Drug Interactions and Receptors

Hello

For our pharmacology tutorial we were provided with software that simulates a guinea pig ileum suspended in a solution and we have to analyse the contraction response of the muscle using antagonist drugs and their effects on the contraction response of this ileum muscle.

Our results showed that at very high doses Hexamethonium reduced the contraction response to almost nothing in the presence of the following agonists: Carbachol, Methacholine, Histamine and Barium Chloride ions...how is this possible if Hexamethonium acts only on ganglia?? It can't bind to histamine receptors for example can it?? So how does the contraction reduce?

Also, anti-histamine drug Mepyramine appeared to reduce the effects of Methacholine, Carbachol, Acetylcholine and Barium Chloride ions as well but how? I thought anti-histamine drugs only bind to histamine receptors so how does this overall reduce the contractility of the ileum muscle??

Any help or explanations would be great, thanks!