Biomedical subjects

S E Webber

Publications and source records attributed to S E Webber.

At least 37 records · Page 2Linked to original sources

PubMed1997

PAF-induced secretory hyperresponsiveness in the ferret trachea to bradykinin and its pharmacological inhibition.

Both PAF (10 microM) and bradykinin (0.1-10 microM) increased lysozyme (from submucosal gland serous cells (+138 and +45% for PAF, 10 microM, and bradykinin, 1 microM, respectively) and albumin (mainly active epithelial transport; +387 and +108%) outputs into the ferret tracheal lumen in vitro and reduced the negativity of the potential difference (PD: -33 and -17%) across the trachea. Since PAF can cause bronchial smooth muscle hyperresponsiveness, we tested whether these effects were interactive, and if PAF would increase the actions of bradykinin. The bradykinin-induced lysozyme and albumin outputs were more than trebled and the PD change was enhanced by PAF, after the immediate secretory effects of the latter had returned to baseline. The secretory and PD responses to PAF were all prevented by the PAF-antagonist WEB 2086 and by a combination of the free-radical scavengers catalase and SOD, indicating that PAF may act on specific receptors to release free-radicals. Nedocromil sodium inhibited the increase in lysozyme and albumin outputs produced by PAF, but had no effect on the PD response. None of the tracheal responses to bradykinin was modified by WEB 2086, catalase and SOD, or nedocromil sodium. The secretory and PD hyperresponsiveness to bradykinin caused by PAF was prevented by WEB 2086 and by catalase and SOD. Nedocromil sodium greatly inhibited the lysozyme and albumin hyperresponsiveness but had no effect on the PD response. Thus PAF may release more than one type of radical which have differential effects on serous cells and albumin transport compared with PD; nedocromil sodium may act only against the radical causing the secretory effects.

Albumins↗

PubMed1997

Ras oncoprotein inhibitors: the discovery of potent, ras nucleotide exchange inhibitors and the structural determination of a drug-protein complex.

The nucleotide exchange process is one of the key activation steps regulating the ras protein. This report describes the development of potent, non-nucleotide, small organic inhibitors of the ras nucleotide exchange process. These inhibitors bind to the ras protein in a previously unidentified binding pocket, without displacing bound nucleotide. This report also describes the development and use of mass spectrometry, NMR spectroscopy and molecular modeling techniques to elucidate the structure of a drug-protein complex, and aid in designing new ras inhibitor targets.

Crystallography, X-Ray↗

PubMed1996

Design, synthesis, and evaluation of nonpeptidic inhibitors of human rhinovirus 3C protease.

The design, synthesis, and biological evaluation of reversible, nonpeptidic inhibitors of human rhinovirus (HRV) 3C protease (3CP) are reported. A novel series of 2,3-dioxindoles (isatins) were designed that utilized a combination of protein structure-based drug design, molecular modeling, and structure-activity relationship (SAR). The C-2 carbonyl of isatin was envisioned to react in the active site of HRV 3CP with the cysteine responsible for catalytic proteolysis, thus forming a stabilized transition state mimic. Molecular-modeling experiments using the apo crystal structure of human rhinovirus-serotype 14 (HRV-14) 3CP and a peptide substrate model allowed us to design recognition features into the P1 and P2 subsites, respectively, from the 5- and 1-positions of isatin. Attempts to optimize recognition properties in the P1 subsite using SAR at the 5-position were performed. In addition, a series of ab initio calculations were carried out on several 5-substituted isatins to investigate the stability of sulfide adducts at C-3. The inhibitors were prepared by general synthetic methods, starting with commercially available 5-substituted isatins in nearly every case. All compounds were tested for inhibition of purified HRV-14 3CP. Compounds 8, 14, and 19 were found to have excellent selectivity for HRV-14 3CP compared to other proteolytic enzymes, including chymotrypsin and cathepsin B. Selected compounds were assayed for antiviral activity against HRV-14-infected HI-HeLa cells. A 2.8 A cocrystal structure of derivative 19 covalently bound to human rhinovirus-serotype 2 (HRV-2) 3CP was solved and revealed that the isatin was situated in essentially the same conformation as modeled.

3C Viral Proteases↗

PubMed1996

Structure-based design of lipophilic quinazoline inhibitors of thymidylate synthase.

