Prostaglandin F2 alpha and the release of LH in sheep

Strategies to improve the success of fixed-time artificial insemination in the ewe

During the sheep breeding season, ovulatory follicles vary widely in age at pessary removal impacting both the timing of oestrus and pregnancy rates following artificial insemination (AI). Ovulatory follicles that emerge between days 7 to 9 of the pessary period are associated with higher fertility whilst those that emerge earlier or later are associated with lower fertility. In this study, two strategies to improve the success of AI by controlling the development of the ovulatory follicle were examined. In the first, ewes were treated with PGF2α at either -12 and/or +6 days (experiment 1) or -27 days (experiment 2) relative to pessary insertion to control the time of emergence of the ovulatory follicle. In the second, ewes were treated with eCG (400 IU per ewe) at either 0 h, -6 h or -12 h relative to pessary removal (experiment 3) to improve the development of young ovulatory follicles. PGF2α administered on day -27 increased the percentage of pregnant ewes by 17.8% and the number of foetuses per 100 ewes inseminated by 33.9%. PGF2α treatment at other times had either no effect or reduced fertility. During the breeding season, treatment with eCG at -12 h improved the synchrony of oestrus, reduced the size of the ovulatory follicle but did not improve pregnancy rate compared with other treatments. Treatment had no effect during the non-breeding season, supporting earlier findings that the quality of young ovulatory follicles differs during the year. In conclusion, PGF2α treatment 27 days before pessary insertion provides a new and cheap strategy to improve the success of fixed-time AI programs.

The use of prostaglandins in controlling estrous cycle of the ewe: a review

This review considers the use of prostaglandin F(2α) and its synthetic analogues (PG) for controlling the estrous cycle of the ewe. Aspects such as phase of the estrus cycle, PG analogues, PG doses, ovarian follicle development pattern, CL formation, progesterone synthesis, ovulation rate, sperm transport, embryo quality, and fertility rates after PG administration are reviewed. Furthermore, protocols for estrus synchronization and their success in timed AI programs are discussed. Based on available information, the ovine CL is refractory to PG treatment for up to 2 days after ovulation. All PG analogues are effective when an appropriate dose is given; in that regard, there is a positive association between the dose administered and the proportion of ewes detected in estrus. Follicular response after PG is dependent on the phase of the estrous cycle at treatment. Altered sperm transport and low pregnancy rates are generally reported. However, reports on alteration of the steroidogenic capacity of preovulatory follicles, ovulation rate, embryo quality, recovery rates, and prolificacy, are controversial. Although various PG-based protocols can be used for estrus synchronization, a second PG injection improves estrus response when the stage of the estrous cycle at the first injection is unknown. The estrus cycle after PG administration has a normal length. Prostaglandin-based protocols for timed AI achieved poor reproductive outcomes, but increasing the interval between PG injections might increase pregnancy rates. Attempts to improve reproductive outcomes have been directed to provide a synchronized LH surge: use of different routes of AI (cervical or intrauterine), different PG doses, and increased intervals between PG injections. Finally we present our point of view regarding future perspectives on the use of PG in programs of controlled sheep reproduction.

Prostaglandins and reproduction in female farm animals

Prostaglandins impact on ovarian, uterine, placental, and pituitary function to regulate reproduction in female livestock. They play important roles in ovulation, luteal function, maternal recognition of pregnancy, implantation, maintenance of gestation, microbial-induced abortion, parturition, postpartum uterine and ovarian infections, and resumption of postpartum ovarian cyclicity. Prostaglandins have both positive and negative effects on reproduction; they are used to synchronize oestrus, terminate pseudopregnancy in mares, induce parturition, and treat retained placenta, luteinized cysts, pyometra, and chronic endometritis. Improved therapeutic uses for prostaglandins will be developed when we understand better their involvement in implantation, maintenance of luteal function, and establishment and maintenance of pregnancy.

