Dose Of GnRH Research Articles

Gonadotropin-Releasing Hormone in Third Ventricular Cerebrospinal Fluid: Endogenous Distribution and Exogenous Uptake

GnRH is detectable in the cerebrospinal fluid (CSF), but its source remains unidentified. Previous studies have harvested CSF for GnRH analysis from the median eminence region, but it is unknown whether GnRH in CSF is restricted to this region. If CSF-GnRH plays a physiological role, through volume transmission, to communicate with brain regions that express GnRH receptors but are not evidently innervated by GnRH neurons, then it is essential to establish whether GnRH is more pervasive throughout the cerebroventricular system. Three cannulae were placed in the supraoptic, infundibular, and pineal recesses of the third ventricle. GnRH was undetectable in lateral ventricle CSF. GnRH pulses were detected in all ewes in infundibular recess CSF, but at sites more rostral (supraoptic) and caudal (pineal), GnRH pulse frequency and amplitude significantly (P<0.05) decreased. A GnRH surge was evident in CSF collected simultaneously from all cannulae, but the amplitude was greatest (P<0.05) at the infundibular recess. A final study established whether iv administered GnRH enters the CSF. A 250-ng GnRH dose did not affect CSF-GnRH concentrations (1.6+/-0.3 pg/ml), but 2.5 microg (2.7+/-0.2 pg/ml; P<0.001) and 1 mg (38.5+/-10.6 pg/ml; P<0.05) significantly increased CSF-GnRH concentrations. The present study shows: 1) the median eminence region is likely to be the major, if not only, source of GnRH entering the cerebroventricular system; and 2) exogenous GnRH crosses the blood-brain barrier, but extremely high doses are required to elevate CSF concentrations to physiological levels. Thus, CSF-GnRH may affect sites that are closer in proximity to the infundibular recess region than previously thought.

Microdose gonadotropin-releasing hormone agonist flare-up protocol versus multiple dose gonadotropin-releasing hormone antagonist protocol in poor responders undergoing intracytoplasmic sperm injection–embryo transfer cycle

To compare the efficacy of microdose GnRH agonist (GnRH-a) flare-up and multiple dose GnRH antagonist protocols in patients who have a poor response to a long luteal GnRH-a protocol. Prospective, randomized, clinical study. University hospital. Forty-two poor responder patients undergoing intracytoplasmic sperm injection (ICSI)-embryo transfer cycle. Twenty-one patients received microdose leuprolide acetate (LA) (50 microg twice daily) starting on the second day of withdrawal bleeding. The other 21 patients received 0.25 mg of cetrorelix daily when the leading follicle reached 14 mm in diameter. Serum E(2) levels, number of growing follicles and mature oocytes, embryo quality, dose of gonadotropin used, cancellation, fertilization, implantation rate and pregnancy rate (PR). The mean serum E(2) concentration on the day of hCG administration was significantly higher in the microdose GnRH-a group than in the GnRH antagonist group (1,904 vs. 1,362 pg/mL). The clinical PRs per started cycle of microdose GnRH-a and GnRH antagonist groups were 14.2% and 9.5%, respectively. There were no statistically significant differences in the other ovulation induction characteristics, fertilization and implantation rates. Microdose GnRH-a flare-up protocol and multiple dose GnRH antagonist protocol seem to have similar efficacy in improving treatment outcomes of poor responder patients.

Luteinized thecoma associated with sclerosing peritonitis — Conservative surgical approach followed by corticosteroid and GnRH agonist treatment — a case report

Background Luteinized thecoma of the ovary associated with sclerosing peritonitis is a rare tumor that has no standard definitive treatment regimen. Case A 25 year-old patient diagnosed with luteinized thecoma and sclerosing peritonitis in the omentum. The patient received high dose corticosteroids (IV Hydrocortisone 500 mg/d) and GnRH agonist (IM Leuprolide 3.75 mg) in order to achieve ovarian suppression and relief of the clinical peritonitis. She was re-admitted two weeks later due to bowel obstruction which was treated conservatively. The steroid regimen was continued by oral intake for 5 weeks with complete remission of the peritonitis related symptoms. The bilateral enlarged ovarian tumor-like solid was the prominent finding in consecutive ultrasound exams with no decrease in size despite of the above mentioned protocol. Thus, the patient was re-operated for exploration and biopsies of the ovary and the pathology report showed no evidence of remnant disease in the ovary, or in the peritoneum. Completing follow-up of 15 months since the last operation, the patient is asymptomatic. She conceived spontaneously and currently is in her 24th week of a normal pregnancy. Conclusion This is the first case report in the English literature of a successful medical conservative treatment of a young patient with luteinized thecoma associated with sclerosing peritonitis that led to complete relief of the symptoms and allowed fertility preservation.

