Effects of LP-805, a new vasodilating agent, on rat thoracic aorta

1. In canine coronary arteries, the contraction induced by prostaglandin F2 alpha (PGF2 alpha), but not by 65.9 mM K+, were relaxed by LP-805 (0.01-10 microM) in a concentration-dependent manner. 2. In rat thoracic aorta, LP-805 (0.1-10 microM) also relaxed the preparations contracted with norepinephrine (NE) and PGF2 alpha, but did not relax the contraction produced by 65.9 mM K+. 3. LP-805 (3-10 microM) inhibited the increase in cytosolic Ca2+ levels and contractions evoked by NE (1 microM) in the absence or presence of external Ca2+ in rat thoracic aorta. 4. LP-805 (0.1-10 microM) inhibited synthesis of IP3 induced by NE (0.3 microM) and cyclic AMP phosphodiesterase activity, and increased intracellular cyclic AMP levels in rat thoracic aorta. 5. These results suggest that a vasodilatory effect of LP-805 is due to inhibiting the increase in cytosolic Ca2+ levels via stimulation of various receptors, modulating second messenger synthesis.