Prostanoid content of human milk: relationships to milk fatty acid content.

Analysis of human milk was conducted to determine if transitions in milk lipid composition and thus the changes in fatty acid synthesis that occur during lactogenesis are related to levels of specific prostanoids present in milk lactated. Serial samples representative of a complete expression and reflecting varying concentrations of milk fatty acids were collected over the first 37 days of lactation. Milk from mothers delivering infants at term and mothers delivering premature infants of 28-33 weeks gestational age was compared to examine potential relationships between prostanoid concentration and gestational age effects on milk lipid content. Milk levels of prostaglandin E, prostaglandin F and the metabolite of prostacyclin--6-keto-prostaglandin F1 alpha were determined by radioimmunoassays. Transitions in fatty acid content for all milk lipid classes were determined by quantitative analysis of fatty acids by glass capillary gas liquid chromatography. During lactation the levels of prostaglandin E correlated with milk content of 6-keto prostaglandin F1 alpha. For term mothers, milk content of prostaglandin E, 6-keto prostaglandin F1 alpha, total fatty acids and medium chain fatty acids increased from early lactation when compared with subsequent days sampled. Levels of these milk constituents observed for early milk of preterm mothers were significantly different when compared with term mothers and in addition did not follow the same longitudinal pattern during subsequent days of lactation. Physiologically significant levels of prostaglandins in milk may reflect the balance between hormonal and subcellular controls over lactogenesis. It is also conceivable that the presence of these prostanoids in milk may influence gastrointestinal physiology and nutrient absorption in the neonate.