Browsing by Author "HuidobroToro, JP"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
- ItemBIBP 3226, suramin and prazosin identify neuropeptide Y, adenosine 5'-triphosphate and noradrenaline as sympathetic cotransmitters in the rat arterial mesenteric bed(1997) Donoso, MV; Steiner, M; HuidobroToro, JPThe physiological role of neuropeptide Y (NPY) and extracellular adenosine 5'-triphosphate (ATP) in sympathetic neurotransmission is becoming increasingly clear, To assess whether NPY and ATP act as cotransmitters together with noradrenaline (NA) in the sympathetic nerves of the superior mesenteric artery, the changes in perfusion pressure of the arterial mesenteric bed caused by nerve stimulation were recorded, Depolarization of the perivascular superior mesenteric arterial nerves caused frequency-and time-dependent increases in the perfusion pressure that were abolished by guanethidine, which implied the sympathetic origin of these responses. Independent perfusion with either 500 nM BIBP 3226, an NPY Y-1 antagonist; 3 mu M suramin, a competitive purinoceptor antagonist; or 0.1 nM prazosin, a competitive alpha-1 adrenoceptor antagonist, evoked approximately a 30% reduction in the rise in perfusion pressure caused by the 20-to 30-Hz electrical depolarization of the perimesenteric arterial nerves, Prazosin (0.1 nM) blocked the increases in perfusion pressure caused by electrical stimulation of the perimesenteric nerves but did not significantly reduce the vasomotor effect of exogenous NA, Likewise, 5-methyl urapidil and chloroethylclonidine, alpha-1 adrenoceptor antagonists with selectivity for the alpha-1A and alpha-1B receptor subtypes, respectively, concentration-dependently decreased the increase in perfusion pressure elicited by electrical stimulation of the perimesenteric nerves at concentrations lower than that required to block the vasoconstriction elicited by exogenous NA. The combined perfusion of 3 mu M suramin plus 0.1 nM prazosin did not result in a complete inhibition of the physiological response. Only upon the simultaneous application of BIBP plus suramin plus prazosin was the rise in perfusion pressure abolished. These results support the working hypothesis that the sympathetic nerves of the rat mesenteric bed release NPY, ATP and NA that act as postjunctional cotransmitters in this neuroeffector junction.
- ItemCentral B-2 receptor involvement in the antinociceptive effect of bradykinin in rats(1996) Pela, IR; Rosa, AL; Silva, CAA; HuidobroToro, JP1 The effect of intracerebroventricular (i.c.v.) injection of bradykinin (BK) and related peptides was tested on the dental pulp electrical stimulation threshold (DPEST) in rats.
- ItemModulation of GABA(A) receptor function by G protein-coupled 5-HT2C receptors(1996) HuidobroToro, JP; Valenzuela, CF; Harris, RATwo classical neurotransmitters, 5-hydroxytryptamine (5-HT) and GABA, coexist in neurons of the medulla oblongata, and activation of 5-HT receptors modulates GABA(A) receptor function in neurons of the ventral tegmental area, substantia nigra and cerebellum. We now report that activation of 5-HT2C receptors produces a long-lasting (20-90 min) inhibition of GABA(A) receptors in Xenopus oocytes coexpressing both types of receptors. 5-HT2C receptors caused a similar to 60% decrease in the GABA(A) receptor E(max) without affecting the EC(50) or Hill coefficient. Intracellular microinjection of 500 mu M BAPTA blocked, whereas microinjection of inositol 1,4,5-triphosphate mimicked the inhibitory action of 5-HT2C receptors. The inhibition was independent of the GABA(A) receptors subunit composition; receptors containing alpha 2 beta 1, alpha 1 beta 1, alpha 1 beta 1 gamma 2L, and alpha 2 beta 1 gamma 2S were inhibited to the same extent by 5-HT2C receptor activation. Moreover, GABA(A) receptors composed of wild-type alpha 2 plus mutant beta 1((S409A)) subunits were inhibited to the same extent as wild-type receptors. The nonspecific protein kinase inhibitor, staurosporine, and the inhibitor of serine/threonine protein phosphatases, calyculin A, did not block the inhibitory effects of 5-HT2C receptors. The results with these inhibitors, taken together with those obtained with GABA(A) receptors with different subunit compositions, suggest that protein kinases or serine/threonine phosphatases are not involved in this GABA(A) receptor modulatory process. Thus, we propose that 5-HT2C receptors inhibit GABA(A) receptors by a Ca2+-dependent, but phosphorylation independent, mechanism and that 5-HT and GABA may act as cotransmitters to regulate neuronal activity. Furthermore, disruption of the cross-talk between these receptors may play a role in the antianxiety actions of 5-HT2 receptor antagonists. Copyright (C) 1996 Elsevier Science Ltd.
