Effects of adrenoceptor antagonists on the hyperthermia and hyperglycemia induced by prostaglandin F2 alpha in rats

We investigated the effects of intraperitoneal administration of adrenoceptor antagonists to the hyperthermia and hyperglycemia induced by prostaglandin F2 alpha (50 micrograms) injected into the third cerebral ventricle in anesthetized rats. Phentolamine inhibited the hyperthermia and hyperglycemia induced by prostaglandin F2 alpha. Prazosin inhibited the hyperthermia induced by prostaglandin F2 alpha, while enhancing the hyperglycemia. Yohimbine inhibited the prostaglandin F2 alpha-induced hyperglycemia without an effect on the hyperthermia. Propranolol had no effect on either prostaglandin F2 alpha-induced hyperglycemia or hyperthermia. These observations suggest that the hyperglycemia induced by prostaglandin F2 alpha is regulated by alpha 2-adrenoceptor systems while the hyperthermia is regulated by alpha 1-adrenoceptor systems in rats.

Manipulation of norepinephrine metabolism with yohimbine in the treatment of autonomic failure

It has been postulated that alpha 2-adrenergic receptors play a modulatory role in the regulation of blood pressure. Activation of alpha 2-receptors located in the central nervous system results in inhibition of sympathetic tone and decrease of blood pressure. This indeed may be the mechanism of action of central sympatholytic antihypertensives such as alpha-methyldopa. Presynaptic alpha 2-receptors also are found in adrenergic nerve terminals. These receptors act as a negative feedback mechanism by inhibiting the release of norepinephrine. The relevance of alpha 2-adrenergic receptors for blood pressure regulation can be explored with yohimbine, a selective antagonist of these receptors. Yohimbine increases blood pressure in resting normal volunteers. This effect is associated with an increase in both sympathetic nerve activity, reflecting an increase in central sympathetic outflow, and in norepinephrine spillover, reflecting potentiation of the release of norepinephrine from adrenergic nerve terminals. These actions, therefore, underscore the importance of alpha 2-adrenergic receptors for blood pressure regulation even under resting conditions. Patients with autonomic failure, even those with severe sympathetic deprivation, are hypersensitive to the pressor effects of yohimbine. This increased responsiveness can be explained by sensitization of adrenergic receptors, analogous to denervation supersensitivity, and by the lack of autonomic reflexes that would normally buffer any increase in blood pressure. Preliminary studies suggest that the effectiveness of yohimbine in autonomic failure can be enhanced with monoamine oxidase inhibitors. Used in combination, yohimbine increases norepinephrine release, whereas monoamine oxidase inhibitors inhibit its degradation. Therefore, yohimbine is not only a useful tool in the study of blood pressure regulation, but may offer a therapeutic option in autonomic dysfunction.

Yohimbine in the treatment of erectile disorder

Yohimbine is an alkaloid derived mainly from the bark of the African tree, Pausinystalia yohimbe. Although many pharmacological properties of yohimbine have been described, at the plasma concentration attained at recommended dosages in man the predominant activity is antagonism of alpha 2-adrenoceptors. For more than 70 years yohimbine has been used as a treatment for male and female sexual difficulties. It has enjoyed a reputation as an aphrodisiac although no effect on sexual drive in humans has been adequately demonstrated. Yohimbine has been evaluated in the management of erectile disorder by means of placebo-controlled but often poorly designed trials. It does appear to have a modest therapeutic benefit over placebo, particularly in essentially psychogenic erectile disorder, and is generally well tolerated. Yohimbine is not licensed in the UK.

Prosexual drugs: empirical status of the "new aphrodisiacs"

The search for an effective aphrodisiac has been a perennial pursuit of most societies throughout history. In the past decade, attention has focused increasingly on the prosexual effects of oral pharmacological agents with central neurotransmitter actions. The role of various dopaminergic, adrenergic, and serotonergic agents, in particular, has been intensively investigated in both human and animal studies. Some of these drugs have been considered for their potential role in the treatment of sexual dysfunction, while others have contributed to our understanding of basic neurophysiological processes in sexual arousal. This review provides a critical evaluation of current laboratory and clinical research on the "new aphrodisiacs," including studies in both patient populations and normal volunteers. Several conceptual and methodological problems are addressed, such as the definition and measurement of sexual response, the need to separate specific and nonspecific drug effects on sexual response, and the lack of studies in women. Although no single drug has proven to be clinically safe and reliably effective for human use, several promising candidates have been identified. Overall, research on prosexual drugs has contributed significantly to our understanding of basic mechanisms in sexual response, as well as providing new treatment options for common sexual disorders.

