Acute effects of unilateral sectioning the superior ovarian nerve of rats with unilateral ovariectomy on ovarian hormones (progesterone,testosterone and estradiol) levels vary during the estrous cycle

The present study analyzed the participation of the left and right superior ovarian nerves (SON) in regulating progesterone, testosterone, and estradiol serum levels in unilaterally ovariectomized rats on each day of the estrous cycle. For this purpose, ovarian hormone concentrations in serum were measured in animals with either sham-surgery, unilateral ovariectomy (ULO), unilateral sectioning of the SON, or sectioning of the SON innervation of the in situ ovary in rats with ULO.     

Unilateral sectioning of the superior ovarian nerve of rats with polycystic ovarian syndrome restores ovulation in the innervated ovary

The present study tested the hypothesis that if polycystic ovary syndrome (PCOS) results from activating the noradrenergic outflow to the ovary, unilaterally sectioning the superior ovarian nerve (SON) will result in ovulation by the denervated ovary, and the restoration of progesterone (P4), testosterone (T) and estradiol (E2) normal serum level. A single 2 mg dose of estradiol valerate (EV) to adult rats results in the development of a syndrome similar to the human PCOS. Ten-day old rats were injected with EV or vehicle solution (Vh) and were submitted to sham surgery, unilateral or bilateral sectioning of the SON at 24-days of age. The animals were sacrificed at 90 to 92 days of age, when they presented vaginal estrus preceded by a pro-estrus smear. In EV-treated animals, unilateral sectioning of the SON restored ovulation by the innervated ovary and unilateral or bilateral sectioning of the SON normalized testosterone and estradiol levels. These results suggest that aside from an increase in ovarian noradrenergic tone in the ovaries, in the pathogenesis of the PCOS participate other neural influences arriving to the ovaries via the SON, regulating spontaneous ovulation. Changes in P4, T and E2 serum levels induced by EV treatment seem to be controlled by neural signals arising from the abdominal wall and other signals arriving to the ovaries through the SON, and presents asymmetry.     

The ability of subordinate follicles of the second follicular wave to become dominant is lost by day 15 of the estrous cycle in cattle

Generally, unilateral ovariectomy before a critical period in the latter part of the estrous cycle induces a transitory increase in plasma FSH, which causes subordinate follicles to develop and maintain ovulation rates characteristic of the species. A limiting period for subordinate follicles to assume dominance and from which ovulation occurs has not been shown for cattle. Growth and/or regression of subordinate follicles were characterized following removal of the dominant follicle at different days of the luteal phase of the estrous cycle in cattle in this study. In the mid-luteal phase (Day 13 or 15), the ovary with the dominant follicle of the second wave was ablated via unilateral ovariectomy; the corpus luteum also was removed. In the late luteal phase (Day 17 or 19), the dominant follicle was ablated with an ultrasonically guided 20 gauge needle. When the dominant follicle was removed on Day 13, the largest subordinate follicle of the second wave of follicular development became dominant and ovulation occurred from this follicle in 4 of 4 animals. However, when the dominant follicle was removed on Day 15, 17 or 19, a new wave of follicular development was induced in 14 of 15 animals. Moreover, the recovered subordinate follicle of the second wave of follicular development had similar growth characteristics to naturally occurring dominant follicles. In conclusion, the subordinate follicle in the second follicular wave in cattle retained the ability to become dominant, but this ability was lost by Day 15 of the estrous cycle. However, cattle then were able to maintain ovulation by developing a new wave of follicular growth.     

