A member of the Apocynea, growing in equatorial Africa.

Composition

An alkaloid has been obtained from the bark, by L. Spiegel, who gave it the name yohimbin. It is a crystallizable principle having the formula C23H49N2O4 . It combines with acids to form salts, of which the most eligible is the hydrochlorate.

The dose of the hydrochlorate of yohimbin is 1/20 to 1/10 gr. This salt may be dispensed in solution. Of a one-per-cent solution the dose should be from one to ten minims.

Physiological Actions

The first study of the actions of yohimbin were made by Oberworth on both cold- and warm-blooded animals. It is a paralyzer of both classes of animals, inhibiting the central nervous system, leaving unimpaired the peripheral nerves and muscles. Electrical, chemical, and mechanical irritation of a motor nerve is followed by active contraction of the muscles to which it is distributed.

Yohimbin inhibits the heart's action finally in cold-blooded animals, stopping it in the diastole. The previous administration of atropine does not prevent this result. It is also a paralyzer of respiration, which becomes irregular in time and volume with the progress of the influence, and if artificial respiration is resorted to, death ensues by failure of the heart.

The blood-pressure falls as soon as the remedy is administered. This is due not to paresis of the muscular walls of the vessels, but to failure of the heart itself. The heart-beats are not increased by section of the vagi nor by the administration of atropine, nor does irritation of the vagus center or the peripheral vagus have any influence on the result. The actions of yohimbin on the circulation are therefore through the sympathetic or the motor ganglia of the heart, or both.

The most important effect is on the genito-urinary apparatus, causing active erections of the penis, emissions, and a general hyperaemia. No structural alterations take place in the kidneys and genitalia, notwithstanding the considerable hyperaemia and excitement which are produced by it in the whole apparatus.

Therapy

The applications of yohimbin to treatment have been thus far limited to a few maladies. In sexual neurasthenia, in impotence due to functional depression of the sexual apparatus, its use is warranted by the results of the observations on animals. As it has a marked and distinctive action on the genito-urinary apparatus, it should prove useful in the chronic forms of albuminuria. It is contra-indicated in acute affections of the kidneys, but in chronic Bright's disease and in such cases of albuminuria as are symptomatic of lowered vital action or depressed function, good results may be expected. This opinion is based on personal observation of appropriate cases, especially of chronic albuminuria, in which it has seemed to lessen the quantity of albumin present and to improve the general state.