Caprine luteinizing hormone isoforms during the follicular phase and anestrus

The relative proportion of the circulating luteinizing hormone isoforms in goats during follicular phase (pre-ovulatory peak; F) and anestrus (A) was investigated. Estrus was synchronized in six goats with a prostaglandin analogue. After estrus was detected, blood samples were taken at 1 h intervals for 24 h. Four anestrous goats received 100 μg i.v. of GnRH and blood samples were collected every 15 min for 5 h. Samples with the greatest LH concentration in follicular phase and after GnRH administration (anestrus) were analyzed by chromatofocusing and eluted with a pH gradient from 10.5 to 3.5. For quantification purposes eluted LH was grouped into basic (pH ≥ 7.5), neutral (pH 7.4–6.5) and acidic isoforms (pH ≤ 6.4) as well as by pH unit. In both physiological conditions (PC), basic and acidic isoforms were greater than the neutral. With this grouping criteria, there was an interaction between PC and pH group, with the proportion of neutral isoforms being greater (p < 0.05) in A (12.0 ± 0.8%) as compared with F (5 ± 2%). Analysis by pH unit showed a very basic group of eluted isoforms (pH ≥ 10), which amounted to a percentage of 6.0 ± 0.4% of the total observed during A, and 3 ± 1% during F (p < 0.05). Predominant isoforms in A eluted in the pH range 9.99–9.0 (42 ± 3%) as compared to 7 ± 3% (p < 0.01) in that pH range in F. In contrast, the predominant isoforms in F eluted in the pH range 8.99–8.0, representing 55 ± 8%, while in A the proportion was 11 ± 2% (p < 0.01). Isoforms eluted at the pH range 7.9–7 represented a significantly greater proportion during A (5.0 ± 0.6%) as compared with F (3 ± 1%). This is the first report on goat LH circulating isoforms. During A the LH isoforms secreted by the pituitary are more basic than during F.     

Progesterone and the distribution of pituitary gonadotropin isoforms in cattle

The objective of the present study was to determine the relative proportion of gonadotropin isoforms in bovine pituitary glands affected by progesterone. Twelve postpubertal heifers (Swiss-Zebu) were assigned to three groups (n=4): intact animals in the luteal phase of the estrous cycle (diestrus group); ovariectomized heifers with (OVXP) or without progesterone treatment (OVX). Prior to pituitary gland collection, a blood sample was taken from each animal to determine the circulating progesterone concentration. Pituitary protein extractions processed by chromatofocusing were eluted with a pH gradient ranging from 10.5 to 3.5. The LH and FSH eluent was grouped on the basis of the following three criteria: (1) as either a basic (pH>or=7.5), neutral (pH 7.4-6.5) and acid (pHor=10.5-3.5); (3) on the basis of distinct isoforms 12 peaks of which (A-L) were identified for LH and 11 (I-XI) for FSH. The analysis by range of pH and by pH of elution in the OVX and OVXP groups showed no difference in the LH and FSH isoform ratio, but diestrus cattle differs having a greater ratio (p<0.05) of basic LH isoforms (87.5+/-0.4%) and lesser ratio (p<0.05) of acid isoforms (5.4+/-0.7%). In the diestrus group, the ratio of acid FSH isoform increased (62.1+/-1.7%), while neutral isoforms decreased (5.7+/-0.4%, P<0.05). The analysis by isoform type of LH revealed a greater proportion of isoforms C (pH 9.4) and E (pH 9.0) in the groups with circulating progesterone when compared to the OVX group. The heterogeneity of FSH was quantitatively similar in most isoforms in the three groups, with the exception of the predominant isoform (VIII, pH 4.9) that was more abundant in the diestrus group (p<0.05). These results indicate that progesterone with other gonad factors influence the pituitary glicosylation altering the relative proportions of gonadotropin isoforms.     

