Palmitate metabolism by isolated sheep rumen epithelial cells.

Ruminal palmitate metabolism was examined using an isolated cell system. Palmitate oxidation to 14CO2 by rumen epithelial cells isolated from the rumens of mature sheep was linear during the course of a 2-h incubation (11.1 nmoles.million cells-1.2 h-1) and 3.6 times the rate of palmitate oxidation by cells isolated from neonatal rumen (3.1 nmoles.million cells-1.min-1). Subsequent experiments were conducted with mature rumen epithelial cells. Neither acetate (50 mM), propionate (10 mM), dibutyryl cAMP (.2 mM), nor insulin (10 mU/mL) altered palmitate oxidation to CO2. However, butyrate (10 mM) addition reduced (P less than .05), and ammonia (15 mM) tended to reduce (P less than .10), palmitate oxidation (51.6 and 82.0% of control, respectively), whereas addition of glucose (2.5 mM) increased (P less than .05) palmitate oxidation (151% of control). Of the compounds tested, only propionate, butyrate, and ammonia reduced palmitate oxidation to total acid-soluble metabolites. Propionate (10 mM) addition completely abolished palmitate oxidation to acid-soluble metabolites. Succinate addition (5 to 50 mM) increased palmitate oxidation to CO2 but exhibited no consistent effect on palmitate oxidation to either acid-soluble metabolites or beta-hydroxybutyrate. Propionate completely abolished palmitate oxidation to beta-hydroxybutyrate, suggesting that propionate-induced inhibition of palmitate oxidation is not mediated via succinate. The data indicate 1) that rumen epithelium is capable of oxidizing palmitate, 2) that ruminal palmitate oxidation may be subject to regulation by developmental factors, and 3) that palmitate metabolism seems to be influenced more by ruminally derived metabolites than by factors derived exclusively from the general circulation.