To develop novel lipophilic thymidylate synthase (TS) inhibitors, the X-ray structure of Escherichia coli TS in ternary complex with FdUMP and the inhibitor 10-propargyl-5,8-dideazafolic acid (CB3717) was used as a basis for structure-based design. A total of 31 novel lipophilic TS inhibitors, lacking a glutamate residue, were synthesized; 26 of them had in common a N-((3,4-dihydro-2-methyl-6-quinazolinyl)methyl)-N-prop-2-ynylaniline+ ++ structure in which the aniline was appropriately substituted with simple lipophilic substituents either in position 3 or 4, or in both. Compounds were tested for their inhibition of E. coli TS and human TS and also for their inhibition of the growth in tissue culture of a murine leukemia, a human leukemia, and a thymidine kinase-deficient human adenocarcinoma. The crystal structures of five inhibitors complexed with E. coli TS were determined. Five main conclusions are drawn from this study. (i) A 3-substituent such as CF(3), iodo, or ethynyl enhances binding by up to 1 order of magnitude and in the case of CF(3) was proven to fill a nearby pocket in the enzyme. (ii) A simple strongly electron-withdrawing substituent such as NO(2) or CF(3)SO(2) in the 4-position enhances binding by 2 orders of magnitude; it is hypothesized that the transannular dipole so induced interacts favorably with the protein. (iii) Attempts to combine the enhancements of i and ii in the same molecule were generally unsuccessful (iv) A 4-C(6)H(5)SO(2) substituent provided both electron withdrawal and a van der Waal's interaction of the phenyl group with a hydrophobic surface at the mouth of the active site. The inhibition (K(is) = 12 nM) of human TS by this compound, 7n, showed that C(6)H(5)SO(2) provided virtually as much binding affinity as the CO-glutamate which it had replaced. (v) The series of compounds were poorly water soluble, and also the potent TS inhibition shown by several of them did not translate into good cytotoxicity. Compounds with large cyclic groups linked to position 4 by an SO or SO(2) group did, however, have IC(50)'s in the range 1-5 microM. Of these, 4-(N-((3,4-dihydro-2-methyl-6-quinazolinyl)methyl)-N-prop-2-ynylamino )phenyl phenyl sulfone, 7n, had IC(50)'s of about 1 microM and was chosen for further elaboration.

Adenocarcinoma↗

PubMed1994

Anti-inflammatory and bronchodilator properties of RP 73401, a novel and selective phosphodiesterase type IV inhibitor.

1. We have investigated the effects of RP 73401, a novel, potent and highly selective cyclic nucleotide phosphodiesterase (PDE) type IV inhibitor, in guinea-pig and rat models of bronchoconstriction and allergic inflammation. In some models, the effects of RP 73401 have been compared with those of the standard PDE type IV inhibitor, rolipram. 2. RP 73401 (0.4-400 micrograms kg-1, intratracheally (i.t.) on lactose) inhibited antigen-induced bronchospasm in previously sensitized conscious guinea-pigs (ID50: 7 +/- 1 micrograms kg-1) and in anaesthetized rats (ID50: 100 +/- 25 micrograms kg-1). Rolipram inhibited the antigen-induced bronchospasm in guinea-pigs with an ID50 of 5 +/- 1 micrograms kg-1. In guinea-pig bronchoalveolar lavage (BAL) fluid, total inflammatory cell and eosinophil numbers were reduced by RP 73401 (ID50s: 3.9 +/- 0.8 micrograms kg-1 and 3.2 +/- 0.7 micrograms kg-1, respectively). In the rat, inflammatory cell numbers are less affected. Only the highest dose of RP 73401 (400 micrograms kg-1) significantly inhibited eosinophil influx (41 +/- 16% inhibition). 3. RP 73401 (0.02-100 micrograms kg-1, i.v.) inhibited PAF-induced bronchial hyperreactivity to bombesin in the anaesthetized guinea-pig (ID50: 0.09 +/- 0.03 micrograms kg-1) and inhibited (0.4-40 micrograms kg-1, i.t.) histamine-induced airway microvascular leakage in the anaesthetized guinea-pig by approximately 60% at all doses. 4. RP 73401 relaxed guinea-pig isolated trachea under basal tone (EC50: 9 nM) and when precontracted with histamine (IC50: 2 nM), methacholine (IC50: 29 nM) or leukotriene D4 (LTD4, IC50: 4 nM). 5. RP 73401 (0.4-100 microg kg-1, i.t.) inhibited bronchospasm induced by histamine (ID.%: 34 +/- 6 microg kg-1), methacholine (ID50: 66 +/- 12 pg kg-1) and LTD4 (ID50: <4 microg kg-1) in the anaesthetized guinea pig.Against these same bronchoconstrictors, rolipram (i.t.) had ID5o values of 44 +/- 4, 72 +/- 18 and<4 pg kg- respectively. RP 73401 (4 and 40 pg kg-, i.t.) increased the magnitude and duration of bronchodilatation produced by salbutamol in the anaesthetized guinea-pig. At doses producing significant bronchodilatation, RP 73401 was without effect on heart rate or blood pressure in the anaesthetized guinea-pig. RP 73401 (0.01 -0.25 mg kg-1, i.v.) did not affect heart rate and produced only a small fall in blood pressure in the anaesthetized rat.6. These data demonstrate that RP 73401 and rolipram inhibit antigen- and mediator-induced bronchospasmin guinea-pigs with the same potency. Furthermore, RP 73401 administered directly into the airways, protects against allergic airway inflammation. These results indicate the importance of PDE IV in regulating smooth muscle and inflammatory cell activity. At doses suppressing the inflammatory response in the lung, RP 73401 had little effect in the cardiovascular system. RP 73401 may have a role as a bronchodilator and, more importantly, as a prophylactic anti-inflammatory agent in the treatment of asthma.

