Aging and cholinergic responses in bovine trachealis muscle

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Abstract
1 The relative potencies of muscarinic agonists on bovine tracheal smooth muscle were unchanged as a consequence of aging and were carbachol > oxotremorine > muscarine > pilocarpine > McNeil A-343. 2 During aging, the potencies of carbachol, oxotremorine, McNeil A-343 and pilocarpine, but not muscarine, were reduced. 3 Maximal induced tensions to all the agents studied were reduced as a consequence of age. 4 Irreversible antagonism with benzilylcholine mustard showed that agonist efficacy was significantly reduced during aging. 5 Estimated receptor occupancy at the EC50 was significantly greater in tracheal tissues from the mature versus immature cows for every agonist studied. 6 The dissociation constants for full agonists (carbachol, oxotremorine and methacholine) were decreased with maturation while the converse was observed with partial agonists (McNeil A-343, pilocarpine). 7 We conclude that there are significant changes in the properties and coupling of muscarinic receptors during aging. These changes may contribute to the reduced airway reactivity seen in vivo.