ENDOCRINE ACTIVITY OF THE CORPUS-LUTEUM AND PLACENTA DURING PREGNANCYIN CHALCIDES CHALCIDES (REPTILIA, SQUAMATA)

The structure of the corpus luteum and the steroidogenic activity of t he corpus luteum and placenta in the viviparous reptile Chalcides chal cides have been investigated. The corpus luteum has a compact structur e, 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 p regnancy showed an intense 3 beta-HSDH reaction, whereas the sections taken in late pregnancy gave weak reactions localized exclusively in t he peripheral luteal cells. In contrast, sections of placentae taken a t the beginning and in the middle of pregnancy always gave negative 3 beta-HSDH reactions, whereas those of late pregnancy were always stron gly positive, localized in the maternal component of the placenta. In vitro, the corpora lutea from early pregnancy secreted significant amo unts of P, whereas appreciable amounts of P were not detected in incub ates of early pregnancy placentae. Near the time of delivery, P levels decreased in the culture medium of the corpora lutea, but increased i n 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 inhibi tor of 3 beta-HSDH) reduced them. The placenta of C. chalcides is sugg ested to have an endocrine function and to replace the corpus luteum i n the production of P when the gland degenerates in late pregnancy. (C ) 1998 Academic Press.