Comparison of multiple dose GnRH antagonist and minidose long agonist protocols in poor responders undergoing in vitro fertilization: a randomized controlled trial

To investigate the efficacy of gonadotropin releasing hormone antagonist (GnRH) in poor responders undergoing in vitro fertilization. Ninety-six patients with poor ovarian response in previous treatment cycles were prospectively randomized into two groups. Forty-four patients were stimulated with GnRH antagonist multidose protocol and 45 patients received a standard long agonist protocol. Ovarian response was evaluated by transvaginal ultrasound and hormonal parameters. Cycle characteristics and treatment outcomes were statistically compared between groups. There was significantly reduced duration of stimulation and consumption of gonadotrophins in the antagonist group when compared to the agonist group. The estradiol concentrations on the day of human chorionic gonadotropin (hCG) injection, the number of oocytes retrieved, and the number of embryos transferred were similar for both groups. In the antagonist group, eight (18.1%) ongoing pregnancies were achieved and in the agonist group, ten (22.2%) clinical pregnancies were achieved but the difference was not statistically significant. The present study was not powered to detect clinically relevant differences between two protocols in outcomes such as pregnancy rate, with confidence.

Evidence for Insulin Suppression of Baseline Luteinizing Hormone in Women with Polycystic Ovarian Syndrome and Normal Women

In women with polycystic ovarian syndrome (PCOS), the relationship of insulin to LH secretion and responses to GnRH remains unresolved. A rigorous analytical examination of this relationship has not been performed. Our objective was to determine the relationship of basal LH secretion and responses to GnRH, insulin, and other endocrine variables in normal and PCOS women. In PCOS and normal women, mean composite 12-h LH secretion was analyzed for correlating factors. LH responses to varying doses of GnRH during a fixed rate of insulin infusion and LH responses to a fixed dose of GnRH during varying doses of insulin infusion were analyzed for contributing factors. Eighteen PCOS and 21 normal women underwent studies of frequent blood sampling and GnRH stimulation before and during insulin infusion at the General Clinical Research Center, University of California, San Diego. Group mean composite 12-h LH levels were assessed with respect to other endocrine variables. In addition, LH responses to GnRH with or without insulin infusion were assessed. In normal women, insulin negatively predicted mean LH. In PCOS, the combined effect of body mass index (negative) and testosterone (positive) predicted LH. The best predictor of LH was body mass index and insulin combined. Basal LH and LH responses to GnRH were unaltered by insulin infusion in normal women. These measures were reduced during insulin infusion in PCOS women. In PCOS, insulin infusion suppresses pituitary response to GnRH. In normal women, insulin negatively correlates with mean LH and suppresses GnRH response at a high infusion rate.

Gonadotropin-releasing hormone regulates spine density via its regulatory role in hippocampal estrogen synthesis

Spine density in the hippocampus changes during the estrus cycle and is dependent on the activity of local aromatase, the final enzyme in estrogen synthesis. In view of the abundant gonadotropin-releasing hormone receptor (GnRH-R) messenger RNA expression in the hippocampus and the direct effect of GnRH on estradiol (E2) synthesis in gonadal cells, we asked whether GnRH serves as a regulator of hippocampal E2 synthesis. In hippocampal cultures, E2 synthesis, spine synapse density, and immunoreactivity of spinophilin, a reliable spine marker, are consistently up-regulated in a dose-dependent manner at low doses of GnRH but decrease at higher doses. GnRH is ineffective in the presence of GnRH antagonists or aromatase inhibitors. Conversely, GnRH-R expression increases after inhibition of hippocampal aromatase. As we found estrus cyclicity of spine density in the hippocampus but not in the neocortex and GnRH-R expression to be fivefold higher in the hippocampus compared with the neocortex, our data strongly suggest that estrus cycle–dependent synaptogenesis in the female hippocampus results from cyclic release of GnRH.

