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.
Isotope Fractionation: Why Aren't We What We Eat?
The isotopic composition of an element records information about its history. Given a fossil, it is possible to analyse the isotopic composition of the elements in the fossil and to use this to reconstruct the diet that the animal consumed. The process of dietary reconstruction, however, is far from simple. Biological systems are quite complex and can themselves introduce isotopic fractionations that may distort the dietary information. The aim of this paper is to review the concepts of isotope fractionation under steady-state conditions to provide a framework for discussion of dietary reconstruction. Among the elements of interest for dietary reconstruction, nitrogen bears a distinct role. This is because nitrogen is almost unique to protein. A secondary aim of this paper is then to review nitrogen metabolism. The final aim is to combine these in postulating a simple isotopic model of nitrogen metabolism.
Correlation between changeable human milk constituents and milk intake in breast-fed babies.
The association of giardiasis and malabsorption of vitamin Bi2 is well known, although the mechanism remains unclear. Invasion of duodenal and jejunal mucosa by the para site8 with resultant reduction of mucosal enzyme activity 9 has been demonstrated, but this is unlikely to account for the abnormal absorption of vitamin B12, since the latter occurs primarily in the distal ileum. Potentiation of the parasite-induced intestinal lesions by bacteria ~0 likewise offers no explanation. Direct uptake of the vitamin by the parasite has been suggeste& but not proved, although this has been shown to be the case with the tapeworm Diphyllobothrium latum. I~ Thus, the parasite load might be an important factor in the interference with vitamin BI2 absorption, In Patient 1 it is possible that the post-treatment improvement in Schilling test results was caused by a reduced level of Giardia infestation, and that with complete eradication of the parasite a fully normal result might be obtained. There is abundant evidence suggesting a role for the immune system in controlling infection with Giardia lamblia. Acquired resistance in man is suggested by the lower prevalence of cysts in stools of long-term residents of areas endemic for giardiasis compared to that in stools of temporary visitors to these areas. 12 Experiments performed in mice have shown that the development of acquired resistance to Giardia requires the presence of an intact cell-mediated immune system. 13 In addition, breast milk of immune mice was found to be protective against infection with Giardia larnblia, ~4 suggesting a role for secretory antibodies in host defense against this parasite. The reported rarity of Giardia infestation in X-linked agammaglobulinemia has, therefore, been perplexing. The three patients described here, however, indicate that it may not be rare. Infestation with Giardia lamblia must not be overlooked as a possible etiology of gastrointestinal symptoms in patients with X-linked as well as in those with common variable agammaglobulinemia.