Catheter ablation using radiofrequency or low-energy direct current in pediatric patients with the Wolff-Parkinson-White syndrome

Percutaneous ablation of accessory pathways was performed in 22 consecutive children and adolescents (9 boys and 13 girls, age range 8 to 18 years). Low-energy direct current (DC) was used exclusively in the first 6 patients, whereas ablation was performed with radiofrequency energy in the following 16. Accessory pathways were located in the left free wall in 15 patients, were posteroseptal in 3, were in the right free wall in 3 and were anteroseptal in 1. A concealed accessory pathway was present in 7 patients (32%). There was no significant difference in clinical or electrophysiologic variables between both groups. Catheter ablation was successful in the initial 6 patients using low-energy DC, as compared with 13 of 16 patients using radiofrequency ablation. Low-energy DC was successful as a backup power source in all 3 patients who had unsuccessful radiofrequency ablation. There was no complication. The median procedural and fluoroscopic times for successful ablation were 2.5 hours and 49 minutes, respectively (p = NS between both power sources). Accessory pathway conduction recurred in 2 patients (33%) who had low-energy DC as compared with 1 (6%) who had radiofrequency ablation (p = NS). These 3 patients had successful reablation of their accessory pathways. In children and adolescents with accessory pathways, both new power sources compare favorably, with an overall success rate of ablation of 100% (22 of 22 patients). Radiofrequency ablation should be used initially because it does not require general anesthesia and is associated with a lower rate of recurrence of accessory pathway conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo central actions of NPY(1-30), an N-terminal fragment of neuropeptide Y

The purpose of the present study was to examine the possible central actions of a N-terminal fragment of NPY, NPY(1-30), on five measures typically influenced by the native peptide: decreased spontaneous activity, enhancement of muscle tone (increased grasping response), catalepsy, hypothermia, and stimulation of food intake. The peptides were administered ICV in doses ranging from 2.5 to 160 micrograms (0.75-48 nmol) and their effects on the three motor variables as well as thermal and feeding responses were evaluated and compared. Globally, results indicate that, similarly to NPY, the N-terminal fragment NPY(1-30), decreased spontaneous activity and induced hypothermia. However, the fragment displayed approximately half of the potency of NPY for producing these effects. On the other hand, contrary to NPY, NPY(1-30) did not affect muscle tone or food consumption and did not induced catalepsy in animals. These results demonstrate for the first time central actions of a N-terminal fragment of NPY and lend further support to the hypothesis that the receptors mediating the central actions of NPY are pharmacologically different.

Aging differentially modifies arterial sensitivity to endothelin-1 and 5-hydroxytryptamine: studies in dog coronary arteries and rat arterial mesenteric bed

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 microM) 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.

Conformational and biological studies of neuropeptide Y analogs containing structural alterations

We evaluated the alpha-helix content, the biological activities and the affinities of a series of neuropeptide Y (NPY) analogs containing structural alterations, mainly in the central portion of the molecule for which a putative alpha-helix arrangement has been proposed. First, we investigated the conformational and pharmacological characteristics of derivatives containing the N-terminal tetrapeptide linked to C-terminal peptide-amide segments of various lengths. In some of these, the missing portion was replaced with epsilon-aminocaproic acid, a flexible arm-linker. Data revealed that (1-4)-Aca-(18-36)NPY is a discontinuous analog almost as potent as the native peptide in a pharmacological preparation enriched in Y2 receptors (rat vas deferens), whereas it is about 5 times less potent in a Y1 bioassay (rabbit saphenous vein). This analog showed a similar profile in [125I]PYY binding assays performed in rat frontoparietal cortex (Y1) and hippocampus (Y2) membrane preparations. In a series of truncated derivatives obtained with the successive removal of the 5-13 to 5-17 segments of the NPY molecule, no apparent correlation was observed between the affinity or potency in bioassays and the alpha-helix content, as measured by circular dichroism spectroscopy. Other truncated analogs, obtained by linking the C-terminal 31-36 fragment to various N-terminal tetrapeptides were also investigated. None showed any affinity in brain membrane preparations (frontoparietal cortex and hippocampus) or activity in the rat vas deferens bioassay. However, a weak short-lasting contraction was measured with some of these analogs in the rabbit saphenous vein, thus suggesting that the 1-4 and 31-36 segments of the molecule contains pharmacophores recognized by the Y1 receptor subtype. The contribution of the arginine residues also was evaluated in relation with the alpha-helix. Their successive substitution with lysine, an excellent helix-promoter, showed that the replacement of Arg-19 or Arg-25, two residues found in the putative alpha-helix, gave active analogs. Furthermore, the substitution of Arg-19 with lysine increased the activity in the rat vas deferens as well as the affinity in the brain membrane binding assays. On the other hand, the substitution of Arg-33 produced a weak agonist, whereas the replacement of Arg-35 generated an inactive analog in the Y2-pharmacological preparation and a very weak competitor in the CNS binding assays. Interestingly, this latter analog was still active in the rabbit saphenous vein, thus identifying the position 35 as an additional potential target for the development of Y1 versus Y2 specific molecules.(ABSTRACT TRUNCATED AT 400 WORDS)