Exogenous PGF2α enhanced GnRH-induced LH release in postpartum cows

This study evaluated the effect of exogenous PGF(2)alpha on circulating LH concentrations in postpartum multiparous (n = 32) and primiparous (n = 46) Brahman cows. The cows were randomly allotted within parity and calving date to receive 0, 1, 2 or 3 mg im PGF(2)alpha (alfaprostol)/100 kg body weight (BW), with or without GnRH on Day 30 after calving. Blood samples were collected at weekly intervals from calving through treatment. Serum progesterone concentrations were determined using RIA procedures to assure that only anestrous cows were treated. Sterile marker bulls were maintained with cows on Coastal bermudagrass pastures until the first estrus was detected. Multiparous cows had a shorter (P < 0.05) interval from calving to estrus than did primiparous cows. Serum LH was affected by time (P < 0.0001), PGF(2)alpha dose (P < 0.0002), GnRH (P < 0.0001), parity by PGF(2)alpha dose (P < 0.0003), PGF(2)alpha dose by GnRH (P < 0.0009), parity by GnRH (P < 0.0008), and by parity by PGF(2)alpha dose by GnRH (P < 0.0005). Multiparous cows not receiving GnRH had higher mean serum LH (P < 0.02), LH peak pulse height (P < 0.03), and area under the LH release curve (P < 0.03) compared with primiparous cows. The number of LH pulses/6 h was greater (P < 0.06) in multiparous than primiparous cows, and was greater (P < 0.02) in multiparous cows receiving 3 mg/100 kg BW than in cows receiving 2 mg/100 kg BW, but not in the controls or in cows receiving 1 mg/100 kg BW. Exogenous GnRH resulted in increased (P < 0.0001) serum LH concentrations in all cows, and LH was enhanced (P < 0.0009) by simultaneous treatment with PGF(2)alpha. Primiparous cows had a greater response (P < 0.0005) to PGF(2)alpha and GnRH compared with multiparous cows. Pituitary release of LH in response to GnRH was enhanced by simultaneous exposure to PGF(2)alpha in Day 30 postpartum cows.

Lack of effects of indomethacin on estradiol feedback control of luteinizing hormone in ovariectomized ewes

We tested the hypothesis that indomethacin, a potent inhibitor of prostaglandin synthesis, would modify estradiol's effects on tonic and surge concentrations of LH in chronically ovariectomized ewes during the anestrous season. Ewes (n = 21) were assigned randomly to one of four treatments: Vehicle+Blank (n = 5); Indomethacin+Blank (n = 6); Vehicle+Estradiol (n = 5); or Indomethacin+Estradiol (n = 5). On d=0 (hr = 0), ewes began to receive i.m. injections of either indomethacin (4 mg/kg body weight) or corn oil every 8 hr for 9 d. Blood samples were collected every 12 min for 6 hr beginning at -6 hr, +18 hr, and on day 8 (relative to initial injections of indomethacin or vehicle) to assess tonic patterns of secretion of LH. At +24 hr, ewes received blank- or estradiol-containing Silastic implants and were bled hourly for 48 hr. On day 9, ewes received 50 micrograms of GnRH i.v. and were bled hourly for 8 hr. Serum samples were assayed for LH. Indomethacin had no effect on the following parameters of LH secretion: 1) mean concentrations (ng/ml; 8.4 +/- .7 vs 8.9 +/- .8; P > .1), 2) pulse frequency/6 hr (4.5 +/- .4 vs 4.1 +/- .4; P > .1) or 3) pulse amplitude (ng/ml; 15.3 +/- 1.1 vs 14.9 +/- 1.2; P > 1). Estradiol elicited a surge of LH which began 18.9 +/- 1.7 hr after implant insertion, reached a mean peak concentration of 95.3 +/- 20.1 ng/ml, and did not differ with respect to indomethacin treatment (P > .1).(ABSTRACT TRUNCATED AT 250 WORDS)

Conception rates in dairy cows after timed-insemination and simultaneous treatment with gonadotrophin releasing hormone and/or prostaglandin F2 alpha

