What neurotransmitter, when stimulating muscarinic receptors, can increase bronchial and salivary mucous production?

Acetylcholine acting on muscarinic receptors (parasympathetic stimulation) increases secretory gland activity, including bronchial mucous production and salivary flow — the physiologic basis for why anticholinergic drugs (which block these receptors) cause dry mouth and reduced secretions as a side effect.