Heterogeneity of allergic airway responses in sheep: differences in signal transduction?

In preliminary studies we have observed that inhaled heparin blocks antigen-induced airway responses in sheep that develop only acute responses to inhaled antigen (acute responders), but not in sheep that develop both acute and later responses (dual responders). Because heparin is an antagonist of inositol triphosphate (IP3) (one of the pathways involved in stimulus-secretion-coupling in mast cells), the differential effect of inhaled heparin in acute responders and dual responders might indicate the involvement of different signaling pathways during IgE-mediated mast cell reactions. Therefore, in this study we compared the effects of heparin on antigen-induced bronchconstriction, allergic cutaneous reaction, and histamine release into bronchoalveolar lavage fluid (BAL) in sheep that develop only acute responses or dual responses to inhaled Ascaris suum antigen. Specific lung resistance (SRL) was measured in 21 sheep (eight acute responders; 13 dual responders) before and after inhalation challenge with antigen, without and after pretreatment with inhaled heparin (1,000 units/kg). Histamine in BAL was measured by RIA before and after segmental antigen challenge, without and after pretreatment with inhaled heparin (eight acute responders; eight dual responders). In acute responders, mean +/- SE SRL increased by 197 +/- 21% with antigen; this was prevented by inhaled heparin (deltaSRL = 15 +/- 7%; p < 0.05). In dual responders, inhaled heparin had no effect on antigen-induced early (deltaSRL = 328 +/- 51% versus 305 +/- 76%) or late (deltaSRL = 201 +/- 33% versus 163 +/- 15%) responses. After segmental antigen challenge, BAL mean +/- SE histamine increased from 2.09 +/- 0.8 nM to 75.4 +/- 21.1 nM in acute responders and 1.58 +/- 0.7 nM to 66.8 +/- 27.3 nM in dual responders (p < 0.01). Inhaled heparin inhibited the increase in BAL histamine by 81% in acute responders (p < 0.05) and by only 19% in dual responders (p = NS). As was seen in the airways, heparin attenuated the allergic cutaneous reaction in acute responders by 46% (p < 0.05), but it was ineffective in dual responders. In contrast, H-7, a nonspecific protein kinase C inhibitor, attenuated the cutaneous reaction in dual responders by 28% (p < 0.05), but it was ineffective in acute responders. These data suggest that heterogeneity of allergic airway response is related to difference in mast cell signal transduction; IP3 is the predominant second messenger in acute responders, whereas non-IP3 pathways may be involved in dual responders.

[The dynamics of urban change: a comparative statistical analysis]. / Dynamique de la transformation des villes: analyse statistique comparative.

PIP: A general review of global historical trends in urbanization is presented, focusing on three basic questions: what stops urban population growth, what is the relationship between economic activity and urban population size, and what factors govern the distribution of urban populations in a given geographical region.^ieng

Inhibition of antigen-induced airway and cutaneous responses by heparin: a pharmacodynamic study.

We have previously shown that heparin attenuates the acute bronchoconstrictor response and immediate cutaneous reaction (ICR) to antigen in allergic sheep. In the present investigation, we studied the pharmacodynamics of the antiallergic action of heparin. Specific lung resistance (sRL) was measured in eight sheep, allergic to Ascaris suum antigen, before and 5 min after inhalation challenge with the antigen. On different experiment days, antigen challenge was repeated after pretreatment with 1) aerosol heparin (1,000 U/kg) administered < or = 20 min, 6 h, 12 h, and 24 h and 2) intravenous heparin (1,000 U/kg) administered < or = 20 min, 1 h, 6 h, and 12 h before antigen challenge. sRL increased by 374 +/- 116% (SE) above baseline with antigen alone. Both aerosol and intravenous heparin attenuated the antigen effects on sRL in a time-dependent fashion. Prolonging the lag time between pretreatment and antigen challenge decreased the inhibitory effect of aerosol heparin; delta sRL was 31 +/- 29, 99 +/- 38, 142 +/- 40, and 306 +/- 60% for < or = 20-min, 6-h, 12-h, and 24-h pretreatment protocols, respectively. In contrast, prolonging the lag time increased the inhibitory effect of intravenous heparin: delta sRL was 246 +/- 64, 66 +/- 26, and 76 +/- 32% for < or = 20 min, 1 h, and 6 h, respectively. In seven additional sheep pretreatment with intravenous heparin (1,000 U/kg) attenuated the ICR also in a time-dependent manner; the inhibitory effect of heparin on ICR to antigen was enhanced 60% by increasing the heparin pretreatment interval from 20 to 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunologic mast cell-mediated responses and histamine release are attenuated by heparin.

