Endocrine activity of the corpus luteum and placenta during pregnancy in Chalcides chalcides (Reptilia, Squamata).

The structure of the corpus luteum and the steroidogenic activity of the corpus luteum and placenta in the viviparous reptile Chalcides chalcides have been investigated. The corpus luteum has a compact structure, almost without internal vascularized connective septa. It begins to degenerate after the middle of pregnancy, when plasma progesterone (P) remains high. The sections of the corpora lutea taken during early pregnancy showed an intense 3beta-HSDH reaction, whereas the sections taken in late pregnancy gave weak reactions localized exclusively in the peripheral luteal cells. In contrast, sections of placentae taken at the beginning and in the middle of pregnancy always gave negative 3beta-HSDH reactions, whereas those of late pregnancy were always strongly positive, localized in the maternal component of the placenta. In vitro, the corpora lutea from early pregnancy secreted significant amounts of P, whereas appreciable amounts of P were not detected in incubates of early pregnancy placentae. Near the time of delivery, P levels decreased in the culture medium of the corpora lutea, but increased in that of the placentae. The addition of pregnenolone (a precursor of P biosynthesis) to the culture medium caused an increase in the luteal and placental P levels, whereas the addition of trilostane (an inhibitor of 3beta-HSDH) reduced them. The placenta of C. chalcides is suggested to have an endocrine function and to replace the corpus luteum in the production of P when the gland degenerates in late pregnancy. Copyright 1998 Academic Press.