Reserpine-induced depletion of neuropeptide Y from cardiovascular nerves and adrenal gland due to enhanced release

Reserpine-induced immunocytochemical change of neuropeptide Y in the hypothalamic arcuate nucleus

The effect of reserpine on neuropeptide Y immunoreactive (NPY-IR) neurons in the rat hypothalamic arcuate nucleus was examined by immunocytochemical techniques. Although only NPY-IR fibers and terminals were distributed in this nucleus in untreated and saline treated rats, single treatment of reserpine (10 mg/kg, i.p.) visualized abundant NPY-IR neuronal cell bodies: the increase began at 12 h of postinjection, reached its maximal level at 48 h, and returned to its normal level at 96 h. Pretreatment of nialamide, a monoamine oxidase inhibitor, prevented these acute reserpine-induced changes, suggesting reserpine acts on NPY neurons through monoaminergic mechanism. Chronic treatment of haloperidol (5 mg/kg, once daily for 5 days) a dopamine receptor antagonist, could induce the similar increase of NPY immunoreactivity. However, interruption of adrenergic and serotonergic neurotransmissions by chronic treatment of propranorol and methysergide, or chemical lesions of ascending noradrenergic and serotonergic pathways by 6-hydroxydopamine and 5,6-dihydroxytryptamine, could not induce any immunoreactive increase of NPY in arcuate neurons. These findings strongly suggest that reserpine-induced NPY increase occurs through dopaminergic afferents in hypothalamic arcuate neurons.

Tetrodotoxin-sensitive release of adrenaline, noradrenaline and neuropeptide Y-like immunoreactivity in the pithed guinea-pig in the absence of electrical preganglionic nerve stimulation

The effect of tetrodotoxin (TTX) on plasma noradrenaline (NA), adrenaline (A) and neuropeptide Y-like immunoreactivity (NPY-LI) levels was evaluated in the pithed guinea pig, in the absence of electrical stimulation and following preganglionic nerve stimulation (PNS). Blood samples for determination of NA, A and NPY-LI were collected 5 min before and 5 min after injection of saline (control group, n = 6) or TTX (13 micrograms/kg, i.v., TTX-treated group, n = 8), respectively. In both groups, blood samples were collected 20 s and 40 s after initiation of PNS. In the absence of electrical stimulation, TTX reduced the plasma NA level by 66%, NPY-LI level by 42%, whereas the plasma A level was not significantly altered by the neurotoxin. In the control group, PNS elicited a 27-fold increase of plasma NA, a 60-fold increase of plasma A and enhanced the NPY-LI levels by 13%. Pretreatment with TTX completely blocked this release of sympathetic transmitters. The present results suggest that a certain degree of spontaneous nerve activity is present in the pithed animal model, also during baseline conditions, since TTX significantly reduced NA and NPY-LI in the absence of electrical stimulation. This spontaneous nerve activity is probably a consequence of local mechanical activity of the pithing rod capable of eliciting action potentials at the preganglionic level of the sympathetic nerve terminals.

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.

Alpha- and beta-adrenoceptor-mediated effects on nerve stimulation-evoked release of neuropeptide Y (NPY)-like immunoreactivity in the pithed guinea pig

The effect of one beta-adrenoceptor agonist and one antagonist on preganglionic nerve stimulation (PNS)-evoked increase of plasma neuropeptide Y-like immunoreactivity (NPY-LI) was studied in the pithed guinea pig, both in the presence and in the absence of the alpha 2-adrenoceptor antagonist yohimbine. Four periods of PNS (8 Hz for 30 s with 20 min intervals) were applied and the increases of mean arterial blood pressure (delta BP), heart rate (delta HR) and plasma NPY-LI (delta NPY-LI) were analysed. Infusion of the non-selective beta-agonist isoprenaline (0.15 micrograms x kg-1 x min-1 i.v.) tended to reduce delta BP in response to PNS and significantly increased HR at baseline without changing the maximal HR response. Pretreatment with yohimbine (1 mg x kg-1 i.v.) significantly increased delta BP in response to PNS by about 20% without any change in basal HR being observed. The non-selective beta-adrenoceptor antagonist propranolol (5 mg x kg-1 i.v.) significantly reduced delta BP and delta HR both in the presence and in the absence of yohimbine. Isoprenaline infusion enhanced plasma delta NPY-LI by 37% in comparison with the corresponding control. This effect of isoprenaline appeared to be slow in onset and could be blocked by propranolol, which per se did not significantly change plasma delta NPY-LI. Pretreatment with yohimbine caused a three to four-fold increase in plasma delta NPY-LI, which was slightly reduced both in the presence of isoprenaline (-39%) and propranolol (-27%). In conclusion, the sympathetic neurotransmission, also with regard to neuronal NPY, seems to have two adrenergic control mechanisms: one inhibitory and one facilitatory mediated by presynaptic alpha 2- and beta-adrenoceptors, respectively. The facilitatory control mechanism could not be demonstrated if the release of neuronal NPY was already greatly enhanced by alpha 2-adrenoceptors.