Albuterol↗

PubMed1994

Permeability of ferret trachea in vitro to 99mTc-DTPA and [14C]antipyrine.

Platelet-activating factor (PAF) and vasoactive drugs were tested on permeability of ferret trachea in vitro by measuring fluxes of 99mTc-diethylenetriamine pentaacetic acid (99mTc-DTPA; hydrophilic) and [14C]antipyrine ([14C]AP; lipophilic) across the tracheal wall. Tracheae were bathed on both sides with Krebs-Henseleit buffer, with luminal buffer containing either 99mTc-DTPA or [14C]AP. Luminal and abluminal radioactivities, potential difference, and tracheal smooth muscle tone were measured. Baseline 99mTc-DTPA and [14C]AP permeability coefficients were -4.7 +/- 0.6 (SE) x 10(-7) and -2.2 +/- 0.1 x 10(-5) cm/s, respectively. PAF (10 microM) increased permeability to 99mTc-DTPA to -35.3 +/- 7.6 x 10(-7) cm/s (P < 0.05), but permeability to [14C]AP did not change, suggesting that paracellular but not transcellular transport was affected. Abluminal and luminal applications of methacholine (MCh, 20 microM), phenylephrine (PE, 100 microM), and albuterol (Alb, 100 microM) caused no change in permeability to 99mTc-DTPA before or after exposure to luminal PAF, but abluminal histamine (Hist, 10 microM) significantly increased permeability. Abluminal Hist decreased permeability to [14C]AP before and after exposure to PAF. MCh, PE, and Hist increased smooth muscle tone; Alb and PAF had no effect. Thus, only PAF and Hist altered permeability to 99mTc-DTPA, and MCh, PE, and Hist changed smooth muscle tone. Tracheal permeability changes were greater for the hydrophilic than for the lipophilic agent.

Animals↗

PubMed1994

Proinflammatory potential of the airway epithelium in bronchial asthma.

Histopathological studies of asthmatic airways removed postmortem or by bronchial biopsy show marked inflammatory changes, notably epithelial cell disruption and damage, and the presence of large numbers of eosinophils. The epithelial damage is seen in mild, asymptomatic asthmatics as well as in patients who have died in status asthmaticus. Damage to the epithelium may also correlate with bronchial hyperreactivity. The epithelium has been suggested to be a target for inflammatory cell mediators and cytokines. Recently, the airway epithelium has itself been shown to produce and release several proinflammatory mediators and cytokines, and to express adhesion molecules for inflammatory cells. The epithelium, thus, may actively participate in the inflammatory changes in asthma, where it may be a source as well as a target. Drug therapy aimed at preventing inflammatory changes in the epithelium, such as cytokine and adhesion molecule expression, may be an important step forward in halting disease progression in asthma.

Animals↗

PubMed1993

Design of thymidylate synthase inhibitors using protein crystal structures: the synthesis and biological evaluation of a novel class of 5-substituted quinazolinones.