GnRH agonist protocol administration in the luteal phase in ICSI-ET cycles stimulated with the long GnRH agonistprotocol: a randomized, controlled double blind study

GnRH agonist administration in the luteal phase was reported to beneficially affect the clinical outcome of intracytoplasmic sperm injection (ICSI) and embryo transfer (ET) cycles. This double blind, randomized, placebo controlled trial evaluates whether a single dose GnRH agonist administered 6 days after ICSI increases ongoing pregnancy rates following ET in cycles stimulated with the long GnRH agonist protocol. Five hundred and seventy women undergoing ET following controlled ovarian stimulation with a long GnRH agonist protocol were included. In addition to routine luteal phase support with progesterone, women were randomized to receive a single 0.1 mg dose of triptorelin or placebo 6 days after ICSI. Randomization was done on the day of ET according to a computer generated randomization table. Ongoing pregnancy rate beyond 20th week of gestation was the primary outcome measure. The trial was powered to detect a 12% absolute increase from an assumed 38% ongoing pregnancy rate in the placebo group, with an alpha error level of 0.05 and a beta error level of 0.2. There were 89 (31.2%) ongoing pregnancies in the GnRH agonist group, and 84 (29.5%) in the control group (absolute difference +1.7%, 95% confidence interval -5.8% to +9.2%). Implantation, clinical pregnancy and multiple pregnancy rates were likewise similar in the GnRH agonist and placebo groups. Single 0.1 mg triptorelin administration 6 days after ICSI following ovarian stimulation with the long GnRH agonist protocol does not seem to result in an increase >or=12% in ongoing pregnancy rates.

The outcome of different dose GnRH agonist suppression on in vitro fertilization-embryo transfer (IVF-ET) cycle outcome in patients with stage III/IV endometriosis

To evaluate the efficacy of different dose of GnRH agonist hormonal suppression on IVF-ET outcome in the patients with moderate or severe endometrosis. Retrospective study in tertiary university hospital encompassing the time period January 1, 2003∼December 30, 2006. Chinese women for IVF-ET with a primary diagnosis of stages III to IV endometriosis surgically confirmed and their first cycles in our center were included. Group I (61 patients) received standard COH employing mid-luteal phase GnRHa down regulation. Group II (35 patients) received monthly GnRHa 3.75 mg IM ×2 followed by ovarian hyperstimulation. Group III (44 patients) received monthly GnRH agonist 3.75 mg IM ×3 followed by ovarian hyperstimulation. All patients received ovarian stimulation with Gonadotrophin and hCG for triggering. Oocytes retrieval were scheduled 36 hours after hCG. Embryos were transferred at 4∼8 cell stage. Pregnancy rate (PR) were defined as sonographically visualized pregnancy sac. One-way analysis of variance (ANOVA) and Chi square analysis where appropriate. There were no significant differences among the groups with regards to age, duration of infertility, fertilization rate, embryos transferred. Women pretreatment with two or three months of GnRHa required significantly higher gonadotropin doses (ampoules:75IU) (group I: 42.76 ± 16.30, group II: 55.94 ± 23.38, group III: 63.88 ± 26.72, P<0.0001) and longer duration of Gn stimulation than women with standard long protocol (group I: 10.69 ± 1.68, group II: 12.59 ± 2.19, group III: 12.33 ± 2.26, P<0.0001). The number of oocytes was lower in group III than group I and II (group I: 10.22 ± 7.18, group II: 10.24 ± 6.89, group III: 7.07 ± 4.96, P=0.034). Pregnancy rate in group II was higher than group I and III, but that was not significant (group I: 28.6%, group II: 45.2%, group III: 35.1%, P>0.05). Implantation rate was also higher in group II than group I and III, but not significantly (group I: 14.9%, group II: 29.3%, group III: 17.57%, P>0.05). The administration of GnRH agonists to COH in women with moderate or severe endometriosis for a period of two to three months tend to increase the pregnancy rate. Two months of GnRHa (3.75 mg IM) prior to IVF appears to be a better option in Chinese women.

