Estrogen and LH dynamics during the follicular phase of the estrous cycle in the Asian elephant

Pituitary and corpus luteum hormone patterns throughout the elephant estrous cycle have been well characterized. By contrast, analysis of follicular maturation by measurement of circulating estrogens has been uninformative. This study tested the ability of a urinary estradiol‐3‐glucuronide radioimmunoassay to noninvasively assess follicular development during the nonluteal phase of the elephant estrous cycle, and to determine the relationship between estrogen production and the “double LH surge.” Daily urine and serum samples were collected throughout seven estrous cycles from three Asian elephants, and urine was collected from an additional three females, for a total of 13 cycles. Serum was analyzed for luteinizing hormone (LH), and urine was analyzed for estrogens and progestins. Elephants exhibited a typical LH pattern, with an anovulatory LH (anLH) surge occurring approximately 21 days before the ovulatory LH (ovLH) surge. The urinary estrogen pattern indicated the presence of two follicular waves during the nonluteal phase. The first wave (anovulatory) began 5 days before the anLH surge and reached a maximum concentration the day before the peak. Thereafter, urinary estrogens declined to baseline for 2 weeks before increasing again to peak concentrations on the day of the ovLH surge. Urinary progestins were baseline throughout most of the follicular phase, increasing 2–3 days before the ovLH surge and continuing into the luteal phase. These results support previous ultrasound observations that two waves of follicular growth occur during the nonluteal phase of the elephant estrous cycle. Each wave is associated with an increase in estrogen production that stimulates an LH surge. Thus, in contrast to serum analyses, urinary estrogen monitoring appears to be a reliable method for characterizing follicular activity in the elephant. Zoo Biol 22:443–454, 2003. © 2003 Wiley‐Liss, Inc.     

Seasonal effects on the endocrine pattern of semi-captive female Asian elephants (Elephas maximus): timing of the anovulatory luteinizing hormone surge determines the length of the estrous cycle

Better breeding strategies for captive Asian elephants in range countries are needed to increase populations; this requires a thorough understanding of their reproductive physiology and factors affecting ovarian activity. Weekly blood samples were collected for 3.9 years from 22 semi-captive female Asian elephants in Thai elephant camps to characterize LH and progestin patterns throughout the estrous cycle. The duration of the estrous cycle was 14.6+/-0.2 weeks (mean+/-S.E.M.; n=71), with follicular and luteal phases of 6.1+/-0.2 and 8.5+/-0.2 weeks, respectively. Season had no significant effect on the overall length of the estrous cycle. However, follicular and luteal phase lengths varied among seasons and were negatively correlated (r=-0.658; P<0.01). During the follicular phase, the interval between the decrease in progestin concentrations to baseline and the anovulatory LH (anLH) surge varied in duration (average 25.9+/-2.0 days, range 7-41, n=23), and was longer in the rainy season (33.4+/-1.8 days, n=10) than in both the winter (22.2+/-4.5 days, n=5; P<0.05) and summer (18.9+/-2.6 days, n=8; P<0.05). By contrast, the interval between the anLH and ovulatory LH (ovLH) surge was more consistent (19.0+/-0.1 days, range 18-20, n=14). Thus, seasonal variation in estrous cycle characteristics were mediated by endocrine events during the early follicular phase, specifically related to timing of the anLH surge. Overall reproductive hormone patterns in Thai camp elephants were not markedly different from those in western zoos. However, this study was the first to more closely examine how timing of the LH surges impacted estrous cycle length in Asian elephants. These findings, and the ability to monitor reproductive hormones in range countries (and potentially in the field), should improve breeding management of captive and semi-wild elephants.     