Time of ovarian follicle selection during the porcine estrous cycle

Two experiments were conducted to: 1) determine the time during the procine estrous cycle when compensation in ovulation rate after unilateral ovariectomy (ULO) ceases to be complete, 2) compare the follicle selection process in gilts selected for high ovulation rate with unselected control gilts and 3) determine the number of follicles on the right ovary at various stages of the estrous cycle. Experiment I included 25 crossbred gilts, while Experiment II included 17 gilts selected for high ovulation rate and 16 unselected control gilts. The right ovary was removed via a mid-ventral laparotomy on either day 13, 15, 17 or 19 of the cycle. In Experiment I, compensation in ovulation rate ceased between days 13 and 15; whereas, in Experiment II, cessation occurred between days 15 and 17. Selected and control gilts responded alike to ULO, indicating similarity in the follicle selection process. Follicle numbers in the right ovary showed a general decline, especially between days 17 and 19, indicating that atresia was occurring during the follicular phase. The results indicate that the selection of ovarian follicles for ovulation at the ensuing estrus occurs before day 17 of the porcine estrous cyle.     

Ipsilateral vagotomy to unilaterally ovariectomized pre-pubertal rats modifies compensatory ovarian responses

The present study evaluates the participation of the vagus nerve in pre-pubertal rats with unilateral ovariectomy on puberty onset, and on progesterone, testosterone and estradiol serum levels, and the compensatory responses of the ovary. Unilateral vagotomy did not modify the onset of puberty in unilaterally ovariectomized rats. Ovulation rates of animals with the left vagus nerve sectioned and the left ovary in-situ was lower than in rats with only unilateral ovariectomy. Sectioning the left vagus to 32-day old rats with the left ovary in-situ resulted in lower compensatory ovarian hypertrophy than in rats with right unilateral ovariectomy. Twenty-eight or 32-day old animals with sectioning of the right vagus nerve and the right ovary in situ showed higher compensatory ovulation. Twenty-eight -day old rats with the right ovary in situ had higher progesterone and testosterone levels than animals of the same age with the left ovary in-situ. Compared to animals with the right ovary in situ, animals treated at 32-days of age, sectioning the ipsi-lateral vagus nerve resulted in higher progesterone levels. Higher progesterone levels were observed in 28- and 32 days old rats with the left ovary in situ and left vagus nerve sectioned. Thirty-two day old animals with the right ovary in situ and right vagus nerve sectioned had higher progesterone levels than rats of the same age with the left ovary in situ and left vagus nerve sectioned. Left vagotomy to 28-day old rats with the left ovary in situ resulted in higher testosterone levels, a reverse response to that observed in animals with sectioning of the right vagus and the right ovary in situ. Thirty-two day old rats with the left ovary in situ and left vagus nerve sectioned showed lower testosterone levels than animals without vagotomy and with the left ovary in situ.     

Changes in serum and ovarian steroids during reproductive development in the female guinea pig

This study was designed to measure ovarian hormones prior to and during the first estrous cycle in guinea pigs. Blood was obtained from 12 animals throughout the first estrous cycle. Ovaries and peripheral serum were obtained from 25 additional animals at various stages of development prior to and after first ovulation. Estradiol, progesterone, androstenedione, and testosterone were measured in all sera and half of the ovaries. The remaining ovaries were fixed for histology. Serum estradiol was nondetectable until a few days before first ovulation, but was present in the ovary throughout development. Serum progesterone was nondetectable until the day of ovulation, but the luteal phase pattern was similar to that observed in adults. Serum androgens were detectable throughout development, with androstenedione higher than testosterone. The immature ovary contained more testosterone than androstenedione, but this pattern was reversed after ovulation. These results indicate that the immature ovary in the guinea pig contains minimal amounts of estradiol and progesterone, the first estrous cycle is similar to that in adults, and that the pattern of ovarian androgen content changes during the peripubertal period.     

Corpus luteum function following single and double ovulation during estrous cycle in Sanjabi ewes

