Luteal maintenance of pregnancy in the African elephant (Loxodonta africana)

Abstract

The ovaries of 8 African elephant fetuses and their mothers between 2 and 22 months of gestation, and those of 2 cycling and 2 lactating elephants, were examined grossly, histologically and immunocytochemically, with emphasis on the development and regression of the accessory corpora lutea (CL) of pregnancy and the steroidogenic capacities of these and the fetal ovaries. The results supported recent findings (Lueders et al. 2011) that the accessory CL form as a result of luteinisation, with and without ovulation, of medium sized follicles during the 3-week interluteal period of the oestrous cycle. They enlarge significantly and become steroidogenically active around 5 weeks of gestation, probably in response to placental lactogen (elPL) which is secreted by the implanting trophoblast of the conceptus. The large luteal cells stained strongly for 3β hydroxysteroid dehydrogenase (3βHSD) activity throughout the 22 month gestation period although they showed vacuolation and other degenerative changes in the final months of gestation coincident with hypertrophy and hyperplasia of 3βHSD-positive interstitial cells in the fetal gonads. It is proposed that the progestagens secreted by the enlarged gonads of the elephant fetus may function both to assist the maternal ovaries in supporting the pregnancy state and to induce torpor and intrauterine immobility of the rapidly growing fetus.