Effects of a selective neuropeptide Y Y2 receptor antagonist, BIIE0246, on Y2 receptors at peripheral neuroeffector junctions.

1. This study investigated the effects of BIIE0246, a novel neuropeptide Y (NPY) Y2 receptor antagonist, on the inhibition of cholinergic neuroeffector transmission in rat heart and guinea-pig trachea and purinergic neuroeffector transmission in guinea-pig vas deferens produced by the NPY Y2 receptor agonist, N-acetyl [Leu28,31] NPY 24-36. 2. In pentobarbitone anaesthetized rats, supramaximal stimulation every 30 s, of the vagus nerve innervating the heart, increased pulse interval by approximately 100 ms. This response was attenuated by intravenous administration of N-acetyl [Leu28,31] NPY 24-36 (10 nmol x kg(-1)). 3. Transmural stimulation of segments of guinea-pig trachea at 1 min intervals with 5 s trains of stimuli at 0.5, 5, 10, 20 and 40 Hz evoked contractions which were reduced in force by N-acetyl [Leu28,31] NPY 24-36 (2 microM). 4. In guinea-pig vasa deferentia, the amplitude of excitatory junction potentials evoked by trains of 20 stimuli at 1 Hz was reduced in the presence of N-acetyl [Leu28,31] NPY 24-36 (1 microM). 5. In all preparations BIIE0246 attenuated the inhibitory effect of N-acetyl [Leu28,31] NPY 24-36 but had no effect when applied alone. 6. The findings support the view that the nerve terminals of postganglionic parasympathetic and sympathetic neurones possess neuropeptide Y Y2 receptors which, when activated, reduce neurotransmitter release.

Sympathetic and parasympathetic interaction in vascular and secretory control of salivary glands in anaesthetised dogs.

The present study was undertaken to examine sympathetic-parasympathetic interactions in the regulation of salivary gland function, with special reference to the possible role of the sympathetic cotransmitter neuropeptide Y (NPY). In dogs anaesthetised with pentobarbitone, electrical stimulation of the parasympathetic nerve to the submandibular gland evoked an increase in glandular blood flow and salivary secretion. Sympathetic nerve stimulation evoked a significant prolonged attenuation of vasodilator and secretory responses to subsequent parasympathetic stimulation. This attenuation was not significantly altered by alpha- and beta-adrenoceptor blockade. Systemic administration of the sympathetic cotransmitter, NPY, mimicked the effect of the sympathetic stimulation by significantly attenuating vasodilatation and salivary secretion. The NPY Y1 receptor agonist, [Leu31, Pro34]NPY and the specific NPY Y2 receptor agonist N-acetyl[Leu28, Leu31]NPY 24-36 both significantly attenuated the vasodilatation and salivary secretion evoked by stimulation of the parasympathetic nerve. The NPY Y1 receptor antagonist, GR231118 significantly antagonised the attenuation of vasodilatation caused by both sympathetic stimulation and the NPY Y1 receptor agonist. GR231118 also inhibited the pressor response of NPY. Intra-arterial injection of methacholine and stimulation of the parasympathetic nerve both caused local vasodilatation in the gland which was significantly attenuated by pretreatment with sympathetic stimulation or the NPY Y1 agonist. The NPY Y2-specific agonist did not attenuate methacholine-induced vasodilatation but did attenuate vasodilatation evoked by parasympathetic stimulation. The results indicate that NPY as a sympathetic cotransmitter may have a role in the regulation of vascular secretory function of salivary glands.

NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31]NPY24-36, reduces renal vasoconstrictor activity in anaesthetised dogs.

