James S. Douglas

Airway responses to histamine, acetylcholine, and propranolol in anaphylactic hypersensitivity in guinea pigs☆☆☆

Abstract Using changes in tidal volume and dynamic lung compliance, airway responses to histamine, acetylcholine, and propranolol were investigated in different groups of guinea pigs before and after active or passive sensitization. The threshold doses to inhaled histamine, acetylcholine, and propranolol were identical before and after sensitization. Similarly, the slope of dose response curves to these drugs and the time course of recovery from airway constriction were comparable in control and sensitized animals. The slopes of dose response curves to histamine and acetylcholine were parallel. Threshold doses to acetylcholine (T ACH ) and histamine (T H ) were proportional. The average ratio TACHTH was 7.7. There was no correlation between threshold doses and slopes of dose response curves for propranolol and those for histamine or acetylcholine. Antigen challenge resulted in decreases of dynamic lung compliance and in increases of airway resistance and frequency, which were maximal 60 to 130 seconds after challenge. When functional parameters after antigen challenge had returned to normal, bronchial responses to histamine, acetylcholine, and propranolol were exaggerated. These exaggerated responses were reproducible, transient, variable from animal to animal, and related to the antigen dose. Guinea pig anaphylaxis does not lead to the prolonged hypersensitivity to chemical mediators, which characterizes human reaginic asthma, but to a temporary enhancement of responses to acetylcholine, histamine, and propranolol.

Tachyphylaxis to β-adrenoceptor agonists in guinea pig airway smooth muscle in vivo and in vitro

Abstract β-Adrenoceptor tachyphylaxis was induced by incubating spirally cut guinea pig tracheas with isoproterenol (2.4 × 10 −7 M) for 20 min. This incubation reduced the relaxant effects of catecholamines but not of dibutyryl cyclic AMP, theophylline or sodium nitrite. Tracheas incubated with norepinephrine, phosphodiesterase inhibitors or cyclic nucleotides became tachyphylactic to isoproterenol. Pretreatment with indomethacin prevented induction of tachyphylaxis. Incubation with adenosine, methoxamine or sodium nitrite did not induced β-adrenoceptor tachyphylaxis. When we gave isoprpterenol intramuscularly to guinea pigs, airway sensitivity to aerosolized histamine was unchanged but the toxicity of parenterally administered histamine was increased. A prolonged treatment with isoproterenol reduced airway sensitivity to histamine aerosols; this reduced sensitivity was reversed by indomethacin. Thus, β-adrenoceptor tachyphylaxis may not explain increased toxicity of parenteral histamine after isoproterenol treatment. Elevated levels of cyclic AMP and an increased synthesis of prostaglandins may result in diminished response to β-receptor stimulation.

Effects of ascorbic acid and indomethacin on the airways of healthy male subjects with and without induced bronchoconstriction

We have investigated the effects of ascorbic acid (1.0 gm orally) and indomethacin (50 mg orally) on airway tone in the basal state in six health nonsmoking male adults. Airway tone was assessed from measurements of specific airway conductance and flow rates interpolated from partial expiratory flow-volume curves by means of whole-body plethysmography and spirometry, respectively. Neither ascorbic acid nor indomethacin alone produced a significant change in basal tone. However, both the duration and intensity of the bronchoconstriction induced by methacholine aerosol (10 mg/ml for 30 sec) were significantly reduced by prior administration of ascorbic acid. This ameliorating action of ascorbic acid was blocked by ingestion of indomethacin. The results suggest that ascorbic acid exerts its effects by altering the production of a bronchodilator prostaglandin.

β-receptors during aging in respiratory tissues

Abstract Specific [ 125 I]hydroxybenzylpindolol binding (33 fmol/mg protein) was detected in tracheal tissues from middle aged (417g) and old (757 g) guinea pigs binding was not measurable in tracheal tissues from young (118 g) animals. Similarly, receptor density increased in bronchial and parenchymal tissues during development but receptor affinity did not change. For any age, the receptor densities were parenchyma>bronchi>tracheas (20/7/1); receptor affinities were identical. The potency of 1-isoproterenol in relaxing bronchial muscle was reduced during development. In vivo, salbutamol reduced airway reactivity to histamine and was most potent in animals exhibiting airway hyperreactivity. In addition, 1-propranolol sensitized airway muscle to the bronchoconstrictor effects of histamine in young guinea pigs; in old guinea pigs of the same airway reactivity, 1-propranolol did not affect the induced bronchoconstriction. Our data suggest that there is a reduced sensitivity of airway muscle to catecholamines during development which may be due, in part, to increased density of β-adrenoceptors which are not involved in eliciting the physiological response.

Influences of gender and maturation of responses of guinea-pig airway tissues to LTD4

LTD4 was more potent in airway tissues from immature male and female guinea-pigs than in those from mature animals. The intrinsic activity of LTD4 relative to carbachol was greatest in tracheal tissues from immature animals. Indomethacin treatment reduced the potency of LTD4 and increased maximal contractile responses in most tissues. The reduced potency of LTD4 as a consequence of maturation may be significant for the decrease in airway reactivity seen in children at adolescence.