Influence of alpha 1- and alpha 2-adrenoceptor antagonist therapy on the development of hypertension in spontaneously hypertensive rats

There is general agreement that the sympathetic nervous system is involved in the development of hypertension in spontaneously hypertensive rats (SHR). However, in a previous study we established that chronic administration of the selective alpha 1-adrenoceptor antagonist terazosin to SHR failed to prevent this phenomenon. In the present study, we extended that investigation further by examining the effects of another selective alpha 1-antagonist (doxazosin), an alpha 2-adrenoceptor antagonist (yohimbine), and a combination of these agents. Chronic administration of doxazosin and yohimbine produced receptor blockade, as determined by their effect on blood pressure (BP) responses to norepinephrine (NE) and phenylephrine. Chronic administration of either antagonist alone or the two in combination failed to prevent the development of hypertension in SHR, however. These findings suggest that although there may be a need for involvement of the sympathetic nervous system in the development of hypertension in SHR, its influence on this process is not mediated through activation of alpha-adrenoceptors.

[Intracavernous infusion of drugs]

In 1982 Virag presented the initial experience of use in diagnosis and treatment of impotence. PGE1 has been showed a safe and effectiveness drug. From september 1989 to october 1991 210 patients with erectile disorders were managed by I.C.I. with PGE1 with minimal side effects.

[Transdermal therapy of erectile insufficiency]

The introduction of intracavernosal (i.c.) administration of vasoactive drugs has revolutionized diagnosis and treatment of sexual impotence. This procedure, though, carries some risks and undesired side-effects, such as fibrosis, priapism, hematomas, etc. Thus, at our Centre has been evaluated the possibility of a transdermal (TS), either active or passive, treatment of impotence. In a first trial, double blind crossover, 62 patients have been treated with yohimbine (YOH) as ointment. About 5 mg of the drug were applied at the balanopreputial sulcus, twice daily. In 10 patients YOH was also assayed by HPLC in the blood drawn from the corpora cavernosa after the application of the drug: a rapid adsorption of the drug was demonstrated and a peak value of 58 ng/ml at 25 min. Treatment with YOH was particularly satisfactory in patients with impotence of recent onset and mild degree, that is without major vascular alterations. The active TD drug administration was tested with papaverine delivered with cavernous bodies by a C.T.D.A.S. (Controlled Transdermal Drugs Administration System). Thin layer chromatography has shown the passage of about 10% of patients a relevant amelioration of erectile function was observed.

Treatment options for men with sexual dysfunction

Erectile dysfunction can occur in men of any age, but it is more common in older men. It is one of the most devastating problems a man can face. An estimated 10 to 12 million American men experience impotence. Increased sexual expectations for an aging population have resulted in an increased interest in the treatment of impotence. Treatment options range from a simple adjustment in medication to surgical implantation of a penile prosthesis. The good news is that sexual function can almost always be restored. The bad news is that many men with chronic erectile dysfunction never seek help. A sensitive nurse who has an understanding of sexual health and functioning and the conditions that interfere with them can steer those who need help in the direction of treatment.

Yohimbine treatment of sexual side effects induced by serotonin reuptake blockers

BACKGROUND

Preclinical and clinical studies suggest that yohimbine facilitates sexual behavior and may be helpful in the treatment of male impotence. A single case report suggests that yohimbine may be used to treat the sexual side effects of clomipramine. This study evaluated yohimbine as a treatment for the sexual side effects caused by serotonin reuptake blockers.

METHOD

Six patients with either obsessive compulsive disorder, trichotillomania, anxiety, or affective disorders who suffered sexual side effects after treatment with serotonin reuptake blockers were given yohimbine on a p.r.n. basis in an open clinical trial. Various doses of yohimbine were used to determine the ideal dose for each patient.

RESULTS

Five of the six patients experienced improved sexual functioning after taking yohimbine. One patient who failed to comply with yohimbine treatment had no therapeutic effects. Side effects of yohimbine included excessive sweating, increased anxiety, and a wound-up feeling in some patients.

CONCLUSION

The results of this study indicate that yohimbine may be an effective treatment for the sexual side effects caused by serotonin reuptake blockers. Future controlled studies are needed to further investigate the effectiveness and safety of yohimbine for this indication.

Fluoxetine-induced sexual dysfunction and an open trial of yohimbine

BACKGROUND

Reports of fluoxetine-induced sexual dysfunction have described orgasmic and erectile difficulties but have neglected possible changes in sexual desire. This prospective study was undertaken to determine the percentages of patients experiencing different types of sexual dysfunction after successful antidepressant treatment with standard doses of fluoxetine. Additionally, an open trial of the alpha 2-adrenoceptor blocker yohimbine as a potential treatment for fluoxetine-induced sexual dysfunction was conducted in nine patients.