Rapid decrease in neuropeptide Y gene expression in rat adrenal gland induced by the alpha 2-adrenoceptor agonist, clonidine

1 The mechanism of regulation of the neuropeptide Y (NPY) gene by pharmacological treatment with the alpha 2-adrenenoceptor agonist, clonidine, was investigated by quantitative Northern blot analysis of the effects of this drug on the NPY mRNA levels in rat adrenal gland and medulla oblongata/pons. 2 In the adrenal gland, clonidine-treatment (50 microgram kg-1, s.c., once daily) resulted in decrease in the amount of NPY mRNA to 44 +/- 10% of the control level in 24 h and then its increase to 162 +/- 16% of the control level after 5 days. Concomitant changes in putative NPY pre-mRNA species (7.0 and 3.3 kb) were observed, probably due to changes at the level of NPY gene transcription. 3 The short-term (24 h) effect of clonidine was blocked by yohimbine (5 mg kg-1, i.p., once daily). Yohimbine alone tended to increase the NPY mRNA level after 24h. 4 The recovery/increase in the NPY mRNA level in the adrenal gland after 5 days treatment with clonidine was similar to its increase after treatment with reserpine (0.5 mg kg-1, i.p., once daily). 5 NPY gene expression in the medulla oblongata/pons was not changed by short- or long-term treatment with clonidine. 6 These results suggest that clonidine suppresses NPY gene expression in the adrenal gland, probably at the level of transcription, by activation of the alpha 2-adrenoceptor.

Effect of captopril on plasma levels of neuropeptide Y (NPY)-like immunoreactivity in the pithed guinea pig

The effect of exogenous angiotensin II (A II) and the angiotensin converting enzyme (ACE)-inhibitor captopril on plasma levels of neuropeptide Y-like immunoreactivity (NPY-LI) has been studied in the pithed guinea pig. Four periods of pre-ganglionic nerve stimulation (PNS, 8 Hz for 30s with 20 min intervals) were applied and the increases of mean arterial blood pressure (delta BP), heart rate (delta HR) and plasma NPY-LI (delta NPY-LI) in response to PNS were analysed in non-pre-treated and captopril pre-treated animals. Captopril (5 mg x kg-1 i.v.) reduced basal blood pressure and delta BP by 20% and 11%, respectively. Infusion of A II (0.5 microgram x kg-1 = min-1 i.v.) caused a significant increase in basal and PNS-induced maximal blood pressure response but reduced delta BP in captopril and non-pre-treated animals by 40% and 16%, respectively. A II elicited a long-lasting increase of basal heart rate by 12% but reduced delta HR by 36% in non-pre-treated animals. However, neither captopril alone nor A II infusion to captopril pre-treated animals significantly changed heart-rate values. The effects of exogenous A II on the cardiovascular responses were abolished by the A II-antagonist saralasin (a bolus injection, 40 micrograms x kg-1 i.v. followed by an infusion, 30 micrograms x kg-1 x min-1), which per se had no significant effect. Captopril pre-treatment reduced basal plasma NPY-LI levels by 38% and delta NPY-LI by 46% in response to PNS 1. However, neither in non-pre-treated nor in captopril pre-treated animals did infusion of A II significantly change the plasma NPY-LI level.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of neuropeptide Y-like immunoreactivity and messenger RNA in rat platelets: the effects of vinblastine, reserpine, and dexamethasone on NPY expression in blood cells

