POSSIBLE INTERACTION OF CHOLINERGIC NERVES WITH TWO DIFFERENT (PRE AND POST) SITES OF THE NEUROMUSCULAR JUNCTION IN GUINEA‐PIG VAS DEFERENS

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Abstract
1. Effects of various durgs on the mechanical responses of the longitudinal smooth muscle of guinea-pig vas deferens evoked by ACh and field nerve stimulation were examined. 2. ACh (28-280 .mu.M) produced a contraction consisting of two phases. The first phase of the contraction was suppressed by guanethidine and by nicotinic antagonists. The second phase was suppressed only by atropine. Both phases were unaffected by TTX or prazosin. 3. Field stimulation (0.1 msec, 40 Hz) evoked contractions which also consisted of two (early and late) phases. Guanethidine (0.1-1 .mu.M) suppressed both phases whilst prazosin (1 .mu.M) suppressed only the late phase. 4. Atropine (0.1 .mu.M) suppressed both phases while physostigmine (5 .mu.M) potentiated both phases of field stimulation-evoked contractions. 5. Pentolinium suppressed both phases of field stimulation-evoked contractions at low concentrations (210 .mu.M), but potentiated then at a higher concentration (10 .mu.M). 6. dTC at a low concentration (0.5 .mu.M) suppressed the early phase, but slightly enhanced the late phase of field stimulation responses. At a higher concentration (20 .mu.M), dTC potentiated both phases of the response. 7. Pentolinium and dTC did not affect the contractions induced by 90 mM-K ions, ATP or NA. 8. These results suggest that cholinergic nerves possess an excitatory action not only directly at the smooth muscle but also at the noradrenergic nerve terminals. The role of each receptor is discussed further.