Effects of Serotonin and Histamine on the contractile activity of smooth-muscle strips of sheep complex stomach.

The effect of histamine and serotonin is studied on strips of the two smooth-muscle layers from the different sections of the complex stomach. Histamine in concentration of 10(-9) to 10(-4) g/ml has no visible effect on preparations from the rumen and reticulum. In strips from the omasum as well as from the proximal and antral regions of the abomasum inhibitory effect is observed mainly with respect to the spontaneous phasic activity of the strips. Serotonin in concentrations of 10(-8) to 10(-4) g/ml has an excitatory effect in almost all preparations studied. Of the forestomach strips it is mostpronouced in rumen strips. The effect consists in an increase of the tone of the preparations. In the proximal region of the abomasum is effect also consists in a rise of the tone, while in strips from the antral region it causes a rise in the amplitude and frequency of the phasic contractions. Serotonin in the concentrations tested has an inhibitory effect only on omasum preparations.