Rat plasma contains high basal levels (220 pmol/liter) of neuropeptide Y (NPY)-like immunoreactivity (LI) compared to pig (30 pmol/liter) and man (25 pmol/liter). The platelet-enriched fraction (PEF), obtained from rat blood contained 10,061 pmol/g NPY-LI. However, in human and pig blood, the PEF contained very low levels of NPY-LI. Gradient centrifugation of rat blood showed the highest concentration of NPY-LI (10.8 +/- 0.4 pmol/g) in the platelet fraction. The mononuclear cell fraction contained 1.64 +/- 0.16 pmol/g, whereas only 0.56 +/- 0.06 pmol/g of NPY-LI was found in the red blood cell/polymorphonuclear cell fraction. Characterization of NPY-LI in rat plasma and platelets by high-pressure liquid chromatography showed one predominating peak which coeluted with synthetic NPY (1-36) as well as three minor peaks, one of which coeluted with oxidized NPY. Analysis of NPY messenger RNA (mRNA) in bone marrow of the rat revealed a 0.79-kb-long NPY mRNA. This size is intermediate to the 0.82-kb NPY mRNA in brain and the 0.76-kb NPY mRNA in spleen. The highest level of NPY mRNA in rat blood was found in the mononuclear cell fraction but NPY mRNA was also detected in the platelet fraction. No NPY mRNA was detected in bone marrow or blood from pig and rabbit or from human blood or bone marrow. Forty-eight hours after treatment of rats with vinblastine the content of NPY mRNA and NPY-LI in rat blood was decreased, while the level of NPY-LI in bone marrow was markedly enhanced. Reserpine treatment caused an increase in NPY mRNA content in bone marrow and spleen. After administration of dexamethasone the level of NPY mRNA increased in both spleen and peripheral blood cells with increased NPY-LI content in the spleen. It is concluded that in addition to megakaryocytes in spleen and bone marrow, platelets and possibly also lymphocytes/monocytes in peripheral blood of the rat contain NPY mRNA and peptide. The expression of NPY mRNA in bone marrow, spleen, and blood is influenced by vinblastine, reserpine, and dexamethasone.

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

Pharmacology of noradrenaline and neuropeptide tyrosine (NPY)-mediated sympathetic cotransmission

Pharmacological and physiological aspects for neuropeptide Y (NPY) and noradrenaline (NA) cotransmission have been studied in the peripheral sympathetic nervous control of blood vessels, heart, spleen and vas deferens. NPY coexists with NA in large dense cored vesicles and is released compared to NA mainly upon high frequency stimulation or strong reflex sympathetic activation. NPY release is inhibited via prejunctional alpha-2 adrenoceptors and adenosine receptors but facilitated by angiotensin II or beta-receptor activation. NPY exerts prejunctional inhibitory actions on both NA and NPY release, enhances the vasoconstrictor effect of NA and evokes potent, long-lasting vasoconstriction. Specific receptor mechanisms for NPY exist at both the pre- and postjunctional levels; a large amidated C-terminal portion of NPY is necessary for receptor binding, inhibition of cyclic AMP formation and vasoconstrictor effects. Denervation results in supersensitivity for both NA and NPY-evoked vasoconstriction. Reserpine pretreatment is associated with depletion of NA as well as NPY; the effect on NPY is entirely dependent on an intact nerve activity. Reserpine treatment combined with preganglionic denervation depletes NA by 99% while NPY levels are maintained intact. The characteristic appearance of the nerve stimulation evoked vasoconstrictor response with a high correlation to NPY outflow after reserpine treatment, suggests that NPY may be involved as a transmitter in a variety of vascular beds. NPY-synthesis in ganglia seems to be regulated by nicotinic receptor activity; secondary stimulation by eg reserpine stimulates and nicotine antagonists decrease NPY-synthesis. Many classical pharmacological agents including guanethidine, clonidine, yohimbine, angiotensin II, nicotine and desipramine influence NPY release. A complex interplay therefore seems to occur at both the pre- and postjunctional levels of transmission for the classical transmitter NA and the coexisting peptide NPY, creating a great diversity of chemical signalling potential.