Patient Friendly IVF — A Gonadotropin Stimulation Protocol of 10-Injections Total

Background: Currently, the majority of mixed-medication stimulation protocols for IVF gonadotropin therapy necessitate 2–4 daily injections for the patient. The addition of needle anxiety to the already stressful IVF therapy may potentially have a negative impact on outcome. The current proposal puts forward a stimulation protocol that utilizes a single gonadotropin injection per day, with a single depot dose GnRH antagonist for down-regulation, for a total of 9–11 injections for the entire cycle.

Hormonal profiles associated with treatment of cystic ovarian disease with GnRH and PGF2α with and without CIDR in dairy cows

This study aimed to investigate ovarian and endocrine responses associated with treatment of cystic ovaries with GnRH, PGF2α, and +/-Progesterone-CIDR placement; and to determine pregnancy establishment following synchronization and timed artificial insemination in cows suffering from cystic ovaries. Ovarian cysts were typed rectally and ultrasonographically into follicular, luteinized and persistent types. Two schedules of treatment were designed, in Schedule-A, 15 cows with follicular (n=7), luteinized (n=3) and persistent (n=5) cysts were used. The cows received 2 injections of 100 ug GnRH (9 days interval) with 25 mg PGF2α administered 7 days after 1 st GnRH dose. In Schedule-B, 14 cows with follicular (n=6), luteinized (n=3) and persistent (n=5) cysts were used. The cows administered GnRH and CIDR concurrently, then 25 mg PGF2α 7 days later. The CIDR was removed 2 days after PGF2α. Cows were inseminated 16 hours after 2 nd GnRH dose. Blood samples were collected to assay progesterone and estradiol levels. In schedule-A, 57.1%, 33.3% and 40% of follicular, luteinized and persistent cysts were ovulated after 1 st GnRH injection, while a total of 100%, 66.7% and 100% were ovulated after 2 nd GnRH dose. The cows with follicular cysts appeared the highest rate of pregnancy (57.1%) followed by the luteinized and persistent cysts (33.3% and 40%). Of a total 15 cystic-treated cows, 7 were confirmed pregnant (46.7%). The concentration of progesterone was significantly (P<0.05) higher at 1 st GnRH injection, then decreased after PGF2α injection and then increased again at 7 day after insemination. In schedule-B, after 1 st GnRH dose, 66.7% of follicular, 0% of luteinized cysts and 80% of persistent were ovulated; with a 57.1% total ovulation rate. Following CIDR removal, 85.7% (12/14) cows ovulated the recruited follicles and developed a corpus luteum. Of a total 14 cystic-treated cows, 8 were confirmed pregnant (57.1%). Plasma estradiol declined following intra vaginal placement of CIDR, but markedly increased one day after removal. Progesterone decreased after CIDR removal, but increased again at presence of palpable corpus luteum. The developed corpus luteum and pregnancy rate were higher in schedule-B (+CIDR) than in schedule-A (-CIDR). In conclusion, treatment of cows with cystic ovaries with GnRH followed by PGF2α 7 days later resulted in recruitment of new healthy follicles, synchronization of ovulation and a marked pregnancy rate (with than without CIDR).

Use of GnRH to induce an accessory corpus luteum in buffaloes fixed time artificially inseminated

The objective of this study was to induce an accessory corpus luteum (CL) in buffaloes fixed time artificially inseminated. Two hundred and forty buffaloes received the treatment sequence GnRH/PGF2α/GnRH after which were inseminated artificially. Six days after the insemination, the animals were divided in two groups (G1 = Control and G2 = GnRH) and received 0 µg or 25 µg of GnRH to induce an accessory CL. After twenty four days (D40), pregnancy diagnosis was performed by ultrasonography and 79 buffalo (G1, n = 39; G2, n = 40) were randomly selected to verify the ovary status by ultrasound. Fifty three pregnant buffaloes (G1, n = 32; G2, n = 21) were followed to verify the birth rate. Data were analyzed by Chi-square test. The conception rate, the accessory CL rate and the birth rate were higher in G2 than in G1 (P<0.05). The use of GnRH to induce an accessory CL in buffaloes increased the conception and birth rates. Thus, the increase of the cost of Ovsynch protocol with the thirty dose of GnRH is rewarded by the increment on conception and birth rates and reduction of days open.

