Hydroxybutyrate, Acetoacetate, and Glucose for Respiration and Lipid Synthesis in the 1%Day-old Rat*

A comparison has been made in vivo between IS+)-3hydroxy[3-Wlbutyrate, o(-)-3-hydroxy[3-“‘Clbutyrate, [3Wlacetoacetate, and n-[Z-Wlglucose for sterol and fatty acid synthesis and respiration in the B-day-old suckling rat. (a) Sterols and fatty acids in spinal cord, brain, and skin were preferentially labeled by these metabolites over sterols and fatty acids in the liver and kidneys. (b) More label was incorporated into sterols and fatty acids in spinal cord, brain, and kidneys from L( + )-3-hydroxy[3-14Clbutyrate than from o(-)-3-hydroxy[3-14CIbutyrate. (c) More label was incorporated into sterols and fatty acids in spinal cord, brain, and skin from DC-)-3-hydroxy[3-14Clbutyrate than from [314Clacetoacetate. (c-z’) In all organs less label was incorporated into sterols and fatty acids from o-[2-14Clglucose than from the other metabolites; unexpectedly poor were the liver and kidneys which contained substantially less label. (e) The retention of label from D( )-3-hydroxy[3-14Clbutyrate in the sterols and fatty acids from spinal cord and brain was investigated. (0 The time course of evolution of W02 over 2% h from each of these metabolites revealed a more rapid utilization of [3-14C]acetoacetate maximum at 10 min than D(-))-3-hydro~y[3-~~Clbutyrate maximum at 30 min; by contrast, label from o-[2-‘4Clglucose and L(+)-3-hydroxy[314Clbutyrate was retained maximally in metabolic pools over a 2-h period, indicating a much slower utilization. (g) The evidence that the L(+)-3-hydro~y[3-‘~Clbutyrate is a favored substrate for the synthesis of sterols and fatty acids but less favored for oxidation, while ~(-)-3-hydroxy[3-‘~Clbutyrate is a favored substrate for oxidation but less favored for the synthesis of sterols and fatty acids, suggests that these isomers are preferentially metabolized in different compartments.