Pilocarpine is a cholinergic agonist that primarily acts on the muscarinic receptors located in the salivary glands. These receptors are part of the parasympathetic nervous system, which regulates secretions such as saliva. When pilocarpine stimulates these muscarinic cholinergic receptors, it mimics the action of acetylcholine, leading to an increase in salivary secretion.

To break down the options:

- Option 1: Inhibiting alpha-adrenergic receptors – This would influence the sympathetic nervous system, but pilocarpine does not act here.
- Option 2: Stimulating muscarinic cholinergic receptors – This is the correct mechanism. Pilocarpine directly binds and activates muscarinic receptors, increasing saliva production.
- Option 3: Blocking beta-adrenergic receptors – Beta-adrenergic receptors are not primarily involved in salivary secretion control; thus, blocking them does not increase saliva.
- Option 4: Activating nicotinic receptors in salivary glands – Nicotinic receptors are mostly found in autonomic ganglia and neuromuscular junctions, not directly in the salivary glands.

In clinical practice, pilocarpine is commonly used to treat conditions like xerostomia (dry mouth), particularly in patients who have undergone radiation therapy affecting salivary glands or in Sjögren’s syndrome.

Key point: Pilocarpine’s therapeutic effect depends on its ability to stimulate muscarinic cholinergic receptors, thereby enhancing parasympathetic activity and promoting salivary secretion.

Reference: Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 13th Edition, Chapter 23, pp. 337-340