Luteinizing hormone release after administration of the gonadotropin-releasing hormone agonist Fertilan (goserelin) for synchronization of ovulation in pigs

The generic GnRH agonist, Fertilan (goserelin), was tested for the ability to induce an LH surge and ovulation in estrus-synchronized gilts. Three experiments were performed to 1) examine the effect of various doses of Fertilan on secretion of LH in barrows, to select doses to investigate in gilts (Exp. 1); 2) determine doses of Fertilan that would induce a preovulatory-like rise of LH in gilts (Exp. 2); and 3) determine the time of ovulation after Fertilan treatment (Exp. 3). In Exp. 1, 10 barrows were injected on d 1, 4, 7, 10, and 13 with 10, 20, or 40 microg of Fertilan; 50 microg of Gonavet (depherelin; GnRH control) or saline (negative control); and sequential blood samples were collected for 480 min. There was a dose-dependent stimulation (P < 0.05) of LH release. Maximal plasma concentrations of LH (LH(MAX)) were 2.1 +/- 0.2, 4.1 +/- 0.3, 2.6 +/- 0.4, and 3.4 +/- 0.3 ng/mL after 10, 20, and 40 microg of Fertilan and 50 microg of Gonavet, respectively, and duration of release was 78 +/- 9, 177 +/- 12, 138 +/- 7, and 180 +/- 11 min, respectively. Fertilan doses of 10 and 20 microg were deemed to be the most suitable for testing in gilts. In Exp. 2, 12 gilts received (after estrus synchronization with Regumate and eCG) injections of 10 or 20 microg of Fertilan or 50 microg of Gonavet 80 h after eCG to stimulate a preovulatory-like LH surge and ovulation. An LH surge was induced in 3 of the 4 gilts in both of the Fertilan groups and in all of the Gonavet-treated gilts. Characteristics of induced release of LH did not differ among groups: LH(MAX), 5.0 +/- 0.9 vs. 4.6 +/- 1.8 vs. 6.6 +/- 1.1 ng/mL; duration, 11.7 +/- 2.0 vs. 12.3 +/- 2.2 vs. 14.3 +/- 0.5 h; interval from GnRH injection to LH(MAX), 4.0 +/- 2.0 vs. 6.7 +/- 1.3 vs. 5.8 +/- 1.6 h. In Exp. 3, estrus-synchronized gilts were injected with 20 microg of Fertilan (n = 8) or 50 microg of Gonavet (n = 4), and the time of ovulation was determined by repeated endoscopic examination. Time of ovulation ranged from 34 to 42 h postGnRH; however, ovulation occurred earlier in the Gonavet compared with the other groups (P < 0.05). Results of these experiments indicate that 1) barrows are an appropriate model for determining GnRH doses that can be effective in inducing a preovulatory-like LH surge in females; 2) the generic GnRH agonist Fertilan, at doses of 10 to 20 microg, can stimulate an LH surge in gilts, with subsequent ovulation; and 3) Fertilan at doses of 10 and 20 microg should be examined further for use in fixed-time insemination protocols.

Dose–response relationship of 15α-hydroxylated sex steroids to gonadotropin-releasing hormones and pituitary extract in male sea lampreys ( Petromyzon marinus)