Heparin has been shown to act as a competitive inhibitor of inositol 1,4,5-triphosphate (InsP3) receptors in various cell types. Because InsP3 is one of the second messengers involved in stimulus-secretion coupling in mast cells, it is possible that heparin may inhibit mast cell-mediated reactions. Therefore, in allergic sheep, we tested this hypothesis in two mast cell-mediated reactions induced by immunologic and nonimmunologic stimuli: immediate cutaneous reaction (ICR) and acute bronchoconstrictor response (ABR). In 12 sheep allergic to Ascaris suum antigen, the surface area of the skin wheal was determined 20 min after intradermal injection (0.05 ml) of increasing concentrations of specific antigen, compound 48/80, and histamine, without and after pretreatment with heparin (100, 300, or 1,000 U/kg i.v.). Antigen, compound 48/80, and histamine produced concentration-dependent increases in ICR. Heparin "partially" inhibited the ICR to antigen and compound 48/80 in a dose-dependent manner without modifying the ICR to histamine. The heparin preservative benzyl alcohol was ineffective. In 11 additional sheep, specific lung resistance was measured before and after inhalation challenges with antigen, compound 48/80, and histamine without and with aerosol heparin pretreatment (1,000 U/kg). Heparin blocked the antigen- and compound 48/80-induced bronchoconstriction without modifying the airway effects of histamine. In isolated human uterine mast cells, heparin inhibited the anti-immunoglobulin E- but not the calcium ionophore- (A23187) induced histamine release. These data suggest that heparin inhibits the ICR and ABR induced by stimuli that produce immunologic and nonimmunologic mast cell degranulation without attenuating the effects of histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of inhaled heparin on immunologic and nonimmunologic bronchoconstrictor responses in sheep.

The glycosaminoglycan heparin has been shown to block inositol triphosphate (IP3) receptors in various tissues. Because IP3 is one of the pathways involved in stimulus-secretion coupling in mast cells, it is possible that heparin may inhibit airway anaphylaxis. Thus, the purpose of the present investigation was to study the effect of inhaled heparin on immunologically and nonimmunologically induced bronchoconstriction in allergic sheep. Specific lung resistance (SRL) was measured in 15 sheep allergic to Ascaris suum antigen, before and after inhalation challenge with the specific antigen, compound 48/80, histamine, and carbachol. On a different day, the animals were pretreated with inhaled heparin and airway challenges with the antigen and agonists were repeated. Antigen alone increased SRL by 367 +/- 119% (mean +/- SE) above baseline (p less than 0.05). Inhaled heparin had no effect on baseline SRL, but attenuated antigen-induced bronchoconstriction in a dose-dependent fashion: mean SRL increased by 313 +/- 87, 151 +/- 69, and 24 +/- 20% above baseline with 100, 300, and 1,000 U/kg of heparin, respectively. Inhaled benzyl alcohol preservative, dextran sulfate, and de-N-sulfated heparin failed to inhibit antigen-induced bronchoconstriction. The dose of heparin (1,000 U/kg) that completely blocked antigen-induced bronchoconstriction also attenuated the bronchoconstriction induced by compound 48/80 (delta SRL = 374 +/- 72 versus 35 +/- 12%), but failed to block the bronchoconstrictor effects of histamine and carbachol. These data suggest that inhaled heparin prevents bronchoconstrictor responses induced by by stimuli that produce immunologic and nonimmunologic mast-cell degranulation in sheep, without attenuating agonist-induced bronchoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperoxia prevents hypoxia-induced bronchial hyperreactivity via a cyclooxygenase-independent mechanism.

