Gonadotropin-releasing Hormone Injection Research Articles

Evidence of estrus before CIDR insertion does not influence pregnancy rate to fixed-timed artificial insemination in beef heifers

Protocols used for fixed-timed artificial insemination strive to synchronize growth of follicular waves and commonly do so by administration of gonadotropin-releasing hormone (GnRH) at the beginning of the treatment. The stage of the cycle at the time of GnRH injection influences the proportion of animals that respond, and cows respond more consistently than heifers. Variability in response to GnRH has been offered as an explanation for why why short-term fixed-timed insemination protocols tend to be less effective in heifers than cows. The dairy industry has used prostaglandin (PG) to "pre-synchronize" cow ovulation before a protocol to improve the proportion of cows that initiate a new wave of follicular growth. Because of the additional cost in time and product, the beef industry has been reluctant to explore this approach. South Dakota State University research has indicated that variability in onset of estrus was reduced when PG was given 3 days before a controlled internal drug release (CIDR) protocol. A reduction in variability of the onset of estrus may improve response to fixed-time artificial insemination. The objective of this study was to determine if the onset of estrus prior to a PG 6-day CIDR protocol would improve pregnancy rates to fixed-time artificial insemination in beef heifers.

Between-female variation in house sparrow yolk testosterone concentration is negatively associated with CYP19A1 (aromatase) mRNA expression in ovarian follicles

Maternally-derived yolk androgens influence the development and long-term phenotype of offspring in oviparous species. Between-female variation in the amounts of these yolk androgens has been associated with a number of social and environmental factors, suggesting that the variation is adaptive, but the mechanisms behind it are unknown. Using two different approaches, we tested the hypothesis that variation in yolk androgen levels across individuals is associated with variation in their capacity to synthesize androgens. First, we injected female house sparrows with exogenous gonadotropin-releasing hormone (GnRH) to maximally stimulate ovarian steroidogenesis. Second, we collected pre-ovulatory follicle tissue and quantified the mRNA expression of four key enzymes of the steroid synthesis pathway: steroidogenic acute regulatory protein (StAR), cytochrome P450-side chain cleavage enzyme (CYP11A1), 17β-hydroxysteroid dehydrogenase (HSD17B1), and aromatase (CYP19A1). Thirty minutes after GnRH injection, androgen concentrations in both the plasma and in the yolks of pre-ovulatory follicles were significantly elevated compared to controls. However, this measure of steroidogenic capacity did not explain variation in yolk testosterone levels, although physiological differences between house sparrows and more widely studied poultry models were revealed by this approach. Steroidogenic enzyme mRNA levels were detectable in all samples and were significantly lower in the most mature pre-ovulatory follicles. Of the four measured genes, CYP19A1 expression exhibited a significant negative relationship with yolk testosterone concentrations in laid eggs, revealing a key mechanism for between-female variation in yolk testosterone. Furthermore, this suggests that any factors which alter the expression of CYP19A1 within an individual female could have dramatic effects on offspring phenotype.

Testosterone production, sexually dimorphic morphology, and digit ratio in the dark-eyed junco

The hormonal environment an individual experiences during development can have lasting effects on behavior, morphology, and physiology. However, measuring endogenous hormone exposure during early embryonic development and relating it to adult phenotype has proved to be challenging. The relative length of digit 2 to digit 4 (2D:4D) in adults is thought to reflect the relative concentration of androgens and estrogens during development and has been used as a morphological proxy of developmental hormone exposure, enabling the exploration of the relationships between individual differences in hormone exposure and phenotype. Here, we use this approach and ask whether 2D:4D relates to the responsiveness of the adult hypothalamicpituitary-gonadal axis and to sexually dimorphic structures (wing, tail, and tarsus length) in a common songbird, the dark-eyed junco (Junco hyemalis). Among males, we found a negative relationship between 2D:4D and the ability to elevate testosterone in response to a physiological challenge, an injection of gonadotropin-releasing hormone. We also found age- and sex-specific relationships between 2D:4D and wing, tail, and tarsus length. We found a positive relationship between 2D:4D and body size measures in females, and second-year and older males, but a negative relationship in first-year males. We conclude that individual variation in exposure to developmental hormones, as reflected by 2D:4D, is correlated with adult hormone production ability and sexually dimorphic morphology in adulthood, suggesting that endogenous variation in steroid hormone exposure may have long-term consequences similar to those seen in experimental manipulations. Key wor ds: digit ratio, gonadotropinreleasing hormone, junco, maternal hormones, testosterone, 2D:4D. [Behav Ecol]

Utility of Basal Luteinizing Hormone Levels for Detecting Central Precocious Puberty in Girls

