TOTAL POTENTIALLY AVAILABLE NUCLEOSIDES OF HUMAN-MILK BY STAGE OF LACTATION

Human milk-borne ribonucleotides reportedly have important physiologic al roles in breast-fed infants. Previous studies measured the free nuc leotide content of human milk. To more fully evaluate the physiologica l capacity of nucleotides in human milk, we determined the monomeric a nd polymeric ribonucleotide and ribonucleoside content of milk pooled from 11 American women. Subsequently, we determined the total potentia lly available nucleosides (TPAN) of pooled and individual milk samples segregated by stage of lactation from 100 women in three European cou ntries to test for effect of culture and diet. The methodology simulat ed in vivo digestion. Polymeric ribonucleotide (primarily RNA), monome ric ribonucleotide, and ribonucleoside-containing adducts (eg, uridine diphosphate hexose) were enzymatically hydrolyzed to their constituen t ribonucleosides, the preferred form for absorption. Free and enzymat ically liberated nucleosides were then measured by HPLC to yield the T PAN value. The mean (+/- SD) TPAN concentration of the 16 pooled Europ ean samples, derived from the 100 individual samples, was 189 +/- 70 m u mol nucleoside/L human milk (range 82-402 mu mol/L). The means (mu m ol/L human milk) of each nucleoside were 38 for uridine, 88 for cytidi ne, 31 for guanosine, and 32 for adenosine. These values included the contribution from the cellular portion of human milk. Only one of the 16 pooled samples contained a measurable amount of inosine (4 mu mol/L ). The potentially available ribonucleosides in the human milk samples were predominantly present as monomeric (36 +/- 10%) and polymeric (4 8 +/- 8%) nucleotides. This study demonstrates that the traditional me asurement of the free nucleotide content of human milk (which accounts for neither polymeric nor cellular nucleotides) underestimates the to tal nucleotides available to the infant by greater than or equal to 50 %.