Prolactin administration during the luteal and follicular phase of the oestrous cycle of gilts

In Exp. I infusions of prolactin (0.5 mg in 2 ml sterile saline) were repeated every 2 h for 36 h on Days 12-13 of the cycle. In Exp. II infusions of prolactin were administered from Days 17 to 19 (60 h) at 2-h intervals. Control gilts were given 2 ml sterile saline at similar intervals during the same period. Basal prolactin concentrations before initiation of infusions ranged from 1.3 +/- 0.1 to 5.6 +/- 2.2 ng/ml in both experiments. By 5 min after a prolactin infusion, mean plasma prolactin concentration ranged from 74.9 +/- 5.8 to 113.0 +/- 9.5 ng/ml, but then declined to approximately equal to 10 ng/ml just before the next infusion of prolactin. Administration of prolactin during the luteal phase of the oestrous cycle of the gilts had no effect on basal levels of progesterone, oestradiol or LH. During the follicular phase there were no differences (P greater than 0.05) between control and prolactin-treated gilt progesterone and LH concentrations, but oestradiol plasma values were decreased (P less than 0.05) on the 2nd and 3rd day of prolactin treatment. Our results would indicate that prolactin does not play a major role in the regulation of the oestrous cycle of the pig.     

Effects of a dominant follicle on ovarian follicular dynamics during the oestrous cycle in heifers

Two hypotheses were tested: (1) a dominant follicle causes regression of its subordinate follicles, and (2) a dominant follicle during its growing phase suppresses the emergence of the next wave. Cyclic heifers were randomly assigned to one of four groups (6 heifers/group): cauterization of the dominant follicle of Wave 1 or sham surgery (control) on Day 3 or Day 5 (day of ovulation = Day 0). Ultrasonic monitoring of individually identified follicles was done once daily throughout the interovulatory interval. The onset of regression (decreasing diameter) of the largest subordinate follicle of Wave 1 was delayed (P less than 0.01) by cauterization of the dominant follicle of Wave 1 on Day 3 compared to controls (mean onset of regression, Days 10.8 +/- 2.1 vs 4.3 +/- 0.4). Cauterization of the dominant follicle of Wave 1 on Days 3 or 5 caused early emergence (P less than 0.01) of Wave 2 when compared to controls (Day-3 groups: Days 5.5 +/- 0.4 vs 9.6 +/- 0.7; Day-5 groups: Days 7.0 +/- 0.3 vs 9.1 +/- 0.4). The results supported the two hypotheses. In addition, cauterization of the dominant follicle of Wave 1 on Days 3 or 5 increased the incidence of 3-wave interovulatory intervals.     

Ovarian response, ova recovery and fertility in merino ewes superovulated either during the luteal phase of their oestrous cycle or after intravaginal progestagen treatment

Five groups of merino ewes were treated with 1000 i.u. of pregnant mare serum gonadotropin (PMSG) as a single injection per ewe. Three of these groups received treatment on days 7,9 and 11 of their oestrous cycle. Oestrus was synchronized with 125 mg of prostaglandin F2(alpha) (PG) given two days after PMSG. Oestrus in the other two groups was synchronized by intravaginal progesterone sponges inserted for 14 days. In one group, the sponges were inserted nine days after oestrus onset. In the other group the stage of the oestrous cycle was unknown. In both these groups, PMSG was given a day prior to sponge removal. No significant differences were recorded for either the mean numbers of corpora lutea, unovulated follicles or ova recovery between the five groups. However, progestagen synchronized ewes yielded significantly more fertilized ova (p < 0.05) than PG synchronized ewes.     

Effects of bovine follicular fluid inhibin on serum gonadotrophin concentrations in ewes during oestrus

Experiments were conducted with ewes to investigate the effects of an enriched bovine follicular fluid inhibin preparation (INH) on gonadotrophin secretion after the onset of oestrus. Administration of INH (10 mg) 1 h after the onset of oestrus did not significantly alter the preovulatory FSH and LH surges or the second FSH peak. To determine the effects of INH on the second FSH surge, ewes were treated with saline (N = 7) or INH (N = 10) at 4 h (10 mg) and 24 h (5 mg) after the peak of the preovulatory LH surge. The second FSH surge was delayed about 24 h (P less than 0.05) in ewes treated with INH; however, the delay did not alter the interval to the next oestrus. In a third experiment, 16 ewes were assigned to 4 groups in a 2 x 2 factorial with the main effects being ovariectomy at 4 h and INH treatment (10 mg) at 4, 20 and 36 h after the peak of the LH surge. Controls received sham ovariectomy and saline injection as appropriate. Ovariectomy resulted in a rapid increase in serum FSH but not LH and this was delayed (P less than 0.05) by INH treatment. These results indicate that inhibin has a selective inhibitory action on FSH secretion in ewes and suggests that the second FSH surge results from increased basal FSH secretion due to decreased endogenous inhibin levels.     

