Differential bronchodilatory effects of terbutaline, diltiazem, and aminophylline in canine intraparenchymal airways.
OBJECTIVE
Intraparenchymal airways are involved in air flow regulation. Relaxation of intraparenchymal airways to volatile anesthetics varied by topographic location. This study was conducted to determine whether other bronchodilators (terbutaline, diltiazem, and aminophylline) relax bronchiolus to a greater degree than bronchus, as seen with volatile anesthetics.


METHODS
In vitro, controlled, randomized study.


METHODS
Animal research laboratory.


METHODS
Adult dogs (n = 9).


METHODS
Proximal (outer diameter, 4-6 mm) and distal (outer diameter, 0.8-1.5 mm) airway rings of dogs were contracted in tissue baths with the effective concentration of acetylcholine that produces half the maximum response. Airway relaxant dose-response curves were constructed to measure isometric tension after administration of terbutaline (concentration range, 10(-8) to 10(-4) M), diltiazem (concentration range, 3 x 10(-7) to 1 x 10(-4) M), and aminophylline (concentration range, 10(-7) to 10(-4) M).


RESULTS
All three bronchodilators caused relaxation of the proximal and distal airways. At the maximum dose, diltiazem (maximum relaxation, 95%+/-2% [proximal], 94%+/-6% [distal]; p > .05) was the most efficacious, followed by terbutaline (maximum relaxation, 72%+/-13% [proximal], 55%+/-9% [distal]; p < .05) and aminophylline (maximum relaxation, 32%+/-10% [proximal], 35%+/-18% [distal]; p > .05. At the concentrations tested, they were equally efficacious. No significant differences in relaxation between proximal and distal airways were noted with diltiazem or aminophylline in the entire dose range. However, terbutaline relaxed the distal airway more than the proximal airway in the entire dose range.


CONCLUSIONS
The results demonstrate that only terbutaline showed a differential airway relaxant effect between proximal and distal airways, as seen with volatile anesthetics.
Akhtar
S
S
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
Mazzeo
A J
AJ
Cheng
E Y
EY
Bosnjak
Z
Z
Kampine
J P
JP
D000628:Aminophylline / Q000494:pharmacology*; D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000187:drug effects*; D001993:Bronchodilator Agents / Q000494:pharmacology*; D015986:Confounding Factors, Epidemiologic; D004110:Diltiazem / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D005260:Female; D066298:In Vitro Techniques; D016014:Linear Models; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects*; D011897:Random Allocation; D013726:Terbutaline / Q000494:pharmacology*
D018685:Anesthetics, Inhalation; D001993:Bronchodilator Agents; D000628:Aminophylline; D004110:Diltiazem; D013726:Terbutaline