Reproductive cycle of the elephant

The combination of a few factors, including poor captive reproduction, secession of importation from the wild and advances in hormone detection and ultrasonography, has contributed to the current knowledge on the elephant reproductive cycle. Several reproductive features in elephants differ markedly from other mammals. These include the urogenital tract anatomy, length and structure of the reproductive cycle, the formation of multiple corpora lutea and the type and secretion pattern of reproductive hormones. Being 13-18 weeks in length, the elephant estrous cycle is the longest amongst all studied non-seasonal mammals to date. Progesterone increases 1-3 days after ovulation, indicating the start of the luteal phase, which lasts 6-12 weeks. This is followed by a 4- to 6-week follicular phase that is concluded by two, precisely spaced and timed, LH surges. In general, the first, anovulatory LH surge occurs exactly 19-21 days before the second, ovulatory surge. Normally, a single follicle is ovulated. However, beside a corpus luteum (CL) forming on the site of ovulation, multiple accessory CLs can be found on the ovaries. Unlike many other species, the predominant progestagen secreted by luteal tissues is not progesterone, but rather its 5-alpha-reduced metabolites. The currently known aspects of the unique estrous cycle in Asian and African elephants, covering estrous behavior, circulating hormones, ultrasonography and anatomy of the reproductive organs as well as hormonal manipulation treatment possibilities, will be reviewed here.     

Role of the double luteinizing hormone peak, luteinizing follicles, and the secretion of inhibin for dominant follicle selection in Asian elephants (Elephas maximus)

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.     

Secretory Pattern of Inhibin During Estrous Cycle and Pregnancy in African (Loxodonta africana) and Asian (Elephas maximus) Elephants

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. Zoo Biol 31:511‐522, 2012. © 2011 Wiley Periodicals, Inc.     

Changes in expression of inhibin subunits in the cyclic golden hamster (Mesocricetus auratus) and the regulation of inhibin alpha subunit production by luteinizing hormone

In the present study, changes in localization of each inhibin subunit in the ovary were investigated during the estrous cycle of the golden hamster. The effect of LH surge on changes in localization in inhibin alpha subunit in the ovary was also investigated. Inhibin alpha subunit was localized in granulosa cells of various stages of follicles throughout the estrous cycle. Inhibin alpha subunit was also present in numerous interstitial cells on days 1 and 2 (day 1 = day of ovulation), but the number of positive interstitial cells was fewer on days 3 and almost disappeared on day 4 of the estrous cycle. Newly formed luteal cells were also positive for inhibin alpha subunit on days 1 and 2. On the other hand, positive reactions for inhibin beta A and beta B subunits were only present in the granulosa cells of healthy antral follicles. However, a positive reaction for inhibin beta B subunit in peripheral mural granulosa cells disappeared on days 3 and 4 of the estrous cycle. Treatment with LHRH-AS at 1100 h on day 4 completely blocked the luteinizing hormone (LH) surge and ovulation, although relatively high concentrations of plasma follicle-stimulating hormone (FSH) were maintained throughout the experiment. There were few positive reactions for inhibin alpha subunit in theca and interstitial cells 24 hr after LHRH-AS injection. The effect of LHRH-AS treatment was blocked by a single injection of 10 IU human chorionic gonadotropin. These results suggest that the major source of dimeric inhibin in the cyclic hamster was granulosa cells of healthy antral follicles. Different distribution pattern of inhibin beta A from beta B subunits in large antral follicles on days 3 and 4 of the estrous cycle suggests different secretion patterns of inhibin A from B on these days. Furthermore, the LH surge may be an important factor to induce production of inhibin alpha subunit in interstitial cells of the cyclic hamster.     

Successful artificial insemination of an Asian elephant at the National Zoological Park

For decades, attempts to breed elephants using artificial insemination (AI) have failed despite considerable efforts and the use of various approaches. However, recent advances in equipment technology and endocrine‐monitoring techniques have resulted in 12 elephants conceiving by AI within a 4‐year period (1998–2002). The successful AI technique employs a unique endoscope‐guided catheter and transrectal ultrasound to deliver semen into the anterior vagina or cervix, and uses the “double LH surge” (i.e., identifying the anovulatory LH (anLH) surge that predictably occurs 3 weeks before the ovulatory LH (ovLH) surge to time insemination. This study describes the 6‐year collaboration between the National Zoological Park (NZP) and the Institute for Zoo Biology and Wildlife Research (IZW), Berlin, Germany, that led to the refinement of this AI technique and subsequent production of an Asian elephant calf. The NZP female was the first elephant to be inseminated using the new AI approach, and was the fifth to conceive. A total of six AI trials were conducted beginning in 1995, and conception occurred in 2000. Semen was collected by manual rectal stimulation from several bulls in North America. Sperm quality among the bulls was variable and was thus a limiting factor for AI. For the successful AI, semen quality was good to excellent (75–90% motile sperm), and sperm was deposited into the anterior vagina on the day before and the day of the ovLH surge. Based on transrectal ultrasound, ovulation occurred the day after the ovLH surge. Pregnancy was monitored by serum and urinary progestagen, and serum prolactin analyses in samples collected weekly. Fetal development was assessed at 12, 20, and 28 weeks of gestation using transrectal ultrasound. Elevated testosterone measured in the maternal circulation after 36 weeks of gestation reliably predicted the calf was a male. Parturition was induced by administration of 40 IU oxytocin 3 days after serum progestagens dropped to undetectable baseline levels. We conclude that AI has potential as a supplement to natural breeding, and will be invaluable for improving the genetic management of elephants, provided that problems associated with inadequate numbers of trained personnel and semen donors are resolved. Zoo Biol 23:45–63, 2004. © 2004 Wiley‐Liss, Inc.     

