Which agent is known for having the greatest antimuscarinic/vagolytic actions?

Gallamine is the agent recognized for its significant antimuscarinic and vagolytic properties. This means that it can block the action of the neurotransmitter acetylcholine at muscarinic receptors, which are found in various locations in the body, including the heart and smooth muscles. By doing so, gallamine can lead to effects such as increased heart rate and decreased secretions, making it valuable in certain clinical situations where such effects are desired.

In contrast, other agents listed do not possess the same level of antimuscarinic effects. Succinylcholine is primarily a depolarizing neuromuscular blocker, and while it does have some physiologic effects on the autonomic nervous system, it is not characterized as an antimuscarinic agent. Pancuronium, while it has some vagolytic action, is not as pronounced as that of gallamine. D-Tubocurarine mainly acts as a neuromuscular blocker without significant vagolytic or antimuscarinic actions. Therefore, gallamine stands out as the most effective choice in terms of antimuscarinic/vagolytic actions.