Myoinositol in human neonates: Serum concentrations and renal handling

Abstract

Free myoinositol (henceforth called inositol) levels were mea-sured in cord blood from newborns, as well as in sera from lealthy infants during the first 6 months of life. Renal excretion of inositol by a group of premature infants during their first 2 nonths of life was also studied. Inositol was measured by a nicrobiologic assay, using an inositol-requiring yeast, Saccha- omyces carhbergensis. Inositol concentration in pooled cord amples of full term normal newborns was 25 ± 5.3 µg/ml. These levels dropped progressively, reaching adult levels (6.9 µg/ml) by the eighth week of life. Mean concentration of nositol in cord blood of premature neonates was 30 µg/ml. In premature infants, the inositol content in the urine was ilways higher than that of the blood; the average urine concenration was 198 µg/ml. Inositol clearance values of premature nfants ranged from 0.10-0.79 ml/min and averaged 0.34 ml/ nin, and were thus lower than the mean inositol clearances of nonuremic normal adults (2.8 ml/min). The total amounts of inositol excreted per day by the premature infants were considerably higher than the amounts ingested. The blood inositol concentrations in infants in this study are similar to those found in adults with impaired renal function. The inositol status of the neonate appears to be determined by a balance between the two factors which tend to increase the amount of inositol available, that is, biosynthesis of inositol and ingestion with the formula; and the two factors which decrease the blood level, i.e., kidney maturation with resultant increased inositol clearance and, possibly, renal enzymatic catabolism of inositol. Speculation: The rat kidney regulates blood inositol concentration via catabolism by an inositol oxidase. Impaired renal function in man is accompanied by raised serum levels of inositol, as well as increased urinary inositol excretion. This is particularly relevant in view of the association of uremic neuropathy with high serum inositol concentration. The current finding of a similar situation in premature infants may lend further support to the assumption that inositol homeostasis in man is achieved by renal enzymatic catabolism, as well as by glomerular excretion. © 1978 International Pediatric Research Foundation, Inc.