A pharmacological and ultrastructural study of alveolar contractile tissue in toad (Bu fo marinus) lung

The structure of the wall of the lung from the toad (Bufo marinus) has been examined using scanning and transmission electron microscopy and the presence of smooth muscle cells in the septal-alveolar walls detected. Responses of toad isolated lung parenchyma strip to agonists causing relaxation and contraction were measured and the potencies of adrenoceptor and 5-hydroxytryptamine receptor antagonists were determined. Results indicated the presence of populations of alpha- and beta-adrenoceptors in toad lung alveoli, both of which mediate relaxation responses. Stimulation of both alpha- and beta-adrenoceptors was required to cause complete relaxation. 5-Hydroxytryptamine also caused complete relaxation. A population of alpha-adrenoceptors mediating contraction may also exist in pulmonary vascular and or septal edge smooth muscle.