Biomedical subjects

A R Leff

Publications and source records attributed to A R Leff.

At least 109 records · Page 6Linked to original sources

PubMed1992

Oxygen metabolism and catecholamine secretion during chloralose anesthesia in lambs.

Anesthetic agents are required when restraining animals in most forms of animal research. In particular, alpha-chloralose is a widely used anesthetic for respiratory and cardiovascular research despite limited controlled studies investigating whether chloralose could represent a variable influencing cardiorespiratory reflexes in acute animal studies. We previously used a chronically-instrumented neonatal lamb model to determine that chloralose had important effects on oxygen delivery and on basal hemodynamics. To investigate the influence of chloralose on oxygen metabolism and catecholamine secretion in relation to these hemodynamic changes, we studied 12 lambs before and after infusion of chloralose (30 mg/kg, i.v.) or control saline vehicle. Chloralose caused no differences in arterial or mixed venous oxygen contents, arterio-venous oxygen difference, or oxygen delivery, consumption, or extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗

PubMed1991

A kinetic assay for eosinophil peroxidase activity in eosinophils and eosinophil conditioned media.

The activity of eosinophil peroxidase (EPO) is commonly employed as a measure of eosinophil activation in biologic fluids. Determination of product formation by this enzyme by end-point measurement may be affected profoundly by substrate concentrations, reaction time and degradation of end-product and enzyme. To determine more accurately EPO concentrations in media conditioned by isolated, purified eosinophils, we have developed a kinetic, colorimetric assay to measure EPO concentration as a function of maximum velocity of reaction (Vmax). An automated method for determining Vmax in a 96-well microplate colorimetric assay was utilized over a wide range of substrate concentrations. Concentrations greater than or equal to 3 x 10(-8) g/ml could be determined reliably with this assay. Peroxidase activity was inhibited in a concentration-dependent manner by the addition of 3-amino-1,2,4-triazole (AMT). The EPO concentration in eosinophils determined by this kinetic method was approximately 1.1 x 10(-5) g/10(6) eosinophils. Eosinophil activation with 10(-6) M f-Met-Leu-Phe (fMLP) caused substantial EPO secretion (9.0 +/- 1.7% vs. 2.9 +/- 0.6% total EPO content for control, P = 0.05) and decrease in eosinophil EPO concentration (92.3 +/- 4.2% of control, P = 0.038). Secretion was enhanced by the addition of 5 micrograms/ml cytochalasin B to 10(-6) M fMLP (25.9 +/- 12.7% total EPO content, P = 0.043 vs. control); similar decreases were noted in eosinophil EPO concentration (71.7 +/- 16.1% of control, P = 0.043). These data demonstrate that determination of EPO secretion by measurement of Vmax is a reliable, accurate method for precise quantification of this enzyme in media containing purified eosinophils or eosinophil products in the absence of other forms of peroxidase activity.

Amitrole↗

PubMed1991

Effect of in vitro preconditioning on tracheal smooth muscle responsiveness.

We evaluated the effect of preconditioning of the isometric contractile response of canine tracheal smooth muscle (TSM) in vitro. Strips of epithelium-free TSM (n = 90) were excised from 16 anesthetized dogs and fixed isometrically in tissue perfusion chambers. Experiments were performed using methods previously reported in which the following parameters were investigated: 1) quiescent equilibration time in the perfusion chamber (0-120 min); 2) effect of repeated exchange of perfusate; 3) method of determining the optimal resting length (Lmax) for presetting of resting tension (RT); 4) effect of precontraction during the equilibration phase on the contractile response to agonists administered subsequently; and 5) method of determining RT on the response to muscarinic stimulation. When other variables were uniform, neither equilibration time nor perfusate exchange affected potency or efficacy of the response generated subsequently to acetylcholine (ACh). However, both potency (range of EC50: -5.71 +/- 0.14 log M to -6.52 +/- 0.24 log M; P less than 0.02) and efficacy (range of maximal active tension: 1,143 +/- 268 g/cm2 to 2,878 +/- 151 g/cm2; P less than 0.001) of ACh were altered substantially as a result of the method used to estimate Lmax. Repeated precontraction by electrical field stimulation or with 127 mM KCl did not alter potency or efficacy of contraction elicited by ACh. Maximal active tension generated with 10(-3) M ACh was 2,878 +/- 151 g/cm2 after 12-15 tetanizing field stimulations and 2,696 +/- 198 g/cm2 after 5-7 contractions with 127 mM KCl (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1991

Inflammation and cell-cell interactions in airway hyperresponsiveness.