Characterization of cholinergic muscarinic receptors in cow tracheal muscle membranes: Effect of maturation☆

The parasympathetic nervous system is important in the control of basal airway muscle tone and caliber. We characterized muscarinic cholinergic receptors in isolated tracheal membranes from cows of three age groups (immature, less than 2 weeks; transition, 3-5 months; and mature, greater than 5 years) using l-[3H]quinuclidinyl benzilate (l-[3H]QNB) as the radioligand. There were significant decreases in the densities of l-[3H]QNB binding sites with maturation (Bmax: 2344 +/- 169 vs 1381 +/- 85 vs 1116 +/- 80 fmol/mg protein for tissues from immature, transition and mature cows respectively). No change in the dissociation constant was observed with maturation (Kd: 0.38 +/- 0.09 vs 0.55 +/- 0.06 vs 0.50 +/- 0.07 nM for tissues from immature, transition and mature animals respectively). The association and dissociation rate constants did not vary between tissues from immature and mature animals. The specific activity of the enzyme, acetylcholinesterase, was correlated with the density of l-[3H]QNB binding sites present in the tracheal homogenates; that is, with maturation, there were significant decreases in acetylcholinesterase activity [0.28 +/- 0.01 vs 0.16 +/- 0.02 vs 0.08 +/- 0.01 mol X l-1 X min-1 X (mg protein)-1 for tissues from immature, transition and mature animals respectively]. All competition binding studies using muscarinic antagonists exhibited single site binding and did not show any differences in drug affinities between the age groups. In contrast, multiple binding sites were observed with carbachol, methacholine and muscarine, and there were significant decreases in receptor affinities for the muscarinic agonists. No changes in the proportion of high and low affinity sites were found. These results indicate that with maturation there are alterations in the properties of muscarinic receptors in tracheal smooth muscle.

Histamine, endogenous prostaglandins and cyclic nucleotides in the regulation of airway muscle responses in the guinea pig

Indomethacin (30 mg/kg, i.p.) reduced pulmonary resistance in guinea pigs but did not affect their sensitivity to histamine. This treatment preferentially reduced the generation of PGE2 by isolated tracheal preparations. The ratios of PGF2 alpha/PGE2 before and after treatment were 1/1 and 6/1, respectively. Chronic indomethacin treatment (30 mg/kg, i.p., twice a day for 4 days) increased histamine sensitivity in vivo 2 fold while a longer treatment (10 days) was without effect. The efficacy of histamine and the potency of isoproterenol in tracheal tissues were unaffected by either treatment. Indomethacin (17 microM for 30 min) relaxed tracheal tissues but not bronchial tissues. Responses of both tissues to contractile agonists were potentiated after indomethacin treatment. The efficacy of histamine was smaller in bronchi than in tracheas. Similarly, PGE2, PGI2 and isoproterenol were less potent in bronchi. Basal amounts of cyclic AMP were higher in bronchi than in tracheas; indomethacin did not affect the basal amounts of cyclic AMP in tracheal tissues but reduced them in bronchial preparations. Histamine elevated cyclic AMP content in both preparations; this elevation was reduced by indomethacin. While prostaglandins play a role in modulating airway responses in vitro, their role in airways in normal animals in vivo is more difficult to demonstrate.

The antagonism of histamine-induced tracheal and bronchial muscle contraction by diphenhydramine: effect of maturation

1 Airway reactivity in spontaneously breathing unanaesthetized female guinea‐pigs was significantly reduced as a consequence of maturation. Threshold doses to histamine (% w/v base) were 0.08% ± .01 and 0.27% ± .04 in immature (110g ± 2; 1 week old) and mature (837 g ± 29; 4 months old) animals, respectively. 2 The potency of 2‐(2‐thiazolyl) ethylamine in tracheal tissues from mature animals was significantly less than that in tissues from immature animals (5.06 ± .03 vs 5.26 ± .07). There was no change in the potency of this agonist in bronchial tissues (5.0 ± .09 vs 4.9 ± .13). 3 Diphenhydramine reduced tissue contractility in tracheal (30% at 0.1 μm; 50% at 3 μm) but not bronchial tissues. The antihistamine in concentrations ranging from 0.1 μm to 3 μm reduced the potency of histamine 2 to 50 fold in both tissues. 4 Schild plots were linear but slopes were significantly less than unity. pA2 values ± 95% fiducial limits derived from data from tracheal tissues of immature and mature animals using constrained Schild plots (unit slope) were 7.7 (7.6−7.7) and 7.1 (7.0−7.2), respectively (P<0.05). pA2 values for diphenhydramine in bronchial tissues using constrained Schild plots were 7.8 (7.7−7.9) and 7.5 (7.3−7.5), respectively (P<0.05). 5 The data emphasize the unique nature of tracheal and bronchial tissues. We conclude that, with maturation, the characteristics of the histamine receptor change. We suggest that the remission of asthma which frequently occurs at puberty may be related to alteration in the properties of membrane receptors.

Histamine tachyphylaxis in canine isolated airways: role of endogenous prostaglandins

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Aging and cholinergic responses in bovine trachealis muscle

1 The relative potencies of muscarinic agonists on bovine tracheal smooth muscle were unchanged as a consequence of aging and were carbachol > oxotremorine > muscarine > pilocarpine > McNeil A‐343. 2 During aging, the potencies of carbachol, oxotremorine, McNeil A‐343 and pilocarpine, but not muscarine, were reduced. 3 Maximal induced tensions to all the agents studied were reduced as a consequence of age. 4 Irreversible antagonism with benzilylcholine mustard showed that agonist efficacy was significantly reduced during aging. 5 Estimated receptor occupancy at the EC50 was significantly greater in tracheal tissues from the mature versus immature cows for every agonist studied. 6 The dissociation constants for full agonists (carbachol, oxotremorine and methacholine) were decreased with maturation while the converse was observed with partial agonists (McNeil A‐343, pilocarpine). 7 We conclude that there are significant changes in the properties and coupling of muscarinic receptors during aging. These changes may contribute to the reduced airway reactivity seen in vivo.