Electrical and mechanical activity of rabbit prostate smooth muscles in response to nerve stimulation

1. The rabbit prostate contains two smooth muscle bundles: one forms the capsule of the prostate and the other runs longitudinally in the outermost layer of the prostate. The former was contracted by exogenously applied noradrenaline (NA) and the latter by acetylcholine (ACh), and were therefore identified as NA-sensitive and ACh-sensitive muscles, respectively. 2. In the NA-sensitive muscle, exogenously applied NA, but not ACh, depolarized the smooth muscle membrane, and this action of NA was antagonized by prazosin but not by yohimbine. The membrane of the ACh-sensitive muscle was depolarized by ACh and hyperpolarized by NA. The former was antagonized by atropine and the latter by phentolamine. 3. In both bundles, electrical stimulation of intramural nerves elicited a biphasic junction potential: an excitatory junction potential (EJP) followed by an inhibitory junction potential (IJP). In the NA-sensitive muscle, the EJP was resistant to alpha-adrenoreceptor antagonists and sensitive to guanethidine, while the IJP was sensitive to apamin and resistant to alpha- or beta-adrenoreceptor antagonists or guanethidine. The EJP and IJP elicited in the ACh-sensitive muscle were inhibited by atropine and apamin, respectively, but both potentials were resistant to alpha- or beta-adrenoreceptor antagonists or guanethidine. 4. Transmural nerve stimulation elicited a twitch contraction in both muscle bundles, and the contractions in the NA-sensitive muscle were partially inhibited by prazosin and blocked completely by guanethidine. The contraction of the ACh-sensitive muscle was blocked by atropine. Contractions produced by exogenously applied NA and ACh were antagonized by prazosin and atropine, respectively. 5. It is concluded that in the rabbit prostate there are two smooth muscles bundles which are respectively contracted with associated depolarization by NA or ACh. The NA-sensitive muscle receives adrenergic excitatory and non-adrenergic non-cholinergic inhibitory innervation. The ACh-sensitive muscle receives cholinergic excitatory and non-adrenergic non-cholinergic inhibitory innervation.