Moxonidine reduces pilocarpine-induced salivation in rats

Cholinergic agonists activate salivation and the alpha2-adrenergic and imidazoline receptor agonists induce opposite effects. In the present study, we investigated the effects of intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of moxonidine (an alpha2-adrenergic and imidazoline receptor agonist) on the salivation induced by the cholinergic agonist pilocarpine. Male Holtzman rats with stainless steel cannula implanted into the lateral ventricle (LV) were used. In rats anesthetized with tribromoethanol (200 mg kg(-1), saliva was collected using pre-weighed small cotton balls inserted in the animal's mouth. The treatment with moxonidine (5, 10 and 20 nmol in 1 microl) injected i.c.v. reduced the salivation induced by pilocarpine (1 mg kg(-1)) injected i.p. (48 +/- 5, 17 +/- 2 and 15 +/- 2 mg min(-1) vs. control, 73 +/- 7 mg min(-1)). The same doses of moxonidine injected i.c.v. also reduced the salivary secretion induced by pilocarpine (500 nmol in 1 microl) injected i.c.v. (44 +/- 1, 14 +/- 2 and 20 +/- 3 mg min(-1) vs. control, 51 +/- 2 mg min(-1)). Injection of moxonidine (20 nmol in 0.1 ml) i.p. produced no change on i.p. pilocarpine-induced salivation (58 +/- 4 mg min(-1) vs. control, 50 +/- 4 mg min(-1)). The results show that central, but not peripheral, injection of moxonidine inhibits pilocarpine-induced salivation, suggesting that central mechanisms activated by alpha2-adrenergic/imidazoline agonists inhibit cholinergic-induced salivation in rats.