Respiratory responses to pirenzepine in healthy subjects.

Since no information is available concerning the action of pirenzepine in vivo on human tracheobronchial tree, we evaluated the respiratory responses to pirenzepine in a group of healthy subjects. This clinical study suggests that pirenzepine exerts its bronchodilatory action on small airways (from 9th generation to distal airways), but not on larger airways, in normal subjects. These results are consistent with a probable presence of muscarinic high affinity receptors (M1 subtype) only in peripheral airways.