Pilocarpine-induced salivation and thirst in conscious rats

The muscarinic receptor agonist pilocarpine is widely used as a sialogogue. It has been well-established that it also induces water intake in animals. However, the mechanisms underlying the relationships between these events are unknown. To address this problem, we examined water intake and parotid salivary secretion in conscious rats. Intraperitoneally injected pilocarpine increased both water intake and salivary secretion. Intracerebroventricularly injected pilocarpine also induced water intake, but not salivary secretion. Intracerebroventricularly applied atropine, a muscarinic receptor antagonist, suppressed the water intake produced by pilocarpine applied intraperitoneally and intracerebroventricularly. However, it did not affect the salivary secretion induced by pilocarpine applied peripherally. We conclude that peripherally applied pilocarpine affects the parotid glands and the thirst center in the central nervous system, while it may induce salivary secretion mainly via peripheral responses, but water intake mainly via the central nervous system.