The design, synthesis, and biological evaluation of a new class of inhibitors of thymidylate synthase (TS) is described. The molecular design was carried out by a repetitive crystallographic analysis of protein-ligand structures. At the onset of this project, we focused on the folate cofactor binding site of a high-resolution ternary crystal complex of Escherichia coli TS, 5'-fluorodeoxyuridylate (5-FdUMP) and a classical glutamate-containing folic acid analog. A preliminary ternary crystal structure of a novel compound was successfully solved. Upon analysis of this initial complex, further structural elaborations were made, and a series of active 5-(arylthio)quinazolinones was developed. The synthetic strategy was based on the displacement of a halogen at the 5-position of a quinazolinone by various aryl thioanions. The compounds were tested for inhibition of purified E. coli and/or human TS, and were assayed for cytotoxicity against three tumor cell lines in vitro. Significant thymidine protection effects were observed with several of the inhibitors, indicating that TS was the intracellular locus of activity.

Crystallography↗

PubMed1993

The effects of indomethacin and thiorphan on bradykinin-induced albumin output and submucosal gland secretion in the ferret trachea in vivo.

In the ferret liquid-filled trachea in vivo, intraluminal bradykinin (BK, 3-300 microM) produced concentration-dependent increases in the output of lysozyme from submucosal gland serous cells and albumin movement into the lumen. Baseline outputs of albumin and lysozyme were not altered significantly by intraluminal indomethacin (10 microM) or thiorphan (10 microM). However, intraluminal indomethacin completely blocked the BK-induced increase in albumin output. Intraluminal thiorphan (10 microM) did not significantly potentiate BK-induced albumin output, although mean output was higher. Neither indomethacin nor thiorphan significantly altered BK-induced lysozyme output, although mean output was reduced in the presence of indomethacin. Thus BK increases albumin output and may increase lysozyme output via the action of cyclooxygenase products. Inhibition of neutral endopeptidase activity may enhance the action of BK on albumin output.

Albumins↗

PubMed1993

Distribution of blood flow in the perfused tracheae of sheep: a search for arteriovenous anastomoses.

The possible existence of arteriovenous anastomoses (AVAs) in the tracheobronchial circulation has been largely ignored; however, their presence would have many implications. Here we have searched for AVAs in the tracheal circulation of seven anesthetized sheep that were ventilated through a low cervical tracheostomy. Arteries to the midcervical trachea were isolated and perfused in situ at systemic blood pressure; blood flow was measured with an electromagnetic flow probe. A vein draining the perfused segment was cannulated. Radiolabeled microspheres (16 microns diam) injected into the arterial inflow of the perfusion indicated the distribution of blood flow (cervical trachea, 69.9 +/- 4.55% (SE); esophagus, 15.1 +/- 3.9%; connective tissue and blood vessels near trachea, 9.5 +/- 1.8%; lymph nodes, 4.0 +/- 2.2%; skeletal muscle, 0.17 +/- 0.07%; trachea below intubation, 0.00%; larynx, 0.00%; other tissues 0.81 +/- 0.32%). Less than 0.6% of the activity was detected in the tracheal venous blood and lungs, indicating little shunting via AVAs. Within the trachea, blood flow (per wet weight of tissue) to the mucosa overlying smooth muscle was approximately 25% of that to the mucosa overlying cartilage. Intra-arterial infusion of methacholine doubled perfusion blood flow without altering the proportion of shunted blood. Within the trachea, blood flow increased most to the mucosa overlying smooth muscle and to smooth muscle. In conclusion the contribution of AVAs to total blood flow in the cervical trachea is < 1%.

Animals↗

PubMed1993

Osmolality affects ion and water fluxes and secretion in the ferret trachea.

