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

Presynaptic neuropeptide receptors

Presynaptic receptors for four families of neuropeptides will be discussed: opioids, neuropeptide Y, adrenocorticotropic hormone (ACTH), and orexins. Presynaptic receptors for the opioids (micro, delta, kappa, and ORL(1)) and neuropeptide Y (Y(2)) inhibit transmitter release from a variety of neurones, both in the peripheral and central nervous systems. These receptors, which were also identified in human tissue, are coupled to G(i/o) proteins and block voltage-dependent Ca(2+) channels, activate voltage-dependent K(+) channels, and/or interfere with the vesicle release machinery. Presynaptic receptors for ACTH (MC(2) receptors) have so far been identified almost exclusively in cardiovascular tissues from rabbits, where they facilitate noradrenaline release; they are coupled to G(s) protein and act via stimulation of adenylyl cyclase. Presynaptic receptors for orexins (most probably OX(2) receptors) have so far almost exclusively been identified in the rat and mouse brain, where they facilitate the release of glutamate and gamma-aminobutyric acid (GABA); they are most probably linked to G(q) and directly activate the vesicle release machinery or act via a transduction mechanism upstream of the release process. Agonists and antagonists at opioid receptors owe at least part of their therapeutic effects to actions on presynaptic receptors. Therapeutic drugs targeting neuropeptide Y and orexin receptors and presynaptic ACTH receptors so far are not available.

On the relation of nitric oxide to nifedipine-induced gingival hyperplasia and impaired submandibular glands function in rats in vivo

Calcium-channel blockers such as nifedipine could be associated with gingival overgrowth. The aim of this study was to examine the role of nitric oxide (NO) on nifedipine-induced gingival hyperplasia along with submandibular secretory function in rats. Animals in divided groups received nifedipine (250 mg/kg diet) alone and in combination with L-arginine (2.25% w/v) or N(omega)-nitro-L-arginine methyl ester (L-NAME) (0.7% w/v) in drinking water for 20 days. Controls received only tap water. Pure submandibular saliva was collected intraorally by micropolyethylene cannula and the mandibular gingiva was examined by means of dissecting microscope for signs of redness, thickness, inflammation and exuda. Twenty-day nifedipine treatment induced gingival hyperplasia accompanied with reduced salivary flow rate and concentrations of total protein, epidermal growth factor (EGF) and calcium in comparison with controls. Co-treatment of animals with nifedipine and L-arginine protected from gingival hyperplasia and retained flow rate, and concentrations of total protein, EGF and calcium in normal levels. Co-treatment of animals with nifedipine and L-NAME potentiated nifedipine-induced gingival hyperplasia and reductions in flow rate and concentrations of total protein, EGF, and calcium. It is concluded that nifedipine-induced gingival hyperplasia is associated with salivary dysfunction. Activation of cGMP-dependent positive signal-transduction mechanisms in salivary glands might be the mechanism for protective effects of NO against nifedipine-induced gingival hyperplasia.

Increased plasma levels of neuropeptide Y in hepatorenal syndrome

BACKGROUND/AIMS

To investigate the relationship between neuropeptide Y (NPY), a potent renal vasoconstrictor peptide released upon marked stimulations of sympathetic nervous system (SNS), and renal and circulatory function in cirrhosis.

METHODS

Plasma levels of NPY (radioimmunoassay) and norepinephrine and renal function parameters were determined in 17 healthy controls, nine patients with cirrhosis without ascites, and 37 patients with cirrhosis and ascites, of whom 12 had hepatorenal syndrome (HRS).

RESULTS

Patients with ascites showed circulating levels of NPY similar to those of patients without ascites and controls (73+/-4, +/-4 and 68+/-4 pmol/l, respectively; NS). However, patients with HRS had significantly increased levels of NPY with respect to the other groups (110+/-6 pmol/l; P<0.001). NPY levels correlated inversely with renal plasma flow and glomerular filtration rate and directly with norepinephrine. In patients with HRS (n=6) treatment with terlipressin and albumin was associated with a marked improvement in circulatory and renal function and marked suppression of NPY and norepinephrine levels.

CONCLUSIONS

Patients with HRS have increased levels of NPY which are related to circulatory dysfunction and SNS activation and may contribute to renal vasoconstriction.

Modulation of immune cell function by the autonomic nervous system

This review discusses some of the major findings implicating the autonomic nervous system in the regulation of immune function. The sympathetic nervous system, the primary focus of this line of research, directly innervates the major lymphoid organs, and physiological release of sympathetic neurohormones at these sites has been documented. Leukocytes have been shown to express receptors for catecholamines, as well as neuropeptide Y, and studies in vitro and in vivo have indicated that occupation of these receptors by the appropriate ligands produces functional changes in immunological cells. Finally, altered sympathetic regulation may underlie some of the immunological abnormalities observed in chronic stress, clinical depression, and ageing.

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.

The neuropeptide Y (NPY) Y1 receptor antagonist BIBP 3226: equal effects on vascular responses to exogenous and endogenous NPY in the pig in vivo

