The persistence of allergen exposure favors pulmonary function decline in workers with allergic occupational asthma.

BACKGROUND: In asthmatics, a rapid decline in pulmonary function is observed, likely as a consequence of airways remodeling. Persistence of allergen exposure in patients with occupational asthma (OA) maintains chronic bronchial inflammation, resulting in a more severe lung function decline. Few studies were performed on the effects of allergen exposure cessation. OBJECTIVE: This study aims at evaluating the influence of allergen exposure cessation on respiratory decline in allergic asthmatic workers. METHODS: Two groups of workers with allergic OA were selected. The first group (30 workers) changed job after the diagnosis and was no more exposed to sensitizing allergens, and the second group (28 subjects) did not and, as a consequence of preventive measures in the work place, was exposed to a lower level of allergens. All were treated with conventional therapy, according to GINA protocols. FEV1 changes during a 12-year period were evaluated. RESULTS: Despite pharmacological therapy, the pulmonary function decay slope was steeper in workers continuously exposed to the sensitizing agent (even at reduced level) than in those with a complete cessation of exposure: final FEV1 loss was 512.5 ± 180 ml versus 332.5 ± 108 ml, respectively. The difference became significant after 4 years from the cessation of the exposure. CONCLUSIONS: The study shows that the cessation of the exposure to allergen in the work place appears the most effective measure in limiting pulmonary function decline in asthmatic workers and underlines the importance of allergic risk assessment and control in the management of occupational asthma.

Environmental pollution and asthma.

Clinical evidences and epidemiological studies show that allergic pathologies of the respiratory tract are increasing in the world areas with high pollution impact, demonstrating how many polluting substances favor both allergic sensitization and the bronchial inflammatory changes characteristic of asthma. It has been shown that asthma, as many other diseases, is a complex interaction between genetic predisposition and environmental stimuli that results in clinical expression of various phenotypes of asthma: allergic, intrinsic etc. Many pollutants have such a potential. Diesel exhaust particles (DEP) can favor allergic sensitization, induce acute asthma attacks and increase bronchial reactivity, acting both on allergen, on bronchial mucosa and on immune cells. In fact, DEP can favor B lymphocytes to shift to a production of IgE and T cells to produce Th2 cytokines. Asthma can be also induced by high exposure to many other substances as NO2 and first of all ozone (O3): strong oxidizing substance that is synthesized, in absence of ventilation, by photochemical reaction due to the combination of ultraviolet sun radiation on exhaust gases as NO2 and hydrocarbons. Ozone is abundant in cities with minimal concentration in the morning gradually increasing during the day until maximal levels in the afternoon and then decreasing during the night. Epidemiological studies show that the number of access to hospital for acute asthma and even the use of bronchodilator by asthmatics increase during the high level periods when Ozone constitute almost 90 percent of the total oxidants in the environment. Particulate matter of very small diameter have a crucial role in favoring asthma attacks, and smaller the substance deeper the penetration in the bronchial tree, with an inflammatory reaction in the peripheral bronchial mucosa characterized by increased vessel permeability, mucosal edema, inflammatory mediator production by damaged epithelium and inflammatory cells that determines acutely a high narrowing of the bronchial lumen and in a long period favor airways remodeling and a rapid decline of respiratory function.

Maintenance venom immunotherapy administered at a 3-month interval preserves safety and efficacy and improves adherence.

BACKGROUND: Hymenoptera venom immunotherapy (VIT) is a safe and effective approach to insect sting allergy. However, after discontinuation, relapses can occur in some patients, especially those with a high occupational risk, and they may need to prolong VIT indefinitely. In order to improve adherence, we propose extending the interval between injections of maintenance VIT (MVIT). OBJECTIVE: To evaluate the safety, efficacy, and patient acceptance of a 3-month interval between MVIT injections in a group of Hymenoptera-allergic patients who are occupationally exposed to insect stings. PATIENTS AND METHODS: We included 72 patients with severe systemic reactions to Hymenoptera stings. MVIT was administered for 4 years at intervals increasing up to 3 months and then continued for a further 2 years. Patients were informed of the risk of relapse after discontinuation and of the need for indefinite treatment at 3-month intervals. RESULTS: During the 3-month interval maintenance phase, only 235 local reactions (17.8%) were observed in 17 patients. Sixty patients experienced 125 field re-stings and only 1 experienced a systemic reaction with generalized urticaria. CONCLUSIONS: The study confirms that the conventional MVIT interval of 4 to 6 weeks can be extended to 3 months in most patients with no adverse events, while maintaining safety and efficacy, improving adherence, and guaranteeing safe continuation of professional activity.