Airway hyperresponsiveness results from the conversion of normally reactive airways to a state of augmented responsiveness to constrictor stimuli. Although the mechanism accounting for the induction of airway hyperresponsiveness remains elusive, recent investigations have suggested that inflammation may be a sine qua non for human asthma. Numerous experimental models have demonstrated the necessity of circulating granulocytes as mediators of augmented bronchoconstriction during immune challenge. It is not known how granulocytes are targeted for selective migration to the conducting airways of the lung during hyperresponsive states; however, recent evidence implicates the upregulation of granulocyte adhesion molecules on both the endothelial and epithelial surfaces of the airway. There is evidence that during migration diapedesis, granulocytes interact with epithelial and endothelial cells to produce regionally secreted mediators that upregulate the responsiveness of adjacent airway smooth muscle and/or cause lumenal edema, thus augmenting the effect of constrictor stimuli. Most evidence suggests that the eosinophil is the most important granulocyte in these responses and that eosinophilic infiltration and activation may account for the unique, spasmodic, and cyclic nature of hyperreactive airways. The molecular biology of the eosinophil granule proteins has characterized four distinct substances, each of which exerts potential cytotoxic effects on airway epithelium by different mechanism. In addition, at least one of these proteins, the major basic protein, appears to cause direct, noncytotoxic stimulation of epithelial secretion that upregulates nonspecifically the response of airway smooth muscle to contractile stimuli. The recognition of inflammation as the essential component to airway hyperresponsiveness provides a fresh approach to a difficult problem and suggests a host of novel therapies for human asthma.

Amino Acid Sequence↗

PubMed1991

Effects of PAF on isolated rat airways perfused with blood-free solution.

We examined the mechanism of constriction and muscarinic augmentation of contraction of airway smooth muscle caused by platelet-activating factor (PAF) in airways from 55 Sprague-Dawley rats perfused through the isolated bronchial circulation (BC) and pulmonary circulation (PC) and isometrically in tissue perfusion chambers. Dose-response curves were generated cumulatively by infusing 10(-10) to 10(-7) mol PAF dissolved in Krebs-Henseleit solution buffer containing 4% bovine serum albumin into the BC or PC. The efficacy of PAF in central airways (BC) was approximately twofold greater in increasing lung resistance (RL) than for more peripheral airways perfused by the PC (P less than 0.05). Tachyphylaxis was demonstrated in both BC and PC for preparations in which a second PAF dose-response curve was generated. Bolus injection of 10(-6) mol of the PAF antagonist, CV-6209, plus 10(-7) mol PAF caused 81% reversal of the maximal BC response. The same dose of CV-6209 reversed the response to PAF in the PC by 99.2%. Initial administration of 10(-6) mol CV-6209 with PAF prevented completely contraction elicited by PAF in the BC and PC. Concentration-response studies also were generated isometrically in tissue perfusion chambers from 64 tracheal smooth muscle strips. Maximal contraction elicited by 10(-6) M PAF was blocked completely with 10(-6) M CV-6209. In separate studies, addition of 10(-6) mol CV-6209 to the BC perfusate caused 93% blockade of the RL response to PAF and 100% inhibition when administered in the PC. Prior administration of PAF caused two- to fourfold augmentation of the contractile response to acetylcholine (ACh) within the same preparation; in the presence of CV-6209, the response to ACh was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1991

Effect of maturational changes in myosin content and morphometry on airway smooth muscle contraction.