Secretory patterns of serum prolactin in Asian (Elephas maximus) and African (Loxodonta africana) elephants during different reproductive states: Comparison with concentrations in a noncycling African elephant

Serum prolactin was quantified in adult female Asian (Elephas maximus) and African (Loxodonta africana) elephants during various reproductive states and the profiles compared to that in a noncycling African elephant. In reproductively normal elephants, there was no effect of season, estrous cycle stage, or lactational status on quantitative or qualitative prolactin secretion (P > 0.05), nor where there any differences (P > 0.05) in overall prolactin concentrations between species. In pregnant elephants, prolactin concentrations remained at baseline for the first 4–6 months of gestation. Thereafter, concentrations during early pregnancy averaged ∼four-fold higher than those during the estrous cycle, increasing to ∼100-fold over baseline during mid- to late gestation in both species. In contrast to cycling elephants, prolactin concentrations in an African elephant exhibiting chronic anovulation (on the basis of an acyclic serum progesterone profile) and mild galactorrhea were consistently about five-fold higher (P < 0.05), suggesting she is hyperprolactinemic. Other endocrinological assesments confirmed the hypogonadal state of this female. Serum estradiol concentrations were consistently at or below detectable levels. Additionally, no preovulatory luteinizing hormone (LH) surges occurred in daily serum samples analyzed over a 12-month period. The pituitary was not totally refractory, however, and responded with a several-fold increase in serum LH concentration (peak, 3.07 ng/ml) over baseline (0.75 ng/ml) after i.v. injection of gonadotropin-releasing hormone. This study describes normal baseline serum prolactin values for Asian and African elephants and is the first to identify hyperprolactinemia as a possible cause of reproductive acyclicity and galactorrhea in an African elephant. Zoo Biol 16:149–159, 1997. © 1997 Wiley-Liss, Inc.     

Response of estradiol and inhibin to experimentally reduced luteinizing hormone during follicle deviation in mares

The increase in LH concentrations at the time of the decrease in FSH concentrations during follicle deviation in mares was studied to determine the role of LH in the production of estradiol and immunoreactive inhibin (ir-inhibin). Ten days after ovulation, all follicles > or =6 mm were ablated, prostaglandin F(2 alpha) was given, and either 0 mg (control group, n = 15) or 100 mg of progesterone in safflower oil (treated group, n = 16) was given daily for 14 days, encompassing the day of diameter deviation. The follicular and hormonal data were normalized to the expected day of the beginning of diameter deviation when the largest follicle first reached > or =20 mm (Day 0). The experimentally induced decrease in LH concentrations during follicle deviation beginning on Day -4 delayed and stunted the increase in circulating concentrations of ir-inhibin and estradiol beginning on Days -3 and -1, respectively, but did not alter the predeviation FSH surge and the initiation of diameter deviation between the two largest follicles. Combined for both groups, the interval to the expected day of deviation was 16.6 days after ovulation when the largest follicle was a mean of 21.6 mm. After deviation, the largest follicle started to regress in the treated group beginning on Day 1 and was associated with decreased concentrations of ir-inhibin and estradiol, and increased concentrations of FSH. The negative influence of the dominant follicle on the postdeviation decrease in FSH observed in the control group was alleviated and concentrations resurged in the treated group. Apparently this is the first in vivo evidence that the increase in LH that precedes follicle deviation has a positive effect in supporting the production of inhibin during diameter deviation. It was concluded that the increase in LH concentrations before diameter deviation played a role in the production of estradiol and inhibin by the largest follicle during deviation.     