- ItemNeuropeptide Y inhibits (3)[H]noradrenaline release in the rat vas deferens independently of cAMP levels(1996) Bitran, M; Torres, G; Tapia, W; HuidobroToro, JPThe purpose of the present investigation was to ascertain the functional significance of the reduction in cyclic AMP (cAMP) levels in the inhibitory action of neuropeptide Y (NPY) on [H-3]noradrenaline ([H-3]NA) release, as well as to further characterize the subtype(s) of NPY receptors involved in the peptide's actions in the rat vas deferens. We studied the effects of NPY, carboxyterminal fragments of this peptide and the NPY analog [Leu(31),Pro(34)]-NPY on three functional responses, namely, the release of [H-3]NA and the associated muscle contractions evoked by electrical stimulation, and the accumulation of cAMP stimulated by forskolin. NPY, a known inhibitor of the electrically-evoked [H-3]NA release and neurogenic contractions is also a potent inhibitor of the forskolin-stimulated cAMP synthesis in the prostatic portion of the rat vas deferens. However, the ability of NPY to inhibit cAMP accumulation is lost upon tissue denervation, suggesting that this is likely to be a prejunctional effect. Elevation of cAMP levels by the use of the cell permeant analog of cAMP, 8-(p-chlorophenylthio)-cAMP (8pCPTcAMP) increases the electrically-evoked release of [H-3]NA. However, the inhibition of [H-3]NA release by NPY is not prevented by 8pCPTcAMP. Structure-activity relationship studies reveal that NPY and related peptides inhibit the release of [H-3]NA, the muscle contractions and the synthesis of cAMP with a similar pharmacological profile. NPY is the most potent inhibitory agent, whereas [Leu(31),Pro(34)]-NPY and NPY13-36, the respective Y-1 and Y-2 selective agonists, display similar potencies to inhibit the three responses. It is concluded that NPY inhibits neurotransmission in the rat vas deferens through the activation of a peptide receptor different from the known NPY-Y-1 or NPY-Y-2 receptor subtypes. NPY receptor activation in the vas deferens is negatively coupled to adenylyl cyclase activity. This intracellular signalling pathway is, however, not likely to mediate the peptide effects on the prejunctional regulation of noradrenaline release.
