Browsing by Author "DONOSO, MV"

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    ADENOSINE 5'-TRIPHOSPHATE (ATP), THE NEUROTRANSMITTER IN THE PROSTATIC PORTION OF THE LONGITUDINAL MUSCLE LAYER OF THE RAT VAS-DEFERENS
    (1994) DONOSO, MV; BATES, F; MONTIEL, J; HUIDOBROTORO, JP
    Suramin (1-100 muM) and alpha,beta-methylene adenosine 5'-triphosphate (AMPCPP, 39 muM), antagonized the motor activity induced by exogenous adenosine 5'-triphosphate (ATP) but not exogenous noradrenaline (NA) in the longitudinal musculature of prostatic (P) and epididymal (E) segments of the rat vas deferens. Likewise, application of these drugs reduced the fast component of the nerve-stimulated contraction in response to a single transmural electrical pulse in E and P. Suramin also blocked in a concentration-dependent fashion, the contractile responses to trains of 1.5, 5, 15 or 30 Hz transmural electrical pulses in P, while it did not affect those in E. AMPCPP obliterated responses to trains of 1.5, 5, and 15 Hz in P, while reducing these responses in E to a significantly lesser extent. Present results strongly support that ATP is the motor transmitter in P, while in E, ATP and NA are likely the co-transmitters responsible for the motor tone.
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    AGING DIFFERENTIALLY MODIFIES ARTERIAL SENSITIVITY TO ENDOTHELIN-1 AND 5-HYDROXYTRYPTAMINE - STUDIES IN DOG CORONARY-ARTERIES AND RAT ARTERIAL MESENTERIC BED
    (1994) DONOSO, MV; FOURNIER, A; PESCHKE, H; FAUNDEZ, H; DOMENECH, R; HUIDOBROTORO, JP
    The influence of age on vascular reactivity to endothelin-1 (ET-1) and 5-hydroxytryptamine (5-HT) was studied in coronary artery rings from dogs of 9 years of age or younger, and dogs older than 9 years. ET-1 caused concentration-dependent contractions that developed about 100% of the 70 mM KCl-induced tension in the younger dogs; those from older dogs did not generate more than 20%. In contrast, 5-HT developed only about 20% of the KCl-induced tension in rings from young dogs, whereas in the older animals, it developed up to 120% of the KCl tension. No significant difference in the tension developed by 70 mM KCl was noted between both groups of dogs. Mechanical denudation of the endothelial cell layer caused a modest, yet significant, leftward shift of the ET-1 and 5-HT concentration-response curves only in the younger dogs. N omega-Nitro-L-arginine (15 mu M) shifted the ET-1 concentration-response curves to the left in rings from both groups of dogs. Rings precontracted with 20 mM KCl relaxed in a concentration-dependent fashion with acetylcholine; its sensitivity was about threefold less in the older group of dogs. To validate the changes in Vascular reactivity with age, a parallel study was performed perfusing the arterial mesenteric bed of rats of 3, 7, and 30 weeks of age. In this experimental model, the efficacy of ET-1 significantly decreased with age and that of 5-HT was significantly increased. The vasomotor reactivity of noradrenaline was modestly affected by aging, whereas the acetylcholine-induced vasorelaxation was significantly reduced with age.
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    ENDOTHELIN-1 (ET)-INDUCED MOBILIZATION OF INTRACELLULAR CA2+ STORES FROM THE SMOOTH-MUSCLE FACILITATES SYMPATHETIC COTRANSMISSION BY POTENTIATION OF ADENOSINE 5'-TRIPHOSPHATE (ATP) MOTOR-ACTIVITY - STUDIES IN THE RAT VAS-DEFERENS
    (1992) DONOSO, MV; MONTES, CG; LEWIN, J; FOURNIER, A; CALIXTO, JB; HUIDOBROTORO, JP
    Endothelin-1 (ET) enhances nerve-stimulated contractions in epididymal (E) and prostatic (P) halves of the rat vas deferens, in addition to raising the basal tone in E. Whereas the peak increase in basal tone occurs in about 30 s, the maximal enhancement of neuro-transmission is observed within 5 min. The latter effect is long lasting is maintained even after extensive tissue washout. Furthermore, ET potentiates, in a concentration-dependent fashion, the adenosine 5'-triphosphate (ATP) or the adenylylimido-diphosphate (AMP-PNP) but not the noradrenaline (NA)-induced motor activity. The ATP motor response is partially blocked in media without Ca2+ plus 0.1 mM EGTA or following tissue incubation in buffer containing 10-50 nM nifedipine. However, these procedures do not modify significantly the ET-induced potentiation of the ATP contractions. The ET-induced potentiation of the ATP motor response is not modified by tissue preincubation in Ca2+-free buffer plus 10-30-mu-m ryanodine or 5-20 mM caffeine. The ET-induced rise in E basal tension is significantly reduced in the absence of external Ca2+ or by nifedipine; ryanodine does not modify this effect. Surgical denervation of the tissues does not obliterate the ET-induced potentiation of the ATP motor responses nor the ET increase in E basal tension in tissues superfused in Ca2+-free media or buffer with 2.5 mM Ca2+. Endothelin-1 does not significantly modify the overflow of H-3-NA, following transmural electrical depolarization of tissue nerve terminals. Hoe 140 did not interfere with the ET activity.