Nonisosmolar solutions were placed in the lumen of the ferret trachea in vitro in an organ bath. Hyposmolar (150 mmol/kg) solutions progressively increased in osmolarity over 1 h. Increases in luminal concentration of impermeant blue dextran occurred only after 5 min, suggesting that the initial changes were due to ion rather than water fluxes. With hyperosmolar solutions the osmolarity decreased over 1 h with no change in blue dextran concentration, indicating that ion but not water fluxes were taking place. Cooling the preparation to 4 degrees C greatly reduced the osmolaity changes with hyperosmolar solutions and halved those with hyposmolar solutions, suggesting that active ion transport was involved. Hyposmolar (75-150 mmol/kg) and hyperosmolar (450-900 mmol/kg) solutions both increased albumin output into the lumen, but the response was prevented by cooling the trachea to 4 degrees C. Hyposmolar and hyperosmolar solutions both increased the output of lysozyme from glandular serous cells into the lumen. The response to hyposmolar solutions was stronger. Cooling the trachea abolished the lysozyme response to hyperosmolar solutions. Thus hypo- and hyperosmolar solutions promote ion transport in directions to restore isosmolarity. Both nonisosmolar solutions promote albumin movement by active transport across the mucosa and lysozyme secretion from submucosal glands, responses inhibited by tracheal cooling and therefore dependent on metabolically active processes.

Albumins↗

PubMed1993

Reflex control of the tracheal vasculature of sheep.

Arteries to the cervical trachea were perfused at constant flow in anesthetized sheep. Perfusion pressures (PP), blood pressure (BP), and changes in tracheal smooth muscle tone (Ptr) were measured. Stimulation of pulmonary C-fiber receptors decreased PP (-6.5%) and BP (-16.8%) and increased Ptr (+61.5%), changes prevented by vagotomy and therefore reflex. Stimulation of cardiac receptors and slowly adapting pulmonary stretch receptors decreased PP (-7.9%) and BP (-21.0) and increased Ptr (+19.0%), changes reversed by vagotomy and therefore reflex. Stimulation and inhibition of slowly adapting pulmonary stretch receptors had no vagal-dependent effect on PP and BP, but inflation decreased (-20.3%) and deflation increased Ptr (+35.2%), effects abolished by vagotomy and therefore reflex. Systemic hypoxia increased PP and BP before and after vagotomy (+12.2 and +40.3%), effects greatly reduced by cutting the carotid body nerves; it increased Ptr (+29.8%), an effect abolished by vagotomy and cutting the carotid body nerves. Systemic hypercapnia increased PP (+16.9%), BP (+20.5%), and Ptr (+36.2%), the first two responses being unaffected by vagotomy and the last almost abolished. Stimulation of carotid body chemoreceptors by KCN increased PP (+22.5%), BP (+104.7%), and Ptr (+8.5%), all responses prevented by cutting the carotid body nerves. Responses to intravenous injections of KCN were similar.

Animals↗

PubMed1992

The effects of intraluminal and extraluminal drug application on secretion and smooth muscle tone in the ferret liquid-filled trachea in vitro.

With the ferret liquid-filled trachea in vitro, intraluminal methacholine (MCh), phenylephrine (PE) and histamine (Hist) increased smooth muscle tone and salbutamol (Salb) decreased tone. Lysozyme output was increased by intraluminal MCh and PE. Albumin transport into the lumen was not altered by intraluminal Hist, Salb or PE. The concentration-response curves for smooth muscle contraction and for lysozyme output to extraluminal MCh lay to the left of those for intraluminal MCh. Indomethacin shifted the smooth-muscle response curves to MCh significantly to the left but did not significantly alter lysozyme output. Extraluminal MCh produced a concentration-dependent increase in albumin output whilst intraluminal MCh did so in one of three studies. Albumin output in response to MCh was not significantly altered by indomethacin. Thus, MCh has a less potent effect on smooth muscle and lysozyme secretion and, to a lesser extent, on epithelial albumin transport when given intraluminally. This may be because the epithelium restricts diffusion of the drug or due to the production of a non-prostanoid factor which inhibits smooth muscle responsiveness. Smooth muscle responsiveness is enhanced by blocking cyclooxygenase activity, suggesting MCh-induced release of a prostanoid with relaxant activity.

Animals↗

PubMed1992

An in vivo preparation for measurement of plasma protein and lysozyme output in the ferret tracheal lumen.