The hallmark of puberty is the progressive increase in gonadotropin-releasing hormone (GnRH) activity, reflected by an increase in the circulating concentration of luteinizing hormone (LH). The GnRH stimulation test is widely used in the evaluation of precocious puberty. The aim of our study was to assess the diagnostic utility of basal LH for the diagnosis of central precocious puberty (CPP) in girls. A total of 803 girls were referred to Ajou University Hospital for evaluation of precocious puberty between 2008 and 2011. All subjects underwent GnRH-stimulation tests as part of their evaluation. Serum LH and follicle stimulating hormone (FSH) were measured by immunoradiometric assay before and after the GnRH injection. Of the 803 subjects, 505 (62.9%) were included in the pubertal response group and 298 (37.1%) were in the prepubertal response group. Basal LH level was identified as a significant predictor for CPP. Based on the ROC curve, the optimal cut off point of basal LH related to 'pubertal response' was 1.1 IU/l, which was associated with 69.1% sensitivity and 50.5% specificity, with an area under the ROC curve of 0.620 (95% CI, 0.581-0.660). It is concluded that a single basal LH measurement can be used as a screening test to identify girls with CPP and to determine who should undergo GnRH stimulation test.

Testosterone elevation and response to gonadotropin-releasing hormone challenge by male Northern Cardinals (Cardinalis cardinalis) following aggressive behavior

There is much discrepancy about the relationship between testosterone (T) and male aggressive behavior. For example, in birds, males of many species significantly elevate T levels during inter-male conflict. However, this is not universal, and in species where males typically do not elevate T during aggressive interactions, concentrations of the hormone are often assumed to be circulating at maximum levels. We examined if male northern cardinals (Cardinalis cardinalis) significantly elevated T during simulated territorial intrusions (STIs). We also examined if individuals had the capacity to further elevate T levels in response to gonadotropin-releasing hormone (GnRH) injections immediately after an aggressive encounter. Our results indicate that male cardinals do not significantly elevate T levels in response to STIs, but have the physiological capacity to significantly elevate T in response to GnRH injections following aggressive interactions. This implies that T levels of individuals captured during STIs were not at maximum concentrations. However, additional findings in this study also suggest the possibility that prolonged social instability could elicit significant elevations in T in males of this species, warranting further investigation.

Optimizing artificial insemination on swamp buffalo (Bubalus bubalis) through synchronization of estrus and ovulation

Artificial insemination (AI) program in swamp buffalo will be more efficient by implementing synchronization of estrus and ovulation. By synchronizing of ovulation, AI can be done at a fixed time schedule without concerning to estrus detection. Gonadotropin Releasing Hormone (GnRH) and human chorionic gonadotropin (hCG) have been used in protocols of estrus synchronization to induce ovulation. A study of AI in swamp buffalo was conducted on 83 buffaloes to evaluate the impact of protocol of estrus synchronization on reproductive efficiency of swamp buffalo. The three protocols used were Ovsynch (GnRH-PGF2α-GnRH-AI), convensional (PGF2a-PGF2a-AI) and Select-Synch (GnRH-PGF2a-AI). Inducing of ovulation were done by administration of GnRH or hCG after prostaglandin (PGF2α) injection. AI was done at 18 and 24 hour after the second GnRH injection (66 hours and 72 hours after PGF2α injection) for Ovsynch method and 72 hours after the last PGF2α injection for convensional and Select-Synch methods. Parameters observed were percentage of estrus and pregnancy from the three estrus synchronization protocols and the differences were analysed by statistics. All of buffaloes (100%) in the three synchronization protocols showed estrus behavior prior to AI. The percentage of pregnancy was 64.71; 77.14 and 83.87% for the Ovsynch, convensional and Select-synch respectively and there was no significantly different (P > 0.05) among the three protocols. hCG administration after the last PGF2α also did not affect pregnancy rate, ie: 76.47 vs 77.78% (with hCG vs without hCG) for the convensional and 88.24 vs 78.57% for the Select-Synch. It is concluded that the synchronization of estrus protocols in this study can synchronize the estrous and ovulation and AI can be done in a fixed-timed and could reach better pregnancy rate of swamp buffalo. Key Words: Swamp Buffalo, Synchronization, Estrus, Ovulation, AI

Progesterone concentrations and pregnancy rates of repeat breeder cows following postinsemination PRID and GnRH treatments*