We tested the hypothesis that prior exposure to alveolar hyperoxia prevents the hypoxia-induced enhancement of bronchial reactivity, possibly via a cyclooxygenase-dependent mechanism. In 15 sheep, specific lung resistance (sRL) was measured before and after 30 min of exposure to either air or a hypoxic gas mixture (13% O2). The sheep then inhaled 50 breaths of aerosolized 5% histamine solution (n = 9) or 10 breaths of 2.5% carbachol solution (n = 9), and measurements of sRL were repeated. On subsequent days the above protocols were repeated after a 30-min exposure to hyperoxia (O2 greater than or equal to 95%), without or after pretreatment with indomethacin (2 mg/kg). After air-sham exposure, carbachol and histamine increased mean sRL to 370 +/- 40 (SE) and 309 +/- 65% of baseline, respectively. Exposure to the hypoxic gas mixture had no effect on baseline sRL but enhanced the airway responsiveness to carbachol and histamine; mean sRL increased to 740 +/- 104 and 544 +/- 76% of baseline, respectively (P less than 0.05). Prior 30-min exposure to hyperoxia prevented the hypoxia-induced enhancement of bronchial reactivity to carbachol (sRL = 416 +/- 66% of baseline) and histamine (sRL = 292 +/- 41% of baseline) without affecting the airway responsiveness to these agents after air. Pretreatment with indomethacin did not reverse the protective effects of hyperoxia or the hypoxia-induced enhancement of bronchial reactivity. We conclude that 1) prior exposure to alveolar hyperoxia prevents the hypoxia-induced enhancement of bronchial reactivity and 2) neither the protective effects of hyperoxia nor the hypoxia-induced enhancement of bronchial reactivity is mediated via a cyclooxygenase-dependent mechanism.

PAF-induced airway responses in sheep: effects of a PAF antagonist and nedocromil sodium.

Platelet-activating factor (PAF) is a potent inflammatory mediator that can cause bronchoconstriction and airway hyperresponsiveness in selected human subjects and animals. The mechanism by which PAF induces these changes is not clearly understood. We therefore studied the effects of intratracheal instillation of PAF (30 micrograms/kg) on airway resistance and airway responsiveness in allergic sheep (n = 7) and attempted to modulate these effects with the specific PAF antagonist, WEB-2086, and the antiasthmatic agent, nedocromil sodium (NED). Specific lung resistance (SRL) was measured to assess bronchial responses to PAF, and airway responsiveness was determined by deriving a provocative dose of carbachol in breath units causing an increase in SRL to 4 L times centimeters of H2O per liters per second (PD4) from carbachol dose-response curves. PAF instillation increased mean +/- SD SRL to 228 +/- 134% above baseline. Two to 4 hours after PAF instillation, PD4 decreased by 55 +/- 9% from a baseline of 39 +/- 9 breath units (p less than 0.05). Airway responsiveness remained increased at 24 hours but returned to baseline by 48 hours. Pretreatment with WEB-2086 (3 mg/kg, intravenously) or NED (1 mg/kg, nebulized) blocked (p less than 0.05) PAF-induced bronchoconstriction and PAF-induced airway hyperresponsiveness. Instillation of lyso-PAF (30 micrograms/kg) did not cause bronchoconstriction or airway hyperresponsiveness. Thus, instilled PAF causes bronchoconstriction and airway hyperresponsiveness in allergic sheep by a receptor-mediated mechanism that likely involves the release of secondary mediators, the latter process being sensitive to NED.

Effect of calcium antagonist gallopamil on antigen-induced early and late bronchoconstrictor responses in allergic sheep.

Calcium channel blockers have been shown to modify acute antigen-induced bronchoconstriction in allergic animals and in some human subjects with bronchial asthma; however, the effects of calcium antagonists on late-phase bronchial responses are not known. In this investigation, we studied the effects of calcium antagonist gallopamil on antigen-induced early- and late-phase bronchial responses in sheep allergic to Ascaris suum antigen. In 11 unsedated sheep, specific lung resistance (SRL) was measured before, immediately after, and serially up to 8 h after inhalation challenge with A. suum antigen. On different experiment days, at least 3 wk apart, the sheep were pretreated with gallopamil, administered either as an aerosol (5 mg, n = 10; 10 mg, n = 9) or as an intravenous injection (20 micrograms/kg, n = 10), and the antigen challenge was repeated. For the control experiments (n = 11), mean +/- SE SRL increased immediately after antigen challenge (early response) to 533 +/- 72% of baseline and again 6 to 8 h after challenge (late response) to 304 +/- 31% of baseline (p less than 0.05). Neither intravenously administered nor aerosolized gallopamil had a significant effect on baseline SRL. Both aerosolized and intravenously administered gallopamil blunted the early response and completely blocked the late-phase bronchoconstrictor response (p less than 0.05). Mean SRL during early phase increased to 208 +/- 39% and 245 +/- 39% of baseline with 5 mg and 10 mg of aerosolized gallopamil and to 191 +/- 35% of baseline with intravenously administered gallopamil, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoxia-induced enhancement of nonspecific bronchial reactivity: role of leukotrienes.

