The mechanical response of the longitudinal smooth muscle of the rat vas deferens to stimulation of its motor nerves by a single pulse has been examined. The motor nerves were stimulated in vivo via the spinal outflows in the pithed rat or in vitro by field stimulation. 2. The contraction in the whole vas consisted of two components, an initial, rapid, brief contraction reaching a maximum at 300 msec and a second, slower and more prolonged contraction reaching its maximum at 600 msec. When the isolated vas was divided into prostatic and epididymal halves the contribution of these two components varied. The initial rapid component was more prominent in the prostatic half and the slower, second component more prominent in the epididymal half. Lowering the bath temperature caused, in both halves, these two components to merge into a single, slow, prolonged response. Both components were more rapid and briefer than the equivalent response of rat anococcygeus. 3. The second, slow component was abolished by alpha-adrenoceptor antagonist drugs, potentiated and prolonged by drugs which inhibit the neuronal uptake of noradrenaline and absent from tissues taken from rats pre-treated with reserpine, suggesting that the neurotransmitter for this component is noradrenaline. 4. These experiments were extended to the mouse or guinea-pig vas deferens. Both showed the same two component mechanical response as the rat vas and in both the second, slow component was preferentially inhibited by alpha-adrenoceptor antagonists and potentiated by drugs blocking noradrenaline uptake. 5. Drugs known to reduce the response to repetitive nerve stimulation of the vas were examined for their effect on the response to a single stimulus. Lysergic acid diethylamide preferentially inhibited the second, slow phase of contraction whereas apomorphine preferentially inhibited the first rapid phase. Guanethidine inhibited responses but any differential effects could not be analysed due to its stimulant properties. 6. These results show that there are two components even to the response to a single stimulus. The second of these appears to be adrenergic while the transmitter responsible for the first remains to be determined.