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    EXTRACELLULAR CALCIUM DEPENDENCE OF THE NEUROTENSIN-INDUCED RELAXATION OF INTESTINAL SMOOTH MUSCLES - STUDIES WITH CALCIUM-CHANNEL BLOCKERS AND BAY K-8644
    (1987) KULLAK, A; DONOSO, MV; HUIDOBROTORO, JP
    To investigate whether the neurotensin-induced relaxation of the rat duodenum and ileum is dependent on the external concentration of calcium, the effect of the neuropeptide was studied in isolated intestinal segments superfused with Tyrode solution containing no calcium, 1 or 2.5 mM Ca2+. The neurotensin-induced intestinal relaxation was reduced when the extracellular calcium concentration was lowered. In addition, the inhibitory effect of neurotensin was cancelled when the tissues were incubated in the presence of diltiazem, methoxyverapamil or nifedipine. BAY K-8644, a structural analog of nifedipine that functions as an agonist of the calcium channel, potentiated the neurotensin-induced smooth muscle relaxation. The facilitatory effect of BAY K-8644 was antagonized by nifedipine, indicating competition between the 2 dihydropyridines. Apamin, the K+ channel blocker, antagonized the neurotensin-induced visceral relaxation, displacing the concentration-response curve of the peptide to the right. Furthermore, apamin also blocked the effect of neurotensin when the neuropeptide was assayed in the presence of BAY K-8644. It is concluded that the smooth muscle relaxation induced by neurotensin is dependent on external calcium, suggesting that the activation of the neuropeptide receptor causes an influx of calcium which leads to the opening of K+ channels before smooth muscle relaxation is triggered.
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    INVOLVEMENT OF CALCIUM CHANNELS IN THE CONTRACTILE ACTIVITY OF NEUROTENSIN BUT NOT ACETYLCHOLINE - STUDIES WITH CALCIUM-CHANNEL BLOCKERS AND BAY-K8644 ON THE RAT FUNDUS
    (1986) DONOSO, MV; HUIDOBROTORO, JP; KULLAK, A
    The contractile activity of neurotensin and acetylcholine on rat isolated fundus strips was examined in preparations maintained on Tyrode buffer containing 2.5, 1.0 or 0 mM Ca2+. While the neurotensin contractions depended markedly on the external Ca2+ concentration, the acetylcholine-induced muscular responses were not significantly affected by omission of calcium in the superfusion media. 2 Pre-incubation for at fundus strips with nifedipine (0.03-3.8 .mu.M), diltiazem (0.5-3.5 .mu.M) or methoxyverapamil (0.3-1.3 .mu.M) antagonized in a non-surmountable fashion the contractile activity of neurotensin but not of acetylcholine. 3 Pretreatment with Bay K 8644 potentiated in a concentration-dependent fashion the contractile activity of rat fundus strips to neurotensin without modifying to any significant degree the acetylcholine-induced contractions. 4 Nifedipine blocked in a concentration-dependent manner by Bay K 8644-induced potentiation of the neurotensin contractile responses in the fundus. 5 Results demonstrate the dependence on external calcium of the contractile activity of neurotensin and the resistance of the muscarinic response to external calcium manipulations. The coupling of the neurotensin receptor to calcium channels is discussed.