Gonadotropin-releasing hormone in third ventricular cerebrospinal fluid of the heifer during the estrous cycle

The release profile of GnRH in cerebrospinal fluid (CSF) and its correlation with LH in peripheral blood of ovary-intact heifers during the estrous cycle were investigated. A silicon catheter was placed into the third ventricle of six heifers using ultrasonography. During the mid-luteal phase, the heifers were injected with prostaglandin F(2alpha) to induce luteolysis. Surges of CSF GnRH (66.7 h after prostaglandin F(2alpha) administration) and peripheral LH (66.3 h) occurred simultaneously and were coincident with the onset of estrus (67.0 h). Duration of elevated GnRH concentration considerably overlapped with the estrous phase in each of the heifers. Mean pulse frequencies of both GnRH and LH were significantly higher during the proestrous and early luteal phases than during the mid-luteal phase, while mean concentration and pulse amplitude of both GnRH and LH were not different between these three phases. Of all the GnRH pulses identified, more than 80% were accompanied by an LH pulse during the proestrous and early luteal phases. However, the proportion of GnRH pulses that were coincident with an LH pulse during the mid-luteal phase decreased to 60%. The results clearly demonstrate that a dynamic (pulse) and longer-term (surge) changes of GnRH release into CSF are physiologically expressed during the estrous cycle in heifers, and the pattern of pulsatile GnRH secretion in heifers depends upon their estrous cycle.     

Pituitary luteinizing hormone microheterogeneity in the afternoon of proestrus in rats: some new insights

OBJECTIVE : The aim of the present report was to determine the possible modifications in rat pituitary LH isoforms induced by the spontaneous increase in GnRH at the time of the preovulatory gonadotropin surge. DESIGN: The changes in the quantitative pattern and relative proportions of pituitary LH isoforms in rats on the afternoon of proestrus [INT-P(PM)] were evaluated by comparison with other stages of the estrous cycle (diestrus-1, diestrus-2 and estrus) and ovariectomized (7 and 30 days earlier) animals killed in the morning and in the afternoon of the corresponding day. METHODS: The chromatofocusing technique (pH gradient 11.00-7.00) was used to analyze the different molecular species of intrapituitary LH. RESULTS: Pituitary LH from diestrus-1 animals, considered as a baseline pattern in the cycling rat, eluted as 11 isoforms distributed in pH 9.62-8.82, with greater percentages in pH 9.50-9.01. Except for INT-P(PM) pituitaries, there were no major differences in the pattern of LH heterogeneity in the pituitaries of rats from various stages of the cycle. In contrast, significant changes in the charge distribution and relative abundance of LH isoforms were found in the pituitaries from INT-P(PM) rats. INT-P(PM) pituitaries resolved in 16 LH isoforms with a significant shift to less alkaline pIs (pH 9.62-8.11), the more abundant being focused within pH 9.00-8.51. Conversely, a shift to more basic isoforms resulted after ovariectomy, leading to the accumulation of less mature isoforms in the gonadotrope. CONCLUSIONS: Presumably, the use of animals on INT-P(PM), at the time of the preovulatory LH surge, made it possible to discriminate such changes in LH isoform distribution. That GnRH, released in association with the rising phase of the LH surge, induces these changes in pituitary LH polymorphism appears to be the most likely possibility. In a previous study we demonstrated that GnRH stimulated galactose incorporation into LH in vitro. In the case of pituitaries from INT-P(PM) rats, the shift toward less alkaline isoforms could potentially result from sialylation of increased terminal galactose.     

Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 +/- 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day -5 and Day +7 and estrous behavior was monitored between Day -4 and Day +7. Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 +/- 0.03 vs 0.46 +/- 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 +/- 3.0 vs 56.3 +/- 4.1 h) and was of greater magnitude (32.15 +/- 3.56 vs 18.84 +/- 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 +/- 0.15 and 1.33 +/- 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.     

Response to GnRH on day 6 of the estrous cycle is diminished as the percentage of Bos indicus breeding increases in Angus, Brangus, and Brahman x Angus heifers