Neuropeptide Y potentiates purinergic as well as adrenergic responses of the rabbit ear artery

The localisation of neuropeptide Y in the rabbit central ear artery and its pharmacological action on this preparation were investigated. Immunohistochemical studies demonstrated the presence of neuropeptide Y-like immunoreactivity in the perivascular nerves supplying the rabbit ear artery. Forty-eight hours after treatment with reserpine (5 mg/kg i.p. 48 h and 3 mg/kg i.p. 24 h prior to the experiment) catecholamine fluorescence in the rabbit central ear artery was abolished and the neuropeptide Y-like immunoreactivity was substantially reduced, suggesting that noradrenaline and neuropeptide Y were colocalised in sympathetic nerves. Contractile responses to exogenous noradrenaline (1 microM) and alpha,beta-methylene ATP (1 microM) were both significantly potentiated following incubation with neuropeptide Y (0.3 microM); the degree of potentiation being similar for both agonists. Electrical field stimulation of the rabbit central ear artery (16 and 64 Hz) produced frequency-dependent contractile responses which were abolished by tetrodotoxin (1 microM) and which were significantly potentiated in the presence of neuropeptide Y (0.3 microM). The responses to stimulation at 16 Hz were enhanced to a greater extent than the responses at 64 Hz. After blocking the noradrenergic component of the neurogenic response with prazosin (1 microM), the residual purinergic component, at both 16 and 64 Hz, was significantly enhanced in the presence of neuropeptide Y. However, following desensitisation of the P2-purinoceptor with alpha,beta-methylene ATP, neuropeptide Y had no significant effect on the residual noradrenergic component.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Influence of reserpine administration on neuropeptide Y immunoreactivity in the locus coeruleus and caudate-putamen nucleus of the rat brain

The effects of treatment with reserpine (10 mg/kg, i.p.) a monoamine depleting agent, on neuropeptide Y immunoreactivity were studied immunohistochemically in neurons of two rat brain structures: locus coeruleus and caudate-putamen nucleus. It was found that reserpine after 24 h increased neuropeptide Y immunoreactivity level but no significant changes were observed 4 and 72 h or 5 days after the injection. The results indicate that despite the known co-existence of neuropeptide Y and noradrenaline in some neurons of the locus coeruleus no concomitant decrease in neuropeptide Y immunoreactivity level was found after reserpine when noradrenaline was depleted from nerve cell bodies and terminals. The increase in neuropeptide Y immunoreactivity observed 24 h after reserpine injection may suggest that the neuropeptide Y-containing neuronal systems of the locus coeruleus and caudate-putamen nucleus are controlled by monoaminergic afferents.

Release and vasoconstrictor effects of neuropeptide Y in relation to non-adrenergic sympathetic control of renal blood flow in the pig

The possible involvement of neuropeptide Y (NPY) in sympathetic control of renal blood flow was investigated in the pig in vivo. Exogenous NPY caused renal vasoconstriction with a threshold effect at an arterial plasma concentration of 164 pmol 6(-1). Stimulation of the renal nerves (0.59, 2 and 10 Hz) in control animals evoked rapid and frequency-dependent reduction in renal blood flow and overflow of NPY-like immunoreactivity (NPY-LI) and noradrenaline (NA) from the kidney, suggesting co-release from sympathetic nerves. Following the administration of the alpha- and beta-adrenoceptor antagonists phenoxybenzamine and propranolol, the vasoconstrictor response to exogenous NA was reduced by 98%, whereas that of NPY was unaltered. The response to nerve stimulation with 0.59 Hz was abolished, whereas relatively slowly developing reductions in renal blood flow by 7 and 28% were obtained upon stimulation with 2 and 10 Hz respectively. The nerve stimulation-evoked overflow of NA at 0.59 and 2 Hz, but not at 10 Hz and not that of NPY-LI, was enhanced after adrenoceptor blockade. Twenty-four hours after reserpine treatment (1 mg kg-1 i.v.) the contents of NPY-LI and NA in the renal cortex were reduced by 80 and 98% respectively. Sectioning of the renal nerves largely prevented the reserpine-induced depletion of NPY-LI, but not that of NA. Nerve stimulation of the denervated kidney with 2 and 10 Hz 24 h after reserpine treatment evoked slowly developing and long-lasting reductions in renal blood flow by 6 and 52% respectively. These responses were associated with overflow of NPY-LI, which was similar to and threefold higher than that observed in controls at 2 and 10 Hz respectively, while no detectable overflow of NA occurred. Repeated stimulation with 10 Hz resulted in a progressive fatigue of the vasoconstrictor response and the associated overflow of NPY-LI, giving a high correlation (r = 0.86, P less than 0.001) between the two parameters. It is concluded that NPY is a potent constrictor of the renal vascular bed. Furthermore, although NA is the likely transmitter mediating most of the responses to low to moderate nerve activation under control conditions, the data suggest that NPY may mediate the non-adrenergic reductions in renal blood flow evoked by high-frequency sympathetic nerve stimulation after reserpine treatment.

