Yohimbine

Absorption

Rapidly absorbed following oral administration. Bioavailability is highly variable, ranging from 7 to 87% (mean 33%).

Description

Yohimbine is a natural alkaloid. It was first extracted from the barks of Corynanthe yohimbe, a species of Rubiaceae trees in West Africa. It was reported that, in the dried bark of Pausinystalia johimbe, the content of mixed alkaloids is higher than 6.1%, in which the main component is yohimbine, indicating a great prospect for development . Yohimbe bark has been used as an aphrodisiac in Africa since ancient times. In 1900, it was applied by Kowit and Muller to patients with impotence and paralytic insensitivity caused by neurasthenia and obtained curative effect. From then on, clinical application of yohimbine began. Currently, yohimbine is a pure plant preparation in the treatment of erectile dysfunction with more affirmation and more applications.

Description

Yohimbine is an indole alkaloid ester first identified in several herbal species by the American botanist R. Raymond-Hamet in 1934. Today its main sources are the African evergreen yohimbe (Pausinystalia yohimbe) and Indian snakeroot (Rauwolfia serpentina). Yohimbe bark is sold over the counter as an herbal aphrodisiac. Yohimbine hydrochloride is a prescription drug that has been used to treat erectile dysfunction with varying results.

Chemical properties

Glistening, needle-like alkaloid, soluble in alcohol and ether, very slightly soluble in water.

Physical properties

Appearance: white powder. Solubility: soluble in ethanol, chloroform, and hot benzene; slightly soluble in water and ether, usually salified by hydrochloric acid to increase its solubility in water. Specific rotatory power (°): D22 +105° (in water). Melting point: 241–246?°C.

History

Yohimbine has been used as an aphrodisiac for many years. At first, pharmacologists attributed its aphrodisiac effects to psychological effects similar to placebo or increasement of peripheral vascular congestion, rather than real sexual stimulation. Physiologists at the Stanford University first conducted a study on the pharmacological effects of yohimbine and found that yohimbine could increase the mating ability of rats , which was then published on Science in 1984 . In addition, researchers in the Queensland University in Canada conducted experiments on 23 patients with sexual dysfunction. Six of them recovered after taking the drug for 10?weeks. In 1987, Canadian scientists confirmed that yohimbine treatment in psychogenic impotence was safe and effective and this drug could restore the patient’ssexual ability . Besides, they proved that this medicine showed good curative effects on organic impotence.

The Uses of Yohimbine

Yohimbine occurs in Corinanthe johimbeK. and Rubiaceae trees. It is also foundin the roots of Rauwolfia serpentina L.and Apocyanaceae. Its derivatives areused therapeutically as adrenergic blockingagents.

The Uses of Yohimbine

Obtained from leaves and bark of Corynanthe johimbe. Formerly used as an aphrodisiac in veterinary medicine, yohimbine works primarily by acting as an antagonist at α2-adrenergic receptors.

Background

A plant alkaloid with alpha-2-adrenergic blocking activity. Yohimbine has been used as a mydriatic and in the treatment of impotence. It is also alleged to be an aphrodisiac.

Indications

Indicated as a sympatholytic and mydriatic. Impotence has been successfully treated with yohimbine in male patients with vascular or diabetic origins and psychogenic origins.

Definition

ChEBI: Yohimbine is an indole alkaloid with alpha2-adrenoceptor antagonist activity. It is produced by Corynanthe johimbe and Rauwolfia serpentina. It has a role as an alpha-adrenergic antagonist, a serotonergic antagonist and a dopamine receptor D2 antagonist. It is functionally related to a yohimbic acid.

Indications

This product is listed in the 2017 edition of the British Pharmacopoeia, 40 editions of the American Pharmacopoeia, and 9.0 edition of the European Pharmacopoeia. The main clinical application of yohimbine includes tablets and injections. It is mainly used to treat various types of impotence and sexual dysfunction in men.

General Description

Yohimbine (Yocon)is a competitive and selective 2-blocker. The compound isan indolealkylamine alkaloid and is found in the bark of thetree Pausinystalia yohimbe and in Rauwolfia root.