Effect of FSH deprivation at specific times on follicular maturation in the bonnet monkey (Macaca radiata)

Cyclic monkeys were deprived of FSH for specific periods on different days of the follicular phase by injecting them with minimal doses of an FSH antiserum characterized for specificity and bioneutralizing ability. The effect of the antiserum on follicular maturation was assessed by determining (a) serum oestrogen concentrations through the midcycle period, (b) serum progesterone concentrations as an index of ovulation and luteal function, (c) laparoscopic examination of the surface of the ovary when necessary, and (d) overall cycle length. While antiserum injection on Day 5 of the cycle caused delay in the oestrogen surge from Days 9 to 11, injection on Day 6 led to the occurrence of two oestrogen surges, on Days 9 and 14. Laparoscopic examination showed that the earlier follicle had disappeared and a new follicle had appeared by Day 14. Antiserum injection on Day 7 of the cycle arrested further growth of the maturing follicle, but a new follicle appeared 9 days later, as indicated by a surge of oestrogen on Day 16. Injection of antiserum beyond Day 7 had no effect on follicular development, ovulation and luteal function. These observations suggest that the mature follicle becomes relatively independent of FSH support about 48 h before ovulation and this event could be a marker for follicular dominance.     

Plasma follicle stimulating hormone and luteinizing hormone patterns during the estrous cycle of ewes

Fifteen Suffolk ewes were used in three experiments to compare plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) patterns during the estrous cycle and to determine whether FSH levels undergo changes in pulse frequency. Luteinizing hormone changed inversely with progesterone levels whereas FSH and progesterone concentrations revealed no obvious relationship. Unlike LH, FSH levels did not pulsate during the follicular phase. Higher FSH levels were detected on days 1, 6 and 12 and lower levels on days 0, 4 and 16. Coincident preovulatory LH and FSH surges were observed and this was the only time FSH and LH levels appeared to be jointly controlled.     

Follicle populations,ovulation rates and plasma profiles of LH,FSH and prolactin in Scottish Blackface ewes in high and low levels of body condition

Scottish Blackface ewes in high body condition (mean score = 2.86) had a higher mean ovulation rate (1.8 v. 0.9; P < 0.05) and more large (⪖ 4 mm diameter) follicles (4.6 v 2.2; P < 0.05) than ewes in low condition (mean score = 1.84) but similar numbers of small (1–4 mm diameter) follicles (6.3 v 6.0; NS). There was little difference in LH profiles with body condition but FSH and prolactin concentrations were significantly greater, during both luteal and follicular phases of the cycle, in ewes in high condition.Despite the relationships between body condition and ovulation rate and between condition and hormone concentrations, within the high condition groups, there was no significant difference in FSH levels with ovulation rate. Prolactin levels were higher in ewes with a single ovulation than in ewes with two or three ovulations. There was a trend towards a higher mean LH pulse frequency in the luteal phase and a higher mean LH pulse amplitude in the follicular phase in ewes with multiple ovulations compared with ewes with a single ovulation. During oestrus, only circulating prolactin concentrations differed with body condition, being significantly higher in ewes in high condition, but mean LH concentrations were higher and FSH concentrations lower in ewes with multiple ovulations. Subsequent luteal function, as measured by circulating progesterone concentrations, was normal in all ewes. It is concluded that body condition affected the size of the large follicle (⪖ 4 mm diameter) population through changes in FSH and possibly pulsatile LH secretion and prolactin secretion during the luteal and follicular phases of the cycle and that the number of follicles that were potentially ovulatory was probably determined during the luteal phase of the cycle. However, their ability to undergo the final stages of development and to ovulate may be related to the amount of LH secreted during the follicular phase.     