Because alveolar hypoxia has been shown to cause an increase of leukotrienes in lung lavage fluid, we tested the hypothesis that enhancement of nonspecific bronchial reactivity during alveolar hypoxia may be mediated by leukotrienes. In nine conscious sheep we determined specific lung resistance (sRL) before and after exposure to either air or a hypoxic gas mixture (13% O2) for 30 min. The sheep then inhaled 50 breaths of aerosolized 5% histamine solution (n = 6) or 10 breaths of 2.5% carbachol solution (n = 6) on different days, and the measurements of sRL were repeated. On subsequent days the above protocols were repeated after pretreatment with aerosolized FPL 57231 (3 ml, 1% solution), a leukotriene receptor antagonist. Inhalation of histamine and carbachol after exposure to air caused an increase in mean sRL to 337 and 342% of base line, respectively (P less than 0.05). Exposure to the hypoxic gas mixture had no effect on sRL but enhanced the histamine- and carbachol-induced increases in mean sRL to 621 and 646% of base line, respectively (P less than 0.05); these increases were significantly higher than those observed after air exposure (P less than 0.05). FPL 57231 prevented the hypoxia-induced enhancement of bronchial reactivity to histamine and carbachol without affecting the airway responsiveness to these agents after air. In another group of eight sheep, aerosolized leukotriene C4, at a dose (50 micrograms) that per se had no affect on sRL, enhanced the bronchial reactivity to carbachol. These data suggest that in sheep during alveolar hypoxia airway hyperresponsiveness may be due to the priming of airway smooth muscle by leukotrienes.

Effect of gallopamil, a calcium channel blocker, on carbachol- and histamine-induced bronchoconstriction in sheep.

We compared the in vivo effectiveness of the calcium channel blockers, gallopamil and verapamil, in inhibiting carbachol- and histamine-induced bronchoconstriction in conscious sheep. In 13 sheep, specific lung resistance (SRL) was measured before and after aerosol challenge with histamine (50 breaths; 5% solution) and carbachol (10 breaths; 2.5% solution), without and with pretreatment with intravenous and aerosolized gallopamil and verapamil. Histamine increased mean SRL by 213%. Intravenous (20 micrograms/kg) and aerosolized (5 mg) gallopamil markedly inhibited the histamine-induced bronchoconstriction. Mean SRL increased by 19% and 23%, respectively, whereas 2.5 mg of aerosolized gallopamil partly inhibited the histamine-induced response with SRL increasing by 115% (p less than 0.05). Carbachol increased mean SRL by 380%. Pretreatment with 2.5 mg of aerosolized gallopamil had no effect on carbachol-induced bronchoconstriction, whereas intravenous and 5 mg of aerosolized gallopamil partly attenuated the carbachol response; mean SRL increased by 204% and 177%, respectively (p less than 0.05). Intravenous (150 micrograms/kg) and aerosolized (10 mg and 20 mg) verapamil did not prevent either histamine- or carbachol-induced bronchoconstriction. These results indicate that gallopamil (parenteral and aerosol) attenuates carbachol- and histamine-induced bronchoconstriction, is more potent than verapamil, and may be of therapeutic potential.

Effect of verapamil on pulmonary and eicosanoid responses to endotoxin in awake sheep.

Leukotrienes have been suggested to play a role in the endotoxin-induced changes of the pulmonary hemodynamics and airway mechanics. Since Ca2+ is necessary for contraction of airway and vascular smooth muscle as well as for activation of phospholipase A2 and 5-lipoxygenase enzymes, we wondered whether the calcium antagonist verapamil would modify the endotoxin-mediated pulmonary effects as well as the generation of circulating eicosanoids. In twelve conscious sheep, measurements of pulmonary vascular resistance (PVR), systemic vascular resistance (SVR), lung resistance (RL), arterial PO2 (PaO2), leukocyte (WBC) count, arterial thromboxane B2 (TxB2), prostaglandin (PG) F2 alpha, and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) concentrations were obtained before and at predetermined intervals after a 10-min infusion of Escherichia coli endotoxin (0.3 microgram/kg). On separate occasions, the sheep received a bolus injection of verapamil (150 micrograms/kg) before endotoxin, followed by a continuous infusion of verapamil [10 micrograms.kg-1.min-1 (n = 5) or 20 micrograms.kg-1.min-1 (n = 7)] for up to 4 h post-endotoxin. Endotoxin caused a biphasic response with an increase in mean PVR and RL to 326 and 276% of base line during phase I (0-1 h) and lesser increases to 177 and 157% of base line during phase II (1.5-4 h), respectively (P less than 0.05). SVR also showed biphasic increases of 44 and 42% during phase I and II, respectively. Mean PaO2 decreased by 16 Torr and WBC count decreased from 6.4 +/- 1.5 to 3.3 +/- 1.1 thousand/mm3, associated with marked increases in plasma TxB2, PGF2 alpha, and 6-keto-PGF1 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of calcium antagonists in bronchial reactivity.