Eventual error caused by dehydration with pachometry.

Among the possible variables responsible for systemic errors in the acquisition of pachometric measurements, the corneal hydration condition plays a determinant role. In the present study, the authors have investigated the importance of this condition with two different pachometers (Storz Corneoscan II and Allergan Humphrey), reproducing an experimental dehydrated condition. The main datum arising from the comparison of the measurements obtained is represented by the different time course of the value of the measurement in the two groups. In fact, confronting the medium initial superimposed thickness value in the two tables (521 vs. 520 microm) there is a substantial difference in the final examination. For the first group of 60 corneas, the thickness values appear almost identical in the different intervals of time (medium initial thickness 521 vs. 512 microm final thickness). For the group examined with the solid-point machine, a decreasing thickness equal to 7% was evidenced (520 vs. 482 microm) with a significant decrease in the corneal thickness after only 45 s.

Regio- and stereoselective cycloadditions of cyclic nitrones to maleic diamide forced in a peptide: synthesis of potent ligands of human NK-2 receptor.

The regioselectivity and the stereoselectivity induced by relatively small peptidomimetic maleic diamide 1 in cycloaddition reactions with cyclic nitrones 2-5 was studied. The high regio- and stereoselectivity observed, sensibly increased by nonpolar solvents, was the effect of a double-asymmetric induction produced by the nitrone substituent on the pseudopeptidic tether. A new class of potent human tachykinin NK-2 receptor ligands was synthesized.

Molecular determinants of peptide and nonpeptide NK-2 receptor antagonists binding sites of the human tachykinin NK-2 receptor by site-directed mutagenesis.

A series of 14 mutants on nine selected residues of the human tachykinin NK(2) receptor was produced and stably transfected into CHO cells to investigate the binding of the peptide MEN 11420 and the nonpeptide SR 48968 antagonists. The main interactions found for MEN 11420 were with Thr171, Tyr206, Tyr266 and Phe270. In the case of SR 48968 crucial residues were Tyr266 and Tyr289. While some overlapping of the binding sites exists, the binding modes suggested by this study appear not to allow structural correlation, and therefore general SAR, between these two antagonists.

Antimuscarinic, calcium channel blocker and tachykinin NK2 receptor antagonist actions of otilonium bromide in the circular muscle of guinea-pig colon.

We have analyzed, by the sucrose gap method, the action of otilonium bromide, a quaternary ammonium derivative in use for the symptomatic therapy of irritable bowel syndrome, on the electrical and mechanical responses initiated by different stimuli in the circular muscle of the guinea-pig proximal colon. Otilonium bromide produced a concentration-dependent inhibition of membrane depolarization (IC50 4.1 microM), action potentials (APs) and contraction (IC50 3.7 microM) produced by the muscarinic receptor agonist, methacholine. It also produced a concentration-dependent inhibition of APs and accompanying contraction (IC50 31 microM) produced by KCl (30 mM), and had a biphasic effect on the cholinergic excitatory junction potential (e.j.p.) produced by single pulse electrical field stimulation: at low concentrations (0.1-0.3 microM) otilonium bromide enhanced the e.j.p. and, at higher concentrations (IC50 22 microM and 16 microM toward depolarization and contraction), produced a concentration-dependent inhibition. Otilonium bromide eliminated the APs superimposed on the depolarization induced by the tachykinin NK1 receptor agonist, [Sar9]substance P-sulphone and suppressed the corresponding contraction (IC50 43 microM) but had little effect on the sustained membrane depolarization induced by this agonist. On the other hand, otilonium bromide produced a similar inhibitory effect on both membrane depolarization and contraction (IC50 38 microM and 45 microM, respectively) induced by the tachykinin NK2 receptor agonist [betaAla8]neurokinin A (4-10). When tested in the presence of nifedipine (1 microM), otilonium bromide had no effect on the membrane depolarization induced by [Sar9]substance P-sulphone but inhibited in a concentration-dependent manner the depolarization induced by [betaAla8]neurokinin A (4-10) (IC50 41 microM). In contrast, the blocker of receptor-operated cation channels, SKF 96365, inhibited with similar potency the depolarization induced by both [Sar9]substance P-sulphone and [betaAla8]neurokinin A (4-10) (IC50 60 microM and 54 microM, respectively). In radioligand binding experiments otilonium bromide produced a concentration-dependent inhibition of the binding of both an agonist ([125I]neurokinin A, Ki 7.2 microM) and an antagonist ([3H]SR 48968, Ki 2.2 microM) to membranes of Chinese hamster ovary cells transfected with the human tachykinin NK2 receptor. In conclusion, the present findings demonstrate that, in the microM range of concentrations, otilonium bromide acts as a muscarinic and tachykinin NK2 receptor antagonist and as a calcium channel blocker. The latter property is likely to account for its ability to suppress contraction initiated by the tachykinin NK1 receptor agonist. Therefore multiple mechanisms of action account for the ability of otilonium bromide to reduce stimulated motility of intestinal smooth muscle.