Evidence for co-transmitter role of neuropeptide Y in the pig spleen

1. The possible involvement of neuropeptide Y (NPY) in relation to noradrenaline (NA) and adenosine triphosphate (ATP) mechanisms in the sympathetic nervous control of the vascular tone and capsule contraction in the blood perfused pig spleen was investigated in vivo. 2. Local injections or infusions of NA, NPY and alpha-, beta-methylene ATP (mATP) caused vasoconstriction (perfusion pressure increase) and capsule contraction (increased venous blood flow). ATP only evoked vasodilatation. NPY was about 50 fold more potent than NA as a vasoconstrictor, and the NPY response was more long-lasting. Reserpine treatment did not change the effects of NPY. 3. Electrical stimulation of the splenic nerves in control animals caused a frequency-dependent, guanethidine-sensitive output of both NPY-like immunoreactivity (-LI) and NA, suggesting co-release. The output of NPY-LI relative to NA was enhanced at high frequency stimulation. Furthermore, alpha-adrenoceptor blockade by phentolamine enhanced both the output of NPY-LI and NA while inhibition of the neuronal uptake of NA with desipramine reduced the low frequency stimulation-evoked overflow of NPY-LI. Preganglionic denervation did not change the output of NPY-LI or NA. 4. Reserpine treatment reduced both the splenic content of NA and NPY-LI. Preganglionic denervation inhibited the reserpine-induced depletion of the NPY content but not of NA in terminal areas. The stimulation-evoked NPY overflow was markedly enhanced, especially at low-frequency stimulation after reserpine, and the plasma levels of NPY-LI in the venous effluent were then in the nmolar range (i.e. where exogenous NPY induced vasoconstriction). The perfusion-pressure increase upon stimulation in reserpine-treated, preganglionically-denervated animals was highly correlated (r = 0.91) to the NPY overflow. The functional 0.5 Hz responses were reduced after reserpine, while at higher frequencies the functional effects were of similar magnitude to controls but longer-lasting. 5. Tyramine induced a release of NA but not of NPY-LI. Furthermore, the increase in perfusion pressure induced by tyramine was absent after reserpine. 6. After tachyphylaxis to the vasoconstrictor effects of mATP, the nerve stimulation-evoked, functional response as well as the NA and NPY-LI overflow were unchanged. After reserpine treatment, both the perfusion-pressure increase and NPY-LI overflow to nerve stimulation were reduced after mATP tachyphylaxis. 7. In conclusion, release of NPY rather than ATP may explain the long-lasting, non-adrenergic, splenic functional responses in reserpinized animals upon sympathetic stimulation. However, NA is most likely the main splenic transmitter when low-frequency stimulation is used under control conditions.

Functional relationship between platelet alpha 2-adrenoceptors and sympathetic nerve activity in man

Functional relationships between platelet alpha 2-adrenoceptors and sympathetic nerve activity were studied in patients with essential hypertension (n = 23), primary aldosteronism (n = 10), and normal subjects (n = 12). The maximum number of binding sites (Bmax) and the dissociation constant (Kd) of 3H-yohimbine on platelet membranes and resting plasma norepinephrine (NE) were similar among these groups of subjects. In all subjects combined, Bmax values were correlated positively (r = 0.471, p less than 0.01) to resting plasma NE and negatively (r = -0.531, p less than 0.01) to the changes in plasma NE when subjects were moved from lying to standing. A 2-4 week treatment with guanabenz or bethanidine induced a parallel fall of both Bmax and plasma NE, whereas administration of reserpine caused a similar fall of plasma NE but Bmax remained unchanged. Kd values were not changed after any of these treatments. The results support the view that platelet alpha 2-adrenoceptor density is functionally regulated in parallel with sympathetic nerve activity rather than plasma NE per se. This hypothesis seems quite reasonable when it is extended to the presynaptic alpha 2-adrenoceptors; otherwise, the negative feedback function on NE release should be lessened and contradictory to its physiological role.