We studied the relationship of airway morphometry, the content of myosin heavy-chain and isoform stoichiometry, and the distribution of bronchoconstrictor responses in the airways of maturing swine. Lungs were excised in 2-wk-old farm swine (2ws; n = 13) and 10-wk-old swine (10ws; n = 13), and tracheal smooth muscle strips and bronchial rings from generations 2-5 were fixed for in vitro isometric measurement of force generation. Split samples were placed in formaldehyde solution or glutaraldehyde for light- or electron-microscopic morphometry or frozen for analysis of tissue myosin content. The rank order of force generation elicited by both receptor- and nonreceptor-dependent mechanisms for both 2ws and 10ws was generation 4 greater than 3 greater than or equal to 2. For all matched airway generations, contractile force was 25-100% greater in 2ws than 10ws. Differences in force generation were not related to morphometric differences in smooth muscle mass content among airways. The relative cross-sectional area of smooth muscle derived by computerized morphometry was 5.5-7% for each airway generation and did not change with age. Electron-microscopic morphometry demonstrated comparable myocyte content within muscle bundles for all airways in both age groups. In generation 4 airways, myocyte size in 2ws (27.3 +/- 0.8 nuclei/2,500 microns2) hypertrophied approximately 15% in 10ws (20.4 +/- 0.6 nuclei/2,500 microns2; P less than 0.01). Tissue content of myosin measured by computerized laser densitometry of gel electrophoresis of homogenates was greater in trachea from 2ws than 10ws (135 +/- 10 vs. 90 +/- 4 micrograms/g tissue; P less than 0.01); homology of 200- and 205-kDa isoforms was confirmed by Western blot against polyclonal myosin antibody and Cleveland digest analysis of each band. Differences in contractile forces between generations in 2ws and 10ws were not correlated to functional myosin isoform content. We demonstrate a maturational downregulation of contractile forces in maturing swine. This response is independent of smooth muscle receptor distribution and is not related to morphological changes in airways muscle mass, cellularity, changes in content of nonmyocyte tissues, or tissue content of functional myosin isoform.

Aging↗

PubMed1991

Ontogenic expression of acetylcholinesterase activity in trachealis of young swine.

Previous investigations have demonstrated that cholinergic contraction of porcine tracheal smooth muscle (TSM) decreases between the second and tenth weeks of life. In this investigation, we hypothesized that the greater contractile response to acetylcholine (ACh) in TSM of 2-wk-old swine (2ws) vs. 10-wk-old swine (10ws) was the result of a relative decrease in activity of acetylcholinesterase (AChase). To examine this hypothesis, we assessed AChase activity directly in homogenates of TSM from eight 2ws and seven 10ws using a newly adapted method that measures the rate of cleavage of acetylthiocholine; enzyme activity was expressed as absorbance units per minute per milligram protein. The AChase from tissues of both age groups saturated at approximately 3 mM substrate. However, maximal AChase activity (Vmax) was significantly greater in 10ws than 2ws. Eadie-Hofstee analysis of enzyme kinetics revealed similar Michaelis-Menten constants for 2ws and 10ws. The concentration of physostigmine (PS), an inhibitor of cholinesterase, that elicited half-maximal inhibition of AChase activity also was similar for 2ws and 10ws. In separate studies, contraction of TSM strips was assessed in vitro at optimal resting length and expressed as a function of maximal force generation to potassium chloride. Strips of TSM from 2ws contracted with greater force than those of 10ws. After pretreatment with 10(-8) M PS, contractile forces were similar in 2ws and 10ws. We conclude that AChase activity measured directly in muscle homogenates is significantly reduced in TSM of 2ws vs. 10ws and that this may result in augmented contraction to ACh under conditions of zero-order kinetics.

Acetylcholine↗

PubMed1991

Extracellular Ca2+ mobilization in potential-dependent contraction of trachealis of maturing swine.

We studied the effect of maturation on potassium-induced parasympathetic activation and Ca2+ entry in tracheal smooth muscle (TSM) from fifteen 2-wk-old (2ws) and sixteen 10-wk-old (10ws) male domestic farm swine. Atropine (10(-7) M) caused inhibition of the maximal contraction elicited by potassium to 50.3 +/- 2.6% maximum of control response (P less than 0.001) in TSM from 2ws but had no significant effect in TSM from 10ws (94.6 +/- 4.2% maximum; P = NS vs. control). Verapamil (10(-7) M) plus 10(-7) M atropine reduced contraction elicited by potassium in both 2ws (23.7 +/- 5.8% maximum; P less than 0.001 vs. control) and 10ws (50.6 +/- 6.3% maximum; P less than 0.001 vs. control, P less than 0.05 vs. 2ws); 10(-6)M verapamil caused greater than 95% blockade of contraction caused by potassium in both 2ws and 10ws. In separate studies, atropine-treated strips were equilibrated with extracellular Ca2+ concentrations ([Ca2+]o) ranging from normal (1X [Ca2+]o) to four times normal (4x [Ca2+]o). Increasing [Ca2+]o increased maximal contractile response in atropine-treated TSM strips from 68.7 +/- 3.8% maximum for 1x [Ca2+]o to 100.8 +/- 4.8% maximum for 4x [Ca2+]o (P less than 0.001) in 2ws. Neither atropine nor [Ca2+]o affected maximal responses of TSM in 10ws (103.5 +/- 3.0% maximum for 1x [Ca2+]o; P = NS vs. control). However, in the presence of atropine and verapamil, 4x [Ca2+]o augmented KCl-elicited contraction of TSM from both 2ws (46.9 +/- 6.3% maximum; P less than 0.01 vs. control) and 10ws (78.6 +/- 2.3% maximum; P less than 0.005 vs. control).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Sensory neuropeptides and airway function.

