Is yohimbine-induced increase in salivary secretion a kinin-dependent mechanism?

Yohimbine: a clinical review

Although yohimbine (YOH) has been available for the treatment of male erectile dysfunction (ED) for longer than Viagra, there is a perception that little is known about the clinical performance of the drug. This review attempts, by comprehensive analysis of the literature, to cover the clinical, pharmacological, and therapeutic profiles of YOH, relevant to its potential utility in the management of patients with ED. Relatively few well-designed studies have been completed. From these, however, it can be concluded that YOH as monotherapy possesses only modest efficacy in ED patients. In acute and chronic (long-term) studies, YOH has been found to be relatively free of side effects over the dose range predicted to be effective in ED. At much higher doses, the most frequently observed effects, consistent with the primary pharmacological action of the drug, are elevation of blood pressure, a slight anxiogenic action, and increased frequency of urination. These side effects are all easily reversible on termination of YOH therapy. There is increasing evidence that the erectogenic action of YOH can be augmented by concomitant administration of agents that augment the release and/or action of nitric oxide in the corpus cavernosum. YOH has yet to be studied in female sexual dysfunction. Overall, the benefit risk profile of YOH would indicate that it has potential, more probably as part of a combination strategy, e.g., with a drug that enhances the nitric oxide pathway, in the treatment of ED.

Evidence for activation of both adrenergic and cholinergic nervous pathways by yohimbine, an alpha 2-adrenoceptor antagonist

Adrenoceptors are involved in the control of the activity of the autonomic nervous system and especially the sympathetic nervous system. Activation of alpha 2-adrenoceptors decreases sympathetic tone whereas their blockade has an opposite effect. However, previous investigations have shown that yohimbine (a potent alpha 2-adrenoceptor antagonist) increases salivary secretion through activation of cholinergic pathways. The aim of the present experiment was to investigate the involvement of both the sympathetic and the parasympathetic system in several pharmacological effects of yohimbine. For this purpose, salivary secretion and various endocrino-metabolic parameters (noradrenaline and insulin secretions, lipomobilization) were evaluated in conscious fasting dogs before and after blockade of either the sympathetic (with the beta-adrenoceptor antagonist agent nadolol) or the parasympathetic (with the anticholinergic agent atropine) systems. Yohimbine alone (0.4 mg.kg-1, i.v.) increased within 5-15 minutes, plasma noradrenaline (600%), insulin levels (300%), free-fatty acids (79%) and salivary secretion (143%). Atropine (0.2 mg.kg-1, i.v.) suppressed yohimbine-induced salivary secretion (90%) but did not significantly modify the yohimbine induced changes in noradrenaline (312%), insulin (277%) and free-fatty acids (102%) plasma levels. Administration of nadolol (1 mg.kg-1, i.v.) did not change the magnitude of the increase in both noradrenaline plasma levels (550%) and salivary secretion (300%) induced by yohimbine. However, nadolol totally blunted the increase in insulin (15%) and free-fatty acids (4%) plasma levels. These results show that yohimbine-induced increase in salivary secretion is a cholinergic effect whereas the increase in insulin and free fatty acids can be explained by an increase in sympathetic tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 3 weeks treatment with yohimbine on salivary secretion in healthy volunteers and in depressed patients treated with tricyclic antidepressants

The effect of yohimbine treatment (4 mg three times daily) for 3 weeks on salivary secretion was investigated. In healthy volunteers, acute administration of yohimbine increased salivary volume within 1 h to a similar extent before and at the end of the treatment period. In depressed patients treated with tricyclic antidepressants (and exhibiting a reduced salivary flow), yohimbine also acutely increased salivary volume. In contrast, the alpha 2-adrenoceptor antagonist failed to modify resting values measured in the morning (i.e. 10 and 14 h after the last administration in healthy volunteers and depressed patients respectively). This result indicates that alpha 2-adrenoceptor antagonists may have a potential therapeutic use in the treatment of dry mouth caused by tricyclic antidepressant drugs.