Angus (n=6), Brangus (5/8 Angus x 3/8 Brahman, n=6), and Brahman x Angus (3/8 Angus x 5/8 Brahman, n=6) heifers exhibiting estrous cycles at regular intervals were used to determine if the percentage of Bos indicus breeding influenced the secretory patterns of LH in response to a GnRH treatment on Day 6 of the estrous cycle. Heifers were pre-synchronized with a two-injection PGF(2 alpha) protocol (25 mg i.m. Day -14 and 12.5 mg i.m. Day -3 and -2 of experiment). Heifers received 100 microg GnRH i.m. on Day 6 of the subsequent estrous cycle. Blood samples were collected at -60, -30, and -1 min before GnRH and 15, 30, 60, 90, 120, 150, 180, 240, 300, 360, 420, and 480 min after GnRH to determine concentrations of serum LH. Estradiol concentrations were determined at -60, -30, and -1 min before GnRH. On Day 6 and 8, ovaries were examined by ultrasonography to determine if ovulation occurred. On Day 13, heifers received 25 mg PGF(2 alpha) i.m. and blood samples were collected daily until either the expression of estrus or Day 20 for heifers not exhibiting estrus to determine progesterone concentrations. There was no effect (P>0.10) of breed on ovulation rate to GnRH as well as size of the largest follicle, mean estradiol, and mean corpus luteum volume at GnRH. Mean LH was greater (P<0.05) for Angus (7.0+/-0.8 ng/mL) compared to Brangus (4.6+/-0.8 ng/mL) and Brahman x Angus (2.9+/-0.8 ng/mL), which were similar (P>0.10). Mean LH peak-height was similar (P>0.10) for Brangus (13.9+/-3.4 ng/mL) compared to Angus (21.9+/-3.4 ng/mL) and Brahman x Angus (8.0+/-3.4 ng/mL), but was greater (P<0.05) for Angus compared to Brahman x Angus. Interval from GnRH to LH peak was similar (P>0.10) between breeds. As the percentage of Bos indicus breeding increased the amount of LH released in response to GnRH on Day 6 of the estrous cycle decreased.     

Prediction of the estrous cycle and optimal insemination time by monitoring vaginal electrical resistance (VER) in order to improve the reproductive efficiency of the Okinawan native Agu pig

The present study was conducted to determine whether vaginal electrical resistance (VER) can be exploited to improve the low reproductive efficiency of the rare Okinawan native Agu pig, in which estrous signs are difficult to ascertain by visual observation. The lowest VER (272.0+/-12.4 units, n=5) and the preovulatory LH surge were detected at 57.6+/-5.3 and 36.8+/-9.6h before the onset of estrus, respectively. The initiation of gradual increase in VER was found after 9.6+/-4.7h following the peak LH, and the higher levels of VER were plateaued during the luteal phase. These VER fluctuations were correlated with changes in plasma LH (P<0.05) and progesterone (P<0.001), but not estrogen. Moreover, the conception rate (41%, n=32) was dramatically improved by artificial insemination at 24 and 34 h after the beginning of the VER increase when compared with insemination at the conventional time (12 and 24h after detection of estrus, 20%, n=45), widely used in commercial pigs (P<0.05). These data suggest that VER fluctuation can be used to estimate the stage of the estrous cycle, and the scheduling artificial insemination according to increase in VER as an index for the preovulatory LH surge could improve Agu reproductive efficacy.     

Influence of GnRH infusion on endocrine parameters and duration of postpartum anestrus in beef cows

The effect of an intravenous infusion of gonadotrophin releasing hormone (GnRH) on the duration of postpartum anestrus in suckled beef cows was studied. Twenty-eight, mature, suckled beef cows were assigned in equal numbers to one of four treatment groups which were based on infusion with saline or GnRH (15ug/hour for 12 hours) and stage postpartum (pp) (20 or 35 days). Serum LH and progesterone were determined by radioimmunoassay for the period which began 5 days pre-infusion and ended at 55 days postpartum (ie: 35 or 20 days post-infusion). Serum LH remained below 5ng/ml during infusion in all control cows. Peak serum LH values, times of LH peaks, and duration of LH responses (means +/- SE) during infusion were 49 +/- 12 ng/ml, 162 +/- 42 minutes and 7.8 +/- 1.3 hours for the 20 day group and 44 +/- ng/ml, 144 +/- 6 minutes, and 8.2 +/- 1.1 hours for the 35 day group respectively. Serum progesterone levels indicated that the proportion of cows showing the onset of estrous cycles within 10 days of infusion was greater in the 20 day pp GnRH group (4/7) than the 20 day pp saline group (0/7) (p < .05) but was not significantly different between the 35 day pp GnRH (4/7) and 35 day pp saline (2/6) groups. The incidence of estrus was not affected by GnRH treatment and was 37% in all cows prior to 55 days pp. It was concluded that infusions of GnRH for 12 hours at a rate of 15 ug/hour could induce estrous cycles in suckled beef cows treated at 20 days postpartum.     