Sensory nerves synthesize tachykinins and calcitonin-gene related peptide and package these neuropeptides together in synaptic vesicles. Stimulation of these C-fibers by a range of chemical and physical factors results in afferent neuronal conduction that elicits central parasympathetic reflexes and in antidromic conduction that results in local release of neuropeptides through the axon reflex. In the airways, sensory neuropeptides act on bronchial smooth muscle, the mucosal vasculature, and submucosal glands to promote airflow obstruction, hyperemia, microvascular hyperpermeability, and mucus hypersecretion. In addition, tachykinins potentiate cholinergic neurotransmission. Proinflammatory effects of these peptides also promote the recruitment, adherence, and activation of granulocytes that may further exacerbate neurogenic inflammation (i.e., neuropeptide-induced plasma extravasation and vasodilation). Enzymatic degradation limits the physiological effects of tachykinins but may be impaired by respiratory infection or other factors. Given their sensitivity to noxious compounds and physical stimuli and their potent effects on airway function, it is possible that neuropeptide-containing sensory nerves play an important role in mediating airway responses in human disease. Supporting this view are the striking phenomenological similarities between hyperpnea-induced bronchoconstriction (HIB) in guinea pigs and HIB in patients with exercise-induced asthma. Endogenous tachykinins released from airway sensory nerves mediate HIB in guinea pigs and also cause hyperpnea-induced bronchovascular hyperpermeability in these animals. On the basis of these observations, it is reasonable to speculate that sensory neuropeptides participate in the pathogenesis of hyperpnea-induced airflow obstruction in human asthmatic subjects as well.

Amino Acid Sequence↗

PubMed1991

Effect of maturation on topographic distribution of bronchoconstrictor responses in large diameter airways of young swine.

We studied the effect of maturation on the topographic distribution of airway constriction in Generations 0 (trachea) through 6 in fourteen 2-wk-old swine (2ws) and sixteen 10-wk-old swine (10ws) in vivo and in excised airways from seven 2ws and seven 10ws in vitro. Animals were anesthetized with chloralose-urethane and received beta-adrenergic blockade and vagotomy prior to generation of random-order, dose-response curves with i.v. methacholine (MCh) and histamine (His) or serotonin (5HT) given intravenously. Lung resistance (RL) was measured, and airway diameter was assessed by tantalum bronchograms obtained at functional residual capacity for each dose of agonist. Baseline RL was substantially greater in 2ws (48 to 62 cm H2O/L/s) than in 10ws (9 to 11 cm H2O/L/s; p less than 0.001 for all groups). Intravenous infusion of 10(-6) mol/kg MCh caused a 416 +/- 110% increase in RL in 2 ws and a 314 +/- 32% increase in RL in 10 ws (p = NS); airway diameter (Daw) decreased by 10 +/- 1% (Generation 2) to 27 +/- 4% (Generation 6) in 2ws and from 8 +/- 2 (Generation 2) to 17 +/- 4% in 10ws. Intravenous infusion of 10(-6) mol/kg His caused a 513 +/- 85% increase in RL in 2ws and a 276 +/- 17% increase in RL in 10 ws (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1991

Epithelial modulation of airway smooth muscle response to endothelin-1.