The actions of neuropeptide Y (NPY) at the autonomic neuroeffector junction have been attributed to two main receptor subtypes. At NPY Y1 receptors, located postsynaptically, NPY has been shown to produce vasoconstriction, or to potentiate the action of other vasoconstrictor agents. At NPY Y2 receptors, located presynaptically on nerve terminals, NPY inhibits the release of neurotransmitter from autonomic nerve terminals. In these experiments we have used the specific NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31]NPY, which lacks local constrictor activity, and have demonstrated inhibition of nerve-evoked vasoconstriction in the renal circulation of anaesthetised dogs in a way that suggests an intra-renal regional specificity. Under control conditions stimulation of the renal sympathetic nerves over a range of frequencies (1-5 Hz) reduced renal vascular conductance and glomerular filtration rate (GFR). Following the injection of the selective NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31]NPY24-36, nerve-evoked reductions in renal conductance were reduced by over 45%. At the lowest stimulation frequencies, reduced vasoconstrictor activity was associated with a marked increase in GFR in the presence N-acetyl [Leu28,Leu31]NPY24-36. At both higher levels of stimulation N-acetyl [Leu28,Leu31]NPY24-36 significantly inhibited vasoconstrictor activity and attenuated the nerve-evoked reductions in GFR. Full recovery of both variables was observed 20 min after N-acetyl [Leu28,Leu31]NPY24-36 injection. N-acetyl [Leu28,Leu31]NPY24-36 produced a similar inhibition of renal vasoconstrictor activity when the renal nerves were left intact and activated reflexly. These results suggest that NPY can act via NPY Y2 receptors to inhibit sympathetic vasoconstrictor activity in the renal circulation of dogs. On the basis of the demonstrated dissociation of effects on vascular conductance and GFR, we suggest that this might result from a preferential action of the NPY Y2 agonist on sympathetic nerves supplying the afferent arteriole of the kidney.

Cardiorespiratory responses to intracerebroventricular injection of neuropeptide Y in anaesthetised dogs.

Cardiovascular and respiratory effects of intracerebroventricular (icv) administration of neuropeptide Y (NPY) and separate, preferential agonists for NPY Y1 and Y2 receptors were observed in anaesthetised dogs. Central injections of NPY resulted in significant cardiac slowing and decreases in arterial pressure. These cardiovascular effects were blocked by central injection of the NPY Y1- preferring antagonist 1229U91. Central injection of NPY did not have a significant effect on ventilation, but the NPY Y1 antagonist 1229U91 administered alone caused a significant increase in ventilation. The NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreased ventilation while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24--36 significantly increased it. A similar inverse relationship was seen with respect to blood pressure, with the NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreasing blood pressure, while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24-36 significantly increased it. These findings suggest a role for NPY Y1 receptors in pathways mediating decreases in ventilation and blood pressure, and for NPY Y2 receptors in those mediating increased ventilation and blood pressure.

Nasonasal reflex mechanisms in anaesthetized dogs.

In dogs anaesthetized with pentobarbitone, we recorded bilateral vascular and secretory responses to unilateral stimulation of intranasal afferent nerves. Nasonasal reflexes evoked by intranasal light mechanical stimulation, intranasal application of cold saline (2 ml at 3 degrees C), capsaicin (0.003-0.3 mmol) and antidromic electrical stimulation (15 V, 0.2 ms) of the trigeminal nerve at 10 Hz for 45 s were recorded. Vascular and secretory responses were studied before and after atropine pre-treatment, after ipsilateral section of the post-ganglionic parasympathetic fibres and the trigeminal nerve, and after administration of the ganglionic nicotinic receptor antagonist chlorisondamine. All stimuli studied induced bilateral increases in nasal arterial blood flow and secretion, although the contralateral responses were smaller under control conditions (p < 0.05). Bilateral vasodilatation evoked by mechanical stimulation, capsaicin and antidromic trigeminal nerve stimulation was resistant to atropine. The ipsilateral non-cholinergic vasodilatation evoked by mechanical stimulation or capsaicin was reduced by 50% (p < 0.05) after section of both trigeminal and post-ganglionic parasympathetic fibres. The remaining ipsilateral vasodilatation induced by these two stimuli was significantly reduced after chlorisondamine. The ipsilateral secretory responses to all stimuli studied were significantly reduced (p < 0.05), but not abolished by atropine. Contralateral secretory responses to all stimuli studied were not affected by atropine, the section of either the parasympathetic or trigeminal nerves, or chlorisondamine, suggesting the activation of local axon reflexes only. We conclude that unilateral intranasal stimulation of primary afferent neurons with light pressure, cold saline and capsaicin induces bilateral vascular and secretory responses via axon reflex mechanisms, as well as the activation of local and central sensory-parasympathetic reflex arcs.

Sympathetic-parasympathetic interactions at the heart in the anaesthetised rat.