This study compared the effect of double and single ovulation on serum progesterone concentrations and luteal characteristics in Sanjabi ewes at different days of the estrous cycle. The estrous cycles of 197 Sanjabi ewes were synchronized by a 12-day treatment with intravaginal sponges (Chronogest^®). Estrus was detected in 144 ewes 27–39 h after sponge removal. Daily blood samples were taken every morning and analyzed for serum progesterone (P4). Ewes were then transported to a local abattoir, where nine ewes were slaughtered on each experimental day (days 1–16 after estrus) for ovary collection. The ovarian follicles were measured and categorized by size (very small <2 mm; small 2–3.5 mm; medium 3.5–5 mm; large >5 mm). On each slaughter day, the number of corpora lutea per ewe was classified as single and double ovulation. The results show that the effect of dominant follicles was less during the mid-luteal phase. Ovulation rate of right, left and both ovaries were (54.9%), (23.6%) and (21.5%), respectively. The incidence of double ovulations was 40.2%. In the case of ewes exhibiting double ovulation, 46.6% occurred unilateral (ewes exhibited both ovulations on the right ovary); whereas 53.4% occurred bilateral (ewes exhibited ovulations on the right and left ovaries). Unilateral double ovulation was not observed in the left ovary. The right ovary appeared to play a significantly greater role in ewes showing single and double ovulations than the left ovary (P < 0.05). Serum progesterone concentration showed minimum and maximum levels of 0.29 ± 0.15 and 5.51 ± 0.75 ng/ml on days 16 and 11 post-estrous, respectively (P < 0.001). The mean volume of individual corpus lutea in ewes with single ovulations was significantly higher than in ewes with double ovulations (P < 0.01). However, the total volume of corpus lutea in ewes with single ovulation was significantly lower than in ewes with double ovulations in some days of estrous cycle (P < 0.01). The serum progesterone concentration was significantly higher in double than single ovulating animals on days 1–16 of the estrous cycle (P < 0.001). These results indicated a relatively high incidence of double ovulation in ewes associated with increasing total luteal volume and high circulating concentrations of progesterone.     

Relationships of liver weight, cholesterol, albumin and alpha2-macroglobulin concentrations with ovarian function in swine

In two genetic swine models selected for diversity in ovulation rates (White composite controls and ovulation rate selection line, n = 131; 1/2 White composite: 1/2 Meishan crossbreds, n = 387), a positive relationship was established with liver weight and ovulation rate (P < 0.01). Serum changes of cholesterol, albumin and alpha2-macroglobulin were monitored during various stages of the luteal phase and follicular phase (days 17 and 19 of the estrous cycle; 1/2 White composite: 1/2 Meishan gilts). Serum cholesterol concentrations increased with liver weights (r = 0.19; P < 0.01) and corpora lutea numbers (r = 0.14; P < 0.01). Albumin concentrations were negatively correlated with corpora luteal numbers (r = -0.3; P < 0.01) but had no relationship with liver weight. Serum concentrations of alpha2-macroglobulin were not related to liver weight or corpora lutea numbers. Circulating concentrations of cholesterol and alpha2-macroglobulin increased with day of the estrous cycle (P < 0.01). Testosterone concentrations were inversely related to circulating cholesterol concentrations during the estrous cycle, but testosterone concentrations on day 17 or 19 of the cycle were unrelated to corpora lutea numbers. Concentrations of estrone on day 17 or 19 (as an index of follicles destined to ovulate) were also not related to numbers of corpora lutea. Many interactions between liver and ovarian function involving metabolic and endocrine systems are plausible, but defined mechanisms resulting in coordinate increases in liver weight and ovulation rates are presently unelucidated.     

The acute effects of bilateral ovariectomy or adrenalectomy on progesterone, testosterone and estradiol serum levels depend on the surgical approach and the day of the estrous cycle when they are performed

Bilateral ovariectomy or adrenalectomy are experimental tools used to understand the mechanisms regulating the hypothalamus-pituitary-ovarian and the hypothalamus-pituitary-adrenal axis. There is evidence that acute unilateral perforation of the dorsal peritoneum in rats results in significant changes in progesterone, testosterone and estradiol serum concentrations. Because different surgical approaches for unilateral or bilateral ovariectomy or adrenalectomy, sectioning the superior ovarian nerve or the vagus nerve are used, we compare the acute effects on hormone serum concentrations resulting from the unilateral or bilateral dorsal approach to performing bilateral ovariectomy or adrenalectomy with those obtained when an unilateral incision is performed in the ventral abdomen. In general, the progesterone, testosterone and estradiol serum concentrations were higher in animals with ventral approach than in those with dorsal surgery, the effects varying depending on the day of the estrous cycle when surgery was performed. The results suggest that the neural signals arising from different zones of the peritoneum and/or the abdominal wall play different roles in the mechanisms regulating steroid hormones concentrations.     

