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Inhibition and excitation of reticulo-rumen contractions following the introduction of acids into the rumen and abomasum



Inhibition and excitation of reticulo-rumen contractions following the introduction of acids into the rumen and abomasum



Journal of Physiology 147(1): 58-73



The relation between pH of rumen contents and motility of the forestomach and the mechanism of action of the effects produced were studied in sheep. Buffered solutions of acetic, propionic and butyric acid (100-200 m[image]) at pH 3.6-5.0 inhibited contractions, caused a marked fall in the pH value and a large increase in the concentration of steam-volatile fatty acid in the carotid blood. The onset of inhibition was not directly related to these changes. Non-fatty acid buffers in a similar pH range and concentration did not inhibit, nor did they produce rapid and marked changes in pH of the carotid blood. Fatty acid vapor inhibited contractions without producing large changes in the blood, although buffered solutions applied to localized areas of the forestomach failed to inhibit contractions. The reticulum and rumen contracted in response to stimulation of the vagus nerve during acid inhibition. Buffered solutions of phosphate, glycine-NaOH and rumen liquor made alkaline with sodium carbonate in the pH range 7.9-10.1 inhibited slightly or not at all. It is concluded that the effects obtained with acid solutions were not simply a local pH effect but were related to the rapid penetration of free fatty acid through forestomach epithelium. Since inhibition was produced by fatty acid vapor with only minor changes in the pH value, concentration of total CO2 and steam-volatile fatty acid of the blood inhibition seems to be due to peripheral stimulation of acid-sensitive receptors in the forestomach rather than to central nervous effects of chemical changes in arterial blood.

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Accession: 014082747

Download citation: RISBibTeXText

PMID: 13673384

DOI: 10.1113/jphysiol.1959.sp006221


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