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 Y (NPY), an endogenous presynaptic modulator of adrenergic neurotransmission in the rat vas deferens: structural and functional studies

The role of neuropeptide tyrosine (NPY) on adrenergic neurotransmission was assessed in the rat vas deferens transmurally stimulated with square pulses of 0.15 or 15 Hz. Nanomoles of NPY inhibited the electrically-induced contractions on the prostatic half but not on the epididymal end of the ductus. NPY was at least 200-fold more potent than norepinephrine or adenosine to produce an equivalent inhibition. Complete amino acid sequence of NPY is required for full agonist activity; deletion of tyrosine at the amino terminus, i.e., NPY fragment 2-36 was 3-fold less potent than the native peptide. NPY fragment 5-36, 11-36 or 25-36 were proportionally less potent than NPY. Avian pancreatic polypeptide was inactive. The presynaptic nature of the NPY activity was established measuring the outflow of 3H-norepinephrine from the adrenergic varicosities of the vas deferens electrically stimulated. In this assay, NPY was more potent than NPY 2-36 or NPY fragment 5-36. No inhibitory action of NPY was detected in K+ depolarized tissues. The inhibitory effect of NPY on the rat vas deferens neurotransmission was not significantly modified by yohimbine, theophylline or naloxone, indicating that the effect of NPY is not due to the activation of alpha 2-adrenoceptors, adenosine receptors or opiate receptors respectively. Picrotoxin or apamin did not modify the inhibitory potency of NPY; verapamil or methoxyverapamil significantly reduced its potency. The inhibitory action of NPY is best explained through the activation of presynaptic NPY receptors that regulate norepinephrine release via a negative feedback mechanism. Structure activity studies give support to the notion of NPY receptors.

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.

Neuropeptide Y (NPY) induced inhibition of preganglionic nerve stimulation evoked release of adrenalin and noradrenaline in the pithed rat

NPY, a peptide with 36 amino acid residues, is co-stored together with noradrenaline (NA) in cardiac and sympathetic perivascular nerves as well as with adrenalin (A) in adrenal chromaffin cells. NPY is released together with NA from sympathetic nerves and with A from the adrenal glands and appears to be involved in the control of sympathetic neurotransmission. The aim of the present study was to analyse the effect of NPY on the preganglionic nerve stimulation (PNS) evoked increases in plasma A and NA concentrations in pithed rats. In the first part of the study (I) only one PSN period (2 Hz for 45 s) was performed in each rat and the control group was compared to the NPY treated group. In the second part of the study (II) two PNS periods (1 Hz for 45 s) were performed in each rat, which either received saline or NPY before the second PNS. Thus, interindividual changes between the responses to the first and second PNS in control and NPY rats could be compared. In both study I and II, systemic infusion of NPY (2 micrograms kg-1 min-1 i.v.) significantly reduced the PNS-induced increase in plasma A by 26% and 42%, respectively (P less than 0.05). However, the increase in plasma NA elicited by PNS was significantly reduced only in study II by 23% (P less than 0.05). Infusion of NPY did not affect basal heart rate in either of the studies, but significantly increased basal blood pressure by about 10 mmHg. The blood pressure responses to PNS were significantly greater in NPY treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Facilitation of the release of noradrenaline and neuropeptide Y by the alpha 2-adrenoceptor blocking agents idazoxan and hydergine in the dog spleen

The release of noradrenaline (NA) together with its possible cotransmitter neuropeptide Y (NPY) was investigated in the perfused dog spleen. The splenic nerve was stimulated electrically at high frequency with bursts, which evoked a simultaneous release of both substances. Infusion of the alpha 2-adrenergic blocking agents idazoxan or hydergine enhanced the amount of NA and NPY in the venous effluent. The present results demonstrate the concomitant release of a classical neurotransmitter and a neuropeptide, and suggest that at high frequency stimulation, regulation of their release operates very similarly.