The sea lamprey ( Petromyzon marinus) is one of the earliest extant vertebrates for which the hypothalamic-pituitary-gonadal (HPG) axis has been shown to control and regulate reproduction in a similar fashion to gnathostome vertebrates. While the two forms of gonadotropin-releasing hormones in the sea lamprey (GnRH I and GnRH III) have been studied extensively, their in vivo effect on synthesis of 15α-hydroxytestosterone (15α-T) and 15α-hydroxyprogesterone (15α-P) have only been partially characterized. In the present study, plasma concentrations of 15α-T and 15α-P were measured in prespermiating sea lampreys that were given a single injection of either GnRH I or GnRH III in doses ranging from 5 to 100 μg/kg, or of pituitary extract (as a source of gonadotropin). Plasma was sampled at 1–6 h and 6–48 h post-injection, in separate experiments, in order to characterize the peak and duration of responses. 15α-T plasma concentrations increased slightly in response to all three treatments, but not in a dose-dependent manner, and the timing of peak concentrations varied between doses. However, 15α-P plasma concentrations showed a greater range of response (between 1 and 100 ng/ml) and were clearly correlated with the injection dose. Plasma concentrations of 15α-P also responded to far lower doses of GnRH I and GnRH III than any other steroid previously investigated in lampreys. The plasma concentrations of 15α-P peaked at 6 h after injection for all three treatments, and levels reached a mean of 53.1 ng/ml. In female lampreys that were injected twice with 50 μg/ml GnRH I or III, 15α-T concentrations did not exceed 0.5 ng/ml and 15α-P concentrations did not exceed 1 ng/ml. These results lend further support to the hypothesis that 15α-P plays an important role in the reproductive endocrinology of male lampreys.

The effect of GnRH, eCG and progestin type on estrous synchronization following laparoscopic AI in ewes

The aim of the experiment was to evaluate the effects of GnRH and/or eCG and progestin type (implant versus CIDR) on the induction of estrus and pregnancy rate following laparoscopic AI (LAI) with frozen semen. In the first trial, ewes ( n = 129) were treated with norgestomet implants for 14 days. At implant removal ewes received eCG (400 IU) and/or GnRH (25 μg) 36 h after removal, resulting in control, eCG, GnRH, and eCG/GnRH groups ( n = 30–34/group). In trial 2, ewes ( n = 36) were treated with intravaginal fluorogestone acetate sponges (FGA) or CIDR for 12 days. After withdrawal, half of the ewes from each progestin group received eCG (400 IU), resulting in sponge, sponge/eCG, CIDR and CIDR/eCG groups ( n = 8–10/group). In both trials, estrous activity was assessed using a vasectomized ram from the time of progestin removal to laparoscopic AI with frozen semen 58–60 h (trial 1) or 54–56 h (trial 2) following cessation of treatment. In trial 1, GnRH decreased ( P < 0.05) the percentage of ewes in estrus (GnRH, 75.8% versus control, 93.8% versus eCG/GnRH, 94.1%), however pregnancy rates were similar in all groups (control, 53.1%; eCG, 70.0%; GnRH, 51.5%; eCG/GnRH, 55.9%, respectively). In trial 2, neither the type of progestin nor eCG treatment effected the percentage of ewes in estrus (sponge, 75.0%; sponge/eCG, 100.0%; CIDR, 100.0%; CIDR/eCG, 90.0%). However, pregnancy rates following LAI were higher ( P < 0.05) when ewes were treated with eCG (progestin + eCG, 73.7% versus progestin alone, 41.2%). Results demonstrate that the source of progestin does not influence the expression of estrus or the proportion of ewes pregnant following LAI. When progestin treatment protocols are used in combination with eCG, pregnancy rates can be increased. A dose of GnRH near the end of progestin treatment may decrease the estrous response, by inducing ovulation before normal expression of estrus.

P-759: Low dose GnRH-a protocol versus GnRH antagonist protocol in the management of poor responders undergoing IVF

P-759: Low dose GnRH-a protocol versus GnRH antagonist protocol in the management of poor responders undergoing IVF

P-15: Early substitution of low dose GnRH antagonist improves ART outcomes in normal responders who have failed a standard, long GnRH agonist protocol

P-15: Early substitution of low dose GnRH antagonist improves ART outcomes in normal responders who have failed a standard, long GnRH agonist protocol

Actions of gonadotropin-releasing hormone analogues in pituitary gonadotrophs and their modulation by ovarian steroids