Consequences of different dietary energy sources during follicular development on subsequent fertility of cyclic gilts

The objective of the present study was to investigate the effects of dietary-induced insulin enhancement during the late luteal phase on subsequent fertility of gilts. Fifty-two littermate cyclic gilts were subjected to dietary treatments where two energy sources were tested: corn starch (T1) and soybean oil (T2). The experimental diets were supposed to provide similar amounts of dietary energy, but from different sources. Gilts were fed ad libitum, starting day 8 of the estrous cycle, until the next standing heat. Blood sampling was performed in a subgroup of 20 gilts on days 14 and 21 of the cycle for analyses of glucose and insulin, and after ovulation detection until 18 h after ovulation for progesterone. All gilts were slaughtered on day 28 of pregnancy and the reproductive tracts recovered for further analysis. T1 gilts showed higher postprandial insulin peak on days 14 and 21 and lower glucose levels 4 h after feeding on day 14 (P<0.05), however, there were no treatment effects on plasma progesterone concentrations. Dietary energy sources did not affect average daily feed intake, body weight and backfat on day 28 of pregnancy. Estrous cycle length, estrus duration and time of ovulation were not affected by previous nutritional treatments either. T1 gilts showed higher ovulation rates, number of embryos, embryo weight and placental weight (P<0.05). There were no treatment effects on pregnancy rate, embryo survival rate and volume of amniotic fluid. A positive correlation between progesterone concentration 18 h after ovulation and ovulation rate was observed (r=0.75; P<0.01). These results suggest that it is possible to manipulate dietary insulin response in cyclic gilts and, thus, improve reproductive efficiency when feeding starch as the main energy source during the late luteal and follicular phases of the cycle.     

Detection of estrous behavior in buffalo heifers by radiotelemetry following PGF2α administration during the early or late luteal phase

This study examined the usefulness of radiotelemetry for estrous detection in buffalo heifers and the impact of prostaglandin F_2α (PGF_2α) administration during the early or late luteal phase on estrous behavior and ovulatory follicle variables. Induction of estrus with PGF_2α at a random stage of the estrous cycle was followed by the arbitrary division of heifers into groups receiving a second dose of PGF_2α during either the early (n = 33) or late (n = 17) luteal phase (6–9 or 11–14 days after estrus, respectively) for the induction of synchronized estrus. The electronic detection of synchronized estrus by radiotelemetry was confirmed using ultrasonography every 6 h until ovulation. Radiotelemetry was 90% efficient and 100% accurate for estrous detection. Intervals between the PGF_2α dose and the beginning of synchronized estrus (40.7 ± 10.9 vs. 56.7 ± 12.8 h) or ovulation (70.0 ± 11.3 vs. 85.6 ± 12.5 h) were shorter (P < 0.05) for heifers receiving PGF_2α during the early luteal phase. PGF_2α administration during the early or late luteal phase produced similar (P > 0.05) results for the duration of estrus, the intervals from the beginning or end of estrus to ovulation, the number and duration of mounts per estrus, the duration of mounts, the diameter of the ovulatory follicle and the luteal profile on day 5 after estrus. In conclusion, radiotelemetry was a suitable tool for the efficient and accurate detection of estrus in buffalo heifers. Treatment with PGF_2α during the early luteal phase had a shorter interval to synchronized estrus and ovulation; however, estrous behavior, ovulatory follicle dynamics and subsequent luteal activity were similar following PGF_2α administration during the early or late luteal phase.     