The objective of this study was to determine the effects of progesterone (PRID) application and gonadotropin-releasing hormone (GnRH) injection after artificial insemination on serum progesterone concentration and pregnancy rates in repeat breeder cows. In group 1, repeat breeder cows received an injection of GnRH on day 12 after artificial insemination. In group 2, repeat breeder cows received PRID from day 4 to day 11; group 3 received PRID from day 11 to day 18. Blood samples were obtained from all treated cows to assay serum progesterone concentrations on application days, 7 days after application, and 21 days after artificial insemination. In the control group repeat breeder cows did not receive any treatment. Blood samples were obtained from all control repeat breeder cows periodically after artificial insemination. Pregnancy rates were 20% in group 1, 26.6% in group 2, 40% in group 3, and 20% in the control group. Serum progesterone concentrations were significantly higher in group 1 and group 3 (P < 0.05) than the control group, 7 days after application. Application of PRID and GnRH after artificial insemination did not significantly improve pregnancy rates, despite the fact that serum progesterone concentrations were higher in treatment groups.

157 PREGNANCIES AND CALVES AFTER TRANSFER OF IN VITRO-PRODUCED RIVER BUFFALO EMBRYOS AFTER CRYOPRESERVATION

In the buffalo, the use of embryo-based biotechnologies for breeding and genetic improvement is still very limited because multiple-ovulation embryo transfer delivers poor results compared with cattle and in vitro embryo production has been used mainly for research purposes. At present, very few reports are available on the transfer of in vitro-produced (IVP) and cryopreserved buffalo embryos. Therefore, the scope of this work was to perform a pilot study to evaluate the viability of frozen-thawed IVP embryos by nonsurgical embryo transfer to recipients in an IVF-embryo transfer program on a farm located on the north coast of Colombia, South America. Buffalo oocytes were recovered at the slaughterhouse from selected donors, matured in vitro for 18 to 20 h in TCM-199 + 10% FCS and 0.5 IU of FSH and 0.5 IU of LH in 5% CO2 at 38.5°C. Four different bulls were used for IVF. After thawing, the semen was separated on a Percoll® gradient and then diluted into SOF-IVF media supplemented with 1 μg mL–1 of heparin and phenylalanine. Presumptive zygotes were cultured in modified SOF supplemented with MEM amino acids for 6 days. Half of the medium was replaced on Day 4 and 6. Developing embryos were selected for freezing on Day 6 and 7. Grade 1 embryos were frozen at the blastocyst stage by slow cooling in 10% glycerol or 1.5 M ethylene glycol. Recipients (heifers n = 79 and uniparous cows n = 17) were synchronized using the CIDR-Synch protocol: on Day 0, gonadotropin-releasing hormone was injected and a CIDR was inserted; on Day 7, prostaglandin F2α was administered; on Day 9, the CIDR was removed; on Day 11, a second injection of gonadotropin-releasing hormone was given; and on Day 17, the embryo was transferred. Each female received, nonsurgically, 1 or 2 embryos in the ipsilateral horn to the functional corpus luteum evaluated by ultrasonography. Pregnancies were evaluated by ultrasonography 30 days after transfer and confirmed by rectal palpation 30 days later. This work was performed in 2 successive experiments during the breeding seasons (January and December, respectively). Overall, 96 recipients were transferred, with 136 embryos obtaining 23 pregnancies (24.2%). There were no statistical differences in pregnancy rate between heifers and cows (25.3 vs 17.7%) and between single (n = 56) and double (n = 39) embryo transfers (21.4 vs 27.5%) by chi square test (P &gt; 0.05). To date, 4 females and 5 males have been born by spontaneous calving (1 stillborn male due to dystocia), 3 pregnancies have been aborted (13%) and 11 pregnancies are ongoing (&gt;7 months). The pregnancy rate obtained in this study in farm conditions (24.2%) is lower than generally obtained with frozen IVP cattle embryos, but it is still a good result in buffalo, where even conventional AI provides a lower success rate as compared with cattle. Finally, this work demonstrates that in vitro embryo production can be successfully implemented in buffalo breeding programs for the exploitation of superior genetics. This work was supported by Regione Lombardia, Por Fers 2007–2013, n°13827741, InnovaB.

Role of Testosterone in Stimulating Seasonal Changes in a Potential Avian Chemosignal

Songbird preen oil contains volatile and semivolatile compounds that may contain information about species, sex, individual identity, and season. We examined the relationship between testosterone (T) and the amounts of preen oil volatile and semivolatile compounds in wild and captive dark-eyed juncos (Junco hyemalis). In wild males and females, we observed an increase in volatile compound relative concentration early in the breeding season. This increase mirrored previously described seasonal elevation in T levels in wild males and females, suggesting a positive relationship between hormone levels and preen gland secretions, and a possible role for these secretions in signaling receptivity. In females, the greatest relative concentrations of most compounds were observed close to egg laying, a time when steroid hormones are high and also the only time that females respond to an injection of gonadotropin-releasing hormone with a short-term increase in T. In a study of captive juncos held on short days, we asked whether the seasonal increases observed in the wild could be induced with experimental elevation of T alone. We found that exogenous T stimulated the production of some volatile compounds in non-breeding individuals of both sexes. However, of the 15 compounds known to increase during the breeding season, only four showed an increase in relative concentration in birds that received T implants. Our results suggest that testosterone levels likely interact with other seasonally induced physiological changes to affect volatile compound amounts in preen oil.