Health Hazard

Pharmacologically, yohimbine is an adrenergic blocking agent. It exhibits hypotensive and cardiostimulant activities. Poisoningfrom excessive doses may become severe,causing convulsions and respiratory failure
LD50 value, intraperitoneal (mice): 16 mg/kg
LD50 value, oral (mice): 37 mg/kg.

Biological Activity

α 2 -adrenoceptor antagonist (pK i values are 8.52, 8.00 and 9.17 for human a 2A , a 2B and a 2C receptors respectively).

Pharmacokinetics

Yohimbine is an indolalkylamine alkaloid with chemical similarity to reserpine. Yohimbine blocks presynaptic alpha-2 adrenergic receptors. Its action on peripheral blood vessels resembles that of reserpine, though it is weaker and of short duration. Yohimbine's peripheral autonomic nervous system effect is to increase parasympathetic (cholinergic) and decrease sympathetic (adrenergic) activity. It is to be noted that in male sexual performance, erection is linked to cholinergic activity and to alpha-2 adrenergic blockade which may theoretically result in increased penile inflow, decreased penile outflow or both. Yohimbine exerts a stimulating action on the mood and may increase anxiety. Such actions have not been adequately studied or related to dosage although they appear to require high doses of the drug. Yohimbine has a mild anti-diuretic action, probably via stimulation of hypothalmic center and release of posterior pituitary hormone. Reportedly Yohimbine exerts no significant influence on cardiac stimulation and other effects mediated by (beta)-adrenergic receptors. Its effect on blood pressure, if any, would be to lower it; however, no adequate studies are at hand to quantitate this effect in terms of Yohimbine dosage.

Pharmacology

Studies have shown that yohimbine has extensive pharmacological effects and has been developed for the clinical treatment of arteriosclerosis, rheumatism, and other diseases. The most obvious pharmacological action is in the treatment of male sexual dysfunction. Yohimbine tablets have been approved by the FDA and circulate in international markets. Yohimbine can selectively block the presynaptic alpha 2 receptors and promote the release of norepinephrine . It stimulates more norepinephrine released by cavernous nerve endings and reduces reflux of phallic vein, which is conducive to congestive erection. A small amount of application can make the perineum swell and stimulate the erection center at the spinal cord, leading to sexual hyperfunction . Yohimbine hydrochloride also has a psychological stimulant effect and increases libido. Like other types of adrenergic blocking drugs, yohimbine’s resistance to adrenergic mediator in blood circulation is much stronger than to sympathetic nerve impulse. Again, like tolazoline, yohimbine shows slight effect in resisting adrenergic response in ocular smooth muscle. This drug does not block the frequency and inotropic effects of epinephrine on mammalian hearts. Yohimbine has minor direct effects on smooth muscle, and its effect on the central nervous system is far less than that of ergot alkaloids, because yohimbine performs an excited-to-paralyzed action. This drug produces diuretic effect, probably due to the stimulation of the hypothalamus, resulting in release of posterior pituitary hormone. In addition, yohimbine has a significant local anesthetic effect .

Clinical Use

Yohimbine increases heart rate and blood pressure as aresult of its blockade of 2-receptors in the CNS. It has beenused experimentally to treat male erectile impotence.

Metabolism

Yohimbine appears to undergo extensive metabolism in an organ of high flow such as the liver or kidney, however, the precise metabolic fate of yohimbine has not been fully determined.

Purification Methods

Crystallise the alkaloid from EtOH, and dry it in a vacuum to remove EtOH of crystallisation. [Van Tamelen et al. J Am Chem Soc 91 7315 1969, Stork

Mode of action

Yohimbine is a selective α2-adrenergic antagonist. It is chemically similar to the alkaloid reserpine. Being a derivative of indolylalkylamine, it selectively blocks α2-adrenergic receptors. It weakens the negative feedback mechanism of norepinephrine release in nerve endings. It has a sympathomimetic effect, and can also cause sympathomimetic action. Additional research is evidently needed to conclusively delineate its pharmacological action.