Studies of rumen epithelial cell metabolism

The metabolism of rumen epithelial cells was studied in two experiments. The first experiment compared the metabolism of cells harvested from steers and ewes to determine the existence of a species effect. The second experiment compared the metabolism of cells harvested from four locations within the ewe rumen to determine if cellular origin has an effect on metabolism. In the first study, rumen epithelial cells were harvested from the anterior cranial pillar (ACP) of 4 ewes and 4 steers fed fescue hay. Whole tissue from ewes (~150 cm²) was excised following death by captive bolt and exsanguination. Rumen epithelial cells were obtained from steers from clipped papillae harvested after exteriorizing the rumen through a rumen fistula. In the second study, tissue (~150 c,²) was excised from the ACP, ventral sac floor (VSF), caudal pillar surface (CPS), and dorsal sac ceiling (DSC) of each ewe rumen. Cells were isolated using a serial tryptic digestion procedure in both experiments. Thereafter, 1 mL of cell isolate was incubated for 2 h in 6 mL of media containing 25 mM propionate and 10 mM butyrate. Incubations were terminated at 0, 30, 60, 90, and 120 min and analyzed for B-hydroxybutyrate (BOHB) and acetoacetate (ACAC) as mitochondrial, and lactate (LACT) and pyruvate (PYR) as cytosolic redox estimators. All metabolite concentrations and ratios increased over the incubations indicating continuous cellular activity. Cell yield averaged 21 and 5 x 10⁶ cells/mL for ewes and steers respectively, and mean cell viability for both was 92% in the first study. Final 2 h concentrations (nmol/10⁶ cells) f BOHB, ACAC, LACT, and PYR were 123 ± 20, 36 ± 17, 25 ± 7, and 2.9 ± 1.1 for ewes, and 177 ± 20, 90 ± 18, 74 ± 7, and 5.6 ± 1.1 for steers. Ratios of BOHB to ACAC and LACT to PYR were 3.4 and 8.8 for ewes, and 1.8 and 13.2 for steers (P > .10). Steers produced BOHB (P < .06), ACAC (P < .01), LACT (P < .01), and PYR (P < .10) at higher levels than did ewes indicating that a species difference existed in the metabolism of rumen epithelial cells. Cell yield was 22, 22, 24, and 14 ± 6 x 10⁶ cells/mL and viability was 92, 92, 94, and 87% for ACP, VSF, CPS, and DSC, respectively in the second study. Final 2 h concentrations (nmoles/10⁶ cells) were 123, 113, 163, and 158 ± 35 for BOHB; 38, 42, 24, and 45 ± 10 for ACAC; 25.3, 20.6, 10.1, and 20.4 ± 5.6 for LACT; and 2.54, .98, 1.06, and 1.31 ± .61 for PYR in the ACP, VSF, CPS, and DSC incubations, respectively. The amount of metabolite produced did not differ (P > .05) between tissues indicating that cellular location was not a significant factor in the metabolism of rumen epithelial cells. These experiments were designed to study various aspects of rumen epithelial cell metabolism. Cells from steers produced more BOHB, ACAC, LACT, and PYR than those from ewes. However, metabolism of cells isolated from different areas of the ewe rumen did not differ.