This study observed the effects of stimulation of the cardiac sympathetic nerve on vagal slowing of the heart in rats, and compared these with any actions of exogenous neuropeptide Y (NPY) and galanin (GAL). In rats anaesthetised with pentobarbitone, stimulation of the cardiac sympathetic nerve for 2 min at 20 Hz in the rat evoked an attenuation of subsequent cardiac vagal action, which could be mimicked by exogenous NPY, but not GAL. The galanin antagonist, GAL1-13/NPY24-36, known to block the inhibitory action of galanin on the cardiac vagus in cats, did not alter the effect of sympathetic stimulation on cardiac vagal activity. We suggest on the basis of results here that in the rat, NPY released during stimulation of the cardiac sympathetic nerve, causes inhibition of acetylcholine release from the vagus nerve.

Structure-activity analysis of N-acetyl [Leu(28,31)] NPY 24-36: a potent neuropeptide Y Y(2) receptor agonist.

Neuropeptide Y (NPY) and a C-terminal analog of NPY, N acetyl [Leu(28,31)] NPY 24-36, act at NPY Y(2) receptors to potently inhibit cardiac vagal activity. The C-terminal analog is equipotent as NPY in inhibiting cardiac vagal activity but does not retain any pressor or Y(1) activity. This study investigates the importance of each amino acid in the 13 residue analog for functional activity by systematically substituting each residue with L-alanine. The inhibitory effect on cardiac vagal action decreased with substitution at residues 25,26,28,29 and 31. No decrease in activity was observed with alanine substitution at residues 24, 27 or 30. Residues 32 and 34 retained activity only at high doses, while residues 33, 35 and 36 were not active following alanine substitution. The difference in potency of the effective analogs suggests secondary structure of the peptide is as important for activity as retaining key amino acids.

Inhibition of vagal vasodilatation by a selective neuropeptide Y Y2 receptor agonist in the bronchial circulation of anaesthetised dogs.

Neuropeptide Y (NPY) is both co-stored and co-released with noradrenaline from sympathetic nerve terminals. In the cardiovascular system, NPY acts on two main receptor subtypes. At postjunctional, or Y1 receptors, NPY can cause both direct vasoconstriction and the potentiation of various constrictor agents. NPY acting at the presynaptic, or Y2 receptor, inhibits the release of neurotransmitter from autonomic nerves. In the present paper, we have used both sympathetic stimulation and the selective NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31] NPY24-36, to examine the role of NPY in the inhibition of vagally mediated vasodilatation in the bronchial circulation of the anaesthetised dog. Stimulation of the cardiac end of the cervical vagus nerve at 1 Hz for 15 s (1 ms, 70 V) increased bronchial vascular conductance by 45%. This increase in flow was abolished by atropine. Sympathetic stimulation for 2.5 min at 16 Hz (1 ms, 20 V) produced a significant (P < 0.05) and prolonged (9 min) inhibition of the subsequent parasympathetically evoked vasodilatation. Similarly, the NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31] NPY24-36, produced a significant (P < 0.05) and prolonged (15 min) inhibition of parasympathetically evoked vasodilatation. When vagus was stimulated at 2.5 Hz for 30 s (1 ms, 70 V), an atropine-resistant, but capsaicin-sensitive vasodilatation was observed. Neither sympathetic stimulation nor the NPY Y2 receptor agonist could be demonstrated to inhibit this vasodilatation. These results suggest that NPY can inhibit cholinergic parasympathetic vasodilatation in the bronchial circulation by an action on NPY Y2 receptors.

A comparison of actions of neuropeptide Y (NPY) agonists and antagonists at NPY Y1 and Y2 receptors in anaesthetized rats.

The pancreatic polypeptide family includes three members, neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP), with sequence homology between members and species varying from approximately 50 to 80%. Some of these peptides were compared in the mammalian cardiovascular system for activity mediated by actions on pre- (Y2) and post-junctional (Y1) NPY receptors. NPY and PYY, with sequence homology of 67% have similar actions on Y1 and Y2 receptors. Rat pancreatic polypeptide (rPP) with sequence homology of approximately 50% is inactive at both. This study reports that the chimeric peptide, hPP1-11/NPY12-36 and the truncated peptide NPY2-36 show similar activity to NPY mediated through both receptor types in vivo, while salmon PYY (sPYY), with 81% homology to NPY, has improved potency at both receptor subtypes. NPY3-36 has equal activity with NPY on actions mediated through Y2 receptors, but significantly reduced activity mediated through Y1 receptors. Two NPY antagonists were also examined: PYX2 was inactive in vivo and 1229U91 showed potent, long-lasting activity on Y1 receptor-mediated effects.

