Acetogenesis does not replace ketogenesis in fasting piglets infused with hexanoate

The current studies were performed to better understand the physiological relevance of acetate in the poorly ketogenic piglet and to determine if endogenous acetogenesis rises with increased mitochondrial fatty acid beta-oxidation, analogous to ketogenesis. Plasma acetate concentration values in newborn, fasted, or suckled piglets (230-343 microM) were at least 10-fold higher than the ketone bodies, a pattern opposite to that in 24- to 48-h suckled rats (77-175 microM). Employing continuous infusion techniques with sodium [3H]acetate tracer in fasting approximately 40-h-old piglets, acetate rate of appearance (Ra) was found to be 34 +/- 4 micromol . min-1 . kg body wt-1. This basal Ra was double that observed in animals coinfused with sodium [1-14C]hexanoate (P < 0.001), despite active oxidation of the latter as determined by 14CO2 production. Active acetogenesis in vivo and relatively abundant acetate in piglet blood are consistent with the hypothesis that acetate plays an important physiological role in piglets. However, the negative impact of hexanoate oxidation upon acetate Ra and the lack of significant changes in circulating acetate in newborn, suckled, and fasted piglets draws into question the extent of analogy between acetogenesis and ketogenesis in vivo.