[Reactivity of internal mammary artery and saphenous vein used in human myocardial revascularization: studies with endogenous vasoconstrictors and vasodilators]

Biopsies of human internal mammary artery and saphenous vein were examined to ascertain the functional integrity of these vessels employed in myocardial revascularization. Studies were performed in vascular rings derived from 28 patients without previous consideration of age, sex, underlying additional pathology or drug treatments previous to and during surgery. Isometric muscle contraction of the circular muscle layer was monitored. Endothelin-1 (ET) is equipotent as a vasoconstrictor in arteries and veins, with a potency at least 10 to 100-fold that of noradrenaline (NA) or serotonin (5-HT). The potency of ET, NA or 5-HT is unaltered by mechanical removal of the endothelial cell layer. Arterial rings precontracted with NA relaxed in a concentration-dependent fashion in the presence of acetylcholine and sodium nitroprusside. Whereas the potency of nitroprusside was unaltered by removal of the endothelium, the efficacy of acetylcholine was greatly reduced. Saphenous vein rings were refractory to acetylcholine but not nitroprusside. Results open new perspectives to explain the larger patency of internal mammary artery grafts as compared to that of saphenous vein grafts in human myocardial revascularization.

Behaviours in trematode cercariae that enhance parasite transmission: patterns and processes

Cercariae, like miracidia, are non-parasitic larval stages implicated in the life cycle of all trematodes for the host-to-host parasite transmission. Almost all cercariae are free-living in the external environment. With a few exceptions (cercariae of Halipegus occidualis (Halipegidae) can live several months, Shostak & Esch, 1990a), cercariae have a short active life during which they do not feed, living on accumulated reserves. Most cercariae encyst as metacercariae in second intermediate hosts which are prey of the definitive host; in certain species, the interruption of the active life is achieved by an encystment in the external environment (or a simple immobile waiting strategy in a few species). In some two-host life cycles, the cercariae develop into adults after penetration (this is the case for various species causing human schistosomiasis). Some cercariae do not leave the mollusc which must then be ingested by the definitive host.

Influence of neuropeptide Y on regional vascular capacitance in dogs

To determine the effect of neuropeptide Y (NPY) on regional vascular capacitances, we measured the regional blood volume (Vb), unstressed volume (V0), blood flow distribution, venous compliance (Cv), venous resistance (Rv), and the time constant of venous drainage (tau v) in the splanchnic and extrasplanchnic circulation of 13 dogs anesthetized with chloralose. Cardiac output was kept constant with circulatory bypass. The extrasplanchnic region was further divided into superior vena caval (SVC) and inferior vena caval (IVC) regions. Vb was measured in the splanchnic and SVC regions using indicator dilution curves and the mean transit times. Changes in venous outflow pressures were used to change regional volumes, and a stop-flow procedure was used to obtain the regional venous filling pressures. This allowed construction of pressure-volume (P-V) curves and the calculation of Cv, Rv, and tau v. Hexamethonium chloride was infused throughout the experiment to prevent autonomic reflexes. Sham injections had no effects on four dogs. In nine dogs, NPY (bolus of 7.4 x 10(-8) or 14.8 x 10(-8) mol and 0.37 mol/min infusion) increased arterial blood pressure from 98.4 +/- 4.2 to 121.3 +/- 6.9 mmHg (P < 0.001), decreased splanchnic Vb from 31.6 +/- 2.1 to 24.9 +/- 1.8 ml/kg (P < 0.01), and decreased splanchnic V0 from 21.8 +/- 2.6 to 12.1 +/- 2.2 ml/kg (P < 0.001). SVC volumes were not affected by NPY. Extrasplanchnic Cv increased with NPY, but splanchnic Cv did not change. Thus exogenous NPY infusion decreases splanchnic capacitance, which could potentially increase venous return and cardiac output.

