Phosphodiesterase inhibitors and endothelin as modulators of respiratory neurotransmission

1. Airway smooth muscle receives cholinergic, adrenergic and non-adrenergic, non-cholinergic (NANC) neural input. In guinea-pig airways cholinergic and NANC nerves provide contractile innervation, while adrenergic and NANC nerves provide relaxant pathways. In contrast, the major relaxant innervation in human airways is NANC in nature. 2. The present review describes the effects of selective phosphodiesterase (PDE) inhibitors on NANC relaxant and contractile responses in guinea-pig trachea as well as on NANC relaxations in human bronchus. 3. The effects of endothelin-1 on cholinergic contractile responses obtained in a variety of species are also assessed.