Sympathetic co-transmission to the cauda epididymis of the rat: Characterization of postjunctional adrenoceptors and purinoceptors

Abstract

1. Electrical field stimulation (10 Hz, 60 V, 1 ms, for 10 s) produced monophasic contractions of isolated preparations of rat cauda epididymis which could be abolished by guanethidine, and attenuated by prazosin and α,β-methylene ATP. 2. The rank order of potency of adrenoceptor agonists in causing contraction of the preparation in the presence of the neuronal uptake blocker, nisoxetine (0.1 μM) was: adrenaline ≥ phenylephrine ≥ noradrenaline > clonidine > methoxamine > metaraminol > dopamine ≥ isoprenaline > xylazine. 3. Responses to the agonists were blocked by prazosin but not by propranolol or idazoxan. 4. The rank order of potency of purinoceptor agonists in causing contraction of the cauda epididymis was: α,β-methylene ATP > β,γ-methylene ATP ≥ 2-methylthioATP > ATP > ADP. AMP and adenosine did not cause contractions. 5. Contractile responses to the purine nucleotide analogues were blocked by repeated application of α,β-methylene ATP. 6. It is concluded that both ATP and noradrenaline may act as co-transmitters in the sympathetic nerves supplying the smooth muscle of the rat cauda epididymis, and that α1-adrenoceptors and P(2X)-purinoceptors are present postjunctionally.