Recently, GnRH antagonists (GnRHant) like cetrorelix and ganirelix have been introduced in protocols of controlled ovarian hyperstimulation for assisted reproductive techniques to prevent premature luteinizing hormone (LH) surges. Here we tested, whether the actions of cetrorelix and the GnRH agonist (GnRHag) triptorelin in gonadotrophs are dependent on the steroid milieu. Furthermore, we characterized the actions of cetrorelix and triptorelin on LH secretion and the total LH pool. Female rat pituitary cells were treated either with 0.1 nM triptorelin for 1, 2, 4 and 6 days or for 1, 3, 5 and 6 h or with 1, 10 or 100 nM cetrorelix for 1, 2, 3 and 5 h or for 10 min. Cells were stimulated for 3 h with different concentrations of GnRH (10 pM–1 μM). For analysis of the total LH pool, which is composed of stored and released LH, cells were lysed with 0.1% Triton X-100 at −80 °C overnight. To test, whether the steroid milieu affects the actions of cetrorelix and triptorelin, cells were incubated for 52 h with 1 nM estradiol (E) alone or with combinations of 100 nM progesterone (P) for 4 or 52 h, respectively. Cells were then treated with 0.1 nM triptorelin for 9 h or 1 nM cetrorelix for 3 h and stimulated for 3 h with different concentrations of GnRH (10 pM–1 μM). The suppressive effect of triptorelin on LH secretion was fully accomplished after 3 h of treatment, for cetrorelix only 10 min were sufficient. The concentration of cetrorelix must be at least equimolar to GnRH to block LH secretion. Cetrorelix shifted the EC50s of the GnRH dose–response curve to the right. Triptorelin suppressed total LH significantly (from 137 to 36 ng/ml) after 1 h in a time-dependent manner. In contrast, only high concentrations of cetrorelix increased total LH. In steroid treated cells the suppressive effects of triptorelin were more distinct. One nanomolar cetrorelix suppressed GnRH-stimulated LH secretion of cells not treated with steroids from 10.1 to 3.5 ng/ml. In cells, additionally treated with estradiol alone or estradiol and short-term progesterone, LH levels were higher (from 3.5 to 5.4 or 4.5 ng/ml, respectively). In cells co-treated with estradiol and progesterone for 52 h LH secretion was only suppressed from 10.1 to 9.5 ng/ml. Steroid treatments diminished the suppressive effect of cetrorelix on LH secretion. In conclusion, the depletion of the total LH pool contributes to the desensitizing effect of triptorelin. The actions of cetrorelix and triptorelin are dependent on the steroid milieu.

Dose dependent effect of GnRH analogue on pregnancy rate of repeat breeder crossbred cows

The aim of this study was to investigate the effect of treating repeat breeder dairy crossbred cows with different doses of GnRH analogue through i.m. at the time of artificial insemination, on pregnancy rates from their first service after treatment and overall pregnancy rates. One hundred and thirty seven crossbred dairy cows with a history of repeat breeding and eligible after 6–8 infertile services but clinically free of diseases were selected for the study. The animals were randomly divided into three groups. Group 1 ( n = 55) cows were treated intramuscularly with each 20 μg Buserelin-acetate (Receptal, Hoechst Roussel Vet GmbH) at the time of artificial insemination. Group 2 ( n = 40) cows were treated intramuscularly with each 10 μg Buserelin-acetate at the time of artificial insemination. Group 3 ( n = 42) cows were treated intramuscularly with saline as control at the time of artificial insemination. The first service pregnancy rates in Groups 1–3 were 45, 25 and 17%, respectively. Similarly, the overall conception rates in Groups 1–3 were 87, 58 and 48%, respectively. The results indicated that the pregnancy rate in crossbred cows could be improved by the GnRH treatment. The higher dose of GnRH significantly increased ( P < 0.05) the first service as well as overall pregnancy rate in a dose dependent manner in repeat breeder crossbred cow bred previously 6–8 times unsuccessfully.

