PHARMACOLOGICAL STUDIES ON THE ROLE OF CHOLINERGIC NERVES IN THE NEUROMUSCULAR TRANSMISSION IN THE CIRCULAR SMOOTH MUSCLE OF GUINEA‐PIG VAS DEFERENS

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Abstract
Effects of various drugs were examined on the mechanical responses of the circular smooth muscle of guinea‐pig vas deferens evoked by field stimulation and ACh. During field stimulation (0.1 msec, 3–80 Hz) a contraction consisting of two (initial and second) phases occurred. In addition, another contraction (after‐response) occurred after the cessation of the stimulation particularly at higher frequencies (40–80 Hz). Guanethidine (2–20 μM) suppressed both the initial and second phases of the field stimulation‐evoked responses. Prazosin (0.1‐1 μM) suppressed the second phase but minimally affected the initial phase. Both phases were suppressed by atropine (0.1‐1 μM.) and potentiated by physostigmine (5 μM). dTC (0.5–20 μM) did not suppress either phase but potentiated the second phase. ACh (0.28–280 μM) produced a contraction, which was reduced by atropine but was little affected by either dTC or TTX. These results suggest that at the postsynaptic site of the neuromuscular junction in this tissue the sympathetic process activates the smooth muscle through two different types of receptor; one is non‐noradrenergic and the other is an α‐adrenoreceptor. In addition, a cholinergic process also activates the smooth muscle through muscarinic receptors.

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