J. Delogne-Desnoeck

The influence of the frequency of nursing and of previous lactation experience on serum prolactin in lactating mothers

Serum prolactin levels were measured for 97 women from Zaire for 22 months postpartum. These 97 women were divided into 3 groups according to how frequently they breast-fed their children. These results were compared with the prolactin levels of 25 nonlactating, nonpregnant women. The prolactin levels increased with the frequency of breast-feeding. The postpartum decrease in serum prolactin is quicker among women who breast-feed less frequently; the serum prolactin levels returned to normal ranges within 6 months postpartum among women who breast-fed their children 1-3 times/day. No correlation could be found between previous breast-feeding or the parity of women and prolactin levels during subsequent pregnancies.

Evidence for a clathrin-mediated recycling of albumin in human term placenta.

Abstract 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 μM), 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 μM), two pharmacological tools known to disturb megalin-mediated albumin endocytosis. By contrast, methyl-β-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 levels of prolactin and milk production in women during a lactation period of thirty months.

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.

Hyperprolactinaemia during prolonged lactation: evidence for anovulatory cycles and inadequate corpus luteum.

Serum progesterone and prolactin were measured in single blood samples collected from 176 mothers during a lactation period of 2 years and from fifty‐six non‐lactating, non‐pregnant and regularly menstruating women from the Kivu region (Zaire). On the basis of serum progesterone levels, evidence of corpus luteum activity was obtained in 61% of non‐lactating women; but only 20% of non‐amenorrhoeic lactating mothers. This suggests an increased incidence of anovulatory cycles and/or cycles with short luteal phases among nursing mothers. The incidence of corpus luteum activity was 8% in amenorrhoeic lactating mothers. In this 8% recurrence of ovulation preceded return of menstruation. Mean serum progesterone was significantly higher and serum prolactin significantly lower in the non‐lactating women than in the nursing mothers. This suggests that although ovulation occurs, corpus luteum activity is inadequate in hyperprolactinaemic nursing mothers.

TIME‐COURSE OF PHYSIOLOGICAL HYPERPROLACTINAEMIA DURING TWO YEARS LACTATION

SUMMARY. In Central Africa, mothers on nursing for 2 years are hyperprolactinaemic during the first 15–18 post‐partum months; serum prolactin levels are some three times higher than in non‐pregnant and non‐lactating women.

Erratum to “Effect of IPs, cAMP, and cGMP on the hPL and hCG secretion from human term placenta”

Nathalie Lambot a,∗, Philippe Lebrun b, Christine Delporte c, Carine De Vriese c, Josiane Delogne-Desnoeck a, Anne Marie Vanbellinghen a, Guy Graff a, Sylvain Meuris a a Laboratory of Experimental Hormonology, Universite Libre de Bruxelles, 808 Lennik Road, Campus Erasme, CP 626, Brussels 1070, Belgium b Laboratory of Pharmacology, Universite Libre de Bruxelles, 808 Lennik Road, Brussels 1070, Belgium c Laboratory of Biochemistry and Nutrition, Universite Libre de Bruxelles, 808 Lennik Road, Brussels 1070, Belgium

Human chorionic gonadotrophin early pregnancy levels are more closely related to changes in β-subunit trophoblast production than to variations in α-subunit production

Summary Human chorionic gonadotrophin (hCG) is composed of two non-covalently bound α and β subunits synthesized from separate mRNAs. The hCG heterodimer and uncombined subunits are secreted during early gestation by trophoblast into the maternal bloodstream and into the exocoelomic cavity on the opposite side of the trophoblastic layer. The aim was to compare the relative amount of hCG and its free subunits in these compartments. Levels of hCG were similar in coelomic fluid and in maternal serum collected from the same women. By contrast, levels of free subunits were higher in coelomic fluid than in maternal serum: 186-fold for free αhCG subunit and 34-fold for free βhCG subunit. These enormous gradients are likely to be related to differences in the clearance rates of hCG and its subunits between maternal and exocoelomic compartments. Considering coelomic fluid as a metabolic cul-de-sac into which hCG and its subunits accumulate and are slowly metabolized, their levels in this fluid may be reasonably considered as a direct reflection of their trophoblastic production. This hypothesis suggests that the amount of free α subunit is in formidable excess when compared to intact hCG and free βhCG subunit and that only a small fraction ( 90% of βhCG.

In-vivo and in-vitro assessment of the influence of ritodrine and oxytocin on the placental secretion of human chorionic gonadotrophin and placental lactogen

The purpose of this study was to evaluate, in vivo and in vitro, the influence of ritodrine and oxytocin on the placental release of human chorionic gonadotrophin (HCG) and placental lactogen (HPL). The in-vivo study was performed on maternal sera collected before and 1 h after the onset of either ritodrine treatment (50 micrograms i.v./min; administered to 15 women at risk of premature labour) or oxytocin infusion (2 mU i.v./min; administered to 21 women for acceleration of slow labour). The in-vitro study was performed on human term placental explants incubated in the presence of 4-400 ng ritodrine/ml or 15-1500 microU oxytocin/ml. HCG and HPL were measured by radioimmunoassay on maternal sera and incubation media. Maternal circulating concentrations of HCG and HPL remained unaffected after 1 h of ritodrine or oxytocin treatment. The in-vitro release of HCG and HPL by placental explants was not modified when ritodrine or oxytocin was added to the incubation media. The lack of influence of ritodrine and oxytocin on the placental secretion of HCG and HPL suggests that beta 2-adrenergic and oxytocin receptors are not involved in the releasing process.