A study of the post-tetanic twitch depression at the prostatic end of the rat vas deferens

The effects of different drugs on the post-tetanic twitch responses of the prostatic end of the isolation rat vas deferens were examined. Following repetitive field stimulation (4–5 Hz for 40–60 s), the post-tetanic twitches (0.2–0.5 Hz) were depressed relative to the steady-state pretetanic twiches. Maximum post-tetanic twitch depression (PTD) occurred 15–30 s after the tetanic stimulation. The PTD was not reversed but deepened and prolonged by the presynaptic ₂-adrenoceptor antagonists idazoxan (RX 781094) or yohimbine (10^–7 M) alone or combined with the neuronal uptake blocker, desipramine (10^–6 M). The PTD was insensitive to the -adrenoceptor blocker, propranolol (10^–6 M), the P₁-purinoceptor antagonist, 8-phenyltheophylline (10^–5 M) or the prostaglandin E synthesis inhibitor, indomethacin (10^–6 M). Pre- and post-tetanic contractions to superfused noradrenaline (NA), adenosine 5-triphosphate (ATP), or ,-methylene ATP (,-mATP) (bolus injections into superfusate, 1–8×10^–5 M) were not significantly (p<0.01) different. The PTD was absent in high magnesium (6.2–11.2 mM) solutions. These results are consistent with the PTD having an intrinsic presynaptic origin. They are discussed in relation to stimulation-induced modulation of transmitter release.