Comparisons of estradiol,LH and FSH patterns in pregnant and nonpregnant beagle bitches

To characterize plasma estradiol, LH and FSH patterns of secretion during the bitch estrous cycle, blood samples were obtained daily from 15 days before until 135 days after the LH surge in 10 pregnant and 10 nonpregnant beagle bitches. After an initial increase between days 15 and 10 and an expected proestrous peak, estradiol concentrations increased again from days 9-12 (corresponding to cytological metestrus) from basal values observed around day 9 after the LH surge, and remained significantly elevated throughout the luteal phase both in pregnant and nonpregnant animals. Concomitantly with the end of the luteal phase, plasma concentrations of estradiol returned to basal values in both groups. During the mid- to late-luteal phase, mean basal LH secretion was significantly elevated throughout in the pregnant relative to the nonpregnant animals. However, in nonpregnant animals, pulsatility was increased and peaks of higher amplitude were observed. The plasma FSH profiles, determined by a specific homologous RIA, differed significantly between pregnant and nonpregnant bitches during the last two-thirds of the luteal phase with a mean FSH level more elevated during pregnancy. The FSH level then decreased around parturition and low concentrations during lactation period were observed. The FSH concentrations remained steady in nonpregnant luteal phases from early luteal phase through mid-anestrus. The differences in pregnant and nonpregnant LH and FSH concentrations suggest pregnancy differences in regulation of the corpus luteum. Finally, the elevated estradiol concentrations observed during the luteal phase of both pregnant and nonpregnant animals suggest that an ovarian production of estrogens may be involved in overall corpus luteum regulation in dogs as in other species.     

Dynamics of circulating concentrations of gonadotropins and ovarian hormones throughout the menstrual cycle in the bonnet monkey: role of inhibin A in the regulation of follicle‐stimulating hormone secretion

In higher primates, increased circulating follicle‐stimulating hormone (FSH) levels seen during late menstrual cycle and during menstruation has been suggested to be necessary for initiation of follicular growth, recruitment of follicles and eventually culminating in ovulation of a single follicle. With a view to establish the dynamics of circulating FSH secretion with that of inhibin A (INH A) and progesterone (P₄) secretions during the menstrual cycle, blood was collected daily from bonnet monkeys beginning day 1 of the menstrual cycle up to 35 days. Serum INH A levels were low during early follicular phase, increased significantly coinciding with the mid cycle luteinizing hormone (LH) surge to reach maximal levels during the mid luteal phase before declining at the late luteal phase, essentially paralleling the pattern of P₄ secretion seen throughout the luteal phase. Circulating FSH levels were low during early and mid luteal phases, but progressively increased during the late luteal phase and remained high for few days after the onset of menses. In another experiment, lutectomy performed during the mid luteal phase resulted in significant decrease in INH A concentration within 2 hr (58.3±2 vs. 27.3±3 pg/mL), and a 2‐ to 3‐fold rise in circulating FSH levels by 24 hr (0.20±0.02 vs. 0.53±0.14 ng/mL) that remained high until 48 hr postlutectomy. Systemic administration of Cetrorelix (150 µg/kg body weight), a gonadotropin releasing hormone receptor antagonist, at mid luteal phase in monkeys led to suppression of serum INH A and P₄ concentrations 24 hr post treatment, but circulating FSH levels did not change. Administration of exogenous LH, but not FSH, significantly increased INH A concentration. The results taken together suggest a tight coupling between LH and INH A secretion and that INH A is largely responsible for maintenance of low FSH concentration seen during the luteal phase. Am. J. Primatol. 71:817–824, 2009. © 2009 Wiley‐Liss, Inc.     

Follicle selection in cyclic guinea pigs with active immunization against inhibin alpha-subunit

Experiments were conducted to elucidate the mechanisms of active immunization against inhibin on ovarian follicular development and selection in guinea pigs. Estrous cycle was synchronized in experimental guinea pigs by implanting progesterone containing tubes. Antibodies that bound 125I-labeled bovine inhibin were produced by all guinea pigs receiving the inhibin vaccine (recombinant ovine alpha-subunit in oil emulsion) without any effects on duration of the estrous cycle. Active immunization against inhibin increased the plasma concentrations of progesterone during the luteal phase and the plasma concentrations of estradiol but failed to increase the plasma concentration of follicle-stimulating hormone (FSH) during preovulatory period. The treatment also increased the number of corpora lutea (from 1.3+/-0.3 to 7.0+/-1.6 per each ovary), and preovulatory sized follicles (from 1.8+/-0.6 to 7.0+/-1.6 per each ovary), and follicles stained positively for inhibin alpha-subunit (from 2.3+/-0.5 to 6.3+/-1.3 per each ovary) significantly. The results indicate that active immunization against inhibin enhances ovulation rate by affecting the follicle selection and only dominant follicle can be stained for inhibin alpha-subunit in guinea pigs. This study is firstly to provide direct evidence that inhibins play important role in follicle selections in guinea pigs.     

