Postprandial changes in the content and composition of nonprotein nitrogen in human milk.
The effect of a meal on human milk (HM) total nitrogen (TN) and nonprotein nitrogen (NPN) content and composition was examined. Two studies were performed in which milk and blood samples were collected 2-3 h after subjects consumed either a test breakfast or lunch. To monitor the rate of transfer of plasma urea into milk, two women were given [15N]2-urea with the meal. Milk TN concentrations were not significantly different from premeal values. However, concentrations of milk NPN, urea nitrogen, and alanine were increased by greater than or equal to 20% over premeal values. [15N]2-Urea appeared in plasma and milk within 15 min and reached maximum enrichments of 10% and 5.5% in plasma and milk, respectively. Several HM NPN components increase in concentration postprandially; however, these concentrations were not always correlated with changes in plasma concentrations, suggesting that milk NPN may also reflect metabolic activities within the mammary gland.
Nutritional Importance of Non-protein Nitrogen
The class of compounds called non-protein nitrogen (NPN) is not a homogeneous group of similar chemicals but rather an operational term for the remainder of nitrogen in milk and formula once the protein fraction has been removed. NPN therefore consists of widely diverse types of compounds, ranging from urea to complex nitrogen-containing oligosaccharides. It is obvious that the capacity of an infant to utilize these compounds and the potential physiological effects that they can exert will also vary considerably.
Simple, rapid, kinetic method for serum creatinine measurement.
A study of the reaction between creatinine and alkaline picrate confirmed that there is a linear relation between absorbance change and creatinine concentration over the entire clinical range of values. The specificity and accuracy of the method are comparable to that of the end-point Jaffe reaction with deproteinization. The test is somewhat imprecise in the low range, but the simple, rapid procedure is appropriate for the monitoring of patients with glomerular disease and those undergoing therapeutic dialysis.