Oscillations in Active Tension in Hamster Aortas: Role of the Endothelium

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Abstract
Hamster thoracic aortas displayed rhythmic oscillations in active tension when stimulated with the αi-adrenergic agonist, phenylephrine, prostaglandin F2α (PGF2α), and a number of other agonists, but not when activated with K+. These oscillations were not affected by adrenergic or cholinergic antagonists, or an inhibitor of prostaglandin synthesis. However, removal of the endothelium from these vessels eliminated this rhythmic activity. Furthermore, exposure to methylene blue or hemoglobin (known inhibitors of endothelium-dependent phenomena) significantly reduced the amplitude and the frequency of the oscillations. Removal of extracellular calcium ions or treatment with the calcium channel blocker, verapamil, also inhibited the oscillations even when active tension was maintained. These data suggest that the oscillations in agonist-induced active tension depend on a functional endothelium, and possibly an endothelium-derived factor, and the influx of extracellular calcium. This study also demonstrates that, like most other species, hamster aortas display endothelium-dependent relaxation to muscarinic agonists, such as methacholine, and the calcium ionophore A23187.