Purified First and Third Trimester Placental Trophoblasts Differ inin VitroHormone Secretion

Abstract

In vitro studies with cytotrophoblasts obtained from term placentas have shown low levels of placental protein hormone secretion during the first 2 days in culture, followed by a marked increase during days 3 and 4. Since maternal serum placental hormone levels at term and during the first trimester differ, it is conceivable that cytotrophoblasts from first trimester placentas will differ in endocrine function from those derived from term placentas. Therefore, we examined the secretion of hCG, hCG alpha, human placental lactogen (hPL), and progesterone (P) both in the basal state and after exposure to 8-bromo-cAMP or endogenous cAMP stimulation with cholera toxin in cytotrophoblasts purified by enzymatic dispersion and Percoll gradient centrifugation from four first trimester and four third trimester placentas. At the time of seeding, all cells were mononuclear, and the degrees of aggregation and syncytia formation were similar in first and third trimester trophoblasts during the 4 days in culture. First trimester trophoblasts secreted greater quantities of hCG than did term trophoblasts, while basal secretion of hCG alpha, hPL, and progesterone were similar. Qualitative differences in the hormone secretory patterns were apparent. hCG secretion by first trimester trophoblasts decreased over the 4 days in culture, while the amounts secreted by third trimester trophoblasts increased. hCG alpha levels increased for 2-3 days in first trimester trophoblasts and then decreased, while hCG alpha increased in term trophoblast medium over the 4 days. The ratio of hCG alpha to hCG in media from first and third trimester cultures reflected the relative ratios of these hormones in placental tissue and maternal serum at analogous stages of pregnancy. hPL concentrations in the medium declined between days 3-4 in first trimester cultures, while they increased between days 3-4 in third trimester cultures. The secretory pattern of P was somewhat more erratic. cAMP stimulation led to a similar rise in hCG, hCG alpha, and P secretion in first and third trimester trophoblasts, and a variable response for hPL secretion. These results indicate that the functional activity of placental trophoblasts in culture depends in part upon the age of the placenta from which the cells are derived. The differences may represent intrinsic differences in function or the presence of inhibitory or stimulatory factors of maternal, fetal, or trophoblast origin.