Function and distribution of autonomic receptors in canine ureteral smooth muscle

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Abstract
There have been only a few reports of the measurement of autonomic receptors in ureteral smooth muscle. Furthermore, it is so difficult to maintain stable spontaneous contractions in the ureter, that either electrical field stimulation or KCl at high concentrations are utilized to induce ureteral contractions in many in vitro ureteral pharmacologic examinations. We used the spiral ureteral strips which generate spontaneous contractions in the ureter in present experiments. Norepinephrine, phenylephrine, clonidine, carbachol, and prostaglandin F2α enhanced the spontaneous contractile force and/or increased the contractile frequency of spontaneous rhythmic contractions in spirally‐incised muscle strips from isolated canine ureters. In contrast, isoproterenol, terbutaline, a β2‐adrenergic agonist, and prostaglandin E2 reduced the spontaneous contractile force and/or decreased the contractile frequency of spontaneous rhythmic contractions. Dobutamine, a β1‐adrenergic agonist, did not affect significantly the spontaneous rhythmic contractions. The effects of the proslaglandins were not influenced by autonomic antagonists or tetrodotoxin. The existence of α1 ‐, α2 ‐, and β‐adrenoceptors and muscarinic cholinergic receptors were demonstrated in the canine ureter using radioligand techniques. The density of α1 ‐receptors binding sites was significantly greater than that of the other receptors examined. Our data show that the sympathetic nervous system is more involved than the para‐sympathetic nervous system in canine ureteral contractile activities, and that α – and β ‐receptors contained in canine ureteral smooth muscle are comprised mainly of the α1 – and β ‐subtypes. It is also suggested that prostaglandins directly affect canine ureteral contraction.