1. The antagonistic effects of the neuropeptide Y (NPY) Y1 receptor antagonist BIBP 3226 on equally prominent vascular responses evoked by sympathetic nerve stimulation and exogenous NPY were compared during different intravenous (i.v.) infusions of the antagonist (0.19-190 nmol kg-1 min-1 for 30 min). 2. High frequency sympathetic nerve stimulation in reserpine-treated pigs in vivo evoked non-adrenergic vasoconstrictor responses in kidney and hind limb, in the latter followed by a long-lasting phase of decreased blood flow. The vascular response in the kidney and the long-lasting phase in hind limb resembled the effects of exogenous NPY administered i.v. (kidney) and intraarterially (i.a.) (in the hind limb, which only responded to higher NPY doses). 3. Plasma levels of BIBP 3226 reached a plateau within 20 min and the inhibitory effects on vascular responses were studied during the last ten minutes of infusion. The elimination of BIBP 3226 from plasma was found to fit a two-compartment model with an alpha-phase of 2.0 +/- 0.2 min and a beta-phase of 20.1 +/- 0.9 min. 4. Significant inhibition of presumably Y1 receptor-mediated vascular responses evoked by both endogenous and exogenous NPY in kidney and hind limb was seen even during low-dose infusion of BIBP 3226 (1.9 nmol kg-1 min-1), when plasma levels of the antagonist reached 59 +/- 8 nM. The maximum inhibitory effects of BIBP 3226 were seen during the highest-dose infusion (190 nmol kg-1 min-1), when the long-lasting vasoconstrictor responses in hind limb to sympathetic nerve stimulation and exogenous NPY administration (i.a.) were abolished. Simultaneously, the vascular responses in kidney to exogenous NPY were inhibited by 89% and to sympathetic nerve stimulation by 60%. 5. It is concluded that BIBP 3226 has a short half-life in plasma and should preferably be given by i.v. infusions to maintain blockade and avoid non-specific effects. Furthermore, BIBP 3226 dose-dependently and with similar potency antagonizes vascular responses to exogenous and endogenous NPY both in the kidney and hind limb of the reserpine-treated pig in vivo. Thus, inhibition of vascular responses to exogenous NPY may be a good indicator of the dose of this antagonist needed to inhibit sympathetic Y1 receptor-transmission.

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.

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.

Inhibition of sympathetic vasoconstriction in pigs in vivo by the neuropeptide Y-Y1 receptor antagonist BIBP 3226

1. Recently, a potent non-peptide antagonist of neuropeptide Y (NPY)-Y1 receptors has been developed. In this study, the selectivity of this compound, BIBP 3226, as a functional Y1 receptor antagonist, and the possible role of endogenous NPY in sympathetic vasoconstriction in different vascular beds have been investigated in anaesthetized pigs. 2. BIBP 3226 specifically displaced [125I]-NPY binding with an IC50 value of 7 nM in membranes of pig renal arteries, which also were responsive to a Y1 receptor agonist, but had only minor effects in the pig spleen (IC50 55 microM), where instead [125I]-NPY binding was markedly inhibited by a Y2 receptor agonist. IC50 values in the same nM range for BIBP 3226 were also observed in rat and bovine cortex and dog spleen. 3. In anaesthetized control pigs in vivo BIBP 3226 (1 and 3 mg kg-1) markedly inhibited the vasoconstrictor effects of the Y1 receptor agonist [Leu31, Pro34] NPY(1-36), without influencing the responses to the Y2 receptor agonist N-acetyl [Leu28, Leu31] NPY(24-36), or to noradrenaline, phenylephrine, alpha,beta-methylene adenosine triphosphate or angiotensin II. 4. High frequency stimulation of the sympathetic trunk in control pigs caused a biphasic vasoconstrictor response in nasal mucosa, hind limb and skin: there was an immediate, peak response, followed by a long-lasting vasoconstriction. BIBP 3226 (1 and 3 mg kg-1) reduced the second phase by about 50% but had no effect on the peak response. In the spleen, kidney and mesenteric circulation (which lack the protracted response) BIBP 3226 was likewise without effect on the maximal vasoconstriction, and did not influence noradrenaline overflow from spleen and kidney. 5. The corresponding S-enantiomer BIBP 3435 had only marginal influence on [125I]-NPY binding (microM range) and did not inhibit the vasoconstrictor effects of any of the agonists used, including the Y1 receptor peptide agonist. Furthermore, BIBP 3435 did not affect the response to sympathetic nerve stimulation. Both BIBP 3435 and BIBP 3226 caused a slight transient decrease in mean arterial blood pressure (by about 5 and 15 mmHg at 1 mg kg-1 and 3 mg kg-1, respectively), accompanied by splenic and mesenteric vasodilatation, suggesting that this effect was unrelated to Y1 receptor blockade. 6. The peptide YY (PYY)- and NPY-evoked vasoconstriction in the kidney of reserpine-treated pigs was markedly reduced (by 95%) by BIBP 3226 while the vasoconstrictor effect in the spleen was attenuated by only 20%. BIBP 3226 did not influence stimulation-evoked NPY release. The vasoconstrictor response in reserpine-treated pigs to single impulse stimulation, which is observed only in nasal mucosa and hind limb, was unchanged regarding maximal amplitude and the integrated effect was only moderately reduced (by about 25%) in the presence of BIBP 3226 (1 mg kg-1). BIBP 3226 (1 mg kg-1) markedly reduced (by 55-70%) the long-lasting vascular response (total integrated blood flow reduction) evoked by sympathetic nerve stimulation at high frequency (40 impulses at 20 Hz) in spleen, kidney, nasal mucosa and hind limb. Furthermore, the maximal amplitude of the vasoconstriction was reduced mainly in the kidney (by 60%) and also in the spleen (by 40%). 7. It is concluded that BIBP 3226 can act as a selective Y1 receptor antagonist in the pig. Endogenous NPY via Y1 receptor activation may play a role in evoking the long-lasting vasoconstriction seen in nasal mucosa, hind limb and skin after high frequency stimulation of sympathetic nerves in control pigs. Furthermore, NPY via Y1 receptor mechanisms seems to be of major importance for the long-lasting component of the reserpine resistant sympathetic vasoconstriction in many vascular beds, and for the maximal vasoconstrictor response in the kidney. Circulating NPY and PYY induce splenic vasoconstriction via Y2-receptors in contrast to neuronally released NPY which mainly activates Y1 receptors.