This study was designed to determine conception rates in dairy cows after timed-insemination and simultaneous treatment with gonadotrophin releasing hormone (GnRH) and/or prostaglandin F2 alpha (PGF2alpha). A total of 2352 cows was randomly assigned to six groups. Cows in Groups 1 to 5 were palpated per rectum to determine the presence of a corpus luteum (CL) on the ovary, and blood samples were obtained for the determination of plasma progesterone (P4) concentrations. Cows with a CL and P4 concentrations >1 ng/ml were treated (Day 0) with PGF2alpha (25 mg, i.m.) and were observed for estrus. Cows in estrus prior to 72 hours after treatment (Group 5, n = 106) were bred, but were not treated. Cows not observed in estrus by 72 hours were divided into four remaining groups, were bred between 72 and 80 hours and were assigned as follows: Cows in Group 1 (n = 203) were not treated; Cows in Group 2 (n = 200) were treated with GnRH (100 ug, i.m.); Cows in Group 3 (n = 201) were treated with PGF2alpha (25 mg, i.m.); and cows in Group 4 (n = 202) were treated with both GnRH and PGF2alpha. Cows in Group 6 (n = 1440) were not treated with PGF2alpha on Day 0 and were estrual cows that were bred on days when cows in Groups 1 to 5 were time-inseminated. The percentage of cows in all groups pregnant at 45 to 50 days after one insemination was compared using analysis of variance (P<0.05). The conception rate of cows in Group 2 was significantly higher than that of cows in Groups 1 to 4. There was a significant group-by-season interaction. Cows treated with GnRH during the spring had a higher conception rate than at other times of the year. Conception rates of cows in Groups 1 to 4 that were inseminated during the summer were low and not significantly different from each other. Conception rates of cows in Groups 5 and 6 inseminated during the summer were not significantly different from each other, but were significantly higher than that of cows in Groups 1 to 4 that were inseminated during the summer.

The relationship between 13,14-dihydro-15-keto PGF2 alpha and LH secretion in bulls

Half-life (t1/2), volume of distribution (Vd) and total body clearance (TBC) of 13,14-dihydro-15-keto PGF2 alpha (PGFM) were measured in order to determine optimal sampling frequency for accurate measurement of PGFM. Three yearling Holstein bulls (349.2 +/- 6.7 kg) and 3 yearling Holstein steers (346.7 +/- 7.0 kg) were utilized in a 3 X 3 Latin square design. Animals were given 0, 25 or 50 micrograms PGF2 alpha I.V.; blood samples collected every 2 min and plasma PGFM determined. The t1/2, Vd and TBC of PGFM were 2.3 +/- .2 min, 43.3 +/- 3.3 liters and 13.7 +/- 1.9 liters/min, respectively and were similar for 25 and 50 micrograms doses. To determine the relationship between endogenous PGFM and LH secretion in bulls, blood samples were collected every 2 min for 12 h in 4 yearling Angus bulls (489.1 +/- 11.6 kg). All animals elicited at least one LH surge and PGFM concentrations were measured in samples coincident with the LH surge. Mean plasma PGFM concentrations were greater prior to the LH surge than during the LH surge. In addition, mean plasma PGFM concentration and frequency of PGFM peaks appeared to increase prior to the LH surge suggesting an association between PGFM and pulsatile LH secretion in the bull.

Induction of oestrus in Saanen goats at early breeding season by intravaginal progesterone sponges (MAP) or by prostaglandin F(2)alpha injections. Effect on different age groups

Twenty-one maiden and 29 pluriparous milking Ankara Saanen goats received either two i.m. injections of PGF(2)alpha (n=25) or intravaginal MAP sponges (n=25) early in November at the start of the breeding season. About twice as many pluriparous goats as maiden goats exhibited estrus after either treatment (87% vs. 47%). Breeding after this induced estrus caused pregnancies in 62% of the pluriparous goats, but only in 24% of the maiden animals. Maximal concentrations of progesterone were reached 11 days after the start of the MAP treatment. Progesterone declined to basal levels two to four days after sponge withdrawal. A significant slower progesterone increase also resulting in lower maximal concentrations could be observed in maiden goats. Luteolysis was evident in all animals within 24 h after PGF(2)alpha injection. Nine goats (six maiden and three pluriparous) did not exhibit Heat after the second injection and showed only a slow increase of progesterone. It seems that noncyclic animals are less sensitive to MAP treatment than to the first PGF(2)alpha injection. Goats at the beginning of the breeding season may react after a premature interruption of corpus luteum function (after second PGF(2)alpha injection) with delayed or inadequate follicular function.