Relevance of aromatic residues in transmembrane segments V to VII for binding of peptide and nonpeptide antagonists to the human tachykinin NK(2) receptor.

We used membranes from Chinese hamster ovary cells stably transfected with the human tachykinin NK(2) receptor, either wild-type or mutated, at four aromatic residues (His(198), Tyr(266), Phe(270), Tyr(289)) located in transmembrane segments V to VII, to assess the role of these residues in the binding of natural tachykinins and peptide and nonpeptide antagonists. Three radioligands, the agonist [(125)I]neurokinin A (NKA), the peptide antagonist [(3)H]MEN 11420, and the nonpeptide antagonist [(3)H]SR 48968 bound to the wild-type receptor with high affinity (K(d) = 2.4 nM, 0.3 nM, and 4.0 nM, respectively). Four of the six mutant receptors tested retained high affinity for at least one of the radioligands. H(198)A mutation abrogated the binding of NKA but not that of MEN 11420 or SR 48968 (K(d) = 4.8 and 11.5 nM, respectively); Y(266)F mutation abrogated the binding of MEN 11420 but not that of NKA or SR 48968 (K(d) = 2.8 nM and 1.2 nM, respectively); F(270)A mutation abrogated the binding of both NKA and MEN 11420 but not that of SR 48968 (K(d) = 1.6 nM); Y(289)F mutation abrogated the binding of SR 48968 but not that of NKA and MEN 11420 (K(d) = 2.0 and 2.9 nM, respectively). Y(266)A and Y(289)A mutations abrogated the binding of all radioligands. Among the unlabeled antagonists, the affinity of the nonpeptide GR 159897, at variance with SR 48968, resulted heavily compromised by H(198)A and Y(266)F mutations; the peptide antagonists R396 and MEN 10376 essentially followed the binding profile of NKA, but R396 showed markedly increased affinity for the Y(289)F mutant receptor. Taken together, these results indicate that different, partially overlapping sets of sites may be involved in the binding of agonists and diverse antagonists to the human tachykinin NK(2) receptor.

Synthesis of biphenylyltetrazole derivatives of 1-aminopyrroles as angiotensin II antagonists.

Based on preliminary molecular modelling study, the synthesis of two different classes of biphenylyltetrazole derivatives of 1-aminopyrroles, as potentially active non-peptide angiotensin II (AII) antagonists, is reported. Some NH-Boc protected l-aminopyrroles were deprotected, N-acylated, N-alkylated with 5-[4'-bromomethyl-1,1'-biphenyl-2-yl]-1-triphenylmethyl-1H-tetrazo le, and then detritylated to give the first class of title compounds. Other 1-NH-Boc protected 1,2-diaminopyrroles were regioselectively subjected to the 1-alkylation with 5-[4'-bromomethyl-1,1'-biphenyl-2-yl]-1-triphenylmethyl-1H-tetrazo le, to the acylation of the amino group at 2-position of the pyrrole ring, and then to the detritylation process to yield the second class of title compounds.