Effects of dose and duration of continuous GnRH-agonist treatment on induction of estrus in beagle dogs: Competing and concurrent up-regulation and down-regulation of LH release

Dose–response estrus-induction trials were conducted during anestrus in 93 treated and 6 control bitches, a continuous administration of the GnRH-agonist lutrelin with a potency 150 × GnRH, and at six different doses from 0.2 to 4.8 μg/kg/d for 7–14 days in 15 groups of six to eight dogs each in defined stages of natural or pharmacologically determined anestrus. Agonist treatment induced clinically and cytologically normal proestrus (in 89% of cases) within 4.8 ± 0.2 × days, and resulted in behavioral estrus (71%), spontaneous late-proestrus LH (and FSH) surges, ovulation (59%) and pregnancy (44%) in a dose dependent manner. Outcomes of ovulation and pregnancy in most cases required that the dose be sufficiently large enough to routinely stimulate a large initial increase in LH and FSH (i.e., ≥0.6 μg/kg/d), and of sufficient duration (i.e., >7 days) to ensure that supra-basal gonadotropin levels persistedntil no longer needed for spontaneous continuation of an induced proestrus. Success additionally required that the GnRH dose be modest enough (i.e., <1.8 μg/kg/d) to not excessively down-regulate spontaneous pre-ovulatory surge release of gonadotropin or be removed shortly before or at the time when the LH surges typically occurred (10–13 days after initiation of treatment). The 1.8 μg dose was compared to saline to assess the time course of its down-regulation action on serum LH in six ovariohysterectomized bitches compared to four saline-related controls. Results in intact bitches receiving the 1.8-μg doses demonstrated an LH-releasing effect for 10–11 days that overlapped a period of obvious down-regulation seen with the same dose after 3 days in the ovariohysterectomized bitches. In the latter, however, complete down-regulation to anestrus-like values did not occur until after 18–21 days of treatment. A dose of 0.6 μg/kg/d for 12 days yielded the best estrus-induction results, including pregnancy rates of 100% in six bitches treated in natural-anestrus bitches, six bitches in which anestrus had been advanced by a luteolytic prostaglandin treatment and in six bitches in which anestrus had been extended by progesterone implants administered for 3 months. Although lutrelin is not commercially available, these results provide guidelines for the development of estrus-inducing protocols with other GnRH-agonists of known biopotencies.

Time and Incidence of Ovulation and Conception Rates After Incorporating Estradiol Cypionate into a Timed Artificial Insemination Protocol

Two experiments were conducted to determine the effect of estradiol cypionate (ECP), when incorporated into a conventional GnRH-PGF2α-GnRH timed artificial insemination protocol (Ovsynch), on systemic estradiol (E2), time and incidence of ovulation, luteal development, and conception rate in Holstein cows. Our objective was to determine if administration of 0.25mg of ECP at the time of the second GnRH injection would effectively synchronize ovulation and increase conception rate. In Experiment 1, lactating Holstein cows (n = 23; 58.7±1.2 d in milk) were synchronized with PGF2α (at d −10). Ten days later, Ovsynch was initiated with the administration of 100μg of GnRH (d 0) followed by PGF2α on d 7. On d 9, cows were assigned randomly to be treated with either GnRH + 0.25mg of ECP (OVS-ECP; n = 11) or GnRH and 1mL of cottonseed oil (OVS-C; n = 12). Ovarian activity was monitored by ultrasonography on d 0, 7, and 9. To determine the time of ovulation, ultrasound examinations were conducted at 12 and 20h posttreatment and then at least every 3h until either 36h posttreatment or ovulation was observed. Blood samples were collected on d 0, 7, 9, and 16 for progesterone analysis. Blood samples also were collected at the time of treatment (d 9, 0h) and at 6, 12, 20, and 28h for E2 analysis. Incidence of ovulation did not differ between treatments. Mean ovulation time relative to the second GnRH administration was similar between treatments. Serum progesterone concentration did not differ between treatments at any time. Serum E2 concentration was not different at the time of treatment (0h); however, mean E2 concentration was greater for the OVS-ECP group at 6 and 12h after treatment compared with OVS-C. In Experiment 2, lactating dairy cows (n = 333) in 3 commercial herds were randomly assigned to OVS-ECP (n = 169) or OVS-C (n = 164). Cows were inseminated 22 to 24h posttreatment. Conception rates did not differ between treatments. Estradiol cypionate treatment was successful in increasing serum E2 when administered at the time of the second dose of GnRH in the Ovsynch protocol. Conception rates, however, were not affected by treatment.