Mechanism of action:
They cause non-depolarizing competitive blockage of ganglia. They compete with acetylcholine at postsynaptic nicotinic receptors.
Since the ganglia of sympathetic as well as parasympathetic nervous system are cholinergic so these agents obstruct the outflow through these systems.
Blockade of sympathetic outflow causes a decrease in firmness of the arterioles resulting in the reduced peripheral vascular resistance leading to postural or orthostatic hypotension.
Blockade of parasympathetic outflow causes:
1. A prominent reduction in the motility of the GI tract.
2. Dry mouth
3. Cycloplegia with a decrease in accommodation.
4. Precipitation of urinary retention in men with prostatic hypertrophy.
Mostly autonomic effects