Increase in ovulation rate after treatment of ewes with bovine follicular fluid in the luteal phase of the oestrous cycle

Administration of charcoal-treated bovine follicular fluid to Damline ewes twice daily (i.v.) from Days 1 to 11 of the luteal phase (Day 0 = oestrus) resulted in a delay in the onset of oestrous behaviour and a significant increase in ovulation rate following cloprostenol-induced luteolysis on Day 12. During follicular fluid treatment plasma levels of FSH in samples withdrawn just before injection of follicular fluid at 09:00 h (i.e. 16 h after previous injection of follicular fluid) were initially suppressed, but by Day 8 of treatment had returned to those of controls. However, the injection of follicular fluid at 09:00 h on Day 8 still caused a significant suppression of FSH as measured during a 6-h sampling period. Basal LH levels were higher throughout treatment due to a significant increase in amplitude and frequency of pulsatile secretion. After cloprostenol-induced luteal regression at the end of treatment on Day 12, plasma levels of FSH increased 4-fold over those of controls and remained higher until the preovulatory LH surge. While LH concentrations were initially higher relative to those of controls, there was no significant difference in the amount of LH released immediately before or during the preovulatory surge. These results suggest that the increase in ovulation rate observed during treatment with bovine follicular fluid is associated with the change in the pattern of gonadotrophin secretion in the luteal and follicular phases of the cycle.     

Episodic secretion of gonadotrophins and ovarian steroids in jugular and utero-ovarian vein plasma during the follicular phase of the oestrous cycle in gilts

Blood samples were collected simultaneously from the jugular and utero-ovarian veins of 13 gilts from Days 11 through 16 of the oestrous cycle. A luteolytic dose (10 mg) of PGF-2 alpha was given on Day 12 to facilitate the natural occurrence of luteolysis and standardize the associated decrease in concentrations of progesterone. The mean interval from PGF to oestrus was 5.5 +/- 0.7 days (mean oestrous cycle length = 17.5 +/- 0.7 days). Mean concentrations, pulse amplitudes and pulse frequencies of oestradiol and progesterone were greater (P less than 0.05) in the utero-ovarian than jugular vein. Secretory profiles of LH and FSH were similar (P greater than 0.05) in plasma collected simultaneously from both veins. Based on these data, temporal relationships among hormonal patterns of FSH and LH in the jugular vein and oestradiol and progesterone in the utero-ovarian vein were examined. Concentrations of progesterone declined (P less than 0.05) between Days 12 and 14, while all secretory variables for oestradiol increased (P less than 0.05) from Day 12 through 16 of the oestrous cycle. The pulsatile secretion of FSH remained relatively constant during the experiment. However, both pulse amplitude and mean concentration tended (P less than 0.2) to be lower on Day 16 compared with Day 12. The episodic secretion of LH shifted from a pattern characterized by high-amplitude, low-frequency pulses to one dominated by numerous pulses of diminishing magnitude between Days 13 and 14. From Days 14 to 16 of the oestrous cycle, 91% of all oestradiol pulses were temporally associated with gonadotrophin pulses composed of both FSH and LH episodes. However, pulses of oestradiol (52%) not associated with an episode of LH and/or FSH were observed on Days 12 and 13. These data demonstrate that during the follicular phase of the pig oestrous cycle substantial oestradiol production occurred coincident with luteolysis and before the shift in the episodic secretion of LH. The pool of follicles which ovulated was probably the source of this early increase in the secretion of oestradiol. Therefore, we propose that factors in addition to FSH and LH are involved in the initial selection of follicles destined to ovulate during the early stages of the follicular phase of the pig oestrous cycle. In contrast, high-frequency, low-amplitude pulses composed of LH and FSH were the predominant endocrine signal associated with oestradiol secretion during the second half of the oestrous cycle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Plasma prolactin concentrations during the oestrous cycle of sows

Plasma prolactin levels were measured in 7 sows during the oestrous cycle after the 1st farrow. Blood samples were taken 4 times during the day (07:00, 11:00, 14:00 and 19:00 h). The prolactin concentration was determined by a double-antibody radioimmunoassay method. There was an increase in plasma prolactin at the second oestrus after weaning, with a peak of prolactin 4 days before oestrus, regardless of the length of the cycle.     