We investigated the role of epithelial modulation of contraction caused by endothelin-1 in airway smooth muscle in guinea pigs in situ. Airway responses were assessed isometrically as tracheal force and simultaneously as change in lung resistance. Intravenous administration of 10(-8) mol/kg endothelin-1 caused a biphasic response in tracheal active tension: initial relaxation (-0.82 +/- 0.22 g/cm after 30 s, p less than 0.05 versus baseline) followed by contraction (1.65 +/- 0.28 g/cm after 7 min, p less than 0.05 versus baseline). Endothelin-1 also elicited immediate bronchoconstriction; lung resistance increased from 0.148 +/- 0.030 to 0.992 +/- 0.274 cm H2O/L/s (p less than 0.005) after 10(-8) mol/kg endothelin-1 given intravenously. Active tension elicited by 10(-8) mol/kg endothelin-1 after removal of the epithelium from the tracheal segment (0.59 +/- 0.16 g/cm) was less than in segments with an intact epithelium (1.65 +/- 0.28 g/cm, p less than 0.01). Both tracheal contraction and bronchoconstriction were attenuated by pretreatment with indomethacin orally, BW 755C intravenously, or substitution of endothelin-C-terminal hexapeptide for endothelin-1. However, the initial tracheal relaxation response was similar after each intervention. These data suggest actions of endothelin-1 that have not been demonstrated previously: (1) endothelin-1 elicits a biphasic response in tracheal smooth muscle (an initial relaxation response elicited by the carboxy-terminal residues and a later contractile response that requires synthesis of a cyclooxygenase mediator) and (2) epithelium adjacent to the airway smooth muscle modulates contraction elicited by endothelin-1.

Animals↗

PubMed1991

Reduced activity of acetylcholinesterase in canine tracheal smooth muscle homogenates after active immune-sensitization.

Previous investigations have suggested that immune-sensitization increases airway smooth muscle responsiveness to cholinomimetic stimulation by reducing the rate of degradation of acetylcholine. To examine the hypothesis that increased cholinomimetic responsiveness of tracheal smooth muscle (TSM) caused by immune-sensitization results from inhibition of acetylcholinesterase (AChase) activity, we developed a method for direct measurement of AChase activity in homogenates of TSM obtained from mongrel dogs actively sensitized in vivo to ragweed pollen extract (n = 7) and sham-sensitized littermate controls (n = 7). For both sensitized and control specimens, saturation of AChase was obtained at approximately 3.12 mM substrate (acetylthiocholine); however, maximal enzyme activity in homogenates of ragweed-sensitized tissues was significantly less (0.862 +/- 0.088 absorbance units/min/mg protein [AU/min/mg]) compared to control homogenates (1.590 +/- 0.129 AU/min/mg; P less than 0.001). Kinetic analysis (Eadie-Hofstee plot) indicated similar Michaelis constants (Km) for AChase from ragweed-sensitized (0.360 +/- 0.063) and control (0.336 +/- 0.062) homogenates (P = NS). The concentration of physostigmine eliciting half-maximal inhibition (Ki) of AChase activity also was similar for tissues from sensitized (-7.92 +/- 0.032 log M) and control animals (-7.86 +/- 0.012 log M; P = NS). Pretreatment with selected mediators of anaphylaxis (10(-4) M histamine, 10(-6) M serotonin, 10(-5) M prostaglandin E2, 10(-6) M prostaglandin F2 alpha, and 10(-7) M leukotriene D4) did not affect AChase activity. Our data demonstrate reduced AChase activity in homogenates of canine TSM after active immune-sensitization in vivo. This corresponds to functional augmentation of cholinomimetic contraction in actively sensitized tissues.

Acetylcholinesterase↗

PubMed1990

Maturation of acetylcholinesterase expression in tracheal smooth muscle contraction.

We examined postganglionic development of acetylcholinesterase (AChase) activity and tracheal smooth muscle (TSM) contraction elicited by cholinomimetic activation and electrical field depolarization in vitro. Epithelium-intact tracheal strips excised from 21 2-wk-old swine (2ws) and 19 10-wk-old swine (10ws) were tethered isometrically at optimal resting length, and responses were expressed as percent of the maximum to 63 mM potassium-chloride (%KCl). Cumulative concentration-response curves to KCl were equivalent for TSM from 2 and 10ws. However, maximal contraction to ACh in 2ws (168 +/- 8.4 %KCl) was greater than for 10ws (142 +/- 2.3 %KCl; P less than 0.02). Stimulus-response curves (field electrodes; AC source) demonstrated greater sensitivity for TSM in 10ws (stimulus causing 50% of the maximal response = 3.32 +/- 0.13 V in 2ws vs. 2.25 +/- 0.12 V in 10ws; P less than 0.001), indicating that the greater cholinomimetic responsiveness of 2ws did not result from augmented presynaptic nerve conduction. The AChase inhibitor, physostigmine, caused 1) greater sensitivity of responses elicited by electrical field stimulation in 2ws (P less than 0.05) but not in 10ws (P = NS), 2) augmentation of maximal responses to exogenous ACh in 10ws (27% increase; P less than 0.01) but not 2ws (2% increase; P = NS), and 3) a greater increase in sensitivity to cholinomimetic activation in 2ws compared with 10ws (P less than 0.02). These data demonstrate increased cholinergic contraction of TSM in 2 vs. 10ws that results at least in part from reduced AChase activity in the trachea of immature animals.

