Effect of various neurotransmitters and electrical field stimulation on smooth muscle preparations from the esophagus of horses.

Abstract

The effects of various neurotransmitters and electrical field stimulation on muscle strips from the distal equine esophagus were studied. Acetylcholine (ACH) caused concentration dependent (1.1-55 x 10(-6) mol/l) contractions of the longitudinal and circular muscle strips from the distal esophagus as well as from the lower esophageal sphincter (LES). Atropine (10(-5) mol/l) blocked these contractions. Noradrenaline (NA) induced concentration related (1.1-55 x 10(-6) mol/l) contractions of the muscle strips from the LES. This excitatory effect of noradrenaline was antagonized by the alpha 1-receptor antagonist prazosin. Tetrodotoxin (5 x 10(-6) mol/l) did not affect the contractile response of the muscle strips to noradrenaline (55 x 10(-6) mol/l). Noradrenaline (1.1-55 x 10(-6) mol/l) had no excitatory effect on the circular and the longitudinal muscle strips from the esophagus. Furthermore, noradrenaline induced a concentration dependent (1.1-55 x 10(-6) mol/l) relaxation of the longitudinal muscle strips from the esophagus. The relaxing effect of NA was antagonized by the beta-receptor antagonist propranolol (10(-5) mol/l). Histamine (10(-7)-10(-6) mol/l) elicited a contraction in 4 out of 18 muscle preparations from the LES. The histamine induced contractions were partly antagonized by the H1-receptor antagonist clemastine (10(-4) mol/l) and fully abolished by the H2-receptor antagonist clemastine (10(-4) mol/l). Electrical field stimulation (EFS, 5 Hz, 2 ms; 500 mA; 10 Hz, 2 ms; 500 mA) produced tetrodotoxin sensitive contractions in all three types of muscle strips. Atropine (10(-5) mol/l) fully suppressed these contractions in most preparations.(ABSTRACT TRUNCATED AT 250 WORDS)