The secretion of bioactive and immunoreactive follicle-stimulating hormone (FSH) and luteinizing hormone (LH) throughout the menstrual cycle of the rhesus monkey (Macaca mulatta)

The present study provides the first evaluation of related changes in serum levels of bioactive FSH (Bio FSH) and immunoreactive FSH (iFSH), and concurrent dynamics of LH and FSH bioactivity throughout the menstrual cycle of the rhesus monkey. Mean concentrations of Bio FSH were elevated on days 0 and 1 (n = 7; P < 0.05; day 0 = preovulatory LH surge). Data from individual animals revealed that an average (± SEM) of 1.43 ± 0.29 and 2.71 ± 0.61 discrete surges of Bio FSH occurred in each monkey's follicular and luteal phase, respectively. Analysis of the collective data indicated that periods of increased Bio FSH secretory activity spanned days −1 to 1 and 8 to 10 (P < 0.025). Increases in serum Bio FSH and iFSH concentrations were not precisely correlated on a daily basis (38.9%), although 72.2% of the peaks of Bio FSH and iFSH surges occurred within a day of one another. Similarly, only 36.1% of the Bio FSH surges were accompanied by elevations in bioactive LH (Bio LH). A significant rise in Bio LH, but not Bio FSH, occurred on day −1 (P < 0.01). Concentrations of Bio LH, but not Bio FSH, were elevated in the early luteal phase (P < 0.01). The bioactivity/immunoactivity ratios (Bio/I) of LH and FSH were maximal on the day of the preovulatory surge (P < 0.01). On day −1, LH Bio/I significantly increased (P < 0.05), but no change in FSH Bio/I was detected. The Bio/I of LH, but not FSH, remained elevated in the early luteal phase. In summary: the relative increase in Bio FSH exceeds iFSH during the preovulatory surge. Surges of Bio FSH occur during the follicular and luteal phases which potentially could support follicle selection/maturation. Divergencies between circulating LH and FSH biopotency may reflect a differential regulation of secretion and/or biosynthesis of these hormones. The prolonged early luteal elevation of LH Bio/I is consistent with the idea of a functional role of elevated LH biopotency in the maintenance of the corpus luteum.     

Plasma gonadotropin and progesterone concentrations during the estrous cycle of Finn, Suffolk and Targhee ewes

Hormonal profiles during the estrous cycle of Finn, Suffolk and Targhee ewes were compared in six ewes of each breed. Blood samples were drawn by venipuncture at 8-h intervals from onset to onset of consecutive estrous periods. Number of corpora lutea (CL) and ovarian follicles >/=3 mm in diameter on Day 10 (estrus = Day 0) were observed using endoscopy. Estrous cycle length was 14.9, 15.6 and 16.4 d (P<0.01) in Finn, Suffolk and Targhee ewes, respectively. Finns had more (P<0.001) CL (3.5) than Suffolks (2.0) and Targhees (1.8), but luteal phase progesterone concentrations were similar among breeds in peak level and area under the curve. In Finn ewes, the amplitude of the preovulatory LH surge was lower (P<0.01) and tended to occur later in estrus; otherwise LH levels and patterns were similar among breeds. A coincident follicle stimulating hormone (FSH) preovulatory surge occurred in most ewes, the amplitude of which was related to that of luteinizing hormone (LH); r = 0.67, P<0.01. Plasma FSH levels and patterns were similar in Finn, Suffolk and Targhee ewes and most ewes had three to four secretory episodes. Follicles >/=3 mm averaged 1.8, 1.0 and 1.2 (P>0.1) in Finn, Suffolk and Targhee ewes, respectively. Results indicate that the higher ovulation rate of the Finn ewe is not elicited by increased FSH levels at any stage of the estrous cycle.     

