Potential Gonadotropin Activity During Early Pregnancy in Elephants

Pregnant elephants have serum progestin levels three or four times that of the luteal phase of a non-conceptual estrous cycle. Unlike other mammals neither the placenta nor the fetal tissue has been shown to contribute to the progestin levels sustained by the primary corpus luteum during pregnancy. Necropsy in pregnant elephant carcasses and ultrasound examination of the reproductive ovaries provided evidence of multiple corpora lutea throughout the pregnancy. The initiating factor for the recruitment of these accessory corpora lutea is hypothesized to be an early pregnancy gonadotropin similar to equine chorionic gonadotropin (eCG) in horses. In order to detect the possible presence of a gonadotropin in pregnant Asian elephants (Elephas maximus), a preliminary in-vivo bioassay was conducted in mice by assessing the ovulation response to elephant serum. Serum from eight pregnant Asian elephants was assigned into five treatment groups and pooled according to the week of pregnancy with pooled serum of non conceptive luteal phase and 0.9% sterile saline acting as controls. The treatments were injected subcutaneously to ten week old female CD-1 strain mice, once daily for three days. After the treatment, both the ovaries were harvested from the mice, and the follicular as well as luteal structures were counted manually under a dissecting microscope. A Kruskal Wallis test, followed by a Dunn’s post-hoc comparison using MINITAB 15 and GRAPH PAD Prism 5 Statistical software, determined a statistically significant increase in the ovulation and follicular activity response in mice subjected to the serum pooled from 13-15 week pregnant elephants. This clearly suggests the presence of an early pregnancy gonadotropin-like content in serum from that group which may be responsible for the recruitment of accessory corpora lutea