Milk progesterone profiles in crossbred Brown Swiss x Nellore cattle following natural service

Ovarian activity and estrous behaviour were monitored through milk progesterone determinations and twice daily visual observations in 70 crossbred Brown Swiss x Nellore cows following natural service. Whole milk samples were collected on the day of estrus (Day 1), Day 11, and every 5 d thereafter until the next estrus or pregnancy confirmation. Seventy percent of the cows behaved as expected, i.e. they showed a 19-to 25-d interval between estrus and the next ovulation, or they became pregnant. Estrous cycles of regular length (18 to 24 d) were found in 54% of the cases. Prolonged luteal phases (interval from estrus to next ovulation > 28 d) were found in 15.7% of cows. Short estrous cycles (interestrous interval < 18 d) were found in 7.1% of the cases. Periods of acyclicity (basal progesterone levels for periods >/= 15 d) were found in 5.8% of the cases, and one cow exhibited estrus while pregnant and had a high progesterone concentration. Cows with a prolonged luteal phase and those with a short estrous cycle had an interval between ovulations of 35.0 +/- 6.7 d (x +/- SD) and 9.6 +/- 3.1 d, respectively. Signs of estrus were not detected in 33.3% of the ovulations confirmed by progesterone determinations. Low conception rates, failures in estrus detection and a high frequency of abnormal postbreeding luteal phases were found.     

Concentrations of luteinizing hormone and oestradiol in plasma and response to injection of gonadotrophin-releasing hormone analogue at selected stages of anoestrus in domestic bitches.

Concentration of plasma luteinizing hormone (LH) and oestradiol concentrations and responses to a standard challenge with a gonadotrophin-releasing hormone (GnRH) analogue were measured at certain stages of anoestrus during consecutive cycles in five beagle bitches. Blood samples were collected every 20 min for 6h followed immediately by injection of GnRH analogue (0.16 micrograms i.v.) and collection of further samples after 10, 20, 40 and 60 min. Five, 10, 17 and three such sampling sequences were obtained during the luteal phase, transition to anoestrus, anoestrus and pro-oestrus respectively (i.e. 154-71, 114-44, 85-11 and 7-1 days before the preovulatory LH peak, respectively). Pulsatile LH secretion occurred spontaneously at all stages of the luteal phase and anoestrus and there was no effect of cycle stage on mean LH concentration or variability. In contrast, oestradiol could not be detected in most samples from early and mid-anoestrus until approximately one month before the preovulatory LH peak, after which average oestradiol concentration and between sample variability appeared to increase. Mean (+/- SEM) oestradiol concentration for all samples collected from 100-75, 74-50, 49-25, 24-10 and 9-1 days before LH peak was 1.4 +/- 0.1, 1.3 +/- 0.1, 2.4 +/- 0.3, 11.0 +/- 1.4 and 36.0 +/- 3.2 pg ml-1, respectively. Plasma LH concentration increased in all bitches after GnRH analogue injection (2.7 +/- 0.7 ng ml-1 at t = 0, 12.5 +/- 1.0 ng ml-1 at t = 10 min, mean +/- SEM, n = 35) regardless of cycle stage.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

An in vitro study of LH release, synthesis and heterogeneity in pituitaries from proestrous and short-term ovariectomized rats