Elevated plasma concentration of neuropeptide Y and low level of circulating adrenaline in elderly asthmatics during rest and acute severe asthma

Twenty-five elderly asthmatic patients attending the internal medicine emergency ward because of an acute exacerbation of asthma were sampled, prior to acute treatment, for determination of systemic venous plasma levels of noradrenaline (NA), adrenaline (A) and neuropeptide Y-like immunoreactivity (NPY-LI). Whereas NA and NPY-LI were about two-fold higher than control values, plasma A levels were not significantly increased. Twelve of the asthmatic patients were also tested at resting stable conditions and were essentially asymptomatic. All values were then similar to those of control subjects (n = 28) except for a significantly higher NPY-LI plasma level in asthmatics. In seven of these patients a near maximal physical exercise test caused significantly increased NA, A and NPY-LI plasma levels. It is concluded that the acute asthma attack is associated with elevated NA and NPY-LI plasma levels, but an impaired A response. Furthermore, that circulating NPY under these conditions has a nervous rather than adrenal origin.

Differential effects of clonidine and reserpine treatment on neuropeptide Y content in some sympathetically innervated tissues of the guinea-pig

The effects of treatment with reserpine and/or the selective alpha 2-adrenoreceptor agonists clonidine and oxymetazoline on tissue levels of neuropeptide Y (NPY)-like immunoreactivity (-LI) and noradrenaline (NA) were studied in the guinea-pig. Clonidine treatment was associated with an increase in the levels of NPY-LI in the right atrium in a time- and dose-dependent manner. A significant (45%) elevation of the right atrial content of NPY-LI was present 2 h after administration of clonidine (50 micrograms kg-1 s.c.). After 24 h of repeated clonidine treatment the atrial levels of NPY-LI had increased by 95%. Following chronic clonidine treatment for two weeks, however, the right atrial NPY levels were similar to those in control animals. The corresponding cell-body content of NPY-LI in the stellate ganglion, remained unaffected by clonidine treatment. The levels of NPY-LI were also increased in the gastrocnemius muscle, spleen and adrenal gland after clonidine treatment while no changes were detected in the vas deferens or hypothalamus. The reserpine-induced reduction of NPY-LI in the right atrium, spleen, gastrocnemius muscle and adrenal gland was markedly inhibited by concomitant clonidine treatment while no effect was observed on NA depletion. The adrenoreceptor antagonists phentolamine, prazosin and yohimbine all inhibited the increase in cardiac content of NPY-LI seen after clonidine treatment. No elevation of tissue content of NPY-LI was observed after oxymetazoline (50 micrograms kg-1 s.c.) which, however, reversed the reserpine-induced depletion of NPY-LI. The reserpine-induced increase in content of NPY-LI in the stellate ganglion was also inhibited by clonidine and oxymetazoline.(ABSTRACT TRUNCATED AT 250 WORDS)

Reserpine-induced depletion of neuropeptide Y in the guinea-pig: tissue-specific effects and mechanisms of action

The effects of treatment with reserpine (5 mg.kg-1, s.c., 24 h prior to sacrifice) or 6-hydroxydopamine (6-OHDA; 250 mg.kg-1, s.c., for 4 days, one week before sacrifice) on the content of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) were compared in a variety of tissues from the guinea-pig. Reserpine and 6-OHDA treatment markedly reduced the NA content of all peripheral organs investigated. Reserpine treatment also caused depletion of the content of NPY-LI in larger blood vessels and in organs containing mainly perivascular nerves. Furthermore, reserpine treatment depleted NPY-LI in the heart, spleen and adrenal gland. In other organs dominated by parenchymal adrenergic innervation such as genital organs (vas deferens, uterus) or iris, treatment with 6-OHDA but not reserpine caused significant depletions of NPY-LI. The urinary bladder and gastrointestinal tract seem to be mainly innervated by non-adrenergic NPY-containing neurons resistant to reserpine and 6-OHDA treatment. The content of NPY-LI was elevated in sympathetic ganglia after reserpine treatment while no increase in axonal transport occurred in the sciatic nerve. Cerebellum was the only studied area in the central nervous system where the NPY content was depleted by reserpine or 6-OHDA treatment suggesting presence of NPY-LI in perivascular nerves. The reserpine-induced depletion of NPY-LI in the spleen, kidney and skeletal muscle was prevented by preganglionic denervation. This suggests that enhanced nerve impulse discharge in sympathetic nerves caused a situation where NPY release exceeded the amount which could be replaced by axonal transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y and noradrenaline mechanisms in relation to reserpine induced impairment of sympathetic neurotransmission in the cat spleen