Changes in patterns of luteinizing hormone secretion before and after the first ovulation in the postpartum mare

To determine whether luteinizing hormone (LH) secretion during the first estrous cycle postpartum is characterized by pulsatile release, circulating LH concentrations were measured in 8 postpartum mares, 4 of which had been treated with 150 mg progesterone and 10 mg estradiol daily for 20 days after foaling to delay ovulation. Blood samples were collected every 15 min for 8 h on 4 occasions: 3 times during the follicular phase (Days 2-4, 5-7, and 8-11 after either foaling or end of steroid treatment), and once during the luteal phase (Days 5-8 after ovulation). Ovulation occurred in 4 mares 13.2 +/- 0.6 days postpartum and in 3 of 4 mares 12.0 +/- 1.1 days post-treatment. Before ovulation, low-amplitude LH pulses (approximately 1 ng/ml) were observed in 3 mares; such LH pulses occurred irregularly (1-2/8 h) and were unrelated to mean circulating LH levels, which gradually increased from less than 1 ng/ml at foaling or end of steroid treatment to maximum levels (12.3 ng/ml) within 48 h after ovulation. In contrast, 1-3 high-amplitude LH pulses (3.7 +/- 0.7 ng/ml) were observed in 6 of 7 mares during an 8-h period of the luteal phase. The results suggest that in postpartum mares LH release is pulsatile during the luteal phase of the estrous cycle, whereas before ovulation LH pulses cannot be readily identified.     

Peripheral inhibin levels in relation to climatic variations and stage of estrous cycle in buffalo (Bubalus bubalis )

The present study investigated the peripheral plasma inhibin levels in relation to 1) the stage of estrous cycle and the effect of climatic variations. Blood samples were collected from cyclic buffalo (n=5) once daily for 32 consecutive days during the tropical hot humid (summer) and cold (winter) seasons. Estrus was recorded by parading a vasectomized bull as well as by plasma progesterone determination. In the winter season, peripheral inhibin concentrations which were lowest (0.35 +/- 0.02 ng/ml) during the mid-luteal phase of estrous cycle (Day 6 to Day 14, Day 0 = day of estrus) increased significantly (P < 0.02) to 0.47 +/- 0.04 ng/ml during the late luteal phase (Day -4 to Day -2) and then further to 0.52 +/- 0.03 ng/ml (P< 0.02) during the periestrus phase (Day -1 to Day 1). Inhibin concentrations then decreased significantly (P < 0.02) to 0.40 +/- 0.03 ng/ml during the early luteal phase (Day 2 to Day 5). In the summer season the differences in peripheral inhibin concentrations among different phases of estrous cycle were found to be nonsignificant. A comparison of the circulating inhibin concentrations between the two seasons indicated that inhibin concentrations were significantly higher in the late luteal phase (P < 0.01) and periestrus phase (P < 0.05) during the winter season compared with corresponding periods during the summer season. The present study suggests that peripheral inhibin concentrations change in the estrous cycle during cooler breeding season and that environmental heat stress can cause a reduction in peripheral inhibin concentrations.     

Gap junctional intercellular communication of bovine luteal cells from several stages of the estrous cycle: Effects of prostaglandin F2α, protein kinase C and calcium