- ItemNeuropeptide Y is a vasoconstrictor and adrenergic modulator in the hamster microcirculation by acting on neuropeptide Y-1 and Y-2 receptors(1995) Boric, MP; Martinez, A; Donoso, MV; HuidobroToro, JPThe microvascular effects of neuropeptide Y, and two analogs with preferential affinity for different neuropeptide Y receptor subtypes, were assessed by intravital microscopy on the hamster cheek pouch. The interaction of neuropeptide Y and its analogs with noradrenaline was also studied. Superfusion with 0.1-300 nM neuropeptide Y caused a concentration-dependent reduction in microvascular conductance that was paralleled by reductions in arteriolar and venular diameters. These effects of neuropeptide Y were equipotent with noradrenaline, but slower to develop and longer-lasting than that of noradrenaline. Neuropeptide Y did not affect permeability to macromolecules, as measured by extravasation of fluorescent dextran. The neuropeptide Y Y-1 receptor agonist, [Leu(31),Pro(34)]neuropeptide Y, mimicked neuropeptide Y with similar potency but shorter duration, while neuropeptide Y-(13-36), a neuropeptide Y Y-2 receptor agonist, was at least 10-fold less potent than neuropeptide Y to induce a delayed and prolonged reduction in microvascular conductance. The joint superfusion of 1 nM neuropeptide Y plus 0.1 mu M noradrenaline did not cause synergism, nor even summation of effects, but reduced the contractile effect of noradrenaline. No synergism was observed after a 10 min priming with 1 nM neuropeptide Y, followed by its joint application with 0.1 mu M noradrenaline, but a significant vasodilation and hyperemia ensued upon stopping noradrenaline application. Priming with 1 nM [Leu(31),Pro(34)]neuropeptide Y prolonged noradrenaline vasoconstriction without evidence of hyperemia. In contrast, priming with 1 nM neuropeptide Y-(13-36) significantly antagonized noradrenaline vasoconstriction. These findings indicate that both neuropeptide Y receptor subtypes are present in arterioles and venules of the hamster, and suggest that their activation with neuropeptide Y induces a rapid (Y-1 receptor subtype activation) and a delayed (Y-2 receptor subtype activation) vasocontractile response. The interaction with noradrenaline is complex, without evidence for synergism, but neuropeptide Y Y-2 receptor activation seems to antagonize noradrenaline and/or to facilitate auto-regulatory vasodilation after the catecholamine-induced vasoconstriction.
- ItemNeuropeptide Y Y-1 receptors are involved in the vasoconstriction caused by human sympathetic nerve stimulation(1997) Racchi, H; Schliem, AJ; Donoso, MV; Rahmer, A; Zuniga, A; Guzman, S; Rudolf, K; HuidobroToro, JPNeuropeptide Y, a novel neurotransmitter, interacts with selective membrane receptors to cause vasoconstriction. Frequency- and concentration-dependent isometric contractions were observed in human inferior mesenteric artery and vein mounted rings that were stimulated with either electrical pulses (70 V, 0.5 ms, 2.5-20 Hz) or noradrenaline. The antagonism elicited by 100 nM tetrodotoxin and 1 mu M guanethidine confirmed the neuronal and sympathetic origins of the vasomotor response. Incubation with BIBP 3226 ((R)-N-2-(diphrnacetyl)-N-(4-hydroxyphenyl)-methyl-D-arginineamide), a selective neuropeptide Y Y, receptor antagonist, significantly reduced the vasoconstriction. The incomplete antagonist activity of BIBP 3226 tends to support the hypothesis of sympathetic co-transmission involving neuropeptide Y, adenosine 5'-triphosphate and noradrenaline. These findings were confirmed in parallel studies using rat superior mesenteric artery and vein ring preparations. (C) 1997 Elsevier Science B.V.