Nitric oxide and parasympathetic vascular and secretory control of the dog nasal mucosa.

Nasal vascular and secretory responses to local intra-arterial injection of acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) and to electrical stimulation of the nasal parasympathetic nerve fibres were recorded in dogs anaesthetized with pentobarbital. The influence of pretreatment with atropine and propranolol and the nitric oxide synthetase (NOS) inhibitor Nomega-nitro-L-arginine (L-NNA) was analysed. As a marker for NOS, NADPH-diaphorase (NADPH-d) histochemistry was studied in the sphenopalatine ganglion, trigeminal nerve and nasal mucosa. Local intra-arterial infusion of ACh and VIP evoked dose-dependent vasodilatation and nasal secretion which were not modified in the presence of L-NNA. The NO donor nitroprusside induced dose-dependent vasodilatation but no secretion. Atropine did not reduce the vasodilatation evoked by the parasympathetic nerve stimulation, but did reduce the secretory response by 55% (p < 0.05). During L-NNA infusion, the atropine-resistant vasodilatation evoked by parasympathetic nerve stimulation was reduced by a further 80% (p < 0.01) and the non-cholinergic secretory response was reduced by a further 30% (p < 0.05). Simultaneous infusion of the NO donor nitroprusside reversed the secretory response but not the vasodilator response to parasympathetic nerve stimulation. Histochemical studies revealed that NADPH-d activity was co-localized with VIP in parasympathetic axons. These observations suggest that NO could act as a non-cholinergic parasympathetic neurotransmitter in the vascular and secretory control of the dog nasal mucosa.

Inhibition of sympathetic cholinergic vasodilatation by a selective NPY Y2 receptor agonist in the gracilis muscle of anaesthetised dogs.

Neuropeptide Y (NPY) is known to be co-stored and co-released from sympathetic nerve terminals. In the cardiovascular system NPY acts on two main receptor subtypes. At the postjunctional or Y1 receptor NPY causes constriction directly in addition to potentiating other vasoconstrictor agents. NPY acting at the prejunctional, or Y2 receptor, inhibits the release of neurotransmitter from autonomic nerve terminals. In these experiments we used the selective Y2 receptor agonist N-acetyl[Leu28,Leu31]NPY24-36 to examine the role of NPY in the modulation of sympathetic vascular control in skeletal muscle in anaesthetised dogs. No systemic pressor or local constrictor activity was observed in response to N-acetyl[Leu28, Leu31]NPY24-36 administration, therefore allowing us to examine the neuroinhibitory actions of NPY in the absence of direct vascular effects on blood flow. Stimulation of the sympathetic nerves to the gracilis muscle engages both sympathetic cholinergic and sympathetic adrenergic fibres and produces an initial vasodilatation followed by a slower vasoconstriction. Nerve evoked vasodilatation was inhibited by over 50% in the presence of the selective NPY Y2 agonist N-acetyl[Leu28,Leu31]NPY24-36. This dilatation was abolished by atropine, confirming its cholinergic nature. N-Acetyl[Leu28,Leu31]NPY24-36 was found to have no effect on nerve evoked vasoconstriction. The results demonstrate a NPY Y2-receptor mediated inhibition of nerve evoked sympathetic cholinergic vasodilatation but not of sympathetic vasoconstriction.

Post-exercise depression of baroreflex slowing of the heart in humans.

In normal human subjects, we tested whether a 20- to 30-min period of rhythmic exercise, intended to provoke strong activation of the sympathetic nerves, would lead to prolonged inhibition of vagally mediated bradycardia evoked reflexly by stimulation of the baroreceptors by neck suction. Negative pressure within the neck cuff (-40 to -80 mmHg) reflexly evoked a reproducible increase in pulse interval. Following exercise, this increase in pulse interval was reduced from 444 +/- 104 ms to 76 +/- 57 ms (mean +/- SEM). Recovery time was 42 +/- 9 min. These findings demonstrate a prolonged attenuation of cardiac vagal action following rhythmic exercise in normal human subjects. It is known that neuropeptide Y (NPY) is released from cardiovascular sympathetic nerves, that it attenuates cardiac vagal action and that plasma levels of NPY are elevated for a prolonged period after exercise. Therefore, it is proposed that NPY, released from sympathetic nerves during exercise, attenuates reflexly evoked cardiac vagal action for a prolonged period after exercise ends.