The mechanisms underlying the reserpine-induced impairment of the functional responses to sympathetic nerve stimulation and output of noradrenaline (NA) and neuropeptide Y (NPY)-like immunoreactivity (-LI) were studied using the isolated blood-perfused cat spleen. Splenic nerve stimulation (10 Hz for 2 min) during control conditions caused perfusion-pressure increase, volume reduction and an increased output of NA and NPY-LI. After administration of phenoxybenzamine, the nerve stimulation-induced perfusion-pressure increase was almost abolished, the volume reduction inhibited and the output of NPY-LI enhanced. After subsequent addition of propranolol, a clear-cut increase in perfusion pressure upon nerve stimulation reappeared. Local infusion of NPY caused a potent, long-lasting, adrenoceptor-resistant increase in perfusion pressure and a relatively smaller volume reduction of the spleen. Twenty-four hours after reserpine pretreatment (1 mg kg-1 i.v.), which depleted the splenic content of NA greater than 95% and NPY-LI by about 50%, the functional responses upon nerve stimulation were markedly reduced. Preganglionic denervation or pretreatment with the ganglionic-blocking agent chlorisondamine did not influence the NA depletion after reserpine treatment. A considerable, adrenoceptor antagonist-resistant, long-lasting functional response as well as a markedly enhanced output of NPY-LI then occurred upon nerve stimulation. In conclusion, reserpine treatment combined with interruption of preganglionic impulse flow reveals non-adrenergic, nerve stimulation evoked splenic functional responses which could be mediated by release of a cotransmitter peptide like NPY.

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.

The visualisation of cardiovascular innervation in the guinea pig using an antiserum to protein gene product 9.5 (PGP 9.5)

The various subpopulations of autonomic and sensory nerves supplying the mammalian cardiovascular system may be demonstrated using specific immunocytochemical and histochemical techniques, but no single marker has previously been available for the visualisation of the entire innervation. Protein gene product (PGP) 9.5 was first identified in extracts of human brain and found to represent a major protein component of the neuronal cytoplasm. We have demonstrated that PGP 9.5 immunoreactivity occurs in the guinea pig cardiovascular innervation and is present in more individual nerve fibres than other general neuronal markers (neuron-specific enolase and neurofilaments). PGP 9.5 immunoreactivity was localized to both intrinsic neurones and nerve fibres in the guinea pig heart. In the vascular system PGP 9.5-immunoreactivity occurred in an extensive plexus of fine perivascular nerve fibres and fascicles running around and along both arteries and veins, mainly at the adventitial-medial border. At the ultrastructural level, this immunoreactive material was localized to the axonal cytoplasm and did not appear to be associated with cytoskeletal elements or secretory vesicles. 6-Hydroxydopamine (6-OHDA) pretreatment resulted in the degeneration of noradrenergic axon terminals containing PGP 9.5, tyrosine hydroxylase (TH) and neuropeptide tyrosine (NPY) immunoreactivities. Most of the perivascular nerve fibres which remained displayed substance P- and calcitonin gene-related peptide (CGRP) immunoreactivity, as well as PGP 9.5 immunoreactivity. Capsaicin pretreatment resulted in a depletion of both substance P and CGRP immunoreactivity, but had no apparent effect on PGP 9.5 immunostaining. In the heart PGP 9.5 immunoreactivity also appeared to be present in presumed postganglionic cholinergic nerves. PGP 9.5 may be a useful marker when examining regional variations in cardiovascular innervation and for determining the relative proportions of nerve subpopulations.

Alpha 2-adrenoceptor-mediated inhibition of nerve stimulation-evoked release of neuropeptide Y (NPY)-like immunoreactivity in the pithed guinea-pig

Clonidine (10 micrograms X kg-1) reduced by almost 50% the increase in plasma neuropeptide (NPY)-like immunoreactivity (-LI) induced by preganglionic nerve stimulation at 8 Hz. This effect was reversed by yohimbine (1 mg X kg-1) which caused a three-fold increase of the plasma NPY-LI. Prazosin (1 mg X kg-1) had no such effect. Guanethidine (5 mg X kg-1) reduced the stimulation-evoked increase in plasma NPY-LI. It is concluded that the release of NPY-LI evoked by nerve stimulation from sympathetic nerve terminals is controlled by a presynaptic alpha 2-adrenoceptor-mediated mechanism.