Adrenergic and 'non‐adrenergic' components in the contractile response of the vas deferens to a single indirect stimulus.

Publisher Website
Google Scholar
Abstract
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. The contraction in the whole vas consisted of 2 components, an initial, rapid, brief contraction reaching a maximum at 300 msec and a 2nd, 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 2 components varied. The initial rapid component was more prominent in the prostatic half and the slower, 2nd component more prominent in the epididymal half. Lowering the bath temperature caused these 2 components in both halves to merge into a single, slow, prolonged response, and before merging both were more rapid and briefer than in the equivalent response of rat anococcygeus. The 2nd, slow component was abolished by .alpha.-adrenoceptor antagonist drugs, potentiated and prolonged by drugs which inhibit the neuronal uptake of noradrenaline [norepinephrine] and absent from tissues taken from rats pretreated with reserpine, suggesting that the neurotransmitter for this component is noradrenaline. These experiments were extended to the mouse or guinea-pig vas deferens. Both showed the same 2 component mechanical response as the rat vas and in both the 2nd, slow component was preferentially inhibited by .alpha.-adrenoceptor antagonists and potentiated by drugs blocking noradrenaline uptake. 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 2nd, slow phase of contraction whereas apomorphine preferentially inhibited the 1st rapid phase. Guanethidine inhibited responses, but any differential effects could not be analysed due to its stimulant properties. There are 2 components even to the response to a single stimulus. The 2nd of these appears to be adrenergic while the transmitter responsible for the 1st remains to be determined.