It is known that acute ovariectomy (OVX) greatly attenuates the pituitary luteinizing hormone (LH) response to gonadotropin-releasing hormone (GnRH) in vitro. The present study evaluated possible quantitative and/or qualitative differences in the biosynthesis and secretion of LH in pituitaries from proestrous and acutely (72 h) OVX rats. Paired anterior pituitary glands were incubated for 4 h in a medium containing +/- 10 nM GnRH. Pituitary and secreted LH were measured by radioimmunoassay with differences in total LH (tissue plus medium) +/- GnRH being indicative of GnRH-stimulated LH synthesis. Qualitative changes in LH were evaluated by isoelectrofocusing (IEF). The results show that the major form of LH stored in and released from the pituitaries consisted of LH molecules with an isoelectric point (pI) in the alkaline pH range (alkaline LH), and a lesser amount (approximately 30%) of LH molecules in the acidic pH range (acidic LH). The ratio of alkaline/acidic LH observed in the pituitary and medium was similar in the proestrous and OVX groups, although the amount of alkaline and acidic LH release in response to GnRH was 2-3 times greater in the proestrous group. In both groups, the alkaline/acidic LH ratio of secreted LH was higher in the presence of GnRH than in its absence. Alkaline LH synthesis was increased by GnRH in both groups, with the response being greater in the proestrous than in the OVX group; GnRH-stimulated acidic LH synthesis was observed only in the proestrous group. In both groups, the amount of LH synthesized was about 60% of the amount released, which suggests that LH synthesis does not fully account for differences in GnRH-stimulated LH release. Treatment of pituitary extracts with neuraminidase decreased acidic LH, and proportionately increased alkaline LH. These results suggest that the quality of LH stored in and secreted from pituitaries of proestrous and OVX rats is similar, and that there is a preferential release of the major alkaline LH isoform in response to GnRH. The ovarian steroid environment, presumably estradiol, proportionately increases the amount of alkaline and acidic LH released, and differentially affects the amounts of the various isoforms synthesized in response to GnRH. The charge heterogeneity of alkaline and acidic LH may be related to the sialic acid content of the LH molecule.     

Effects of 72 hr calf removal and/or gonadotropin releasing hormone on luteinizing hormone release and ovarian activity in postpartum beef cows

A study was conducted to determine the pituitary and ovarian responses to 72 hr calf removal (CR) and/or gonadotropin releasing hormone (GnRH) in beef cows. Forty-eight Angus, Simmental, and Charolais crossbred cows in moderate body condition were allotted to an experiment of 2 x 2 factorial design involving CR and GnRH. At 30 to 32 days postpartum, calves were removed for 72 hr from the CR and CR plus GnRH groups. All cows were injected (i.m.) with saline or 200 mug of GnRH at 33 to 35 days postpartum. Saline or GnRH was injected 5 hr before calf return. Plasma luteinizing hormone (LH) was measured in blood samples collected every 30 min for 5.5 hr beginning 30 min prior to injection of saline or GnRH. Plasma progesterone was measured in blood samples collected 0, 7, and 14 days after GnRH injection and 7 and 14 days following the first detected estrus. There were no differences (P>0.05) in the interval to peak LH release or the magnitude of the LH release between the GnRH and CR plus GnRH groups; however, the GnRH induced release of LH was greater (P<0.05) over time when preceded by CR. Plasma progesterone concentrations were increased on day 7, compared to day 0, after GnRH injection in 57% and 50% of the animals in the GnRH and CR plus GnRH groups, respectively. However, behavioral estrus was not observed in any of the cows between days 0 and 7 after GnRH injection. A higher (P<0.05) percentage of the cows injected with GnRH formed luteal tissue compared to cows injected with saline; however, the luteal lifespan following GnRH injection was decreased relative to the luteal lifespan following the first observed estrus. The mean interval from calving to first estrus was decreased (P<0.05) by 17 days in the CR group relative to the other groups, and calf removal had no detrimental effect on milk production at 80 days postpartum or on calf weaning weights at approximately 7 months of age. In summary, 72 hr CR decreased the postpartum interval and increased the pituitary responsiveness to GnRH. Pretreatment with 72 hr CR did not alter circulating progesterone concentrations or luteal lifespan of corpora lutea induced by GnRH.     

Effects of ovarian input on GnRH and LH secretion immediately postovulation in pony mares

The potential involvement of ovarian factors in regulating GnRH and LH postovulation was studied in ovarian intact (Group 1; n=3) and ovariectomized (OVX; Group 2; n=3) mares (OVX within 12 hr of ovulation). Blood samples were collected every 10 min for 6 hr from jugular vein (JV) and intercavernous sinus (ICS) during estrus and on Day 8 postovulation for LH and GnRH analysis. Additionally, JV samples were collected twice daily (12-hr intervals) for 30 days for LH and progesterone (P4) analysis. A significant treatment x day effect (P<0.0001) describes declining plasma LH concentrations in intact mares, and regression analysis indicated that response curves were not parallel (P<0.001). Plasma LH concentrations remained elevated in OVX mares. LH increased further in OVX mares by Day 8 post-OVX (P<0.06), reflecting the increased (P<0.07) LH episode amplitude. GnRH decreased from estrus to Day 8 in both groups reflecting an effect of sampling period (P<0.03). GnRH episode amplitude declined (P<0.08) from estrus (62.8+/-3.1 pg/mL) to Day 8 (46.3+/-3.1 pg/mL) in OVX mares, but not in control mares (intact estrus, 36.5+/-6.4; intact Day 8, 37.5+/-7.3; OVX estrus, 62.8+/-3.1; OVX Day 8, 46.3+/-3.1 pg/mL). In conclusion, we propose that postovulatory LH decline requires ovarian feedback in mares, and that OVX alters GnRH secretory dynamics such that LH concentrations does not decline postovulation and, in fact, is further elevated with time after OVX.     

