Abstract. The objective of the present study was to define the secretion of prolactin (PRL) in pregnant African and Asian elephants. Levels of immunoreactive (ir-) PRL in serum and placental homogenates were measured by a heterologous radioimmunoassay (RIA) based on an ovine and human RIA system, and the localization of ir-PRL in the placenta was detected by immunohistochemistry using anti-human PRL. Circulating ir-PRL clearly showed a biphasic pattern during pregnancy in African and Asian elephants. Serum levels of ir-PRL started to increase from the 4 -6th month of gestation and reached the first peak level around the 11-14th month. A second peak of circulating ir-PRL levels was observed around the 18-20th month of gestation followed by an abrupt decline after parturition. In contrast, in a case of abortion of an African elephant, the second peak of ir-PRL was not observed, and the levels remained low for about four months until parturition. The weight of the fetus delivered at the 17th month of gestation was 23.5 kg, which was quite small compared with normal fetuses in previous reports. Ir-PRL was detected in placental homogenates, and immunolocalization was observed in trophoblasts in both the African and Asian elephants, indicating that the placenta is the source of ir-PRL during pregnancy in elephants. The present results clearly demonstrated that circulating ir-PRL shows a biphasic pattern during normal pregnancy and that the placenta appears to be an important source of circulating ir-PRL during pregnancy in both African and Asian elephants. Key words: Female elephant, Fetal growth, Placenta, Pregnancy, Prolactin (J. Reprod. Dev. 58: [105][106][107][108][109][110][111] 2012) G estation and parturition are dramatic events for a female animal. The secretion of prolactin (PRL) shows remarkable changes during gestation and at parturition in many species [1][2][3][4][5]. The major source of PRL is the anterior pituitary gland, and its major functions during mammalian gestation are development of the mammary glands and stimulation of milk production. PRL secretion is stimulated by several environmental factors including pregnancy, suckling stimulation and stress [2,[6][7][8][9][10][11][12].Reproductive endocrinology including secretion of PRL has been studied in elephants previously [13][14][15][16][17][18][19][20][21][22]. However, many mysteries, such as the source and the function of PRL during pregnancy, still remain. It is known that PRL is derived from the placenta in humans and rats [2,[23][24][25][26]. Placentation begins at the second to third month after ovulation in elephants [27]. The placenta ultimately forms a zonary shape, and its weight at term ranges from 8.3 to 22.2 kg in elephants [28].The objectives of the present study were to investigate the secretory pattern of immunoreactive (ir-) PRL in pregnant elephants. In addition, the immunoreactivity of ir-PRL was detected in the term placental tissues of both of African and Asian elephants by radioimmunoassay and immunohistochemistry. Materi...

The ovary of female elephants has multiple corpora lutea (CL) during the estrous cycle and gestation. The previous reports clearly demonstrated that inhibin was secreted from lutein cells as well as granulosa cells of antral follicles in cyclic Asian elephants. The aim of this study is to investigate the inhibin secretion during the pregnancy in African and Asian elephants. Two African elephants and two Asian elephants were subjected to this study. Circulating levels of immunoreactive (ir-) inhibin and progesterone were measured by radioimmunoassay. Four pregnant periods of an African elephant and three pregnant periods of an Asian elephant were analyzed in this study. Circulating levels of ir-inhibin started to increase at 1 or 2 week before the ovulation and reached the peak level 3 or 4 weeks earlier than progesterone during the estrous cycle in both African and Asian elephants. After last luteal phase, the serum levels of ir-inhibin remained low throughout pregnancy in both an African and an Asian elephant. The mean levels of ir-inhibin during the pregnancy were lower than the luteal phase in the estrous cycle despite high progesterone levels were maintained throughout the pregnancy. These results strongly suggest that CL secrete a large amount of progesterone but not inhibin during the pregnancy in elephants.

Urinary steroid hormones and luteinizing hormone (LH) were monitored in a female pileated gibbon. The LH concentration almost peaked the day after estrogens peaks. The progesterone increased sharply after the LH peaks. Our results revealed for the first time the relationship between daily changes in urinary hormones throughout normal menstrual cycles in pileated gibbon.