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    INVOLVEMENT OF ET(A) RECEPTORS IN THE FACILITATION BY ENDOTHELIN-1 OF NONADRENERGIC NONCHOLINERGIC TRANSMISSION IN THE RAT URINARY-BLADDER
    (1994) DONOSO, MV; SALAS, C; SEPULVEDA, G; LEWIN, J; FOURNIER, A; HUIDOBROTORO, JP
    1 Endothelin-l (ET-1; 3-10nM) raised the tone of rat bladders bathed in buffer containing atropine (1 mu M) plus guanethidine (3.4 mu M). In addition, ET-1 potentiated, in a concentration-dependent fashion (1-10nM), the contractions evoked by both transmural nerve stimulation and applications of exogenous adenosine 5'-triphosphate (ATP). 2 The threshold concentration of ET-1 required to facilitate non-adrenergic non-cholinergic (NANC) transmission and potentiate ATP-induced contractions, was about 10 fold lower than that required to increase the bladder tone (3nM). 3 The ET-l-induced increase in basal tension reached its maximal effect within 60-90s. In contrast, the 7.8 mu M ATP-induced contractions increased by 50% within the first minute following incubation with 10nM ET-1 but required about 5 min to develop the maximal effect. 4 The ET-l-induced potentiation of NANC or ATP responses was long-lasting and persisted in spite of extensive washing. The recovery of the bladder excitability depended on the concentration of ET-1. Following the application of 3nm ET-1, recovery required 30 min; applications of 10nM ET-1 required at least 60 min for full recovery. 5 The ET-1-induced potentiation of responses was selective for ATP and related structural analogues. ET-1 did not modify the contractions induced by acetylcholine, 5-hydroxytryptamine, prostaglandin F-2 alpha or bradykinin. 6 The potency of ET-2 was similar to that of ET-1. ET-3 and ET-C-terminal hexapeptide were inactive up to 100M. Sarafotoxin S6b was 2 to 3 fold less potent than ET-1 whereas sarafotoxin S6c (100nM) was inactive. AGETB-9 and AGETB-89, two ET(B) receptor agonists, were also inactive (up to 100nM). 7 Removal of one or both disulphide bonds in ET-1 and tryptophan-21 formylation of ET-1, resulted in inactive peptides (up to 100nM). 8 The ET-1 receptor antagonists, BE-18257B and FR139317, blocked both the ET-1-induced rise in tone and the potentiation of ATP responses in a concentration-dependent fashion. FR139317 was at least 30 fold more potent than BE-18257B. Both antagonists blocked at lower concentrations the ET-1 increase in bladder tone as compared to the ATP potentiation. The antagonism was slowly reversible. 9 Results are consistent with the presence of ET(A) receptors in the rat bladder, which mediate both actions of ET-1. The interaction of ET-1 with purinergic mechanisms is discussed.
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    INVOLVEMENT OF POSTJUNCTIONAL PURINERGIC MECHANISMS IN THE FACILITATORY ACTION OF BRADYKININ IN NEUROTRANSMISSION IN THE RAT VAS-DEFERENS
    (1989) DONOSO, MV; HUIDOBROTORO, JP
    To investigate the nature of the bradykinin-induced potentiation of electrically driven muscle twitches in the isolated vas deferens, bradykinin, noradrenaline and adenosine 5''-triphosphate (ATP) concentration-response curves were made with control, reserpinized and chemically sympathectomized rats. Bradykinin potentiated the ATP- but not the noradrenaline-induced contractions in the epididymal and prostatic segments of the ductus. The epididymal segment of the ductus did not respond to transmural electrical stimulation following reserpine treatment. Bradykinin potentiated the muscular contractions caused by exogenous ATP but not by noradrenaline. In contrast, the transmurally evoked twitches of the prostatic portion of the ductus remained almost unaltered; bradykinin increased the motor effect of ATP without modifying the potency of noradrenaline. All neuronally induced contractile activity was absent in sympathetomized rats; bradykinin potentiated the contractile effect of ATP without altering the noradrenaline-induced contractions. These results suggest that bradykinin potentiates the ATP-evoked contractions by acting postjunctionally.
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    PHARMACOLOGICAL CHARACTERIZATION OF CGRP1-RECEPTOR SUBTYPE IN THE VASCULAR SYSTEM OF THE RAT - STUDIES WITH HCGRP FRAGMENTS AND ANALOGS
    (1990) DONOSO, MV; FOURNIER, A; STPIERRE, S; HUIDOBROTORO, JP
    In order to examine whether the truncated fragments of hCGRP, hCGRP(8-37) or hCGRP(12-37), behave as competitive CGRP receptor antagonists in the vascular system of the rat, systemic blood pressure was continually monitored in pentobarbital-anesthetized Sprague-Dawley rats. The IV administration of 7.9-527 pmol hCGRP/rat caused dose-related reductions in mean arterial blood pressure that lasted, depending on the dose, about 3-10 min. In contrast, hCRRP fragments 8-37 or 12-37 proved inactive up to 60,000 pmol/rat. Pretreatment with either 10 or 30 nmol hCGRP(8-37) or 20 or 90 nmol hCGRP(12-37)/rat reduced the magnitude of the CGRP-induced hypotensive responses caused by 79 pmol hCRGP/rat; pretreatment with 10 nmol of the hCRGP fragments displaced about 3-fold the hCRGP as well as the [Cys(ACM)2.7]hCGRP dose-response curve to the right in a parallel fashion. The specificity of hCGRP(8-37) as a CGRP receptor antagonist was documented by the finding that it did not antagonize the hypotensive responses induced with bradykinin, histamine or substance P.