(-)-Amidephrine, a selective agonist for alpha 1-adrenoceptors.

The alpha-adrenoceptor activity of (-)-amidephrine in the isolated vas deferens of the rat was characterized. In this preparation (-)-amidephrine showed a selective activity on alpha 1-adrenoceptors, and failed to exert any effect on alpha 2-adrenoceptors. The alpha 1-adrenoceptor antagonists prazosin (pA2 8.19 and 8.48) and E-643 (pA2 8.36 and 8.25) inhibited the agonist activity of (-)-amidephrine and (-)-phenylephrine. The pA2 values obtained did not differ significantly, indicating that the two agonists exert their effect on the same receptor. The slopes of Schild plots were not significantly different from 1, suggesting that the inhibition was truly competitive in nature.