Relaxation of equine tracheal muscle in vitro by different adrenoceptor drugs |
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| Authors: | K TÖRNEKE C INGVAST LARSSON L- E APPELGREN |
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| Institution: | Swedish University of Agricultural Sciences, Faculty of Veterinary Medicine, Department of Pharmacology and Toxicology, BMC, Box 573, SE- 751 23 Uppsala, Sweden |
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| Abstract: | Strips of tracheal smooth muscle from 12 horses were contracted by carbachol in tissue baths under isometric conditions. This contraction (?50% of maximum: EC50) was relaxed completely with adrenoceptor drugs. The only exception was clenbuterol, where the degree of relaxation was ?90%. In all horses the EC50-value for isoprenaline (mean 1.6 × 10?8M) was less than that for adrenaline (mean 9.6 × 10? 8M) and noradrenaline (mean 1. 8 × 10- 6M). The potency ratio was 1 < 6 < 110 which indicates that the β2-subtype dominates among the β-adrenoceptors of equine airways. All preparations were also very sensitive to the specific and potent β2-receptor agonists clenbuterol (mean 5.7 × 10? 9M) and procaterol (mean 3.6 × 10?10M). No differences in EC50-values due to age, sex and breed were observed in this material. The standard deviation of the mean EC50-values seems to be larger for the specific β2-adrenoceptor agonists than for the unspecific. A reason for this could be differences in the pattern of the β-adrenoceptor population. |
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