78 THE WHOLE BODY TURNOVER RATES OF rRNA AND tRNA ARE CORRELATED WITH THE BASAL METABOLIC RATE IN MAMMALS OF DIFFERENT SIZE

Abstract

We have developed a noninvasive method to determine whole body turnover rates of tRNA, rRNA and mRNA in mammals by measuring specific, quantitatively excreted modified RNA catafaolites (nucleosides, nucleobases) in urine by HPLC. An investigation of the turnover rates of rRNA and tRNA in pigs, human adults, preterm infants, sheep, goats, rats, hamsters, mice ranging in mean body weight from 126 kg (pigs) to 0.028 kg (mice) reveals that the rRNA and tRNA turnover rates per unit body weight correlate with the basal metabolic rates (BMR) per unit body weight (calculated by the formula: BMR (kJ × d−1) = 240 × kg body weight0.74). The correlation coefficient between the BMR of the 7 species and the rRNA turnover rates is 0.995; that between the BMR of 6 species (mice excluded) and the tRNA turnover rates is 0.998. We believe that our method for determining the whole body turnover rates of different RNA classes will be useful to assess the metabolic state in mammals. This method could turn out to be useful for early diagnosis and thus for the prevention of metabolic stress (e.g. caused by food deficiency and/or infections) as well as for monitoring therapeutic success.