Abstract
Muhlmann, 1 and later Dakin 2 determined that catechol and certain of its derivatives that resemble epinephrine in their skeletal structure were capable of raising the blood pressure of the anesthetized rabbit. Barger and Dale 3 found that catechol raised the blood pressure of the decapitated cat, showing that this drug acts peripherally to the vasomotor center. They claimed also that catechol did not dilate the pupil of the intact animal, but did cause contraction of the isolated virgin cat uterus, and drew the conclusion that catechol raises the blood pressure by direct muscle stimulation, rather than by sympathetic imitation.
We have confirmed their results, on blood pressure and pupil, but have determined further that catechol depresses the uterus and intestine of many animals. On the basis of these findings, it occurred to us to test anew the suggestion of Dakin that epinephrine owes much of its typical sympathomimicity to the catechol group.
Our results show that catechol, ethylcatechol, acetocatechol, and chloracetocatechol possess sympathomimetic powers (Table I). In this, inhibitory effects predominate, so that when an organ contains but one type of sympathetic innervation, as in the dilator pupili, the nictitating membrane, or the intestine, that action is brought out by these drugs. On the other hand, when both motor and inhibitor fibers of the sympathetic are present in the same organ, as in the blood vessels and uterus, the inhibitory action predominates, although the action of catechol is not reversed after ergotoxine. In epinephrine, the motor effects are much more in evidence than the inhibitor, but other non-catechol containing amines such as ephedrine seem incapable of strong inhibitory activity, especially in the presence of motor fibers.
Chloracetylcatechol is the most powerfully sympathomimetic drug of our series.
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