Evidence for an angiotensin receptor in esophageal smooth muscle of the opossum
Mukhopadhyay, A.K.; Leavitt, L.
American Journal of Physiology 235(6): E738-E742
1978
ISSN/ISBN: 0002-9513 PMID: 216272 Document Number: 133416
The purpose of this investigation was to study the effect of i.v. bolus administration of angiotensin II (AII) on the in vivo opossum lower esophageal sphincter (LES). Studies were performed on 41 adult opossums (Didelphis virginiana) with an assembly of intraesophageal catheters perfused with distilled water and connected to pressure transducers and a recorder. Drugs were injected i.v., intra-arterially in the left gastric artery (LGA), or in the wall of the esophagus (EW). Injection of 0.03, 0.06, 0.12, 0.25, 0.5 and 1 .mu.g/kg i.v. of AII produced 17, 37, 82, 137, 247 and 276% increases in LES pressure. Atropine (40, 250 and 500 .mu.g/kg i.v.), hexamethonium (15 mg/kg), and bilateral cervical vagotomy did not antagonize the effect of AII. The effect of AII was nearly completely blocked by saralasin, an angiotensin receptor blocking agent, 1 mg/kg i.v. (P < 0.001), and saralasin injected in the LGA, 250 .mu.g/kg (P < 0.001). Tetrodotoxin, injected in the EW, inhibited the effect significantly (P < 0.005). Phentolamine administered i.v. (2 mg/kg), an alpha adrenergic antagonist, antagonized the effect of AII on the LES significantly (P < 0.02), as did verapamil (100 .mu.g/kg), a Ca antagonist (P < 0.001). The LES has AII specific stimulatory receptors. AII acts both directly on the receptors in the LES as well as indirectly via the adrenergic nervous system. It is likely that the effect of AII involves a Ca-dependent pathway.