Cellular interactions mediated by both contact-dependent and contact-independent mechanisms are probably important to maintain luteal function. The present studies were performed to evaluate the effects of luteotropic and luteolytic hormones, and also intracellular regulators, on contact-dependent gap junctional intercellular communication (GJIC) of bovine luteal cells from several stages of luteal development. Bovine corpora lutea (CL) from the early, mid and late luteal phases of the estrous cycle were dispersed with collagenase and incubated with no treatment, LH, PGF or LH + PGF (Experiment 1), or with no treatment, or agonists or antagonists of protein kinase C (TPA or H-7) or calcium (A23187 or EGTA; Experiment 2). After incubation, media were collected for determination of progesterone concentrations. Then the rate of GJIC was evaluated for small luteal cells in contact with small luteal cells, and large luteal cells in contact with small luteal cells by using the fluorescence recovery after photobleaching technique and laser cytometry. Luteal cells from each stage of the estrous cycle exhibited GJIC, but the rate of GJIC was least (P<0.05) for luteal cells from the late luteal phase. LH increased (P<0.05) GJIC between small luteal cells from the mid and late but not the early luteal phase. PGF increased (P<0.05) GjIC between small luteal cells from the mid luteal phase and diminished (P<0.05) LH-stimulatory effects on GjIC between small luteal cells from the late luteal phase. Throughout the estrous cycle, TPA decreased (P<0.05) the rate of GjIC between large and small, and between small luteal cells, and A23187 decreased (P<0.05) the rate of GJIC between large and small luteal cells. LH and LH + PGF, but not PGF alone increased (P<0.05) progesterone secretion by luteal cells from the mid and late luteal phases. Agonists or antagonists of PKC or calcium did not affect progesterone secretion by luteal cells. These data demonstrate that both luteal cell types communicate with small luteal cells, and the rate of communication depends on the stage of luteal development. LH and PGF affect GjIC between small luteal cells during the fully differentiated (mid-luteal) and regressing (late luteal) stages of the estrous cycle. In contrast, at all stages of luteal development, activation of PKC decreases GjIC between small and between large and small luteal cells, whereas calcium ionophore decreases GjIC only between large and small luteal cells. Luteotropic and luteolytic hormones, and intracellular regulators, may be involved in regulation of cellular interactions within bovine CL which likely is an important mechanism for coordination of luteal function.     

The relationship between vaginal mucous impedance and serum concentrations of estradiol and progesterone throughout the sheep estrous cycle

The objective of this experiment was to assess the relationship between electrical resistance of the vaginal mucosa and serum concentrations of estradiol (E2) and progesterone (P4) during the estrous cycle in ewes. Vaginal impedance was recorded daily using a 2-electrode impedometer in 10 nonprolific Western white-faced and 7 prolific Finn ewes, during the mid-breeding season (October to December). Transrectal ultrasonography of ovaries was performed once a day to confirm ovulation and monitor follicle growth (follicles > or =3 mm in diameter) and development of corpora lutea (CL). Jugular blood samples were collected daily for radioimmunoassay (RIA) of estradiol and progesterone. In all ewes, a decline in vaginal impedance (to <40 ohms) was closely associated with the onset of behavioral estrus. In both breeds of sheep, there was no significant correlation between daily serum concentrations of estradiol and vaginal impedance throughout the estrous cycle. Daily serum concentrations of progesterone and the E2:P4 ratio were correlated with vaginal impedance during the period of luteolysis and follicular phase in both breeds (Western white-faced ewes: r = 0.62, P = 0.0002 and r = -0.56, P = 0.0002; Finn ewes: r = 0.61, P = 0.001 and r = -0.45, P = 0.03, respectively) and early in the cycle (Days 0 to 2, Day 0 = day of ovulation) in white-faced ewes (r = 0.61, P = 0.0003 and r = -0.36, P = 0.052, respectively) but not during the remaining portion of the luteal phase in either breed. In conclusion, vaginal mucous impedance appears to be primarily controlled by progesterone, but it also changes in response to shifts in the E2:P4 ratio when progesterone concentrations are low. Impedometric characteristics of the vaginal mucosa in cyclic ewes are an indicator of serum concentrations of progesterone and E2:P4 ratios during the terminal stage of the estrous cycle.     

Persistence of the luteal phase following ovulation during altrenogest treatment in mares

