A contribution to the pharmacology of yohimbine (an experimental research)

Abstract

SUMMARY OF THE CHIEF PHARMACOLOGICAL-ACTIONS OF YOHIMBINE.:CENTRAL NERVOUS SYSTEM: Yohimbine has a selective action on the coordination centres and the medulla. Doses which affect these profoundly leave the cerebrum and spinal cord slightly if at all affected. Large doses abolish the power of progression and of maintaining equilibrium, depress or paralyse the respiratory and vasomotor centres. Small doses stimulate the vasomotor, and especially the respiratory, centres.CIRCULATORY SYSTEM: Large doses arrest the heart in diastole. Smaller doses slow the heart by lengthening the diastolic pauses. Very small quantities influence the frog's heart, slowing the rate of beat, increasing the expansion, without rendering the systole less complete, thus augmenting the output per single beat. Blood pressure experiments on mammals also give indirect indications of this action produced by small doses.The blood vessels of the frog are only very slightly affected by direct perfusion of yohimbine through them, Very small doses cause a slight and transient stimulation of the vasomotor centre of mammals. It is depressed by larger doses, leading to a marked dilatation of the vessels.NERVE: Yohimbine, applied in strong solutions directly to tai, nerve trunk, prolongs the refractory period of nerve, and eventually abolishes its conductivity. In this condition_ of Prolonged refractory period, it has been possible to demonstrate actualfatigue of nerve , consequent upon its activity, and Yohimbine is probab the best agent that has hitherto been used for studyil the processes of fatigue and recovery in nerve.After large doses of Yohirbine . in the frog , it is impossible, by stimulating the motor nerve, to product tetanus of the muscle. This action on the motor nerve is probably one factor in the production of paralysis by Yohimbine.Yohimbine is a local anaesthetic.SKELETAL MUSCLE: is affected by only relatively strong solutions, but such a strength of solution as may be present in the blood after lethal and large sublethal doses, renders muscle easily fatigued.INDICATIONS FOR THE THERAPEUTIC USE OF YOHIMBINE:It has already been used as a local anaesthetic and as an aphrodisiac, and these actions have been investigated by previous research. The latter action is probably on of the least important effects of Yohimbine, and only one result of a general action on the nervous and vascular systems.RESPIRATORY STIMULANT: Especially in cases of poisoning by snake venom &c. where death is often largely duie to paralysis of the respiration, the need for a promrt vigorous respiratory stimulant is accepted. The use of Atropine which has the highest reputation in this direction, has not been attended with conspicuous success. It may be that the use bf Yohimbine would be subject to the same limitations as Atropine, but it would seem that this action of Yohimbine certainly merits attention.ACTION THE HEART: The practical impossibility of obtaining in animals those pathological conditions of the heart for which cardiac remedies are useful, rende s mere physiological experiment a somewhat indecisive recommendation for the use of a drug in morbid heart conditions.Very small quantities of Yohimbine have bee shown to sloe the frog`" heart and increase the extent of its expansion. The completeness of its contraction is not diminished, so that it empties itself of a larger quantity of blood with each single beat. These actions might be found useful therapeutically. Yohirnbine differs from Strophanthas and Digitalis in not prolonging the duration, or greatly increasing the vigour of systolic contraction, so that while it might not . be useful alone, it might prove a satisfactory adjunct to other heart remedies in certain conditions.