Differential transcription of multiple copies of a silk worm gene encoding tRNA(Gly1)

Ten different tRNA(Gly1) genes from the silk worm, Bombyx mori, have been cloned and characterized. These genes were transcribed in vitro in homologous nuclear extracts from the posterior silk gland (PSG) or nuclear extracts derived from the middle silk gland or ovarian tissues. Although the transcription levels were much higher in the PSG nuclear extracts, the transcriptional efficiency of the individual genes followed a similar pattern in all the extracts. Based on the levels of in vitro transcription, the ten tRNA(Gly1) genes could be divided into three groups, viz., those which were transcribed at very high levels (e.g., clone pR8), high to medium levels (e.g., pBmi1, pBmp1, pBmh1, pBmt1) and low to barely detectable levels (e.g., pBms1, pBmj1 and pBmk1). The coding sequences of all these tRNA genes being identical, the differential transcription suggested that the flanking sequences modulate their transcriptional efficiency. The presence of positive and negative regulatory elements in the 5' flanking regions of these genes was confirmed by transcription competition experiments. A positive element was present in the immediate upstream A+T-rich sequences in all the genes, but no consensus sequences correlating to the transcriptional status could be generated. The presence of negative elements on the other hand was indicated only in some of the genes and therefore may have a role in the differential transcription of these tRNA(Gly1) genes in vivo.

Localization and characterization of PACAP receptors in the rat cerebellum during development: evidence for a stimulatory effect of PACAP on immature cerebellar granule cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors are abundant in the brain and particularly in the cerebellum of adult rats. In contrast, the occurrence of PACAP binding sites has not been investigated during ontogenesis. The aim of the present study was to determine the distribution and biochemical characteristics of PACAP binding sites in the rat cerebellum during postnatal development, and to examine the effect of PACAP on immature cerebellar granule cells. Autoradiographic studies revealed that PACAP binding sites are transiently expressed in a germinative matrix of the cerebellar cortex, the external granule cell layer, and in the medulla, from postnatal days 8 to 25. A population of PACAP binding sites persisted in the internal granule cell layer in the mature cerebellum. Emulsion-coated cytoautoradiography, performed on cultured immature granule cells from eight-day-old rat cerebellum, demonstrated that transient PACAP binding sites are expressed by cerebellar immature granule cells. Biochemical characterization of binding revealed the occurrence of two classes of PACAP recognition sites exhibiting, respectively, high (Kd = 0.39 +/- 0.08 nM) and low (Kd = 21.2 +/- 9.4 nM) affinity for PACAP27. The two naturally occurring forms PACAP38 and PACAP27 were equipotent in competing for [125I]PACAP27 binding. In contrast, the [Des-His1]PACAP38 analog was eight times less efficient and vasoactive intestinal polypeptide only induced weak displacement of the binding. Exposure of cultured immature granule cells to PACAP27 resulted in a dose-dependent stimulation of the production of cAMP, indicating that PACAP binding sites represent authentic receptors positively coupled to adenylate cyclase. These results show that PACAP receptors are actively expressed in the cerebellum of rats during postnatal development. The presence of functional PACAP receptors in the external granule cell layer suggests that PACAP may play a role in the control of proliferation and/or differentiation of granule cells.