Defects of tyrosine289phenylalanine mutation on binding and functional properties of the human tachykinin NK2 receptor stably expressed in chinese hamster ovary cells.

A point mutation was made at position 289 in the transmembrane segment 7 of the human tachykinin NK2 receptor to yield a tyrosine/phenylalanine (Tyr/Phe) substitution. Chinese hamster ovary cells stably transfected with the wild-type or Tyr289Phe mutant NK2 receptor both bound neurokinin A (NKA) and the synthetic NK2 receptor-selective agonists, GR 64349 and [betaAla8]NKA(4-10), with high and even affinities. Neurokinin B (NKB) and substance P (SP) also displayed sizeable binding affinities, albeit with lower affinity as compared to NKA. In a functional assay (production of inositol-1,4,5-trisphosphate, IP3), NKA, GR 64349, and [betaAla8]INKA(4-10) stimulated IP3 accumulation via the wild-type and mutant receptors with similar potencies. On the other hand, NKB and SP exhibited a dramatic reduction in their agonist efficacies at the mutant receptor, NKB acting as a partial agonist (maximum effect = 50% of the response to NKA) and SP being totally inactive. The results obtained with phenoxybenzamine inactivation experiments indicated that a large and similar receptor reserve existed for both the wild-type and the mutant receptor. SP, which displayed sizeable binding affinity for the mutant receptor but did not stimulate IP3 accumulation, antagonized the agonist effect of NKA. The antagonist action of SP at the mutant NK2 receptor cannot be ascribed to receptor internalization. The Tyr/Phe replacement at position 289 markedly reduced the binding affinity and antagonist potency of the non-peptide ligand, SR 48968, without affecting the binding affinity and antagonist potency of the bicyclic peptide antagonist MEN 11420. The results indicate that the hydroxyl radical function of Tyr289 in transmembrane segment 7 of the human NK2 receptor is, directly or indirectly, involved in stimulus transduction when the NK2 receptor is occupied by NKB or SP, but not when using NKA or NK2 receptor-selective agonists.

Independent coupling of the human tachykinin NK2 receptor to phospholipases C and A2 in transfected Chinese hamster ovary cells.

The human tachykinin NK2 receptor stably expressed in Chinese hamster ovary cells (CHO-hNK2R cells) was characterized by studying the effect of neurokinin A (NKA), the preferred natural ligand, and that of other agonists and antagonists in both binding experiments and functional assays. Competition experiments using [125I]NKA showed that CHO-hNK2R cells express binding sites which have high affinity for NKA (Ki=3.4+/-0.9 nM), GR 64349 (Ki=12+/-3 nM) and [betaAla8]NKA(4-10) (Ki=21+/-8 nM) and for the antagonists MEN 10627 (Ki=0.55+/-0.2 nM), and MEN 11420 (Ki=2.4+/-0.8 nM). In contrast, the tachykinin NK1 and NK3 receptor agonists [Sar9,Met(O2)11]SP and senktide, respectively, were recognized with low affinity (Ki>10 microM). NKA (EC50=68+/-18 nM) induced a rapid and concentration-dependent increase in the intracellular level of inositoltrisphosphate (IP3). The concentration-response curve to GR 64349 (EC50=155+/-14 nM) was close to that of NKA, whereas [betaAla8]NKA(4-10) (EC50=445+/-78 nM) and SP (EC50=3197+/-669 nM) were 7- and 50-fold less potent, respectively. In addition, NKA stimulated the release of arachidonic acid and the production of prostaglandin E2 (PGE2) in a concentration-dependent manner. Also in this assay, NKA was found to be more potent than the other agonists tested (the EC50 values were 3+/-0.3, 9+/-3, 7.8+/-0.9 and 217+/-37 nM for NKA, GR 64349, [betaAla8]NKA(4-10) and SP, respectively). MEN 10627 and MEN 11420 were potent and competitive antagonists in blocking NKA-induced IP3 formation and PGE2 release: MEN 10627 and MEN 11420 displayed comparable potencies in blocking the two functional responses initiated by occupancy of the NK2 receptor by NKA. Pretreatment of the cells with pertussis toxin (500 ng/ml for 18 h) did not significantly modify the basal or stimulated phosphatidylinositol turnover but reduced the basal and NKA-induced PGE2 release by about 35%. The phospholipase C inhibitor U-73122 (10 microM) prevented the NKA-induced formation of IP3 but did not affect PGE2 release. Conversely, the phospholipase A2 inhibitor quinacrine (100 microM) blocked the release of arachidonic acid and PGE2 without affecting the NKA-stimulated formation of IP3. Chelation of extracellular calcium with 3 mM EGTA inhibited the NKA-induced PGE2 release by 81% but was without effect on basal and NKA-stimulated IP3 production. The calcium channel blockers verapamil (10 microM) and omega-conotoxin GVIA (0.1 microM) did not modify the basal PGE2 production and had no significant effect on the response to tachykinins while the blocker of non-selective cation channels, SKF-96365 (10 microM), inhibited the response to NKA by about 74%. SKF-96365 did not affect the basal or the NKA-induced IP3 formation. In conclusion, our data demonstrate that the human tachykinin NK2 receptor expressed in CHO cells displays binding affinity and functional properties which are those of a native NK2 receptor. No pharmacological evidence for heterogeneity of the human NK2 receptor was obtained in this study. Our findings indicate that the human tachykinin NK2 receptor is independently coupled to both PLC and PLA2 signaling pathways. Activation of the PLA2 pathway may be linked to the opening of a voltage-independent cation channel which activates a Ca2+-dependent PLA2.

