ABSTRACT. Reproduction of captive elephants in zoos has shown a low fecundity and requires improvement. One of the reasons for low fecundity is ovarian dysfunction in many female elephants. To investigate whether prolactin has a correlation with ovarian function in female elephants, the serum concentrations of prolactin, progesterone and estradiol-17 in four African female elephants (one cycling female and three non-cycling female elephants) were measured. Cyclic patterns of prolactin and estradiol-17 were observed in the cycling female elephant, which tended to be high during the follicular phase and low during the luteal phase. On the other hand, a cyclic pattern of prolactin was not observed in the non-cycling female elephants. One of the three non-cycling females (Mako) had developed breasts and showed significantly higher average levels of prolactin than the other female elephants. These results suggested that high concentrations of circulating estradiol-17 during the follicular phase stimulated prolactin secretion. They also suggested that hyperprolactinemia in Mako was one of the causes of the developed mammary glands and ovarian dysfunction.
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.
ABSTRACT. To define the source of circulating inhibin in female Asian elephants, the immunolocalizations of the inhibin , A and B subunits, 3-hydroxysteroid dehydrogenase (3-HSD), aromatase cytochrome P450 (P450arom) and cytochrome 17-hydroxylase P450 (P450 c17) were investigated. Concentrations of immunoreactive (ir-) inhibin, progesterone and follicle-stimulating hormone (FSH) during the estrous cycle were measured by radioimmunoassay. Inhibin immunoreactivity in follicular fluid and homogenate of corpora lutea was also measured. Immunolocalizations of inhibin subunits, 3-HSD, P450arom and P450c17 were detected in the granulosa cells of antral follicles and luteal cells. The follicular fluid contained high levels of ir-inhibin and bioactive inhibin. The homogenate of corpora lutea also contained ir-inhibin. Serum ir-inhibin remained at low levels during the early non-luteal phase, began to increase from the late non-luteal phase and continued to increase during the early luteal phase. Serum ir-inhibin showed maximal levels in the middle of the luteal phase and gradually decreased to baseline three weeks prior to progesterone decline. The serum ir-inhibin levels were positively correlated with progesterone throughout the estrous cycle. On the other hand, ir-inhibin was negatively correlated with FSH during the late non-luteal and early luteal phases. These findings strongly suggest that the corpus luteum is one of the sources of inhibin as well as granulosa cells in the Asian elephant.
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...
ABSTRACT. This study was conducted to determine the correlation between reproductive hormones and musth in a male African elephant. Changes in circulating luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone and immunoreactive (ir-) inhibin and the degree of musth were evaluated for 4 years. LH increased 4 weeks before musth began. The highest concentrations of testosterone and ir-inhibin were observed from April to October. There were positive correlations among testosterone, ir-inhibin and musth behavior. These findings suggested that the surge-like LH in the pre-musth period might stimulate secretion of testosterone and ir-inhibin and thus initiate the musth behavior. This study also suggested that the high LH level before musth might be a useful biomarker for the beginning of the musth season.KEY WORDS: African elephant, inhibin, luteinizing hormone, musth, testosterone.J. Vet. Med. Sci. 73(3): 379-383, 2011 Musth is a unique phenomenon that occurs either annually or semiannually in adult male African (Loxodonta africana) [7,16,17] and Asian (Elephas maximus) elephants [5,11]. During musth, male elephants have elevated levels of androgens, especially androstenedione and testosterone [1,6,7,10,15,18,20,21,24]. Musth bulls were reported to have elevated levels of luteinizing hormone (LH) in both African [1] and Asian [15] species. Secretory patterns of follicle stimulating hormone (FSH) and immunoreactive (ir-) inhibin in male elephants have never been reported before. In captivity, both African and Asian bulls in musth exhibit aggression towards their mahouts or handlers [5,10,20], which is extremely dangerous for zoo staff, veterinarians and researchers who manage breeding programs. Thus, our understanding of markers for prediction of musth needs to be improved. The objective of this study was to investigate secretion of reproductive hormones associated with musth characteristics in a male African elephant in Japan.A male African elephant named "Tamao" (Fig. 1A) was studied for 4 years, from 33 to 37 years of age. It was housed at the Tama Zoological Park, Hino City, Tokyo, Japan, together with 4 female African elephants. All elephants were housed outside during the daytime (0900 hr-1600 hr) and inside the building at night throughout the year. Blood samples were collected weekly between 0800 hr and 0900 hr from an ear vein without anesthesia. The samples were centrifuged, and sera were stored at -20C until hormonal analysis. The appearance of characteristic behavioral and physical changes was recorded daily during the 4-year period. The bull elephant was classified as being in musth when one or a combination of the following behavior and/or physical changes were continuously (for more than 3 days per week) observed: increased aggressive behavior, temporal gland secretion (TGS; Fig. 1B) and urine dribbling (UD; Fig. 1B) as described previously [3]. Since TGS can occur in African bulls under stress or social excitation, TGS was considered as an indicator of musth only if it occurred ...
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.
In this case report, the authors investigated immunolocalization of inhibin α and inhibin/activin βA and βB subunits, as well as steroidogenic enzymes, in the testes of an African elephant. Testes were collected from a reproductively active male African elephant (24 yr old) at autopsy. Histologically, all types of spermatogenic cells including mature-phase spermatozoa were found in the seminiferous tubules. Positive immunostaining for inhibin α and inhibin/activin βA and βB subunits was observed in Sertoli and Leydig cells. In addition, P450scc, 3βHSD, P450c17, and P450arom were also detected in the cytoplasm of Leydig cells. These results suggested that Leydig cells of adult African elephant testes have the ability to synthesize progestin, androgen, and estrogen, whereas both Sertoli and Leydig cells appear as a major source of inhibin secretion in the male African elephant.
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