Localization, characterization and activity of pituitary adenylate cyclase-activating polypeptide in the frog adrenal gland

Pituitary adenylate cyclase-activating polypeptide (PACAP) has recently been isolated from the frog brain and the sequence of the peptide appears to be strikingly similar to that of mammalian PACAP. In the present study, we have investigated the localization of PACAP in the frog interrenal (adrenal) gland by immunocytochemistry using antisera directed against PACAP 38 or PACAP 27. Two types of PACAP-immunoreactive fibres were observed: thick varicose fibres coursing between adrenal cells and thin processes located in the walls of blood vessels irrigating the gland. Bilateral transection of the splanchnic nerves did not affect the intensity and distribution of PACAP immunoreactivity. The mean +/- S.E.M. concentration of PACAP, measured by radioimmunoassay in crude adrenal extracts, was 0.65 +/- 0.16 nmol/g wet tissue. Two molecular forms of PACAP in the adrenal gland were characterized by reversed phase high-performance liquid chromatography combined with radioimmunoassay quantification. The elution profiles revealed the existence of two peaks exhibiting the same retention times as synthetic frog PACAP 38 (fPACAP 38) and PACAP 27, the predominant form being PACAP 38. The possible involvement of PACAP in the regulation of adrenal steroidogenesis was investigated in vitro using a perifusion system for frog adrenal slices. Graded doses of fPACAP 38 (0.1-10 mumol/l) increased the secretion of both corticosterone and aldosterone in a dose-dependent manner. Administration of repeated pulses of fPACAP 38 (1 mumol/l), at 120-min intervals, led to a reproducible stimulation of corticosteroid secretion without any tachyphylaxis. Prolonged infusion (2 h) of the peptide induced a rapid increase in corticosterone and aldosterone output, followed by a gradual decline in the secretion rate, suggesting the occurrence of a desensitization phenomenon. Synthetic porcine vasoactive intestinal peptide, which is structurally related to PACAP, was about ten times less potent than fPACAP 38 in stimulating steroidogenesis while the [Des-His1]-fPACAP 38 analogue was 100 times less effective. These results demonstrate that a peptide closely related to fPACAP 38 is present in fibres innervating the frog adrenal gland and could participate in the regulation of corticosteroid secretion, particularly during neurogenic stress.

Vascular responses to endothelin-1 following inhibition of nitric oxide synthesis in the conscious rat

1. The objectives of the present experiments were to assess the role of endogenous nitric oxide (NO) in mediating and/or modulating the effects of endothelin-1 (ET-1) on blood pressure and microvascular permeability in conscious rats. 2. Intravenous administration of the NO synthesis inhibitors, NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine methyl ester (L-NAME) at a dose (25 mg kg-1 or 2 mg kg-1, respectively) which evoked maximum increase in mean arterial blood pressure (MABP) significantly attenuated (by about 40%) the vasodepressor response and potentiated (by 100-180%) the pressor response to ET-1 (1 nmol kg-1, i.v.) compared to the effects of ET-1 in animals where the peripheral vasoconstrictor effects of L-arginine analogues were mimicked by an infusion of noradrenaline (620-820 ng kg-1 min-1). Similar inhibition of the depressor and potentiation of the pressor actions of ET-1 were observed when the MABP which had been elevated by L-NMMA or L-NAME was titrated to normotensive levels with hydralazine or diazoxide before injection of ET-1. 3. L-NAME (2 mg kg-1) increased the vascular permeability of the large airways, stomach, duodenum, pancreas, liver, kidney and spleen (up to 280%) as measured by the extravasation of Evans blue dye. The permeability of pulmonary parenchyma, skeletal muscle and skin was not affected significantly by L-NAME treatment. Elevation of MABP by noradrenaline infusion did not evoke protein extravasation in the vascular beds studied with the exception of the lung. In the large airways, tissue Evans blue content was similar following noradrenaline infusion and L-NAME.4. Both the pressor and permeability effects of L-NAME (2 mg kg-1) were effectively reversed by L-arginine (300 mg kg- 1) but not by D-arginine (300 mg kg-1 ). The D-enantiomer of L-NAME, D-NAME(2 mg kg-1) had no effect on the parameters studied.5. Protein extravasation was significantly enhanced by ET-1 (1 nmol kg-1) in the upper and lower bronchi, stomach, duodenum, kidney and spleen (up to 285%). This was potentiated by L-NAME(2 mg kg-1), resulting in marked increases in tissue Evans blue accumulation (up to 550%) in these tissues. The effects of L-NAME and ET-1 were additive in the trachea, duodenum, pancreas and liver.Combined administration of L-NAME plus ET-1 significantly increased protein extravasation in the pulmonary parenchyma, where neither L-NAME nor ET-1 alone caused significant increases.6. Noradrenaline infusion (620-820 ng kg-1 min-1) potentiated the permeability action of ET-1(1 nmol kg-1) in the pulmonary circulation, whereas it did not modify ET-1-induced protein extravasation in the other vascular beds.7. These results indicate that endogenous NO mediates, in part, the vasodepressor effect and attenuates the vasopressor action of ET-1 and modulates the effects of ET-1 on vascular permeability. These findings confirm the role of NO in the maintenance of blood pressure and suggest an important role for NO in the regulation of microvascular permeability.

