY (10(-9) mol/L) by microdialysis in the A1 area resulted in the reduction of NE concentration; epinephrine and dopamine levels were also decreased. In contrast, methionine-enkephalin, another neuropeptide, had no effect on the extracellular catecholamine concentrations in the A1 area. Since neurons of the A1 group project almost exclusively to forebrain structures inhibiting sympathetic activity, it is concluded that decreases of NE and other catecholamines in afferent pathways regulating the caudal ventrolateral medulla may lead to an enhanced sympathetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)