Activity of centrally truncated analogues of neuropeptide Y at Y1 and Y2 receptor subtypes in vivo.

Neuropeptide Y (NPY), a sympathetic cotransmitter, has both prejunctional and postjunctional actions in the cardiovascular system. In anaesthetized rats, the bioassay system used here, NPY attenuates cardiac vagal action (a prejunctional or Y2 action) and increases blood pressure (a postjunctional or Y1 action). Several NPY analogues were tested against NPY. In these, centrally located amino acid sequences of various lengths were removed, and replaced with simpler 'spacers'. As the parent NPY molecule is considered to exist in a U-shape, these central truncations were intended to shorten the depth of the U, while maintaining the integrity of its two ends. The centrally truncated NPY analogues examined here retain activity at both receptor subtypes in vivo. These findings indicate that the U-shape of the parent molecule probably exists to assist stability, but that receptor binding occurs through sequences closer to the termini.

Sympathetic and parasympathetic interaction in vascular and secretory control of the nasal mucosa in anaesthetized dogs.

1. In dogs anaesthetized with pentobarbitone, electrical stimulation of the parasympathetic nerve fibres to the nasal mucosa evoked frequency dependent increases in both nasal arterial blood flow and nasal secretion. Blood flow was measured using a transonic flow probe placed around the artery. 2. Sympathetic nerve stimulation for 3 min at 10 Hz evoked significant and prolonged (> 30 min) attenuation of the vasodilator and secretory responses to subsequent parasympathetic stimulation. 3. Intravenous and intranasal administration of the neuropeptide Y (NPY) analogue N-acetyl [Leu28,Leu31] NPY 24-36, a selective NPY Y2 receptor agonist (20 nmol kg-1), significantly attenuated both vasodilator and secretory effects of subsequent parasympathetic nerve stimulation. When given intravenously, the inhibitory effect of this Y2 receptor agonist on vascular and secretory effects of parasympathetic nerve stimulation was rapid in onset (5 min) and lasted for more than 60 min. The modulatory effect of the Y2 receptor agonist was also seen with intranasal administration, but was slower in onset (15 min), and lasted less than 45 min. The effects of the intranasal pretreatment with the Y2 receptor agonist were significantly prolonged in the presence of the endopeptidase inhibitor phosphoramidon (10 nM). 4. Atropine pretreatment did not significantly reduce the change in vascular conductance evoked by parasympathetic nerve stimulation. Subsequent pretreatment with the NPY Y2 receptor agonist N-acetyl [Leu28,Leu31] NPY 24-36 reduced the stimulation induced increase in conductance by 30%. Nasal secretion was reduced by 70% following pretreatment with atropine and a further 30% by pretreatment with the NPY Y2 receptor agonist. Dose dependent vasodilator and secretory effects of local intra-arterial infusion of acetylcholine and vasoactive intestinal peptide were not modified by the NPY Y2 agonist. 5. Total protein and albumin concentration were measured in nasal lavage fluid collected after nerve stimulation. Atropine pretreatment increased the percentage of the total protein that was albumin in nasal lavage fluid. Neither sympathetic nerve stimulation nor Y2 receptor agonist pretreatment further modified the albumin exudation (a marker of vascular permeability) in nasal fluid lavage collected after parasympathetic nerve stimulation. 6. We propose that sympathetic nerve stimulation releases NPY, which acts on Y2 receptors, probably located on parasympathetic nerve endings, to attenuate both vasodilatation and nasal secretion evoked by subsequent parasympathetic nerve stimulation. This effect is also observed after pretreatment with the Y2-selective NPY analogue N-acetyl [Leu28,Leu31] NPY 24-36.

Effects of pituitary adenylate cyclase-activating polypeptide on cardiovascular and respiratory responses in anaesthetised dogs.

This study examines some of the cardiovascular and respiratory effects of pituitary adenylate cyclase-activating polypeptide (PACAP) in anaesthetised dogs. Intravenous injection of PACAP 27 caused an increase in arterial blood pressure and an increase in heart rate. The blood pressure response was significantly reduced by adrenoceptor blockade suggesting a mechanism of action mediated in part via catecholamines. The heart rate increase was unaltered by adrenoceptor blockade suggesting a direct effect of PACAP 27. PACAP 27 also caused potentiation of cardiac slowing caused by stimulation of the vagus nerve. In addition, PACAP 27 powerfully stimulated breathing. This was probably evoked by stimulation of arterial chemoreceptors, because bilateral section of the carotid sinus nerves abolished this effect. PACAP 27 had no effect on the ability of the cardiac sympathetic nerve to increase heart rate, nor on the interaction between the sympathetic and parasympathetic systems in the heart.