Characterization of [3H]MEN 11420, a novel glycosylated peptide antagonist radioligand of the tachykinin NK2 receptor.

[3H]MEN 11420, a radiolabeled glycosylated peptide antagonist of the tachykinin NK2 receptor, has been investigated in ligand-receptor binding assays using membranes of CHO cells transfected with the human tachykinin NK2 receptor. [3H]MEN 11420 bound to a single class of high affinity binding sites: its binding was inhibited by natural tachykinins (potency ranking: NKA >> SP > or = NKB), as well as by peptide (MEN 11420 > MEN 10376 >> R 396) and nonpeptide (SR 48968 > GR 159897) selective NK2 receptor antagonists. These data indicate that [3H]MEN 11420 is a potent radioligand for the human tachykinin NK2 receptor that may represent a useful tool for studying ligand-receptor interactions at the molecular level.

Chronic diffuse interstitial fibrosis of the lung in uranium miners.

Many uranium miners have been disabled by and died of pulmonary fibrosis that was not recognized as an occupational disease. A review of animal studies, complications from whole body irradiation, pulmonary function, and mortality studies of uranium miners led us to suspect radiation-induced chronic diffuse interstitial fibrosis in miners who had inhaled excessive radon progeny. A selected group of uranium miners (22) with severe respiratory disease (but no rounded nodules in chest films) were studied. Lung tissue from five disclosed severe diffuse interstitial fibrosis, with "honeycomb lung" in all. Some also had small anthrasilicotic nodules and birefringent crystals. Although quartz crystals probably contributed, we concluded that the predominant injurious agent in these cases was alpha particles from radon progeny. This disease, after a long latent period, usually results in pulmonary hypertension, shortness of breath, and death by cardiopulmonary failure.

Antihistaminic and antiallergic properties of dextro-mequitamium iodide in upper and lower guinea pig airways: comparison with azelastine.

