THE EFFECTS OF PENTOBARBITONE AND URETHANE ON PULMONARY AIRWAY RESISTANCE IN GUINEA‐PIGS AND THEIR INTERACTIONS WITH DRUGS

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Abstract
1 Propranolol increased pulmonary airway resistance (PAR) in the conscious guinea-pig, whereas atropine had no effect, suggesting the existence of a continual sympathetic bronchodilator tone. 2 The direct bronchoconstrictor effects of histamine, acetylcholine and 5-hydroxytryptamine were modified by autonomic reflexes: a bronchodilator one, abolished by propranolol, and a cholinergic bronchoconstrictor one, seen with histamine. 3 Pentobarbitone increased PAR, an effect which was reduced by propranolol but which was unaffected by atropine. The bronchoconstrictor effects of histamine, acetylcholine and 5-hydroxytryptamine were potentiated by pentobarbitone. 4 Pentobarbitone therefore appears to inhibit the adrenergic bronchodilator tone and to depress adrenergic reflexes, these being the preponderant autonomic influences in these experiments. 5 Like pentobarbitone, urethane increased PAR in the conscious guinea-pig and potentiated the bronchoconstrictor effects of the three amines. These actions are similarly attributed to a reduction in adrenergic influences.

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