Colloidal effect of albumin on the placental lactogen and chorionic gonadotrophin releases from human term placental explants.

Albumin has been reported to stimulate the release of placental lactogen and chorionic gonadotrophin from human term placental explants within physiological concentrations. This study aimed at characterizing further its effect on the placental hormonal secretion. The placental lactogen and chorionic gonadotrophin secretory response of incubated explants to 5% albumin was reproduced by colloidal agents, i.e., dextran (4.5%) and polygelin (4%), indicating that a rise in colloidal osmotic pressure can elicit hormonal release from the syncytiotrophoblast. Their secretory effects were not modified by the absence of extracellular calcium or the presence of verapamil in the medium. The three agents also provoked a marked increase in (45)calcium outflow from preloaded and perifused explants that persisted in absence of extracellular calcium. These data indicate that the triggering effect of albumin on placental lactogen and chorionic gonadotrophin release can be partly reproduced by colloidal agents and is independent of extracellular calcium.

Physiological concentrations of albumin stimulate chorionic gonadotrophin and placental lactogen release from human term placental explants.

This study investigates whether albumin, a major plasma protein in direct contact with the trophoblast in vivo, can modulate human chorionic gonadotrophin (HCG) and human placental lactogen (HPL) releases from placental explants. Incubating explants with a near physiological, i.e. 5%, concentration of human or bovine albumin during 30 min increased HCG and HPL release by at least 150%. This albumin effect was not mediated by any difference in hormone adsorption onto glass surfaces. In contrast to the sustained stimulation of hormone releases elicited by the addition of 10 mmol/l extracellular calcium, the albumin-mediated secretory responses were transient. However, the albumin- and calcium-stimulatory effects were abolished at 4 degrees C, depressed by 0.36 mmol/l cycloheximide or 1 mmol/l colchicine and potentiated by 40 micromol/l cytochalasin B. Moreover, the stimulatory effect of albumin on the hormone releases was not modified in the absence of Ca(2+) or in the presence of 1 or 10 mmol/l Ca(2+) in the extracellular milieu. These data suggest that albumin is involved, at physiological concentration, in the secretion of HCG and HPL by human placenta. The cellular mechanism(s) underlying the albumin-mediated secretory responses may be partly different from those involved during the calcium-mediated stimulation.

Secretory characteristics and viability of human term placental tissue after overnight cold preservation.

Collection of human term placentae for research purposes is generally limited during working hours. Preserving placental tissue overnight might help to postpone experiments and, by extent, to increase material availability. In this study, fragments from normal placentae were incubated at 37 degrees C either immediately after delivery or after preservation at 4 degrees C in a HEPES-buffered solution or in a Roswell Park Memorial Institute (RPMI) 1640 culture medium. Protein, human chorionic gonadotrophin (HCG), human placental lactogen (HPL) and lactate dehydrogenase (LDH) contents within preserved explants were similar to those within freshly delivered ones. In contrast, HCG and HPL amounts released during incubation of preserved tissue were lower than with freshly delivered tissue. Differences were significant only during the first 3 h of incubation. Hormone releases were similarly Ca(2+)-stimulated, and Co(2+)- and low temperature-inhibited in preserved and freshly delivered tissues. After preservation, LDH leakage was also reduced. Furthermore, before and after 37 degrees C incubation during 6 h, preserved tissue was morphologically indistinguishable from freshly delivered tissue and showed neither higher incidence of DNA fragmentation, nor elevated caspase-3 activity, both of which are markers of apoptosis. This study validates an original, useful and rapid method to preserve placental tissue. Consequently, this preservation model may facilitate the study of physiological processes regulating placental hormone secretion in normal and pathological conditions.

Apoptosis in human term placenta is not increased during labor but can be massively induced in vitro.

Apoptosis in human placental villi is reported to increase until close to delivery. However, the involvement of the apoptotic process in the initiation of labor, and more particularly in relation to the decrease in placental perfusion during uterine contractions, remains unknown. The purpose of the study was to examine the reactivity of the apoptotic machinery in term placentae obtained before or after the onset of labor and after in vitro incubations. The incidence of apoptotic nuclei (< 1%) as evidenced by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method, and the histological distribution of immunoreactive Bcl-2, Bax, and Bcl-x proteins, were similar in placentae collected after delivery and before the onset of labor and in placental explants maintained overnight at 4 degrees C in a minimal salt-Hepes medium. By contrast, 28% of nuclei contained fragmented DNA when placental explants were incubated overnight at 37 degrees C. This marked increase was associated with a decrease in the intensity of the Bcl-2 immunostaining and an increase in the intensity of Bax and Bcl-x immunostaining. In conclusion, the present study clearly evidences the presence of an active apoptotic machinery in term placental cells that is not involved in normal parturition.