Yohimbine

YOHIMBINE, Yohimbinum (Spiegel), C₂₂H₂₆N₂O₃, a crystalline dextrorotatory alkaloid, obtained from the bark of the Corynanthe Yohimbe tree (also written as Johimbe and Johimbinum), family Rubiaceae (Cameroon region in tropical Africa). Some chemists (Fourneau) and pharmacologists (Cushny) identify it with quebrachine. In the native region of the tree, its bark has long been used by natives as an aphrodisiac. In experiments on animals (preferably dogs), even small doses of Y. (from 0.1 mg and slightly more per 1 kg of body weight) cause increased and deepened breathing, excitation similar to cocaine, and increased blood filling of the skin and visible mucous membranes, occurring due to the local vasodilatory effect of Y. on blood vessels. This action extends to the sexual organs, leading to strong dilation of the vessels of the testes and to erection resulting from the swelling of the cavernous bodies. The latter differs from that occurring under physiological conditions in that it involves only an increase in arterial inflow without difficulty in venous outflow, and therefore it is often not sufficiently complete. At doses that cause dilation of superficial vessels, blood pressure changes only very slightly; this indicates that here there is mainly a change in the distribution of blood. With increasing doses, strong vasodilation occurs with a fall in blood pressure. Excitation of the central nervous system is characterized, according to observations by several authors, by an increase in reflex excitability of the sacral part of the spinal cord occurring even with small doses, which leads to an increase in reflexes from the genitalia. Thus, tactile irritation of the external genitalia easily causes erection (it is possible that here also plays a role the increase in local sensitivity occurring due to sharp hyperemia). With increasing doses, poisoning develops with a sequential intensification of symptoms: shortness of breath, trembling (and convulsions), salivation, vomiting, diarrhea, etc. At doses above 1 mg per 1 kg of body weight, the effect on the sexual sphere becomes no longer so clear, being overshadowed by other symptoms. This obviously explains the negative conclusions of Kravkov, who in his experiments on dogs used exactly these doses. On the heart, Y. acts only in very large doses, directly depressing its muscle. Death occurs with symptoms of paralysis of the central nervous system, and dogs tolerate doses above 10 mg per 1 kg of body weight. - Y. has found application as an aphrodisiac (increasing potency) in both medical and veterinary practice. Yohimbine is also used in various combinations in the treatment of hypertension; opinions about its benefit in hypertension differ considerably. Y. has a certain local anesthetic effect, which led to the proposal to use it in ophthalmic practice (in 1% solutions). In this case, one must take into account its vasodilatory effect; The pharmacological effect of Y. when administered orally is significantly less reliable than when administered subcutaneously. With prolonged use of Y., no habituation to it is observed. - Yohimbinum hydrochloricum - a water- and alcohol-soluble salt; a more stable preparation compared to pure Y.; 0.005-0.01 several times a day. Maximum 0.03 per dose and 0.1 per day. - Dynatin - a combination of papaverine with tartaric acid Y. in tablets of 0.01 and ampoules of 0.015 and 0.025. - Vasotonin - a combination of 0.01 yohimbine and 0.05 urethane in tablets and ampoules.