PALMITATE METABOLISM BY ISOLATED SHEEP RUMEN EPITHELIAL-CELLS

Ruminal palmitate metabolism was examined using an isolated cell system. Palmitate oxidation to (CO2)-C-14 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 < .05], and ammonia [15 mM] tended to reduce [P < .10], palmitate oxidation [51.6 and 82.0% of control, respectively], whereas addition of glucose [2.5 mM] increased [P < .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.