Milk lactoferrin (LF), lysozyme (LZ), and secretory IgA (sIgA) were measured cross-sectionally in 127 Zaïrean mothers, lactating greater than or equal to 18 mo. The 54 urban mothers were of marginal nutrition status [body mass index (BMI) 22.6 +/- 2.6 kg/m2 and albumin 33.1 +/- 4.5 g/L]. The neighboring rural mothers were of significantly (P less than 0.001) poorer nutrition status (BMI 20.5 +/- 2.2 kg/m2 and albumin 27.7 +/- 5.4 g/L). In both urban and rural mothers, as lactation progressed LF decreased by 33% and 55% whereas sIgA remained unchanged and LZ steadily increased. There was more LZ and sIgA in rural milk, contrasting with the poorer maternal nutrition. As calculated from individual milk yields, the urban infants were fed daily with twice as much LF and sIgA but with similar amounts of LZ as were the rural infants. In the early stage of lactation, the milk of both groups of Zaïrean mothers contains more sIgA than that of a group of west European (Belgian) mothers (n = 20), but the LF and LZ contents were rather similar.

During human pregnancy, the trophoblast layer is in direct contact with maternal albumin. In contrast to immunoglobulins, albumin does not cross the placental barrier. However, albumin affects the trophoblast placental lactogen and chorionic gonadotroph secretion. The present study investigated the interaction between albumin and syncytiotrophoblast using human term placental explants. Bovine serum albumin, labeled with either 125I or fluorescein isothio-cyanate, was taken up rapidly by placental explants. This process was temperature-sensitive. The internalized labeled BSA quickly outflowed from the tissue at the maternal side, largely without any major modification in molecular weight. Colchicine (1 mM), which disrupts the microtubule network, or cytochalasin B (40 microM), which disassembles filamentous actin, did not interfere with the placental transmembrane movements of labeled BSA. Megalin, clathrin, and caveolin 1 are three membrane proteins associated with albumin endocytosis in other tissues, but only megalin and clathrin were detected in the syncytiotrophoblast layer by immunohistochemistry. The uptake of labeled BSA into placental explants was not modified by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (1 mM) or 5-nitro-2-(3-phenylpropylamino)benzoic acid (100 microM), two pharmacological tools known to disturb megalin-mediated albumin endocytosis. By contrast, methyl-beta-cyclodextrin (10 mM) and chlorpromazine (1.4 mM), both of which disrupt the clathrin-mediated endocytotic system, significantly reduced the uptake of labeled BSA. These data suggest, to our knowledge for the first time, that maternal albumin is actively internalized into the human trophoblast according to an apical recycling pathway. This temperature-sensitive process does not depend on an intact cytoskeleton, but it is associated with a clathrin-mediated endocytotic system.

Serum prolactin has been measured in single blood samples collected within the first 22 post-partum months from 97 nursing mothers from an urban area (Bukavu) of Zaire. Nursing mothers are hyperprolactinemic, higher serum prolactin levels being associated with more frequent suckling episodes per day. Furthermore, serum prolactin declines rapidly in mothers who are giving the breast less than four times per day: the levels are within the normal range found in non-lactating women after the 6th post-partum month. Among mothers giving the breast more than six times per day, serum prolactin does not decline significantly during the 1st post-partum year.Previous lactation experiences do not facilitate the effect of nursing on prolactin secretion during subsequent lactations.

Serum prolactin was measured in single blood samples collected from 219 nursing mothers of the Kivu region (Zaïre) during 30 post-partum months. In addition the number of feeding episodes per day and the amount of milk given to the child in 24 h were recorded. The mean serum prolactin levels remained around 1000 mu/l during the first 15 months of lactation and fell during the next 3 months to 550 mu/l. A decline in milk production per day occurred during the second year, but it was less marked than that of prolactin. This decline seemed to be associated with the decline in suckling frequency as the quantity of milk given per feed remained almost unchanged throughout lactation. The average amount of milk given by mothers with serum prolactin levels in the range of values seen in non-lactating and non-pregnant women (about 500 mu/l) is nevertheless of some 35 g per feeding or 260 g per day. These results demonstrate that milk production can be maintained in women with normal levels of prolactin and suggest that prolactin plays a permissive role in established lactation.

Basal serum-prolactin concentrations were high until 15 months post partum in nursing mothers in Central Africa (Lwiro). They were significantly lower in menstruating than in amenorrhoeic nursing mothers. These results support the hypothesis that prolactin is involved in the long-lasting amenorrhoea which occurs in regions where breast-feeding is prolonged for up to 2 years after delivery.