Einbau von15N-Glyzin in VLDL und LDL: In-vivo-Synthese von Apolipoprotein B beim Menschen postabsorptiv und im Fastenzustand

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Abstract
In vivo synthesis of apolipoprotein B 100 (ApoB) was recently determined in man using stable isotopes. With this procedure we analyzed (1) the effect of fasting on synthesis of ApoB from very low density lipoprotein (VLDL) and (2) tracer enrichment in low density lipoprotein (LDL). After a 36-hour fasting period and in the post-absorptive state 4 healthy subjects were given a priming dose (8.7 µmol/kg) of15N glycine followed by a constant infusion (10 µmol/kg/h for 8 h) to achieve 5% tracer enrichment in the plasma pool of glycine. The K-values, i.e. fractional synthetic rates/hr of ApoB from VLDL were 0.53±0.26 vs. 0.43±0.16 (p>0.05). Tracer enrichment in ApoB from LDL at the end of the infusions was 0.19% vs. 1.46% in ApoB from VLDL. The results indicate that (1) in young healthy postabsorptive individuals about 40% of ApoB from VLDL in plasma is synthesized per hour, (2) fasting does not materially affect fractional ApoB synthesis and (3) at 5%15N enrichment in plasma glycine, tracer enrichment in ApoB from LDL is at the lower limit of detection for the procedure employed.