METHOD

Over a 2-year period, outpatients who had fulfilled DSM-III-R criteria for major depression and subsequently responded to treatment with fluoxetine 20-40 mg were asked to report and describe changes in sexual function. A small number of consecutive nongeriatric patients complaining of new onset sexual dysfunction were invited to participate in an open trial of yohimbine 5.4 mg t.i.d.

RESULTS

Fifty-four (34%) of 160 outpatients reported the onset of sexual dysfunction after successful treatment with fluoxetine: 16 (10%) of the 160 patients reported decreased libido, 21 (13%) patients reported decreased sexual response, and 17 (11%) patients reported declines in both areas. Eight of nine patients reported improvement in sexual function with yohimbine, although five patients reported side effects that led to discontinuation in two cases.

CONCLUSION

These findings suggest that (1) fluoxetine-induced sexual dysfunction may include decreased sexual desire as well as decreased physical functioning and may occur more frequently than previously appreciated and (2) fluoxetine-induced sexual dysfunction may be treatable with yohimbine.

Effects of yohimbine as a reversing agent for ketamine-xylazine anesthesia in budgerigars

Fourteen adult budgerigars (Melopsittacus undulatus) were anesthetized with a combination of ketamine hydrochloride (40 mg/kg) and xylazine hydrochloride (10 mg/kg) intramuscularly. Forty-five minutes after ketamine-xylazine injection, one of four yohimbine hydrochloride doses (0.0, 0.11, 0.275, or 0.44 mg/kg, IM) was administered in a 0.7% saline vehicle. Latencies were recorded in minutes from yohimbine injection until subjects' behavior indicated three different points of recovery: 1) lifting the head, 2) standing unaided without ataxia, and 3) perching. Means for all three recovery point latencies were significantly reduced by 0.275 mg/kg of yohimbine compared with saline vehicle alone. Mean latencies among treatment groups for each of the three recovery points were not significantly different, other than control versus treated groups. Based on these results, we recommend a yohimbine dose of 0.275 mg/kg as an effective reversing agent for ketamine-xylazine anesthesia in budgerigars.

[Endocavernous drug infusions revisited]

From the beginning of the eighties papaverine was well established as the drug of choice for diagnosis and management of vasculogenic impotence. In the second half of the eighties decade many authors referred on experimental use of PGE1 in erection disease. PGE1 has been showed a safe and effectiveness drug. During the period September 1989-October 1990 at our Institution 98 pts. with erectile disorders were managed by I.C.I. with PGE1. Out of 98 cases 88 had success. Prolonged erection occurred in 4 pts. (4.2%). 10 pts. showed only tumescence. So there are been treated by I.C.I. with combined papaverine and PGE1 with better results. No side effects were formed in 10 pts. managed by self-injection of PGE1.

Does yohimbine act as a slimming drug?

Yohimbine, an alpha 2-receptor antagonist, was examined for its suitability in the treatment of obesity. Twenty female obese outpatients were subjected to a 3-week low-energy diet (1,000 kcal/day), after which they were randomly allocated according to a double-blind study protocol to two treatments: 10 subjects received 5 mg yohimbine per os 4 times a day and 10 received a placebo for 3 weeks, in addition to a low-energy diet of 1,000 kcal/day. Before inclusion in the study, as well as the end of each of the 3-week treatment periods, thermogenesis (resting and exercise energy expenditure) was assessed by indirect calorimetry; serum noradrenaline concentration was taken as an index of sympathetic system activity and serum glycerol level as an index of lipolysis. Yohimbine significantly increased the mean weight loss in patients on a low-energy diet: 3.55 +/- 0.24 kg (yohimbine) vs. 2.21 +/- 0.37 kg (placebo), P less than 0.005. With yohimbine, a steady level of effort-induced energy expenditure and sympathetic system activity was maintained. No significant effect of yohimbine on lipolysis was observed under the experimental conditions of this study. In another group of 15 obese inpatients (11 women and 4 men) the influence of 15 mg yohimbine per os vs. placebo on gastric emptying of a radiolabelled solid meal was examined in a double-blind manner with the use of a gamma camera. No significant effect of yohimbine on gastric emptying was revealed--the mean gastric transit time was 42.0 +/- 0.4 min after placebo and 41.8 +/- 0.5 min after yohimbine. The results obtained warrant further research on the applicability of alpha 2-receptor inhibitory drugs as a supplementary management in the treatment of obesity.

Yohimbine does not affect fat distribution in men

Forty-seven men with a mean age of 42 years were assigned in random, double-blind fashion to treatment with either placebo or high-dose yohimbine (peak dose, 43 mg/day). Thirty-three subjects completed the six-month program. Variables assessed throughout the study included: body weight and body mass index; total cholesterol and HDL; body fat; and fat distribution as measured both by waist-to-hip ratio and by CT scan. Treatment with yohimbine had no effect on any variable in comparison with the control group.