- ItemPharmacological characterization of the ET(A) receptor in the vascular smooth muscle comparing its analogous distribution in the rat mesenteric artery and in the arterial mesenteric bed(1996) Donoso, MV; Faundez, H; Rosa, G; Fournier, A; Edvinsson, L; HuidobroToro, JPThe potency of ET-1, ET-2, and ET-3 to contract the isolated perfused rat arterial mesenteric bed was 2.73 +/- 0.57, 1.63 +/- 0.32, and 144 +/- 30 nM, respectively. The vasomotor effect of the ETs was slow in onset, persistent but reversible. Sarafotoxin S6b mimicked the ETs with a potency twofold lower than ET-1; sarafotoxin S6c and the C-terminal hexapeptide of ET-1 was inactive. ET(B) agonists such as IRL-1620 and AGETB-89 were inactive as vasoconstrictors within the range of concentrations examined. Minor chemical modifications of ET-1 amino acids residues in position 7 or 21 decreased significantly the peptide potency; ET-I analogues with one or none of the disulfide bonds resulted inactive. The vasomotor effect of ETs was blocked in a competitive, reversible, and selective manner by FR 139317 and BQ-123, the latter being about threefold less potent than the former antagonist. The potency of FR 139317 was 20-fold higher to antagonize ET-3 than ET-1, and threefold higher to block ET-2 than ET-1. In strict analogy to FR 139317, BQ-123 was 12-fold more potent to antagonize ET-3 than ET-1, and fourfold more potent to antagonize ET-2 than ET-1. Upon removal of the endothelial cell layer, the vasomotor potency of ET-1 or the antagonist potency of FR 139317 remained unaltered, suggesting that the vasomotor receptors are localized in the arterial smooth muscles. The ET-l-induced vasomotor responses desensitized, an effect not crossed to noradrenaline (NA); perfusion with 10 mu M indomethacin did not alter the vasomotor potency of ET-1, excluding the participation of eicosanoids in the arteriolar effects of ET-1. In isolated rings of the rat mesenteric artery, set to record isometric contractions of the circular muscular layer, the potency of the ETs and their structural analogues was as follows: ET-2 = ET-1 = sarafotoxin S6b > ET-3 > sarafotoxin S6c. The C-terminal hexapeptide of ET-1 and [Ala(1,3,11,15)]ET-1 were inactive. The ET-1-induced vasoconstriction was antagonized in a concentration-dependent fashion by FR 139317. These results allow to conclude that the ET(A) receptors present in the arterial mesenteric circulation are localized in the vascular smooth muscle of the large-sized arteries as well as the smaller arterioles and precapillary vessels of the rat arterial mesenteric bed. Copyright (C) 1996 Elsevier Science Inc.
- ItemStimulation of the sympathetic perimesenteric arterial nerves releases neuropeptide Y potentiating the vasomotor activity of noradrenaline: Involvement of neuropeptide Y-Y-1 receptors(1997) Donoso, MV; Brown, N; Carrasco, C; Cortes, V; Fournier, A; HuidobroToro, JPNeuropeptide Y (NPY) appears to be involved in the sympathetic regulation of vascular tone. To assess the putative role of NPY in mesenteric circulation, the release and biological effect of NPY were examined after electrical stimulation of perimesenteric arterial nerves, Nerve stimulation with trains of 2-30 Hz increased the perfusion pressure of the arterially perfused rat mesenteric bed in a frequency-and time-dependent fashion, Trains of 15-30 Hz significantly displaced to the left, approximately threefold, the noradrenaline (NA)-induced presser concentration-response curve, in addition to increasing significantly its efficacy. Perfusion with 10 nM exogenous NPY mimicked the electrical stimulation effect, causing a threefold leftward shift of the NA concentration-response curve and increasing the maximal NA response. These effects were antagonized by 100 nM BIBP 3226, indicating the activity of NPY-Y-1 receptors. Electrical stimulation of the perimesenteric nerves released immunoreactive NPY (ir-NPY) in a frequency-dependent fashion; the ir-NPY coelutes with synthetic NPY as confirmed by HPLC. Both the electrically induced presser response and the calcium-dependent release of NPY were obliterated in preparations perfused with 1 mu M guanethidine or in rats pretreated intravenously for 48 h with 6-hydroxydopamine, thus revealing the sympathetic origin of these phenomena. Only a small proportion of the total NPY content in the perimesenteric arterial nerves is released after electrical stimulation. Chromatographic studies of the physiological sources of the ir-NPV support that NPY fragments are generated via peptidase degradation. The present findings demonstrate that NPY is re[eased from the perimesenteric arterial sympathetic nerves and acts, via the activation of NPY-Y-1 receptors, as the mediator responsible for the potentiation of NA's effect on perfusion pressure in the isolated rat mesenteric bed.