An in-vivo ferret tracheal preparation has been developed to study the appearance in the liquid-filled trachea of fluorescein-labelled plasma proteins (FLP) and of lysozyme from submucosal gland serous cells. In order to investigate the influence of nervous activity on the appearance of FLP and lysozyme in the tracheal lumen, the effects of intraluminal bradykinin (an inflammatory mediator and sensory nerve stimulant), intraluminal capsaicin (a stimulant of C-fibres) and electrical stimulation of the cut peripheral end of the right cervical vagus nerve have been measured. Vagal stimulation (10 V, 10 Hz, 1 ms, 90-120 s) increased the secretory rate of lysozyme. It had no effect on FLP rate of output. Intraluminal bradykinin (100 microM) produced a small but significant increase in FLP output but had no effect on lysozyme secretion. Intraluminal capsaicin (33 microM) had no effect on FLP output and had variable effects on lysozyme output. Tracheal pressure was increased by vagal stimulation but was unaffected by bradykinin and capsaicin. Thus, bradykinin increases plasma protein output, probably by an action on the epithelium, whilst vagal stimulation and capsaicin stimulate submucosal glands. This method could be used to determine the factors which alter the rate of movement of plasma proteins into the airway lumen and the secretion of submucosal glands in vivo.

Animals↗

PubMed1992

Evidence for an atypical, or beta 3-adrenoceptor in ferret tracheal epithelium.

1. A preparation of the ferret trachea in vitro was used to examine the effects of three selective beta-adrenoceptor agonists on lysozyme secretion from submucosal gland serous cells and epithelial albumin transport into tracheal mucus following sustained, submaximal stimulation of mucus production with methacholine (20 microM). 2. Prenalterol, salbutamol and BRL 37344 all enhanced methacholine-induced albumin output. BRL 37344 was 10,000 times more potent than salbutamol, and salbutamol was slightly more potent than prenalterol. The concentrations required to increase albumin output by 100% (EC100%) were 1.4 nM, 0.7 mM and approximately 1.0 mM for BRL 37344, salbutamol and prenalterol, respectively. All three agonists inhibited methacholine-induced lysozyme output, with salbutamol being 60 times more potent than BRL 37344, and BRL 37344 being approximately 100 times more potent than prenalterol. 3. The selective beta 2-adrenoceptor antagonist, ICI 118551, inhibited the increase in albumin output produced by BRL 37344, but much more potent at inhibiting the response to salbutamol; the pA2 for ICI 118551 was 5.55 and 7.18 (P less than 0.001) when the agonist was BRL 37344 and salbutamol, respectively. ICI 118551 also attenuated the inhibition of lysozyme output produced by the two agonists, but was 10-30 times more potent at inhibiting this response than the albumin response to BRL 37344 and salbutamol. 4. The greater potency (4-5 orders of magnitude) of BRL 37344, compared to the beta 1- (prenalterol) and beta 2- (salbutamol) adrenoceptor selective agonists, in stimulating methacholine-induced albumin transport suggests that tracheal epithelium possess an atypical, or beta 3-adrenoceptor similar to that previously reported for adipocytes and gastrointestinal smooth muscle. The weak antagonism of the response to BRL 37344 by ICI 118551 would also be consistent with an atypical adrenoceptor mediating the albumin transport response. Inhibition of methacholine-induced serous cell lysozyme output would appear to be mediated predominantly by beta2-adrenoceptors.5. In view of the possible beneficial protective effects of albumin in airway surface liquid, selective beta3-agonists like BRL 37344 might have potential value in the prevention and/or treatment of inflammatory airway disease.

Adrenergic beta-Agonists↗

PubMed1992

Platelet-activating factor relaxes ferret tracheal smooth muscle and reduces transepithelial potential difference in vitro.

1. The effects of platelet activating factor (PAF) were examined on the smooth muscle tone, mucus volume, lysozyme and albumin outputs and potential difference (PD) across the ferret tracheal wall. 2. PAF (0.1-10 microM) had no direct effect on mucus volume, lysozyme or albumin output from the ferret trachea. PAF produced concentration-dependent relaxations of the tracheal smooth muscle and reductions in PD across the tracheal wall. There was no change in the histological appearance of the trachea after exposure to PAF. 3. The PAF-induced smooth muscle relaxation was not affected by FPL55712, a combination of mepyramine and cimetidine, or by a combination of the oxygen free-radical scavengers catalase and superoxide dismutase (SOD); but was abolished by indomethacin or the PAF-receptor antagonist WEB2086. 4. The PAF-induced reduction in PD was not affected by indomethacin, FPL55712 or mepyramine and cimetidine, but was prevented by catalase and SOD, and by WEB2086. 5. We conclude that PAF relaxes ferret tracheal smooth muscle in vitro by receptor-mediated release of a bronchodilator prostaglandin, possibly PGE2. PAF also reduces PD across the trachea suggesting changes in epithelial function; however, there is no histological epithelial damage after PAF. The reduction in PD with PAF is probably produced by receptor-mediated release of oxygen free-radicals. The cellular source of these free-radicals and of the dilator prostaglandin is unclear.

