Factors affecting fatty acid oxidation in bovine mammary tissue

Abstract

Oxidation of fatty acids was studied in bovine mammary tissue slices in order to evaluate their potential contribution to energy metabolism. Rates of fatty acid oxidation decreased with increasing chain length: acetate > octanoate > palmitate or oleate. Rates of oxidation of long chain, but not short chain, fatty acids increased over time, which could not be explained by carnitine palmitoyltransferase (CPT) activity. This phenomenon is not an artifact of the incubation system or caused by substrate solubility, as rates of palmitate oxidation were constant in rat kidney cortex slices. Preincubating mammary tissue with or without unlabeled palmitate showed that increasing rates of palmitate oxidation is not caused by use of endogenous fatty acids. Palmitate at 0.26 mM, equivalent to arterial fatty acid concentration, gave maximal rates of oxidation. The &oxidation enzymes may restrict fatty acid oxidation as oxidation of [ 1-14 C] palmitate exceeded that of [U-14C] paimitate. Acetate inhibited palmitate oxidation (75%) but not esterffication, suggesting that acetate inhibits palmitate oxidation by substrate competition at the mitochondrial level or via malonyl-CoA inhibition of CPT. Glucose inhibited palmitate oxidation (67%) and stimulated esterification. Low palmitoyl-CoA levels would favor glyceride synthesis over oxidation, since the apparent K m for palmitoyl-CoA of the glycerol-3phosphate acyltransferases is lower than that for CPT. Thus, glucose presumably diverts palmitate from oxidation to glycerolipids. Clofenapate, a glyceride synthesis inhibitor, decreased triacylglycerol formation, and marginally increased palmitate oxidation. We estimated that long chain fatty acids can potentially account for 6-10% of the oxidative metabolism of mammary tissue.

Effects of AMP-activated protein kinase (AMPK) signaling and essential amino acids on mammalian target of rapamycin (mTOR) signaling and protein synthesis rates in mammary cells

“…Tissue remained viable during the incubation as evidenced by 2 H 5 -Phe incorporation into mammary protein over the last 45 min of the incubation. Label incorporation rates were found to be linear for 8 h (unpublished data), consistent with the findings of others (Bauman et al, 1973;Dimenna and Emery, 1980;O'Quinn et al, 2002), where various metabolic and synthetic processes remained linear for at least 2 h when mammary tissue was incubated in this manner.…”

Essential Amino Acids Regulate Both Initiation and Elongation of mRNA Translation Independent of Insulin in MAC-T Cells and Bovine Mammary Tissue Slices

“…Tissue remained viable during the incubation as evidenced by 2 H 5 -Phe incorporation into mammary protein over the last 45 min of the incubation. We did not test for linearity throughout the incubation; however, others have found that various metabolic and synthetic processes remained linear for at least 2 h when mammary tissue was incubated in this manner (30)(31)(32)(33)(34).…”