Perturbation of estradiol-feedback control of luteinizing hormone secretion by immunoneutralization induces development of follicular cysts in cattle

We used immunoneutralization of endogenous estradiol to investigate deficiencies in the estradiol-feedback regulation of LH secretion as a primary cause of follicular cysts in cattle. Twenty-one cows in the prostaglandin (PG) F(2alpha)-induced follicular phase were assigned to receive either 100 ml of estradiol antiserum produced in a castrated male goat (n = 11, immunized group) or the same amount of castrated male goat serum (n = 10, control group). The time of injection of the sera was designated as 0 h and Day 0. Five cows in each group were assigned to subgroups in which we determined the effects of estradiol immunization on LH secretion and follicular growth during the periovulatory period. The remaining six estradiol-immunized cows were subjected to long-term analyses of follicular growth and hormonal profiles, including evaluation of pulsatile secretion of LH. The remaining five control cows were used to determine pulsatile secretion of LH on Day 0 (follicular phase) and Day 14 (midluteal phase). The control cows exhibited a preovulatory LH surge within 48 h after injection of the control serum, followed by ovulation of the dominant follicle that had developed during the PGF(2alpha)-induced follicular phase. In contrast, the LH surge was not detected after treatment with estradiol antiserum. None of the 11 estradiol-immunized cows had ovulation of the dominant follicle, which had emerged before estradiol immunization and enlarged to more than 20 mm in diameter by Day 10. Long-term observation of the six immunized cows revealed that five had multiple follicular waves, with maximum follicular sizes of 20-45 mm at 10- to 30-day intervals for more than 50 days. The sixth cow experienced twin ovulations of the initial persistent follicles on Day 18. The LH pulse frequency in the five immunized cows that showed the long-term turnover of cystic follicles ranged from 0.81 +/- 0.13 to 0.97 +/- 0.09 pulses/h during the experiment, significantly (P < 0.05) higher than that in the midluteal phase of the control cows (0.23 +/- 0.07). The mean LH concentration in the immunized cows was also generally higher than that in the luteal phase of the control cows. However, the LH pulse and mean concentration of LH after immunization were similar to those in the follicular phase of the control cows. Plasma concentrations of total inhibin increased (P < 0.01) concomitant with the emergence of cystic follicles and remained high during the growth of cystic follicles, whereas FSH concentrations were inversely correlated with total inhibin concentrations. In conclusion, neutralization of endogenous estradiol resulted in suppression of the preovulatory LH surge but a normal range of basal LH secretion, and this circumstance led to an anovulatory situation similar to that observed with naturally occurring follicular cysts. These findings provide evidence that lack of LH surge because of dysfunction in the positive-feedback regulation of LH secretion by estradiol can be the initial factor inducing formation of follicular cysts.     

Follicle and systemic hormone interrelationships during spontaneous and ablation-induced ovulatory waves in mares

The characteristics of ovulatory follicular waves were studied for spontaneous waves and waves induced during the next estrous cycle by ovarian follicle ablations and administration of PGF2alpha 10 days after ovulation in 21 mares. In the induced group, both the days of the FSH surge and day of deviation were more synchronized, LH concentrations were greater before and after deviation, estradiol concentrations were greater after deviation, and the ovulatory follicle grew at a faster rate (3.4+/-0.2 compared with 2.7+/-0.1 mm/day). The frequency of two dominant follicles/wave was not different between induced waves (7 of 21) and spontaneous waves (9 of 21), but both dominant follicles ovulated more frequently in induced waves (6 of 7 waves compared with 0 of 9).     

Plasma levels of LH, FSH, prolactin, oestradiol-17beta and progesterone during natural and induced oestrus in the dairy goat

The patterns of LH, FSH, prolactin and oestradiol-17beta, before and during natural oestrus, and of progesterone during the following cycle were studied in four French Alpine dairy goats and compared with those obtained after synchronization of oestrus in the same animals. The highest concentration of oestradiol-17beta was measured at the beginning of oestrus and was followed 3 hours later by simultaneous rises of LH, FSH and prolactin. A second FSH peak was observed 48h after the first one. On D(3) (D(0) = day of oestrus) progesterone concentration was over 1 ng/ml. The luteal phase lasted 15 days. Peak concentrations of oestradiol-17beta and progesterone were higher in animals when oestrus was induced. This was attributed to their higher ovulation rate. The second FSH peak was lower, and the interval between oestradiol-17beta peak and gonadotrophin surge longer, than at natural oestrus.