Effects of systemic administration of indomethacin to cyclic ewes on endometrial concentrations of prostaglandins effects on estrous cycle length and on progesterone, luteinizing hormone and prolactin patterns

Experiments were designed to evaluate in cyclic sheep the effects of systemic administration of a prostaglandin synthetase inhibitor (Indomethacin). Indomethacin (100 mg, 3 times daily, S.C.) was administered from day 7 of the estrous cycle for 16 days to five ewes in which the cycle was synchronized as well as the cycles of five control ewes. All control ewes had cycles of approximately 17 days duration, but three of five Indomethacin treated ewes showed no estrous behavior before their slaughter at 23 days after induced ovulation. Autopsy revealed normal corpora lutea which had not undergone luteolysis, as confirmed by progesterone determination in blood. The two remaining Indomethacin treated ewes showed an estrous behavior on day 19 and 20 respectively together with a "preovulatory surge" of luteinizing hormone and prolactin which was not followed by follicular rupture. These results show that inhibition of PGF2 alpha synthesis by systemic administration of Indomethacin to the ewe is able to prevent luteolysis. When luteolysis did occur however, it was not followed by an ovulation despite a normal gonadotropin surge, indicating that inhibition of prostaglandin synthesis by systemic administration of Indomethacin interferes with the luteolysis and follicle rupture processes.

Serum FSH, LH and testosterone in the male rhesus following prostaglandin injection

Adult male rhesus were treated with PGE2, PGF2 alpha or the 13,14-dihydro-15-keto metabolite of PGE2 in a randomized crossover design. Serum concentrations of FSH, LH and testosterone were determined and compared to the respective values in the same uninjected animals. No significant changes were noted in controls or following the metabolite injection. FSH increased gradually for 4 hours after metabolite treatment. In contrast, injection of PGF2 alpha was followed by an abrupt (within 15 minutes) increase in LH and testosterone. FSH increased gradually in 2 of 3 treated animals. Injection of PGE2 was followed by a similar abrupt increase in LH concentration. This was not always associated with a significant increase in testosterone or FSH. These results demonstrate that injections of PGE2 or PGF2 alpha can change serum gonadotropin and testosterone concentrations in male rhesus monkeys, and that the effects of these two prostaglandins are qualitatively different.

The effect of intra-amniotic prostaglandin F2alpha on anterior pituitary hormone release during midtrimester abortion

The effect of intra-amniotic administration of prostaglandin F2alpha (PGF2alpha) on pituitary hormone release was studied in women undergoing midtrimester abortion. Serum prolactin (PRL), growth hormone (GH), thyrotropin (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured prior to and at 15-minute intervals for 2 hours following intra-amniotic administration of 40 gm of urea alone, 20 mg of PGF2alpha and 40 gm of urea, or an equal volume of normal saline. Serum PRL levels were significantly higher at sampling times from 15 through 120 minutes when both PGF2alpha and urea were administered than after saline or urea alone. The elevation in serum GH following PGF2alpha and urea was not significantly greater than for urea alone. The GH response in the women receiving normal saline was significantly less than for the two groups of women receiving the abortifacients. These results indicate that the GH response was related to the stress effects of the abortifacients. There was no difference in the TSH, LH, and FSH responses for the three groups. These results suggest that PGF2alpha selectively causes pituitary release of PRL in women during midtrimester pregnancy.

Prostaglandins inhibit testosterone secretion by mouse testes in vitro

Production of testosterone (T) by decapsulated mouse tests in vitro was significantly inhibited by adding prostaglandin (PG) A1, PGA2 or PGE1 to the incubation medium. Prostaglandin A1 at a concentration of 10(-6)M inhibited T production in this system both in the presence of moderate amounts of hCG (12.5 or 25.0 mIU/ml), and in the absence of gonadotropins. However, in the presence of very high levels of hCG (125.0 mIU/ml), all PGs tested appeared to have had a slight potentiating effect on T production when added in concentrations ranging from 10(-7) to 10(-5)M, and the inhibition of T accumulation in the medium was consistently observed only when the concentration of PGs was increased to 10(-3)M. These results suggest that a direct effect of PGs on testicular steroidogenesis may account for, or contributes to, the decrease in peripheral T levels observed after administration of PGs in vivo.

Prostaglandins, possible mediators of the effects of oestrogens on luteinizing hormone output

A possible mechanism for the positive and negative feed-back effects of oestrogen on luteinizing hormone (LH) output is suggested. It is proposed that oestrogens may influence prostaglandin synthesis in the hypothalamus in relation to LH releasing hormone (LH.RH) synthesis and release. Changes in oestrogen level or in the oestrogen to progesterone ratio may alter the ratios of prostaglandin concentrations in the hypothalamus, and so modulate LH.RH output through effects on sympathetic neurotransmission, protein synthesis or LH.RH release.