Effects of follicular status at treatment on follicular development and ovulation in response to FSH in Spanish merino ewes

Cyclic Spanish Merino ewes were treated on Day 13 of the estrous cycle with 12 mg, i.m., FSH-P in saline (n = 9) or propylene glycol (n = 24), currently with 100 micrograms, i.m., Cloprostenol (Day 0). From Day-6 to Day 0, the ewes were observed daily by transrectal ultrasonography, after Day 0, ultrasonography was performed every 12 h for 72 h. Sizes and locations of > or = 2 mm follicles were recorded at each observation. The ovulation rate was determined by laparoscopy on Day 7 after estrus. The number of ovulations ranged from 0 to 6 in ewes treated with FSH-P in saline and from 0 to 16 in ewes receiving FSH-P in propylene glycol (P < 0.05). In the latter group, the response was bimodally distributed; about half of the females had 1 ovulation, whereas the remainder had > 4 with a mean of 7 ovulations. The ovulation rate was associated with 2 characteristics of the largest follicle present at treatment (Day 0). First, if the largest follicle on Day 0 had not changed in diameter from Day-1 to Day 0, then 7 of 9 ewes had > 3 ovulations; if the largest follicle had either increased or decreased, only 8 of 24 ewes had > 3 ovulations (P < 0.05). Second, there was a linear trend (P < 0.07) for ovulation rate to decrease as the persistence of the largest follicle at treatment increased; no ewe in which the largest follicle on Day 0 remained present for more than 36 h ovulated more than 6 follicles. As with the ovulation rate, the numbers of large follicles on Days 1.5, 2 and 2.5 varied with the interaction of change in diameter of the largest follicle on Day 0 from Day-1 to Day 0 and with vehicle. In summary, the superovulatory response was affected by the change in diameter from Day-1 to Day 0 of the largest follicle on Day 0 and the period required for that follicle to regress after treatment with FSH-P and cloprostenol.     

Ovulation rate and embryo survival in Damline ewes after treatment with bovine follicular fluid in the luteal phase of the oestrous cycle

Treatment of Damline ewes with twice daily i.v. injections of bovine follicular fluid during the luteal phase for 10, 6 or 2 days before prostaglandin-induced luteolysis resulted in an increase in ovulation rate. This was associated with a large rebound increase in plasma concentrations of FSH after the last injection of bovine follicular fluid. While conception rate was not affected by bovine follicular fluid treatment, a higher percentage embryonic loss was observed between Days 3 and 34 of pregnancy in the 10-day treatment group only compared to controls. This reflected the increase in ovulation rate above the optimum for embryonic survival in this breed. The present results suggest that the increase in ovulation rate induced by bovine follicular fluid treatment in the luteal phase of the cycle before mating would result in a significant increase in the number of lambs born.     

Secretion of LH, FSH and oestradiol-17 beta during the follicular phase of the oestrous cycle in the ewe

Plasma concentrations of LH, FSH and oestradiol-17 beta were measured in blood samples taken at 15 min intervals for 48 h during the follicular phase of four Merino ewes. The amplitude of pulses of LH and the mean concentration of LH were higher at the beginning of the follicular phase, 36-24 h before the preovulatory surge of LH (amplitude 2.4 ng ml-1, mean concentration 3.9 ng ml-1), than at the end, 24-0 h before the preovulatory surge (amplitude 1.2 +/- 0.1 ng ml-1; mean concentration 1.4 +/- 0.1 ng ml-1). There was no change in the inter-pulse interval during this time (mean 74 +/- 5 min). Over the same period, oestradiol levels increased from 7-8 pg ml-1 to a peak of 10-15 pg ml-1. Mean FSH concentrations declined (36-24 h: 3.6 ng ml-1 vs 24-0 h: 1.8 +/- 0.3 ng ml-1) before rising at the time of the preovulatory surge of LH and again 24 h later. It was concluded that the biphasic response of LH to oestrogen that is seen in ovariectomized ewes may also operate during the follicular phase of the oestrous cycle in entire ewes.     

The measurement of total plasma oestrogens during the follicular phase of the mare's oestrous cycle

The measurement of total plasma oestrogens (conjugated and unconjugated) gives 100 times higher levels than the specific measurement of 17β oestradiol. Such high levels are easy to measure and give a good picture of the follicular activity of the mare. A correlation was found between length of follicular phase of the cycle and oestrogen levels at the time of luteolysis (r = 0.47) or preovulatory oestrogen levels (r = +0.40).     

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.     

