RELATIONSHIP BETWEEN THE LEVELS OF INTRACELLULAR CYCLIC NUCLEOTIDES AND MECHANICAL RESPONSES INDUCED BY DRUGS

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Abstract
The [guinea pig] tracheal smooth muscle dissected free from connective tissues was used as a test preparation, since isoprenaline caused a decrease in [cyclic]GMP in the muscle while it caused an increase in cGMP in the remaining tracheal tissue. Acetylcholine, histamine and papaverine increased both cAMP and cGMP levels in the tracheal muscle. Isoprenaline increased the cAMP level but decreased the cGMP level. When tracheal muscle was incubated with isoprenaline in the presence of acetylcholine, isoprenaline did not cause a decrease in cGMP but rather a significant increase in cAMP after only 1 min incubation. The relaxation of the tracheal muscle by isoprenaline is initiated by the increase in cAMP but is not associated with the change in cGMP.