1. The ability of dextro-mequitamium iodide (d-Meq) to antagonize bronchomotor and inflammatory effects mediated by histamine and antigen challenge in the upper or lower guinea pig airways or both and its potential activity against the recruitment and activation of eosinophils in the bronchial wall have been evaluated in comparison with azelastine. 2. In receptor-binding studies, d-Meq displayed a nanomolar affinity for H1 and muscarinic receptors, and it was endowed with potent bronchodilating properties in the nanomolar range toward tonic contractions induced by histamine and carbachol. 3. d-Meq (100-1,000 nmol/guinea pig) and azelastine (100-5,000 nmol/guinea pig) administered by aerosol significantly inhibited histamine- and antigen-induced increases in insufflation pressure in sensitized animals. 4. d-Meq (1,000-6,000 nmol/kg i.v.) dose dependently inhibited the histamine- or antigen-induced increase in vascular permeability in the upper airways. 5. d-Meq was more effective against histamine than antigen challenge, and its potency was similar or greater than that of azelastine. 6. Aerosolized d-Meq (1,000 nmol/animal) reduced antigen-induced eosinophil accumulation in the bronchoalveolar lavage (BAL) fluid from sensitized guinea pigs. 7. Eosinophils recovered from the BAL fluid of antigen-challenged animals showed an increased chemotaxis in response to LTB4 or platelet-activating factor. Both d-Meq and azelastine (300 nmol/animal) reduced this increase without affecting direct chemotaxis induced by leukotriene B4 (LTB4). 8. These findings provide evidence that local administration of d-Meq might be useful in the treatment of allergic disorders, such as rhinitis and asthma.

MEN 11420 (Nepadutant), a novel glycosylated bicyclic peptide tachykinin NK2 receptor antagonist.

1. The pharmacological profile was studied of MEN 11420, or cyclo[[Asn(beta-D-GlcNAc)-Asp-Trp-Phe-Dap-Leu]cyclo(2beta-5beta )], a glycosylated derivative of the potent, selective, conformationally-constrained tachykinin NK2 receptor antagonist MEN 10627 (cyclo(Met-Asp-Trp-Phe-Dap-Leu)cyclo(2beta-5beta)). 2. MEN 11420 competitively bound with high affinity to the human NK2 receptor stably transfected in CHO cells, displacing radiolabelled [125I]-neurokinin A and [3H]-SR 48968 with Ki values of 2.5+/-0.7 nM (n = 6) and 2.6+/-0.4 nM (n = 3), respectively. 3. MEN 11420 showed negligible binding affinity (pIC50 < 6) at 50 different receptors (including tachykinin NK1 and NK3 receptors) and ion channels. 4. In the rabbit isolated pulmonary artery and rat urinary bladder MEN 11420 potently and competitively antagonized tachykinin NK2 receptor-mediated contractions (pK(B) = 8.6+/-0.07, n = 10, and 9.0+/-0.04, n = 12; Schild plot slope = -1.06 (95% c.l. = -1.3; -0.8) and -1.17 (95% c.l. = -1.3; -1.0), respectively). MEN 11420 produced an insurmountable antagonism at NK2 receptors in the hamster trachea and mouse urinary bladder. However, in both preparations, the effect of MEN 11420 was reverted by washout and an apparent pK(B) of 10.2+/-0.14, n = 9, and 9.8+/-0.15, n = 9, was calculated in the hamster trachea and mouse urinary bladder, respectively. 5. MEN 11420 showed low affinity (pK(B) < 6) at guinea-pig and rat tachykinin NK1 (guinea-pig ileum and rat urinary bladder) and NK3 (guinea-pig ileum and rat portal vein) receptors. On the whole, the affinities (potency and selectivity) showed by MEN 11420 for different tachykinin receptors, measured either in binding or in functional bioassays, were similar to those shown by the parent compound, MEN 10627. 6. The in vivo antagonism of the contractions produced by [betaAla8]neurokinin A(4-10) (1 nmol kg(-1)) was observed after intravenous (dose range: 1-10 nmol kg(-1)), intranasal (3-10 nmol kg(-1)), intrarectal (30-100 nmol kg(-1)) and intraduodenal (100-300 nmol kg(-1)) administration of MEN 11420. MEN 11420 was more potent (about 10 fold) and longer lasting than its parent compound MEN 10627, possibly due to a greater metabolic stability. 7. A dose of MEN 11420 (100 nmol kg(-1), i.v.), that produced potent and long lasting inhibition of the contraction of the rat urinary bladder induced by challenge with the NK2 selective receptor agonist [betaAla8]neurokinin A(4-10) (10-300 nmol kg(-1)), was without effect on the responses produced by the NK1 receptor selective agonist [Sar9]substance P sulphone (1-10 nmol kg(-1)). 8. These findings indicate that MEN 11420 is a potent and selective tachykinin NK2 receptor antagonist. The introduction of a sugar moiety did not produce major changes in the affinity profile of this antagonist as compared to MEN 10627, but markedly improved its in vivo potency and duration of action. With these characteristics, MEN 11420 is a suitable candidate for studying the pathophysiological significance of tachykinin NK2 receptors in humans.

