Extent of propionate metabolism during absorption from the bovine ruminoreticulum.

1. Solutions containing acetate, [2-(14)C]propionate and butyrate were placed into the ruminoreticulum of calves to measure the extent to which propionate is metabolized by ruminoreticulum epithelium. In response to five different combinations of pH and total volatile fatty acid concentrations, propionate absorption rates ranged from 89 to 341mmol/h. 2. The extent of propionate conversion into lactate, calculated from both concentration and specific radioactivity in portal and arterial blood, averaged 4.9 (range 2.5-9.1)%. 3. Circulating glucose synthesized from propionate had a higher specific radioactivity than arterial lactate and was converted into lactate by gastrointestinal tissues. Thus conversion of propionate into lactate was overestimated but was corrected to average 2.3 (1.0-4.6)%. 4. The estimates of propionate conversion into lactate were negatively correlated with its rate of absorption.