Acetylcholine↗

PubMed1990

Epithelium-dependent contraction of airway smooth muscle caused by eosinophil MBP.

We have identified two distinct functions of the epithelium of guinea pig airways that modulate airway smooth muscle contractility in the presence of the major basic protein (MBP) of human eosinophilic granules: 1) active force generation resulting less than 1 min after epithelial contact with MBP; and 2) sustained, augmented force generation that does not depend on cytotoxic interference with the synthesis of an epithelial-derived inhibitory factor. To evaluate these influences, an in situ preparation of guinea pig trachea was developed that permitted direct, on-line measurement of isometric force generation in the underlying muscle. Direct application of 10(-8) mol/cm2 MBP to the surface of the epithelium elicited force generation that did not require the presence of a contractile agonist. Force generation began less than 1 min after MBP application and reached maximum active tension (AT) of 0.97 +/- 0.38 g/cm at 30 min (P less than 0.05 vs. baseline). Denatured MBP did not elicit active tension. MBP also caused augmented contraction to intravenous acetylcholine (ACh); 30 min after topical application of MBP, AT generated by 3 x 10(-7) mol/kg iv ACh was 0.85 +/- 0.14 vs. 0.55 +/- 0.08 g/cm in control animals (P less than 0.05). Threshold response to ACh (-8.1 +/- 0.3 log mol/kg) also decreased significantly after MBP (-9.1 +/- 0.4 log mol/kg) vs. baseline (P less than 0.01). Removal of the epithelium (confirmed histologically) abolished both direct contraction and augmented force generation to ACh caused by topical application of MBP to the airway muscle. These data suggest actions of MBP that have not been demonstrated previously: 1) activation of epithelial function that causes direct contraction of airway smooth muscle; and 2) independence of the MBP-induced effects from active tone elicited by other agonists. We also demonstrate that augmented contraction that does not depend on MBP blockade of tonic inhibitory secretion from the epithelium.

Acetylcholine↗

PubMed1990

Sympathetic secretory response to hypercapnic acidosis in swine.

We studied the effect of graded acute hypercapnic acidosis (HA) on sympathetic neural activation in 15 juvenile farm swine in vivo. In seven animals with acute HA, plasma norepinephrine (NE) concentration increased progressively from 189 +/- 34 to 483 +/- 80 pg/ml (P less than 0.04) as arterial CO2 partial pressure (PaCO2) increased in steps from 40 to 80 Torr (pH 7.17 +/- 0.01). Plasma epinephrine (EPI) concentration increased from 30 +/- 15 to 125 +/- 66 pg/ml (P = NS) over the same change in PaCO2. At PaCO2 of 110 Torr, plasma NE increased 3.4-fold above maximal basal concentrations; plasma EPI was 1.8-fold greater than basal under the same conditions. With HA, systemic vascular resistance (SVR) decreased from 1,748 +/- 110 to 1,392 +/- 145 dyn.s.cm-5 (P less than 0.0002), cardiac output (CO) increased from 3.4 +/- 0.3 to 4.3 +/- 0.3 l/min (P less than 0.01), and heart rate (HR) increased from 117 +/- 11 to 154 +/- 17 beats/min (P less than 0.03). To demonstrate that catecholamine secretion was related directly to acidosis caused by an increase in PaCO2, HCO3- was infused in eight other swine to buffer extracellular acute HA (pH 7.37 +/- 0.01 at PaCO2 of 80 Torr). Buffering attenuated the increase in plasma NE, which remained within the normal range at PaCO2 of 80 Torr. The decrease in SVR and increases in CO and HR also were also attenuated by HCO3- buffering of HA. We demonstrate the effects of graded acute HA on endogenous secretion of catecholamine and on the associated hemodynamic responses in swine.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗

PubMed1990

Distribution of airway narrowing during hyperpnea-induced bronchoconstriction in guinea pigs.