Calcium (Ca) ions play an important pathophysiologic role in allergic reactions. Thus, mediator release from mast cells, synthesis of some newly formed chemical mediators, airway smooth muscle contraction, and nerve-impulse conduction are all dependent on the availability and flux of Ca ions. It is likely, therefore, that Ca antagonists would modify allergic bronchoconstriction. In vitro, Ca antagonists have been demonstrated to inhibit mediator release (histamine, slow-reacting substance of anaphylaxis, and platelet-activating factor) from mast cells, passively sensitized human lung fragments, and leukocytes. Ca antagonists have also been found to inhibit synthesis of leukotrienes in rat lungs and cyclooxygenase products in sheep, possibly by inactivating phospholipase A2 and/or 5-lipoxygenase. In addition, nifedipine, verapamil, and gallopamil have demonstrated inhibition of airway smooth muscle contractions to histamine, carbachol, and antigen in various species. In vivo effects of Ca antagonists are variable, depending on the species, experimental design, the stimulus or the agonist, and the Ca antagonist used. Animal studies have demonstrated the inhibition of histamine, methacholine, citric acid, and prostaglandin F2 alpha-induced bronchoconstriction in guinea pigs and dogs by intravenous nifedipine. In contrast, verapamil inhibited antigen-induced bronchoconstriction in allergic sheep without any effect on histamine- and carbachol-induced responses. Ca antagonists (nifedipine and verapamil) have been of limited value in human subjects and generally have no significant bronchodilating activity. Both nifedipine and verapamil prevent the exercise-induced asthma and partly attenuate the histamine and methacholine-induced bronchoconstriction. Oral nifedipine is generally more effective than oral verapamil against acute antigen-induced bronchoconstriction; however, this efficacy may be limited by systemic side effects. Inhaled Ca antagonists may be more effective and free of systemic side effects, as demonstrated by greater efficacy of inhaled verapamil. A new Ca antagonist, gallopamil (a methoxy derivative of verapamil), is being investigated as an aerosol, and preliminary studies in animals and humans have found it fourfold to seventeenfold more potent than verapamil. In sheep, gallopamil has been found to attenuate histamine, carbachol, and platelet-activating factor-induced bronchoconstriction, as well as to inhibit early and late-phase allergic airway responses. Studies in human subjects have also demonstrated the inhibition of antigen-induced bronchoconstriction by inhaled gallopamil, with efficacy comparable or better than cromolyn sodium.(ABSTRACT TRUNCATED AT 400 WORDS)

Maternal hypoxic ventilatory response, ventilation, and infant birth weight at 4,300 m.

To test the hypothesis that increased hypoxic ventilatory responsiveness (HVR) raised maternal ventilation and arterial oxygenation during high-altitude pregnancy and related to the birth weight of the offspring, we studied 21 residents of Cerro de Pasco, Peru (4,300 m), while eight of them were 36 +/- 0 wk pregnant and 15 of them 13 +/- 0 wk postpartum. HVR was low in the nonpregnant women (mean +/- SE shape parameter A = 23 +/- 8) but increased nearly fourfold with pregnancy (A = 87 +/- 17). The increase in HVR appeared to account for the 25% rise in resting ventilation with pregnancy (delta VE observed = 2.4 +/- 0.7 l/min BTPS vs. delta VE predicted from delta HVR = 2.6 +/- 1.7 l/min BTPS, P = NS). Hyperoxia decreased ventilation in the pregnant women (P less than 0.01) to levels similar to those measured when nonpregnant. The increased ventilation of pregnancy raised arterial O2 saturation (SaO2) from 83 +/- 1 to 87 +/- 0%, and SaO2 was correlated positively with HVR in the pregnant women. The rise in SaO2 compensated for a 0.9 g/100 ml decrease in hemoglobin concentration to preserve arterial O2 content at levels present when nonpregnant. Cardiac output in the 36th wk of pregnancy did not differ significantly from values measured postpartum. The increase in HVR correlated positively with infant birth weight. An increase in HVR may be an important contributor to increased maternal ventilation with pregnancy and infant birth weight at high altitude.