Effects of yohimbine on submaxillary salivation in dogs

Abstract

1 The effects of yohimbine (0.5mg kg-i.v.) on both resting and parasympathetic and sympathetic stimulation-induced submaxillary salivary responses were investigated in the anaesthetized dog. 2 Salivary secretion was increased significantly for a period of 45min following an injection of yohimbine. 3 Sectioning of the chorda tympani (but not the cervical sympathetic) nerve abolished the yohimbine-induced increase in resting salivary secretion and potentiated that elicited by electrical stimulation of the chorda tympani nerve. 4 These results show that yohimbine increases submaxillary secretion by inhibition of presynaptic a2-adrenoceptors located on the chorda tympani, which inhibit cholinergic transmission.

Pharmacokinetic study of yohimbine and its pharmacodynamic effects on salivary secretion in patients treated with tricyclic antidepressants.

“…Plasma levels of yohimbine measured 90 min after yohimbine administration were higher under clomipramine or related compounds than in controls. These results confirm the interaction described above and could explain the time course of the effects of yohimbine in patients treated by tricyclic antidepressants: 4 h after 10 mg and 3 h after 4 mg. This duration is not in accordance with the short half-life of yohimbine: ti,, = 0.6 h [9,10].…”

“…The increase in plasma noradrenaline levels is explained by the blockade of oc2-adrenoceptors located on the sympathetic nerve endings and on central neurones leading to a rise in noradrenaline release [2]. A similar time course was observed for salivary secretion: its mechanism involves a blockade of presynaptic 0L2-adrenoceptors located on the chorda tympani leading to inhibition of cholinergic transmission [4]. The stimulant effect of yohimbine on salivary secretion was accompanied by improved buccal comfort as revealed by the visual analogue scale.…”

“…Among these side effects, tachycardia and tremor could be a manifestation of panic attack induced by yohimbine, but none of these patients mentioned a psychic symptoms of anxiety. The occurrence of these side effects led us to investigate in a second protocol the effect of a lower dose of yohimbine (4 mg). This dose increased salivary volume in patients by tricyclic antidepressants but not in healthy volunteers.…”

“…Until now, few drugs have clearly demonstrated their efficacy in the treatment of this side effect. Acute administration of yohimbine, a selective antagonist for a2-adrenoceptors [2,3], was found to increase salivary outflow in animals [4,5] as well as in healthy volunteers [6]. This acute effect was also observed in depressed patients treated with tricyclic antidepressants and suffering from dry mouth [7].…”

Mechanisms of sympathetic enhancement and inhibition of parasympathetically induced salivary secretion in anaesthetized dogs

“…Sympathetic contraction of myoepithelial cells has been found to be exclusively an a-adrenergic activity; this is in agreement with our finding that the sympathetic enhancing effect is via an aladrenergic activity. It has also been shown that the myoepithelial cells are affected by both divisions of the autonomic nervous system in the same direction (Garrett, 1987 Some workers have reported a presynaptic a2-adrenoceptor inhibition of cholinergic transmission in the dog submandibular gland, based on the finding that intravenous yohimbine induces spontaneous salivary secretion with the response abolished after the section of the chorda tympani nerve (Montastruc et al, 1989). Postsynaptic M2-adrenoceptor receptors have been localized in the submandibular gland of some animal species (Bylund & Martinez, 1981).…”