Evidence for in vivo interactions between neuropeptide Y-related peptides and sigma receptors in the mouse hippocampal formation

Recently, it was proposed that neuropeptide Y (NPY) and peptide YY (PYY) could act as endogenous ligands for sigma binding sites, as both NPY and PYY competed with high affinity (nanomolar) for 3H-(+)SKF 10,047 binding sites in rat brain membrane homogenates (Roman et al., 1989). However, various laboratories failed to replicate these in vitro findings. In order to clarify this apparent discrepancy and investigate further possible interactions between NPY and sigma related sites, we evaluated the effects of NPY, PYY and homologs, as well as nonrelated peptides, on in vivo 3H-(+)SKF 10,047 binding parameters in the mouse hippocampal formation. As expected, haloperidol (2 mg/kg), a prototypical sigma receptor ligand, competed for 90% of in vivo hippocampal labeling observed following a peripheral intravenous injection of 3H-(+)SKF 10,047. Intracerebroventricular injections of 300-3000 pmol of either NPY, PYY, NPY2-36, or the Y1 agonist Leu31,Pro34-NPY inhibited significant proportions (17-35%) of haloperidol-sensitive in vivo 3H-(+)SKF 10,047 hippocampal labeling. However, a Y2 receptor agonist, NPY13-36, and nonrelated peptides such as neurotensin and vasoactive intestinal polypeptide, as well as adrenalin, failed to alter in vivo 3H-(+)SKF 10,047 hippocampal binding. It thus appears that NPY, PYY, and a selective Y1 agonist can interact in a concentration-dependent manner, with in vivo 3H-(+)SKF 10,047 labeling in the mouse hippocampal formation. This effect demonstrates selectivity as a Y2 agonist, unrelated peptides, and adrenalin failed to alter in vivo sigma labeling. This in vivo interaction may be relevant to some of the respective biological actions of NPY and sigma-related molecules.

Predictive factors for spontaneous closure of atrial septal defects diagnosed in the first 3 months of life

OBJECTIVES

To establish the rate of spontaneous closure of atrial septal defects diagnosed before age 3 months, 101 infants (mean age 26 days) with an interatrial shunt confirmed by Doppler echocardiography were followed up for an average of 265 +/- 190 days.

BACKGROUND

Even if interatrial shunts in the newborn are frequently encountered, little is known about their natural history.

METHODS

Defect diameter on two-dimensional echocardiography and width of color flow jet were measured in the subcostal view. Right and left ventricular diameters and atrial septal curvature were also studied. Kaplan-Meier curves were obtained to predict age of spontaneous closure in relation to initial defect diameter.

RESULTS

There was no significant correlation between the diameter of the atrial septal defect and right ventricular/left ventricular ratio or type of septal curvature (vertical or concave toward the left atrium). The classic predominance of girls over boys was observed only for defects > 5 mm. An overall rate of spontaneous closure of 87% was observed. Frequency and timing of closure were inversely correlated to atrial septal defect diameter: closure occurred in 100% (32 of 32) of defects in group 1 (diameter < 3 mm), 87% of defects (39 of 45) in group 2 (diameter 3 to 5 mm), 80% of defects (16 of 20) in group 3 (diameter 5 to 8 mm). Spontaneous closure did not occur in four patients of group 4 (defect > or = 8 mm) during an average follow-up interval of 417 days (range 294 to 597 days).

CONCLUSIONS

These results suggest that infants with an atrial septal defect < 3 mm need not be followed up as 100% of these defects will be closed by age 18 months; those with a defect 3 to 5 or 5 to 8 mm should be evaluated by the end of the 12th and the 15th month, respectively, when > 80% of these defects will be closed. An atrial septal defect with a diameter > or = 8 mm may have little chance of closing spontaneously and the possibility of surgical correction should be considered. Defects < 3 mm probably do not constitute a cardiac malformation in light of their natural evolution and gender distribution.