Opioid modulation of LH secretion during the oestrous cycle of heifers

Injections of an opioid agonist (bremazocine) and/or an antagonist (quadazocine) were given to heifers during the luteal or follicular phase of the oestrous cycle. Quadazocine was injected (210 mg/injection) three times at 2-h intervals, and bremazocine was injected (0.45 mg/injection) every 15 min for 6 h. Blood samples were taken every 15 min beginning 6 h before treatments started and continued for 18 h. LH secretion patterns were not affected by quadazocine in the luteal-phase heifers, but quadazocine and bremazocine had marked effects during the follicular phase. Quadazocine increased LH secretion by increasing peak height but not peak frequency. Bremazocine decreased LH secretion through both peak height and frequency. This decrease was of greater magnitude than the increase due to quadazocine. When quadazocine and bremazocine were given together, these effects were cancelled and none of the effects carried over into the bleeding period after treatments stopped. No apparent interruption of follicular maturation was detected since all follicular-phase heifers were detected in oestrus at normal intervals. We conclude that heifers in this experiment did not have an opioid-mediated mechanism for progesterone suppression of LH but that an opioid mechanism for modulating LH does exist during the follicular phase.     

Effects of FGA and PMSG on follicular growth and LH secretion in Suffolk ewes

The effects of fluorogestone acetate (FGA) and/or pregnant mare serum gonadotrophin (PMSG) on follicular growth and LH secretion in cyclic ewes were determined. Suffolk ewes (n = 40), previously synchronized with cloprostenol were divided into 4 experimental groups (n = 10 ewes per group). Group I served as the control, while groups II, III and IV received FGA, PMSG, FGA and PMSG respectively. Four ewes of each group underwent daily laparascopy for 17 d. All the ovarian follicles >/= 2 mm were measured, and their relative locations were recorded on an ovarian map in order to follow the sequential development of each individual follicle. Comparisons were made of the mean day of emergence and the mean number of small, medium and large follicles, the atresia rate and the ovulation rate. For each group, 3 waves of follicular growth and atresia were observed during the cycle. During luteal phase, FGA treatment accelerated the mechanisms of follicular growth but reduced the number of large follicles and increased the atresia rate. In the follicular phase, FGA treatment was detrimental to both the number of large follicles and the ovulation rate. By contrast, PMSG enhanced recruitment of small follicles and the ovulation rate. Serial blood samples were collected during the luteal and follicular phases to study LH secretion. None of the treatments had any effect on LH secretion patterns.     

Influence of short-term fasting during the luteal phase of the estrous cycle on ovarian follicular development during the ensuing proestrus of ewes

In order to study the effects of storage media and time of storage on the viability of unfertilized eggs of endangered Caspian brown trout (Salmo trutta caspius), the ova of this fish was stored in coelomic fluid and Cortland artificial media at 2–3 °C for 120 h. In this research, Cortland artificial medium was buffered with 20 mM of three different buffers: Hepes (C₈H₁₈N₂O₄S), Tris–HCl (C₄H₁₁NO₃–HCl) and sodium salt Hepes (C₈H₁₇N₂O₄SNa). The pH of these media were adjusted according to natural pH of coelomic fluid. The eggs that stored in these media fertilized at times 0 h (eggs fertilized prior to storage), 48, 72 and 120 h of post-stripping, using fresh and pooled sperm obtained from four to six males. According to the results of present study, time of storage showed a significant (p < 0.05) main effect on eyeing, hatching and eyed eggs mortality rates. Eyeing and hatching rates significantly (p < 0.05) decreased from 97.4 ± 2.1% and 95.1 ± 4.4% at time 0 (eggs fertilized prior to storage) to 77.9 ± 3% and 65.5 ± 5% after 120 h of storage. Within a similar period of time, eyed eggs mortality significantly (p < 0.05) increased from 2.4 ± 2.4% to 17.2 ± 3.9%. No significant (p > 0.05) main effect was found among media buffered with Tris–HCl (82.8 ± 3.2%, 73.4 ± 5.4%, 12.1 ± 4.5%), Hepes (88.2 ± 3.4%, 80.7 ± 5.5%, 9.3 ± 3.4%), sodium salt Hepes (77.8 ± 3.8%, 69.3 ± 5.7%, 12.2 ± 3.9%) and coelomic fluid (84.8 ± 3.8%, 77.7 ± 5.1%, 8.9 ± 2.7%) for eyeing, hatching and eyed eggs mortality rates. There was a negative correlation (r = −0.895, p < 0.001) between eyed eggs mortality and hatching rates. In conclusion, unfertilized eggs of endangered Caspian brown trout can be successfully stored for 48 h without significant loss of fertility. But, storage for 120 h results in the falling of hatching rate. In addition, no significant difference was found between viability rates of ova stored in coelomic fluid and artificial media, 120 h post-storage. It reveals that artificial media could be substituted for coelomic fluid as storage medium at least for 120 h in Caspian brown trout.