Animals↗

PubMed1992

PAF-induced muscarinic cholinoceptor hyperresponsiveness of ferret tracheal smooth muscle and gland secretion in vitro.

1. The effects of exposure of the ferret trachea in vitro to platelet activating factor (PAF) were examined on methacholine-induced smooth muscle contraction, mucus volume and lysozyme outputs, and albumin transport across the tracheal epithelium. 2. Methacholine (0.1-30 microM) produced concentration-dependent increases in tracheal smooth muscle tone and mucus volume, lysozyme and albumin outputs from the trachea. 3. The concentration-response curves for methacholine-induced smooth muscle contraction, mucus volume and lysozyme outputs were all shifted upwards after exposure of the trachea to PAF (1 microM) with a significant increase in maximum response for each variable. The EC50 values for methacholine-induced smooth muscle contraction and mucus volume output were significantly reduced after PAF exposure suggesting an increase in the potency of methacholine. The concentration-response curve for methacholine-induced albumin output was shifted downwards after PAF exposure with a greatly reduced maximum but no change in the EC50 for methacholine. 4. PAF-induced hyperresponsiveness of methacholine-induced smooth muscle contraction, mucus volume and lysozyme outputs was not affected by indomethacin, FPL55712, or mepyramine and cimetidine, but was prevented by catalase and superoxide dismutase (SOD), and by WEB2086. Similarly, PAF-induced inhibition of methacholine-stimulated albumin output was prevented by catalase and SOD, and by WEB2086. 5. We conclude that PAF induces hyperresponsiveness of ferret tracheal smooth muscle and submucosal gland secretion (including lysozyme secretion from serous cells) to methacholine. This hyperresponsiveness is probably produced by receptor-mediated release of oxygen free-radicals. The inhibition of methacholine-induced albumin flux suggests a loss of epithelial function which is also probably mediated by release of free-radicals. The mechanism by which the free-radicals produce the changes in responsiveness to methacholine, and the cellular source of the free-radicals, remain to be established.

Albumins↗

PubMed1992

Tracheal blood flow and luminal clearance of 99mTc-DTPA in sheep.

Tracheal blood flow and 99mTc-labeled diethylenetriamine pentaacetic acid (DTPA) clearance were measured in the sheep trachea in vivo. The tracheal arteries were isolated and perfused. An isolated segment of tracheal lumen was filled with Krebs-Henseleit solution containing 99mTc-DTPA, and radioactivity was measured in blood from a catheterized tracheal vein. Infusions at constant pressure of methacholine (n = 5), albuterol (n = 6), and histamine (n = 5) increased arterial inflow [+250 +/- 73.0, +74.2 +/- 22.9, +68.9 +/- 39.2% (SE), respectively] and venous outflow (+49.5 +/- 13.8, +11.6 +/- 4.5, +6.2 +/- 13.9%) but decreased 99mTc-DTPA output (-36.8 +/- 8.4, -20.4 +/- 6.2, -58.1 +/- 11.7%) and concentration (-53.9 +/- 10.1, -27.3 +/- 7.5, -49.3 +/- 14.4%). Phenylephrine (n = 9) decreased arterial inflow (-49.4 +/- 10.0%) and venous outflow (-4.1 +/- 5.9%) but increased 99mTc-DTPA output (+74.6 +/- 44.2%) and concentration (+94.4 +/- 56.6%). When the tracheal arteries were initially perfused at constant flow and the flow rate was then changed, 50% increases in flow (n = 5) increased perfusion pressure (+35.9 +/- 2.2%) and venous outflow (+10.5 +/- 3.8%) but decreased 99mTc-DTPA output (-24.4 +/- 7.8%) and concentration (-30.4 +/- 8.8%). Decreases in flow of 50% (n = 3) and 100% (n = 10) decreased perfusion pressure (-34.2 +/- 4.2, -80.1 +/- 3.5%, respectively) and venous outflow (-11.0 +/- 4.8, -29.7 +/- 7.2%) but increased 99mTc-DTPA output (+45.9 +/- 27.5, +167.4 +/- 70.4%) and concentration (+64.7 +/- 26.7, +305.7 +/- 110.2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Albuterol↗