Regional variation in the distribution of alpha-adrenoreceptors in the vas deferens of the rat.

Experiments were performed with preparations obtained by medial transection of the rat vas deferens. Eight sympathomimetic drugs: noradrenaline, alpha-methylnoradrenaline, phenylephrine, dopamine, tyramine, amphetamine, cocaine and isoprenaline, were applied to preparations which were field-stimulated at 10 sec intervals. On the testicular half of the tissue all except isoprenaline enhanced twitches and/or caused contractions. These effects were blocked by alpha-adrenoreceptor antagonists. On the urethral preparation all except phenylephrine, which often enhanced twitches, inhibited responses to field stimulation. These effects were not blocked by alpha-adrenoreceptor antagonists or by propranolol, though the latter blocked inhibitory effects of isoprenaline on both segments. Inhibitory responses to tyramine persisted in urethral segments treated with cocaine and in urethral segments taken from reserpine-treated rats, and thus tyramine may have some direct action. No regional variation was observed in response to acetylcholine or carbachol. High potassium concentrations were equally effective in contracting both segments, but the time courses of contractions differed. These experiments confirm a density gradient of excitatory alpha-adrenoreceptors along the length of the rat vas deferens.