title: Role of the double luteinizing hormone peak, luteinizing follicles, and the secretion of inhibin for dominant follicle selection in Asian elephants (Elephas maximus).
abstract: Elephants express two luteinizing hormone (LH) peaks timed 3 wk apart during the follicular phase. This is in marked contrast with the classic mammalian estrous cycle model with its single, ovulation-inducing LH peak. It is not clear why ovulation and a rise in progesterone only occur after the second LH peak in elephants. However, by combining ovarian ultrasound and hormone measurements in five Asian elephants (Elephas maximus), we have found a novel strategy for dominant follicle selection and luteal tissue accumulation. Two distinct waves of follicles develop during the follicular phase, each of which is terminated by an LH peak. At the first (anovulatory) LH surge, the largest follicles measure between 10 and 19.0 mm. At 7 ± 2.4 days before the second (ovulatory) LH surge, luteinization of these large follicles occurs. Simultaneously with luteinized follicle (LUF) formation, immunoreactive (ir) inhibin concentrations rise and stay elevated for 41.8 ± 5.8 days after ovulation and the subsequent rise in progesterone. We have found a significant relationship between LUF diameter and serum ir-inhibin level (r(2) = 0.82, P < 0.001). The results indicate that circulating ir-inhibin concentrations are derived from the luteinized granulosa cells of LUFs. Therefore, it appears that the development of LUFs is a precondition for inhibin secretion, which in turn impacts the selection of the ovulatory follicle. Only now, a single dominant follicle may deviate from the second follicular wave and ovulate after the second LH peak. Thus, elephants have evolved a different strategy for corpus luteum formation and selection of the ovulatory follicle as compared with other mammals.
authors.affiliation: Leibniz Institute of Zoo and Wildlife Research, Berlin, Germany. lueders@izw-berlin.de
authors.forename: Imke
authors.initials: I
authors.lastname: Lueders
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Taya
authors.forename: Gen
authors.initials: G
authors.lastname: Watanabe
authors.forename: Yuki
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Saroch
authors.initials: S
authors.lastname: Kaewmanee
authors.forename: Cheryl
authors.initials: C
authors.lastname: Niemuller
authors.forename: Charlie
authors.initials: C
authors.lastname: Gray
authors.forename: Wolf Jürgen
authors.initials: WJ
authors.lastname: Streich
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hildebrandt
mesh_terms: D000818:Animals; D003338:Corpus Luteum / Q000502:physiology; D004606:Elephants / Q000502:physiology*; D030762:Estrous Cycle / Q000097:blood; D005260:Female; D005498:Follicular Phase / Q000097:blood; D006107:Granulosa Cells / Q000378:metabolism; D007265:Inhibins / Q000097:blood / Q000378:metabolism*; D034461:Luteinization / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood*; D009929:Organ Size; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000502:physiology*; D010053:Ovary / Q000000981:diagnostic imaging; D010061:Ovulation Detection / Q000662:veterinary*; D011374:Progesterone / Q000097:blood / Q000378:metabolism; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D007265:Inhibins; D007986:Luteinizing Hormone