Method for the quantification of alginate in microcapsules

Alginate is a key reagent in the preparation of microcapsules for cell transplantation. To address the question of the intracapsular alginate concentration, a sensitive assay has been developed to quantify the alginate content of microcapsules. The method is based on the metachromatic change induced by alginate binding to the dye, 1,9-dimethyl methylene blue (DMMB). The assay has a high sensitivity and precision. It covers a wide concentration range enabling the measurement of alginate in dilute supernatants as well as in microcapsules. For the latter, the membrane is initially dissolved by incubating the microcapsules in an alkaline medium. The effect of potentially interfering substances (poly-L-lysine (PLL), citrate, chloride, sodium) and of pH has been studied. Poly-L-lysine interfered with the assay at pH 6.5 but not at pH 13. Interference by sodium augmented with increasing sodium concentration and reached a plateau at 200 mM. This problem was overcome by routinely adjusting all samples to 500 mM sodium. The other substances tested had a negligible effect on the assay. The reliable measurement of alginate with this new assay will allow the optimization of the intracapsular alginate concentration.

Relaxation by dexamethasone of isolated guinea-pig airways precontracted with endothelin-1

Dexamethasone (1-100 microM) produced concentration-dependent relaxations of isolated guinea-pig tracheal and bronchial strips precontracted with endothelin-1 (100 nM), which were not affected by the removal of the epithelium. Dexamethasone neither induced relaxation of tissues precontracted with carbachol (0.1 microM) or KCl (25 mM) nor inhibition of endothelin-1 (1-100 nM)-induced peak contractions after 10-min preincubation of the tissues with dexamethasone. These findings indicate that acute corticosteroid treatment can reverse the bronchoconstrictor action of endothelin-1.

D-myo-inositol 1,2,6-trisphosphate blocks neuropeptide Y-induced facilitation of noradrenaline-evoked vasoconstriction of the mesenteric bed

Perfusion of the rat mesenteric bed with 0.1 or 10 nM neuropeptide Y potentiated the noradrenaline-induced increase in mesenteric pressure; the peptide did not modify basal perfusion pressure. While perfusion with 0.1 nM neuropeptide Y significantly increased the maximal noradrenaline-evoked vasoconstriction without modifying its EC50, 10 nM neuropeptide Y potentiated the maximal noradrenaline effect and significantly shifted its concentration-response curve to the left. Perfusion with 1-10 microM D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol) reduced, in a concentration-dependent fashion, the neuropeptide Y-induced potentiation of the noradrenaline-evoked vasoconstriction without altering the potency or maximal response evoked by the catecholamine alone. Perfusion with 0.1 nM neuropeptide Y plus 1 microM alpha-trinositol completely abolished the neuropeptide Y-induced facilitation of the noradrenaline effect. alpha-Trinositol 1 microM in the presence of 10 nM neuropeptide Y caused a nonparallel rightward shift of the noradrenaline concentration-response curve as compared to that obtained in the presence of 10 nM neuropeptide Y alone. The alpha-trinositol blockade of the facilitatory action of neuropeptide Y was reversible.

Antagonism of the inhibitory action of neuropeptide Y (NPY) in guinea-pig trachea by the C-terminal fragment NPY (2-36)

The C-terminal fragment of neuropeptide Y (NPY), NPY(2-36) was used as a means of discriminating between two differently located NPY receptor sites in guinea-pig trachea. Both NPY and NPY(2-36) reduced the maximal relaxation elicited by vasoactive intestinal peptide (VIP). In contrast, the C-terminal fragment did not mimic the inhibitory action of NPY on the noradrenaline-(NA) evoked response. However, pretreatment of the trachea with 30 nM NPY(2-36), 5 min before generating NA and VIP concentration-response curves in the presence of NPY, abolished the inhibitory effect of NPY on NA-elicited response but did not affect the modulatory action of NPY on VIP-induced relaxation. These results suggest that the two differently located NPY receptor sites in guinea-pig trachea are of two distinct subpopulations.