NONINVASIVE URINARY INDICATORS OF CATABOLISM INVESTIGATED BY EXPERIMENTAL FOOD DEFICIENCY IN RATS

Abstract

We aim at measuring whole-body metabolic activity, especially metabolic imbalance caused e.g. by hunger (Schoch et al, ESPGAN 1988, Ped Res 24: 419). Particularly sensitive indicators of metabolic stress are the protein turnover marker 3-methylhistidine (m3His; from actin and myosin) and the mRNA turnover marker 7-methylguanine (m7Gua), both of which are quantitatively excreted in urine and measured by HPLC. Our results with young rats (Table) show that m3His excretion rises from the first day of food restriction (negative r values), whereas m7Gua excretion drops (positive r values) after a transient increase. We conclude that in food deficiency muscle protein is broken down to ensure continued synthesis of vital proteins; concomitantly, after a transient breakdown of mRNA leading to increased m7Gua excretion whole-body mRNA turnover is slowed down. Our results demonstrate that m3His and m7Gua excretion move in opposite directions with decreasing food intakes. Therefore increased m3His/m7Gua ratios, which can be measured in spot urine samples, may turn out to be a valuable noninvasive indicator of catabolism caused by food deficiency.