Two experiments were conducted to test the efficacy of altrenogest treatment in mares. The response to 15-d altrenogest treatment (Experiment 1) was characterized in 20 mares that were given 22 mg daily of altrenogest in oil (n = 10) or in gel (n = 10) from Day 10 to 25 after ovulation. In 17 mares, luteolysis occurred during altrenogest treatment (Day 17.7 +/- 0.5), while 2 mares retained their corpus luteum (CL), and 1 mare had a diestrous ovulation on Day 16, resulting in a prolonged luteal phase. Ten of the 17 mares in which the CL had spontaneously regressed returned to estrus after the end of treatment, and ovulated 5.7 +/- 0.8 d after the end of altrenogest treatment. Two of these 17 mares ovulated 2 and 3 d after the end of altrenogest treatment but ovulation was not accompanied by estrous behavior, and 5 mares ovulated during altrenogest treatment resulting in an interovulatory interval of 22.4 +/- 1.1 d (range: 20 to 25d). Five mares which ovulated during altrenogest treatment and 2 mares which ovulated during silent estrus after the end of altrenogest treatment failed to regress the CL around 14 d post ovulation, and had a prolonged luteal phase. In Experiment 2, the effect of altrenogest administered from luteolysis to ovulation on duration of the subsequent luteal period was analyzed. In 6 mares altrenogest was begun on Day 14 post ovulation and continued until the hCG-induced ovulation. The interval from ovulation during altrenogest treatment to spontaneous luteolysis was 45.6 +/- 2.4 d (range: 40 to 54d) in altrenogest-treated mares and was significantly longer than in 10 untreated control mares (14.5 +/- 0.3 d, range: 13 to 16d). The results suggest that the oil and gel altrenogest preparations are equally effective in modulating estrous behavior and time to estrus and ovulation. Altrenogest treatment started late in diestrus appears to result in a high incidence of ovulation during treatment and when luteolysis and ovulation occur during treatment; the subsequent luteal phase is frequently prolonged due to failure of regression of the CL.     

Estrus induction in white rhinoceros (Ceratotherium simum)

The estrous cycle length in the white rhinoceros (Ceratotherium simum) is either 4 or 10 wk. The cause(s) for this variation as well as the poor fertility rate in captivity remains under debate in this species. Most captive adult white rhinoceros undergo long anovulatory periods without luteal activity which are considered a major reason for their low reproductive rate. In this study, the synthetic progestin chlormadinone acetate (CMA) was tested in combination with hCG or the GnRH analogue deslorelin for its efficiency to induce ovulation in fourteen females without luteal activity and in three, regular cycling females. HCG (N = 12), injectable GnRH analogue (N = 8) and GnRH analogue implants (N = 15) were given to induce ovulation after CMA treatment. Treatment success was determined using both transrectal ultrasonography and progesterone metabolite EIA analysis. A preovulatory sized follicle (3.5 ± 0.1 cm) or a corpus luteum (5.1 ± 0.7) was present on the ovary one day after induction in 93.1% of the treatments. Despite this high rate of ovarian response, ovulation rate differed between the study groups. The ovulation rate for hCG, injectable GnRH analogue and GnRH analogue implants was 66.7%, 62.5% and 93.3%, respectively. Ovulation rate in cyclic females treated with GnRH implants was 100% (6/6) compared with 89% (8/9) in females without luteal activity receiving the same treatment. The length of the estrous cycle when induced with hCG was 4 wk (85.7%). The estrous cycle when induced with GnRH analogue was predominantly 10 wk long. Two females without luteal activity treated with GnRH became pregnant. In conclusion, CMA in combination with GnRH analogue implants was highly effective to induce ovulation in white rhinoceroses and thus can contribute to efforts aimed at increasing natural mating and reproductive rates in the captive white rhinoceros population.     

Ontogeny of mitochondrial steroidogenesis in the guinea pig gonad

To determine whether steroidogenesis in the developing guinea pig may be limited by the formation of pregnenolone, cholesterol side chain cleavage activity was ascertained at various stages of development. The conversion of [1,2-³H]cholesterol to [1,2-³H]pregnenolone was detected in mitochondria isolated from fetal guinea pig ovaries and testes as early as day 35 of gestation, while no metabolism was noted in day 30 animals. Moreover, no [l,2-³H]progesterone was formed during the 60 minute incubation. From day 35 of gestation to the day of birth, the percentage of pregnenolone formed per testis (total activity) increased, while total activity in the ovary declined. In contrast, gonadal mitochondria from adult guinea pigs converted cholesterol to both pregnenolone and progesterone and total activity in these animals was substantially higher than in their fetal counterparts. In the three females examined, the rate of pregnenolone and progesterone synthesis varied according to the stage of the estrous cycle during which these animals were sacrificed. Conversion of pregnenolone to progesterone was most rapid in the early luteal phase animal, while conversion of cholesterol to pregnenolone occurred more rapidly in the periovulatory animals than in ovarian mitochondria from the late luteal phase of the cycle. The results indicate that during prenatal and postnatal development of the gonad, cholesterol side chain cleavage activity changes and that mitochondria may acquire a Δ⁵-3β-hydroxysteroid dehydrogenase.     

