3H‐Noradrenaline Release and Mechanical Response in the Field Stimulated Mouse Vas Deferens

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Abstract
Isolated mouse vas deferens was preincubated with3H‐noradrenaline (3H‐NA) and then mounted in a small glass chamber where it was superfused with buffer and stimulated by an electrical field. Tritium overflow into the buffer and mechanical activity was followed.Almost all the radioactivity taken up and retained in the vas deferens, and about 75 % of the tritium overflow during stimulation was due to3H‐NA. Stimulation for 30 sec at 4–16 Hz caused a biphasic contraction of the vas deferens with an initial rapid twitch and a second tetanus‐like phase of contraction. The stimulation‐induced tritium overflow during stimulation at 16 Hz for 30 sec was 1.8 %(i.e.1.8 % of the total tritium content of the vas deferens was overflowing in response to stimulation). The fraction of the tritium content of the vas deferens overflowingperimpulse at different frequencies of stimulation was the same at 1–16 Hz and was around 3.5 xlO“5. Upon stimulation for various time periods (10–120 sec) the stimulation‐induced overflow was found to be proportional to time. The mechanical response, on the other hand, decreased upon prolonged stimulation.No contractions were elicited in vas deferens from mice pretreated with 6‐OH‐dopamine. Atropine did not affect the response to stimulation. No contraction and no stimulation‐induced overflow was obtained when tetrodotoxin was added to the superfusing buffer. Inhibition of neuronal uptake of NA by desipramine potentiated the contraction caused by stimulation, but the stimulation‐induced overflow was almost unchanged. The a‐receptor blocking drugs phentolamine and phenoxybenzamine decreased the second phase of contraction and increased the stimulation‐induced overflow. Papaverine inhibited the contraction and increased the stimulation‐induced overflow. Stimulation of a‐receptors by methoxamine potentiated the contraction and decreased the stimulation‐induced overflow.From the drug‐experiments it is concluded that a decreased effector response is accompanied by an increased3H‐NA release, while an increased effector response is accompanied by a decreased3H‐NA release. The results indicate the existence of a transsynaptic regulatory mechanism for NA release.