The Role of the Soft Pellets in the Production of Lactic Acid in the Rabbit Stomach

Abstract

It is known from the literature that lactic acid is produced in the rabbit stomach and that the accumulation of the acid is accompanied, paradoxically, by an increase in pH. The bacteria in soft pellets are likely candidates for the role of lactic acid production; with this in mind the distribution of soft pellets and of lactic acid in the stomach was studied. It was found that pellets taken from the rectum contain lactic acid and that the pellets after ingestion are lodged in the fundus of the stomach. Consistent with this is the fact that the absolute amount and the concentration of lactic acid are highest in the fundus. The soft pellets possess a tough membrane which remains morphologically intact for at least 6 hours after ingestion. The membrane encloses a collection of bacteria including lactobacilli, and homogenates of the pellets possess marked amylase activity and a high level of phosphate buffer which maintains the pH of the homogenate at about 6.0 to 6.5. Consistent with these facts, the homogenates can form lactic acid from starch and from glucose. The high pH maintained by the buffer permits fermentation of carbohydrate to take place in intact pellets, even when the external medium of the stomach is strongly acid. The buffering action of the pellets can explain the apparent contradiction of an increase in pH in the stomach associated with lactic acid accumulation. It is concluded that the fundus of the rabbit stomach, loaded with soft pellets, is analogous to the rumens of sheep and cattle.