Passive immunization of the pig against gonadotropin releasing hormone during the follicular phase of the estrous cycle

Three experiments were conducted to determine the effects of passively immunizing pigs against gonadotropin releasing hormone (GnRH) during the follicular phase of the estrous cycle. In Experiment 1, sows were given GnRH antibodies at weaning and they lacked estrogen secretion during the five days immediately after weaning and had delayed returns to estrus. In Experiment 2, gilts passively immunized against GnRH on Day 16 or 17 of the estrous cycle (Day 0 = first day of estrus) had lower (P<0.03) concentrations of estradiol-17beta than control gilts, and they did not exhibited estrus at the expected time (Days 18 to 22). When observed three weeks after passive immunization, control gilts had corpora lutea present on their ovaries, whereas GnRH-immunized gilts had follicles and no corpora lutea. The amount of GnRH antiserum given did not alter (P<0.05) serum concentrations of LH or pulsatile release of LH in sows and gilts. In Experiment 3, prepuberal gilts were given 1,000 IU PMSG at 0 h and GnRH antiserum at 72 and 120 h. This treatment lowered the preovulatory surge of LH and FSH, but it did not alter serum estradiol-17beta concentrations, the proportion of pigs exhibiting estrus, or the ovulation rate. These results indicate that passive immunization of pigs against GnRH before initiation of or during the early part of the follicular phase of the estrous cycle retards follicular development, whereas administration of GnRH antibodies during the latter stages of follicular development does not have an affect. Since the concentration of antibodies was not high enough to alter basal or pulsatile LH secretion, the mechanism of action of the GnRH antiserum may involve a direct ovarian action.     

Endocrine and reproductive responses of beef cattle to a synthetic gonadotropin-releasing hormone agonist (fertirelin acetate)

A synthetic gonadotropin-releasing hormone (GnRH) agonist (fertirelin acetate, FA) was administered to beef cattle within 12 h after onset of estrus (Day = 0) to study effects on subsequent endocrine responses and fertility. In Study 1, 16 crossbred beef heifers were injected with either 100 mug FA (n = 8) or saline (n = 8) at 6 or 12 h (n = 7; n = 9) after onset of estrus. Concentrations of luteinizing hormone (LH) over time were affected (P<0.01) by the interaction of treatment and interval from onset of estrus to treatment. Heifers treated with FA at 6 h after onset of estrus exhibited the greatest increase in LH after treatment. There was no effect of treatment, interval from onset of estrus to treatment or treatment by interval interaction on duration of the estrous cycle, on concentrations of progesterone from Days 1 through 14 posttreatment, or on concentrations of progesterone prior to subsequent estrus (Day -10 through 0, posttreatment estrus). In summary, FA administered to beef cattle within 12 h after onset of estrus effectively increased peripheral plasma concentration of LH, but this increase had no effect on subsequent luteal function as measured by duration of the estrous cycle or concentrations of plasma progesterone. In Study 2, 86 parous beef cows were bred artificially to one of two bulls following natural or prostaglandin F(2)alpha induced estrus. Cows received either no treatment or 50 or 100 mug FA at the time of AI. There was no effect of treatment, breed, parity, technician, service sire or interactions on conception rate (mean = 76.7%). Although not significant, the numerical pattern of conception rate among experimental groups (control = 71.4%, 50 mug FA = 76.7%, 100 mug FA = 82.1%) supports further investigation of this GnRH agonist with larger numbers of cattle.     

