Relaxation of equine tracheal muscle in vitro by different adrenoceptor drugs.

The research assesses the effect of different adrenoceptor drugs on the relaxation of horse tracheal muscle when contracted using carbachol. The study found that beta 2-adrenoceptor drugs dominated in relaxing equine airways.

Method and Materials

• Researchers conducted in-vitro testing on tracheal smooth muscle strips taken from 12 horses.
• These muscle strips were met with a contractive force through the application of carbachol in tissue baths under isometric conditions.

Testing and Results

• The muscle contraction was then measured when subjected to various adrenoceptor drugs. The contraction was approximately 50% of the maximum, labeled as an EC50 value.
• It was found that all tested drugs successfully relaxed the muscle strip contraction entirely, except for the drug, clenbuterol, which only managed about 90% relaxation.
• Among the used drugs, isoprenaline had a lower EC50-value (mean 1.6 x 10(-8) M) than adrenaline (mean 9.6 x 10(-8) M) and noradrenaline (mean 1.8 x 10(-6) M).

Implication

• From the potency ratio of 1 < 6 < 110 observed, the research suggests that the beta 2-subtype is the prevailing beta-adrenoceptor for equine airways.
• The muscle preparations were exceptionally sensitive to the specific and potent beta 2-receptor agonists clenbuterol and procaterol. Their mean EC50-values were 5.7 x 10(-9) M and 3.6 x 10(-10) M respectively.
• There were no observed differences in EC50-values related to horse age, sex, or breed.

Conclusion

• The variations in standard deviation of the EC50-values seem to be larger for the specific beta 2-adrenoceptors than the unspecific ones.
• This could be attributed to differences in the dispersion of the beta-adrenoceptor population.