Increasing minute ventilation of dry gas shifts the principal burden of respiratory heat and water losses from more proximal airway to airways farther into the lung. If these local thermal transfers determine the local stimulus for bronchoconstriction, then increasing minute ventilation of dry gas might also extend the zone of airway narrowing farther into the lung during hyperpnea-induced bronchoconstriction (HIB). We tested this hypothesis by comparing tantalum bronchograms in tracheostomized guinea pigs before and during bronchoconstriction induced by dry gas hyperpnea, intravenous methacholine, and intravenous capsaicin. In eight animals subjected to 5 min of dry gas isocapnic hyperpnea [tidal volume (VT) = 2-5 ml, 150 breaths/min], there was little change in the diameter of the trachea or the main stem bronchi up to 0.75 cm past the main carina (zone 1). In contrast, bronchi from 0.75 to 1.50 cm past the main carina (zone 2) narrowed progressively at all minute ventilations greater than or equal to 300 ml/min (VT = 2 ml). More distal bronchi (1.50-3.10 cm past the main carina; zone 3) did not narrow significantly until minute ventilation was raised to 450 ml/min (VT = 3 ml). The estimated VT during hyperpnea needed to elicit a 50% reduction in airway diameter was significantly higher in zone 3 bronchi [4.3 +/- 0.8 (SD) ml] than in zone 2 bronchi (3.5 +/- 1.1 ml, P less than 0.012).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Endotoxin in vivo impairs endothelium-dependent relaxation of canine arteries in vitro.

We studied the effect of endotoxin administration in vivo on arterial smooth muscle responses in vitro, testing the hypotheses that endotoxin augments adrenergic vasoconstriction and impairs endothelium-dependent vascular relaxation. Ten mongrel dogs were anesthetized and mechanically ventilated. Five received a bolus infusion of Escherichia coli endotoxin (5 mg/kg), and the remainder received a sham infusion. After 4 to 5 h, the anesthetized dogs were rapidly exsanguinated, and femoral, renal, and superior mesenteric arteries were removed. Arterial rings were mounted on force transducers in organ baths; contraction to phenylephrine or potassium-substituted Krebs-Henseleit solution (KCl), and relaxation to nitroprusside or acetylcholine were studied. Smooth muscle contractions to phenylephrine or KCl were similar between sham and endotoxin for each agonist. Also, nitroprusside-elicited relaxation from half-maximal phenylephrine-elicited contraction was similar. However, relaxation elicited by acetylcholine was markedly impaired in vessels from endotoxin-treated dogs. The negative log molar concentration of acetylcholine producing 50% relaxation for femoral arteries was 7.38 +/- 0.11 (endotoxin) versus 8.09 +/- 0.12 (control, p = 0.002), for renal arteries it was 6.71 +/- 0.33 (endotoxin) versus 7.81 +/- 0.18 (control, p = 0.019), and for mesenteric arteries it was 7.27 +/- 0.03 (endotoxin) versus 7.95 +/- 0.15 (control, p = 0.002). These results demonstrate that endotoxin treatment impairs endothelium-dependent relaxation of canine arteries in vitro. The data suggest that vascular changes in endotoxemia are accompanied by alteration in endothelial cell function, perhaps through altered endothelial production of vasodilatory mediators.

Acetylcholine↗

PubMed1990

Effect of cooling on the responsiveness of canine tracheal muscle.

Airway cooling causes bronchoconstriction in many persons who have asthma. To determine the direct effect of cooling on the response of tracheal muscle to parasympathetic and muscarinic stimuli in situ, the temperature of a segment of canine cervical trachea was adjusted to 37 degrees, 30 degrees, or 25 degrees C by superfusing temperature-controlled saline over its epithelial surface. The contractile response of the tracheal muscle to electrical stimulation of the vagus nerves and to intra-arterial acetylcholine was then determined. Cooling the segment to 25 degrees C decreased the contraction induced by parasympathetic stimulation. However, cooling did not alter the contraction induced by intra-arterial acetylcholine. Parallel studies were conducted in vitro using nine excised tracheal muscle strips taken from the same section of trachea in three additional dogs. Cooling the tracheal muscle to 25 degrees C in vitro increased the maximal contraction induced by both electrical field stimulation and by acetylcholine. Thus, cooling in situ does not alter the response of tracheal muscle to muscarinic stimuli and inhibits the response to parasympathetic stimuli. These data indicate that augmentation of the tracheal muscle response elicited by cooling in vitro does not reflect the response in situ. They suggest that a direct effect of cooling on airway smooth muscle response to parasympathetic and muscarinic stimuli does not account for cooling-induced bronchoconstriction in vivo.

Acetylcholine↗