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.

Structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog ANA-NPY.

Neuropeptide Y analog ANA-NPY or [Leu-17, Gln-19, Ala-20, Ala-23, Leu-28, Leu-31]NPY(13-36)-amide binds to postjunctional or Y1 receptors to raise blood pressure and to prejunctional or Y2 receptors to inhibit neurotransmitter release. ANA-NPY affects Y2 receptors in the same way as intact NPY but exhibits far less potent effects on Y1 receptors. The structure of ANA-NPY was examined using two-dimensional proton nuclear magnetic resonance spectroscopy. Complete assignment of all backbone and side chain hydrogens was accomplished with totally correlated spectroscopy (TOCSY) experiments providing through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy (NOESY), providing the through-space and sequential backbone connectivities. The tertiary solution structure of the peptide was performed using distance geometry and dynamic simulated annealing. ANA-NPY exhibits a helical structure with strong amphipathic character with a bend around Glu-24 indicating that the C-terminal segment 25-35 forms a single alpha-helical motif.

Selective regional vasoconstriction underlying pressor effects of galanin in anaesthetized possums compared with cats.

1. Intravenous administration of porcine galanin (5 nmol kg-1) caused a rise in mean blood pressure in the brush-tailed possum, Trichosurus vulpecula, from 58 +/- 1.6 to 106 +/- 1.6 mmHg. This effect is in contrast to the cat, in which no significant change in blood pressure was recorded in response to galanin (88 +/- 2.3 vs. 86 +/- 2.4 mmHg). 2. Cardiac output and regional blood flow distribution were assessed by distribution of radioactive microspheres in four anaesthetized possums and four cats, before and after administration of galanin. 3. Cardiac output was 289.8 +/- 14.0 ml min-1 in the cat and 189.9 +/- 25.5 ml min-1 in the possum. Galanin administration did not significantly change cardiac output in either species. 4. In the possum, galanin administration caused large increases in resistance to flow in the spleen, gut, adrenal glands, kidney, skin and carcass. The largest increase was in the kidneys, where renal blood flow fell to 6% of control levels. 5. In the cat, changes in resistance were small. Small increases in resistance to flow in muscle and carcass were offset by small decreases in resistance in the lungs and kidneys. 6. The results suggest that the pressor effect of galanin in the possum is the result of direct vasoconstrictor action in several vascular beds, in contrast to the cat, in which such effects are few and weak.

Neuropeptide Y analog with selective antagonism of effects mediated by postjunctional Y1 receptors.

Neuropeptide, a 36 amino acid peptide, is one of the most ubiquitous neuropeptides in the nervous system. It is released during stimulation of sympathetic nerves and is implicated as an important neurotransmitter regulating cardiovascular activity. Administration of neuropeptide Y results in vasoconstriction and inhibition of neurotransmitter release. However, the absence of any effective inhibitors of neuropeptide Y action have precluded the examination of its possible role in hypertension. Here we describe a synthetic hexapeptide (BRC 672), corresponding to residues 22-27 of neuropeptide Y. Following the administration of BRC 672 (6.7 mumol/kg), neuropeptide Y-induced pressor responses were reduced by 32-48% in a dose-dependent fashion. The inhibition was specific for neuropeptide Y, as the pressor response to phenylephrine, an alpha-adrenoceptor agonist, was unchanged. It was selective for the postsynaptic (neuropeptide Y Y1 receptor-mediated) vasoconstrictor activity, because the presynaptic (neuropeptide Y Y2 receptor-mediated) cardiac vagal inhibition evoked by injection of neuropeptide Y to rats was not affected. The hexapeptide inhibited the neuropeptide Y-induced increase in cytosolic free Ca2+ in mammalian cells expressing the cloned human neuropeptide Y Y1 receptor. Injections of BRC 672 significantly reduced blood pressure in anaesthetised rats and in conscious spontaneously hypertensive rats. Resting arterial blood pressure decreased from 136 +/- 4 mm Hg to 122 +/- 3 mm Hg and remained depressed 2 h after the administration of the hexapeptide in anaesthetised rats. In spontaneously hypertensive rats blood pressure was decreased for up to 4 h.