Continuous administration of low-dose GnRH in mares I. Control of persistent anovulation during the ovulatory season

Three experiments were conducted during the operational breeding season to confirm that continuous, subcutaneous infusion of low-dose GnRH would not disrupt established estrous cycles (Experiment 1), and test the hypotheses that a similar treatment would stimulate secretion of LH and induce development of ovulatory follicles in persistently anovulatory mares (Experiments 2 and 3). Treatment with GnRH (5 microg/h) increased (P<0.001) serum P4 during the luteal phase (7.7+/-0.5 versus 6.4+/-0.5 ng/mL), tended to increase serum LH (2.6+/-0.27 versus 1.9+/-0.25 ng/mL), and did not modify interovulatory intervals. In Experiment 2, GnRH treatment (2.5-5 microg/h) of persistently anovulatory mares increased (P<0.001) serum LH compared to controls (0.5+/-0.08 versus 0.1+/-0.03 ng/mL), with all GnRH-treated and no Control mares ovulating. Mares exhibiting Delayed Recrudescence (n=29) or Lactational Anovulation (n=18), were assigned randomly in Experiment 3 to receive either (1) GnRH/GnRH (n=23); 2.5 microg GnRH/h for 14 d (Period I) and 5 microg/h during the subsequent 28 d (Periods II and III); or (2) Control/GnRH (n=24); no treatment during Period I (control period) and GnRH treatments as in 1 during Periods II and III. Percentage of mares ovulating and pregnant during Period I was greater (P<0.05) for GnRH-treated than Control mares. Thereafter, cumulative ovulation frequency (85%), pregnancy (72%) and cycles/conception (1.3+/-0.2) were similar between groups; however, interval to conception was reduced (P<0.01) by 10.3 d in GnRH/GnRH compared to Control/GnRH.     

LH secretion and response to GnRH during seasonal anoestrus of the Pére David's deer hind (Elaphurus davidianus)

The pattern of LH secretion and response to exogenous GnRH was determined on 5 occasions during seasonal anoestrus of the Père David's deer hind. LH pulse frequency was low (3.3 +/- 0.6 pulses/18 h) in early anoestrus (February), increased significantly in mid-anoestrus (April; 8.4 +/- 1.4 pulses/18 h) and thereafter declined slightly in late anoestrus (June; 6.3 +/- 0.25 pulses/18 h). Mean LH concentrations also showed significant changes during anoestrus with higher levels in mid-anoestrus (April; 0.85 +/- 0.12 ng/ml) when compared with other times (0.53 +/- 0.05, 0.60 +/- 0.10, 0.68 +/- 0.06 and 0.71 +/- 0.05 ng/ml for February, March, May and June, respectively). LH pulse amplitude showed no significant changes during the study. The LH response to intravenous injections of 2 micrograms GnRH was lowest in early anoestrus (February), increased significantly in mid-anoestrus (April) and remained high through late anoestrus. The response during the luteal phase was similar to that seen during late anoestrus. These results indicate that seasonal anoestrus in the Père David's deer hind is not a uniform state but is characterized by an early period of 'deep' anoestrus.     

Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers

Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.     

Effect of estradiol on secretion of luteinizing hormone during the follicular phase of the bovine estrous cycle

Mean concentrations of luteinizing hormone (LH) increase during the follicular phase of the estrous cycle in cows. The working hypotheses in the present study were (1) that increasing concentrations of 17 beta-estradiol (E2) during the follicular phase of the estrous cycle cause an increase in mean concentration of LH by increasing amplitude of pulses of LH, and (2) that increasing E2 concentrations during this stage of the estrous cycle decrease frequency of pulses of LH in bovine females. Day of estrus was synchronized in seventeen mature cows. Treatments were initiated on Day 16 of the experimental estrous cycle (Day 0 = estrus). At Hour 0 (on Day 16), 4 cows were lutectomized. Lutectomy of these cows (EE; n = 4) allowed for endogenous secretion of E2. The remaining cows were ovariectomized at Hour 0 and were assigned to one of three E2 treatments: luteal phase E2 (LE, n = 5), increasing then decreasing E2 (DE, n = 5), and no E2 (NE, n = 3). Cows in the group that received LE were administered one E2 implant at Hour 0, which provided low circulating concentrations of E2 similar to those observed during the luteal phase of the estrous cycle. Cows in the group that received DE were administered one E2 implant at Hour 0, and additional implants were administered at 8-h intervals through Hour 40; then, two implants were removed at Hours 48 and 56, and one implant was removed at Hour 64.(ABSTRACT TRUNCATED AT 250 WORDS)