Genesis of basal sphincter pressure: effect of tetrodotoxin on lower esophageal sphincter pressure in opossum in vivo.

Currently it is believed that lower esophageal sphincter closure is maintained by tonic neurohormonal activity. Studies were performed to evaluate the role of neural and myogenic activity in the genesis of resting sphincter pressure in the opossum. The neural activity in the sphincter was blocked by intravenous administration of the puffer fish poison, tetrodotoxin, in intact animals. The respiration in these animals was assisted with a respirator, their blood pressure was supported by intravenous administration of Ringer's solution, and their body temperature was maintained by heating lamp. The lower esophageal sphincter pressures were measured with water-filled and continuously perfused catheters which were anchored to the lower esophageal sphincter using a new technique. Tetrodotoxin blocked the sphincter response to neural stimulation with vagal stimulation, esophageal distention, and local electrical stimulation of the sphincter. The mean resting sphincter pressure before tetrodotoxin was 59.0 +/- 2.6 mm Hg, and it was 64.4 +/- 6.9 mm Hg after tetrodotoxin (P greater than 0.05). During neural block with tetrodotoxin, the sphincter response to administration of isoproterenol or bethanechol was similar to that during the control period (P greater than 0.05). These studies show that: (1) Tetrodotoxin can be administered in intact animals to achieve complete block of neural activity in the lower esophageal sphincter; (2) sphincter muscle is not adversely affected by tetrodotoxin; and (3) block of neural activity does not alter the resting lower esophageal sphincter pressure.