Increased blood LH and testosterone after administration of prostaglandin F2alpha in bulls

Two types of experiments were conducted to determine the relationship of changes in blood luteinizing hormone (LH) and testosterone in bulls given prostaglandin F2alpha (PGF2alpha). Episodic surges of LH and testosterone occurred in tandem, apparently at random intervals, on the average once during the 8-hr period after bulls were given saline. In contrast, after sc injection of 20 mg PGF2alpha, blood serum testosterone increased synchronously to a peak within 90 minutes four-fold greater than pre-injection values, and the testosterone surges were prolonged about three-fold compared to those in controls. Each of the PGF2alpha-induced surges of testosterone was preceded by a surge of blood serum LH which persisted for about 45 minutes and peaked at about 3 ng/ml. In a second experiment, PGF2alpha was infused (iv, 0.2 mg/min) for 20 hr; blood plasma testosterone increased from 7.0+/-0.6 to 16.0+/-1.5 ng/ml within 2.5 hr and remained near this peak for 10 hr. Then testosterone gradually declined to about 9 ng/ml at the conclusion of the 20-hr infusion. These changes in testosterone were paralleled by similar changes in blood plasma LH, although LH declined 3 hr earlier than testosterone. Random episodic peaks of blood plasma LH and testosterone typical of untreated bulls resumed within 8 hr after conclusion of PGF2alpha infusion. In both experiments, the surge of testosterone after PGF2alpha was preceded by increased blood LH. We conclude that increased LH after administration of PGF2alpha probably caused the increased testosterone. However the mechanisms of these actions of PGF2alpha remain to be determined.

Site of the in vivo stimulatory effect of prostaglandins on LH release

A possible direct effect of prostaglandins E1 and E2 (PGE1 and PGE2) on luteinizing hormone (LH) release at the pituitary level was studied in vitro using anterior pituitary cells in primary culture, a system approximately 10-fold more sensitive to stimulation of LH release than previously used hemipituitaries. No effect of PGE1 or PGE2 could be detected on the time course of basal or LH-RH-stimulated LH release or on the LH responsiveness to LH-RH. This absence of a direct effect of PGEs at the pituitary level on LH release was confirmed by in vivo experiments using female rats under Surital anesthesia in the afternoon of proestrus. After intravenous injection, under these conditions, 15(S)-15-methyl PGE2 was 3-5 times more potent than PGE2 to increase plasma LH levels while PGE1 had about 50% the potency of PGE2. Injection of sheep anti-LH-RH serum one hour before PGE1 or PGE2 injection not only lowered basal plasma LH levels but prevented the rise induced by PGEs. These data indicate clearly that the increased plasma LH levels observed after in vivo PGE injection are secondary to a stimulation of LH-RH release while PGEs do not appear to have a significant effect on LH release at the pituitary level.

Blood LH after PGF2alpha in diestrous and ovariectomized cattle

Two experiments were conducted to determine whether the increased serum LH which occurs within 12 hr after a luteolytic dose of PGF2alpha is dependent upon changes in progesterone or estradiol secretion. In the first experiment, exogenous progesterone abolished the increase in serum LH caused by a subcutaneous injection of 25 mg PGF2alpha in diestrous heifers, but not in ovariectomized heifers. In the second experiment, progesterone pessaries were removed at 6 hr after a subcutaneous injection of 25 mg PGF2alpha. LH remained at pre-PGF2alpha values while the pessaries were in place, but began to increase within 1 hr after they were removed. Blood estradiol also remained at pre-PGF2alpha values until the pessaries were removed, and began to increase at 2 hr after pessary removal. We conclude that the increase in serum LH within 12 hr after PGF2alpha treatment in diestrous cattle is dependent upon withdrawal of progesterone; it is not due to increased serum estradiol.

Prostaglandin F2alpha production by the brain during estrogen-induced secretion of luteinizing hormone

The arteriovenous difference in the concentration of prostaglandin F2alpha (PGF2alpha) across the brain of the anestrous sheep was measured before and during the induction of luteinizing hormone secretion with 17 beta-estradiol. The results indicate that (i) the brain in vivo is a significant source of PGF2alpha, (ii) the release of PGF2alpha from the brain occurs in pulses with a circhoral rhythm, and (iii) the process through which estrogen exerts its negative and positive feedback effects on luteinizing hormone secretion may involve amplitude modulation of PGF2alpha output from the brain.