Regulation of insulin-like growth factor binding protein-6 expression in the reproductive tract throughout the estrous cycle and during the development of the placenta in the ewe

Insulin-like growth factors (IGF-I and IGF-II) are essential for normal uterine development and have been particularly implicated in fetal and placental growth. A family of six IGF binding proteins enhance or attenuate IGF-stimulated cell proliferation. In this study we have used in situ hybridization to map the distribution of IGFBP-6, one of the lesser known of the IGFBPs, in sections of the uterus collected from cyclic, anestrous, and ovariectomized nonpregnant ewes and from the uterus and placenta of early pregnant (13-55 days) and unilaterally pregnant ewes. In nonpregnant ewes IGFBP-6 mRNA (measured as arbitrary optical density units from autoradiographs) was abundant in the periepithelium and caruncles, with lower levels in the endometrial stroma and myometrium. In most regions IGFBP-6 mRNA showed cyclic variations with concentrations maximal around ovulation and the early luteal phase. In addition, 16 out of 25 ewes expressed IGFBP-6 mRNA in their endometrial glands between estrus and Day 2. Measurements of IGFBP-6 mRNA were high in anestrous ewes (equivalent values to ovulation) but low in ovariectomized ewes (equivalent values to mid to late luteal phase). In pregnant ewes IGFBP-6 mRNA was found in similar regions to those recorded during the cycle. In the periepithelium and caruncular stroma IGFBP-6 mRNA levels were higher during early pregnancy than in the midluteal phase. In the unilateral pregnant ewes there was no difference in IGFBP-6 mRNA measured between pregnant and nonpregnant horns. In conclusion, IGFBP-6 mRNA is differentially regulated during the estrous cycle and pregnancy and may be functionally important in modulating IGF activity in the uterus and placenta by virtue of its strong affinity and ability to regulate IGF-II mediated actions.     

Changes in activities of superoxide dismutase, nitric oxide synthase, glutathione-dependent enzymes and the incidence of apoptosis in sheep corpus luteum during the estrous cycle

Anti-oxidative enzymes play a role in protecting cells from oxidative stress-induced cell death. The present study was conducted to evaluate whether the anti-oxidant and pro-oxidant enzymatic capacities of the sheep corpus luteum (CL) are correlated with steroidogenic and structural status of the gland during the estrous cycle. Steroidogenic activity, apoptosis and superoxide dismutase (SOD1 and SOD2), nitric oxide synthase (NOS), glutathione peroxidase (GPX), glutathione reductase (GSR) and glutathione S-transferase (GST) activities were determined in the CL at specific developmental stages of the luteal phase. The intensity of apoptotic DNA fragmentation, characteristic of physiological cell death, was much greater in CL at late luteal phase than at early and mid-luteal phase, concomitantly with the diminution in the plasma progesterone concentrations from mid-to late luteal phase. SOD1 and GPX activities increased from early to mid-luteal phase, and increased further at late luteal phase. SOD2 and GST activities were not different between early and mid-luteal phase, but increased at late luteal phase. GSR activity was not different between any luteal phase examined. NOS activity decreased from early to mid- and late luteal phase. These results show that the activities of SOD1, SOD2, NOS, GPX, GSR and GST in the sheep CL are subject to major changes during the estrous cycle, and that the anti-oxidant and pro-oxidant enzymatic capacities of luteal cells are not correlated with cell steroidogenic status and integrity during the late luteal phase.