Placentation in the African elephant (Loxodonta africana). V. the trophoblast secretes placental lactogen

Objectives: To determine if elephant placenta secretes a lactogenic hormone which may function as the principal luteotrophin to maintain ovarian luteal function throughout gestation. Study design and main outcome measures: To label biopsies of endometrium and placenta recovered from African elephant culled professionally throughout gestation with an anti-human prolactin polyclonal antibody in a conventional immunocytochemical staining technique. Results: All trophoblast cells covering the placental villi and forming 'plugs' in the apical endometrial glands stained strongly and precisely with the anti-human prolactin antiserum throughout gestation. Conclusions: Elephant trophoblast secretes a placental lactogen (elPL) which may stimulate both the development and secretory function of the large accessory corpora lutea of elephant pregnancy and provide the mitogenic stimulus for placental differentiation and development.