Further examination of the inhibitory actions of alpha 1-adrenoceptor agonists in rat vas deferens.

The inhibitory actions of alpha 1-adrenoceptor agonists were examined in the isolated bisected vas deferens of the rat. The calcium entry facilitator Bay K 8644 markedly potentiated the isometric contraction to a single stimulus pulse in epididymal portions of rat vas deferens: subsequent amidephrine produced an inhibition which was antagonised by the alpha 1-adrenoceptor antagonist, prazosin, but not by the alpha 2-adrenoceptor antagonist, yohimbine. The alpha 1-adrenoceptor agonists amidephrine and cirazoline failed to inhibit the transmitter overflow to trains of pulses at a frequency of 2 Hz in epididymal portions, but also failed to abolish the nifedipine-resistant adrenergic contraction to trains of pulses at 2 Hz in epididymal portions. It is concluded that alpha 1-adrenoceptor agonists have inhibitory effects which may be by action at presynaptic alpha 1-adrenoceptors.