We examined the capacity of trophoblast-derived interleukin-6 (IL-6) to stimulate secretion of placental hormones, including hCG. IL-6 stimulated hCG secretion by trophoblasts to a level similar to that stimulated by a GnRH analog. The analog, however, released hCG by an IL-6-independent mechanism because PM-1, a monoclonal antibody specific for IL-6 receptors (R), failed to block GnRH-mediated responses, but completely blocked IL-6-mediated hCG secretion, suggesting the existence of two distinct regulatory pathways for hCG release. Immunohistochemical analysis with another IL-6-R-specific antibody, MT-18, showed that IL-6-R was located only on the trophoblast layer of the placenta. Our data revealed the existence of a local regulatory network by which trophoblast-derived IL-6 interacts with IL-6-R on the trophoblasts, resulting in hCG release. Thus, two different regulatory networks, an IL-6 and IL-6-R system and a GnRH and GnRH-R system, regulate hCG release by human trophoblasts independently.

The activity of the hypothalamo-pituitary adrenal axis was examined, by measuring the levels of immunoreactive (IR) corticotropin-releasing hormone (CRH), adrenocorticotropin (ACTH) and cortisol (F) in human plasma during normal pregnancy and after delivery with or without complications and during normal postpartum using a specific RIA. The level of IR-CRH in maternal plasma increased progressively during pregnancy, increased further at delivery and declined rapidly to the non-pregnant level on the 1st day postpartum. The level of IR-F in maternal plasma also increased progressively during pregnancy, increased further at delivery, but decreased slowly postpartum, not returning to the non-pregnant level within 5 days. Significant correlations were found between the level of IR-CRH and IR-ACTH, IR-CRH and IR-F, and IR-ACTH and IRF in maternal plasma both during pregnancy and after delivery. It is noteworthy that the concentration of IR-CRH in the maternal plasma at delivery was higher in multiple pregnancy than in normal pregnancy, and that the level of IR-CRH in the umbilical cord in uncomplicated cases was much lower than that in the maternal plasma, and was significantly lower than those in the umbilical cord plasma in cases of asphyxia, IUGR or premature delivery. The level of IR-F, not IR-CRH and IR-ACTH, at normal vaginal delivery was significantly higher than that at elective cesarean section. On these results, we investigated the feto-maternal-hypothalamo-pituitary adrenal axis during pregnancy and delivery, in which CRH plays an important role.

Interleukin-1 (IL-1) has a unique activity to stimulate the release of multiple hormones in a number of human and murine endocrine systems. IL-6 also expresses such activities by activating IL-6-receptor (R)-mediated signal transduction pathways. Since the placenta produces both of these cytokines and endocrine hormones such as hCG, we investigated how these cytokines regulate hCG release by normal trophoblasts. Trophoblasts purified by Percoll density gradient released hCG from 120 min after stimulation with recombinant (r) IL-1 alpha, and its release was dependent on the rIL-1 alpha concentration used. The rIL-1 alpha-stimulated trophoblasts released a molecule with IL-6 activity antecedently, as determined by an IL-6-dependent cell line, MH60.BSF2 cells. The IL-6 identity of the released molecule was confirmed by goat anti-IL-6 antiserum. rIL-1-mediated hCG release from trophoblasts was completely abrogated to the basal level by pretreatment of the trophoblasts with PM1, an anti-IL-6-R monoclonal antibody. Identical results were observed with rIL-1 beta. These results showed that rIL-1-induced hCG release was totally dependent on IL-6- and IL-6-R-mediated signal transduction in human trophoblasts. The presence of peripheral monocytes in the purified trophoblast fraction, however, induced a rapid decrease in IL-6 and hCG release after their maximal release, suggesting some regulatory interaction between trophoblasts and the monocytes. In contrast, rIL-1-mediated enhancement of IL-6 and hCG secretion by purified trophoblasts was no longer observed at 24 h compared with that of the unstimulated trophoblasts, while spontaneous hCG secretion was significantly inhibited by pretreatment of trophoblasts with PM1. The results showed that IL-6 and hCG secretion might also be regulated by a number of agents besides IL-1, and that hCG secretion as well as its release is dependent on IL-6 and IL-6-R system in trophoblasts.