Gastrointestinal pH in Rats as Determined by the Glass Electrode. ∗

Abstract

Investigators have reported many studies on gastrointestinal pH in animals, using various methods of determination—hydrogen electrodes, quinhydrone electrode, and colorimetry. The results have all been somewhat open to question because of the possible inaccuracy of these methods in a medium such as intestinal contents. For the range of pH encountered in such work, the glass electrode seems to be the method of choice. We have used glass electrodes prepared by the methods of MacInnes and Dole 1 or Robertson. 2 The electrical apparatus developed for this work was that described by Rose-bury. 3

Four hundred and fifty-five albino rats were used. Groups were placed on various diets: (I) a “normal” diet which included corn, wheat, barley, oats, soy bean, milk, meat scrap, alfalfa, NaCl, and CaCO₃; (II) diet I + 10% lard; (III) diet I + 30% lard; (IV) bread; (V) potato; (VI) suet; (VII) lean beef; (VIII) McCollum's 4 rachitic diet 3143; (IX) diet VIII + 2% cod liver oil; (X) Steenbock's 5 diet 2965; (XI) diet X + 2% cod liver oil; (XII) Zucker's 6 diet 401; (XIII) diet XII + 2% cod liver oil; (XIV) diet XII +15% cod liver oil. The rats on the last 3 and the suet diets showed consistent malnutrition.

The rats were killed by a blow on the head or by chloroform, and the abdomen opened immediately. The stomach, the small intestine in 3 approximately equal lengths, the cecum, and the colon were quickly tied off and removed and the contents gently expressed under oil. The contents were then diluted sufficiently with water and the pH determined.

Plotting histograms of the incidence of the data revealed that if calculated as pH the occurrences closely approximated the normal bell-shaped curve.