Effects of a new 2-piperazinotetralin on alpha-1 and alpha-2 adrenergic receptors in isolated rat vas deferens.

The pharmacological action of a newly synthesized piperazine derivative of 2-aminotetralin (P11) on pre- and postsynaptic alpha-adrenoceptors of isolated rat vas deferens has been investigated. P11 shifted noradrenaline concentration-effect curves to the right. The pA2 value was 5.88 for P11, 5.38 for phentolamine, and 7.73 for prazosin. The maximum effect of the agonist was enhanced by P11 and phentolamine, but this enhancement was less pronounced in the presence of 1 X 10(-5) M cocaine and 1 X 10(-6) M propranolol. 1 X 10(-6) M to 1 X 10(-5) M P11 increased the contractions of a field-stimulated vas deferens and antagonized the effects of clonidine (1 X 10(-9) M on the same preparation. The IC50 values of P11, phentolamine and prazosin were 0.40 microM, 0.03 microM and greater than 10.0 microM, respectively. The results show that P11 possesses alpha 1-and alpha 2-adrenolytic activity. The effect of P11 on these receptors most likely participates in the mechanisms of its hypotensive action.