Cardiac output and mixed venous oxygen content measurements by a tracer bolus method: theory.

We present a bolus method of inert-gas delivery to the lungs that facilitates application of multiple inert gases and the multiple inert-gas-exchange technique (MIGET) model to noninvasive measurements of cardiac output (CO) and central mixed venous oxygen content Reduction in recirculation error is made possible by 1) replacement of sinusoidal input functions with impulse inputs and 2) replacement of steady-state analyses with transient analyses. Recirculation error reduction increases the inert-gas selection to include common gases without unusually high (and difficult to find) tissue-to-blood partition coefficients for maximizing the systemic filtering efficiency. This paper also presents a practical method for determining the recirculation contributions to inert expired profiles in animals and determining their specific contributions to errors in the calculations of CO and from simulations applied to published ventilation-perfusion ratio (V/Q) profiles. Recirculation errors from common gases were found to be reducible to the order of 5% or less for both CO and whereas simulation studies indicate that measurement bias contributions from recirculation, V/Q mismatch, and the V/Q extraction process can be limited to 15% for subjects with severe V/Q mismatch and high inspired oxygen fraction levels. These studies demonstrate a decreasing influence of V/Q mismatch on parameter extraction bias as the number of inert gases are increased. However, the influence of measurement uncertainty on parameter extraction error limits improvement to six gases.

Tachykinin NK2 receptors: characterization in the rat small intestine by the use of a peptide agonist and a nonpeptide antagonist as radioligands.

The tachykinin NK2 receptors present in membranes of rat small intestine were characterized by means of tachykinin receptor agonists and antagonists, by using the natural agonist, NKA, or the nonpeptide antagonist SR 48968, as radioligands. The affinity of the antagonists was independent of the radioligand used, whereas the NK2 receptor selective agonists showed a different binding profile according to the radioligand. In particular, when using [125I]NKA, NKA and NKA(4-10) bound to a high affinity site, whilst [beta-Ala8]NKA(4-10) and GR 64349 bound to a high and a low affinity site; the high affinity site was still detected in the presence of 100 microM GppNHp which produced a strong inhibition of the specific binding of [125I]NKA. On the other hand, when using [3H]SR 48968, NKA bound to a high affinity site, [beta-Ala8]NKA(4-10) bound to a low affinity site and NKA(4-10) and GR 64349 bound to a high and a low affinity site; in this case, the high affinity site was no longer detected in the presence of 1 microM GppNHp, which did not reduce the specific binding of [3H]SR 48968 to NK2 receptors. We interpreted these data as an indication that in the rat small intestine membranes [125I]NKA labels multiple conformations of G protein-coupled NK2 receptor which are distinguished by the use of selective receptor agonists, but not by peptide or nonpeptide antagonists.

Tachykinin receptors and intestinal motility.

Substance P (SP) and neurokinin A (NKA) are synthesized by enteric cholinergic motorneurons that project to the longitudinal and circular muscle of the mammalian intestine. Thus, acetylcholine, SP, and NKA are the excitatory neuromuscular transmitters in the intestine. Tachykinin NK1 and NK2 receptors are expressed by smooth muscle cells in most regions of the intestine: the corelease of SP and NKA from nerves thus realizes paradigms of tachykininergic cotransmission. Examples have been found in which a cooperative model can be applied to account for the action of SP-NKA acting at NK1 and NK2 receptors (e.g., circular muscle of guinea-pig duodenum), as well as examples in which the message produced by activation of the two receptors diverges sharply in producing responses that have a markedly different time course and use different effector systems (e.g., circular muscle of guinea-pig colon). NK3 receptors are expressed on both excitatory and inhibitory motor neurons: indirect contractions (via release of acetylcholine and tachykinins) and relaxations (via release of nitric oxide) can be evoked in the gut by selective stimulation of NK3 receptors. Although a role of NK3 receptors in certain enteric reflexes has been evidenced, the importance of this system in mediating hexamethonium-resistant enteric transmission appears less important than previously speculated.