Placentation in the African elephant, Loxodonta africana. I. Endocrinological aspects

Abstract

Placental and fetal tissues were recovered from the uteri of 59 pregnant elephant that ranged in estimated age from day 18 to month 21 of gestation. Incubation of placenta and fetal gonad, alone or in combination, with tritium-labelled cholesterol, pregnenolone and androstenedione failed to yield any labelled progestagens or oestrogens from placenta, but did produce small amounts of labelled progesterone and 5alpha-dihydroprogesterone from fetal gonad. Immunochemical staining of tissues with four antisera specific for enzymes involved in the steroidogenic pathway revealed no staining in sections of placenta but positive labelling for P450 side chain cleavage enzyme (SCC450) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) of the interstitial cells that comprise the bulk of the enlarged fetal gonads during the second half of gestation. Saline extracts of placental tissue showed no activity in three different gonadotrophin assays. In view of this endocrinological inactivity in the zonary elephant placenta and the probable reliance on maternal luteal sources of progestagens for maintenance of the pregnant state, the argument is advanced that uncomplicated abortion would probably follow a single administration of a PGF analogue given at any stage of pregnancy. If so, the treatment might constitute an efficacious method for controlling population increases in elephants maintained in enclosed game parks in Africa.