Competitive females are successful females; phenotype, mechanism, and selection in a common songbird

In a variety of taxa, male reproductive success is positively related to expression of costly traits such as large body size, ornaments, armaments, and aggression. These traits are thought to improve male competitive ability, and thus access to limited reproductive resources. Females of many species also express competitive traits. However, we know very little about the consequences of individual variation in competitive traits and the mechanisms that regulate their expression in females. Consequently, it is currently unclear whether females express competitive traits owing to direct selection or as an indirect result of selection on males. Here we examine females of a mildly dimorphic songbird (Junco hyemalis) to determine whether females, show positive covariance in traits (morphology and behavior) that may be important in a competition. We also examine whether trait expression relates either to testosterone (T) in terms of mechanism or to reproductive success in terms of function. We found that larger females were more aggressive and that greater ability to produce T in response to a physiological challenge consisting of a standardized injection of gonadotropin releasing hormone (GnRH) predicted some measures of female body size and aggression. Finally, we found that aggressive females had greater reproductive success. We conclude that testosterone may influence female phenotype and that females may benefit from expressing a competitive phenotype. We also suggest that the mild dimorphism observed in many species may be due in part to direct selection on females rather than simply a correlated response to selection in males.

Non-breeding gonadal testosterone production of male and female Northern Cardinals ( Cardinalis cardinalis) following GnRH challenge

Yearly, testosterone (T) levels fluctuate as many vertebrates cycle through reproductive and non-reproductive periods. Among many temperate birds, it is well established that levels of T peak as gonads recrudesce for breeding and then fall as gonads regress prior to the non-breeding season. While the tissues producing breeding season T are well studied, the tissues responsible for non-breeding T have received less investigative attention. We examined the ability of male and female Northern Cardinals ( Cardinalis cardinalis) to elevate gonadal T following standardized injections of gonadotropin-releasing hormone (GnRH) across three non-breeding seasons. Males and females were capable of significantly elevating gonadal T production following GnRH injections during periods of reproductive quiescence. The magnitude of T elevation varied across the non-breeding season, but not between sexes. To our knowledge, this is the first report of a significant increase in gonadal T production following GnRH injections administered in the non-breeding season.

Comparison of the CIDR Select and 5-day Select Synch + CIDR protocols that included limited estrus detection and timed insemination for synchronizing estrus in beef heifers

The objective of this study was to compare AI pregnancy rates between the 5-d Select Synch + CIDR (5dCIDR; CIDR = controlled internal drug-release insert) and CIDR Select (CS) programs in replacement beef heifers with a limited period of estrus detection and AI followed by a timed insemination (TAI) of heifers not exhibiting estrus. Crossbred beef heifers (n = 318) were equally and randomly assigned to either the 5dCIDR or CS treatment. The 5dCIDR treatment consisted of gonadotropin-releasing hormone (GnRH) at CIDR insertion, followed 5 d later by CIDR removal and administration of two 25-mg doses of prostaglandin F2α (PGF) administered approximately 12 h apart. The CS treatment consisted of insertion of a CIDR for 14 d, an injection of GnRH 9 d after CIDR removal, and administration of PGF 7 d following GnRH. In both treatments, heifers were detected for estrus for 52 h following PGF, and those exhibiting estrus were inseminated based on the AM/ PM rule. Heifers not observed in estrus were TAI 72 h after PGF, concurrent with GnRH administration. Ten days following TAI, bulls were placed with the heifers for approximately 45 d. Estrus response tended (P = 0.07) to be greater in the CS treatment than in the 5dCIDR treatment. However, conception rate of heifers exhibiting estrus, TAI conception rate, overall AI pregnancy rate, and breeding season pregnancy rate did not differ (P > 0.10) between treatments. In conclusion, 5dCIDR and CS protocols were equally effective at synchronizing estrus in replacement beef heifers.

Effects of Induction of Ovulation with GnRH or hCG on Follicular and Luteal Blood Flow in Holstein–Friesian Heifers

The objective of this study was to compare the effects of gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) on follicular blood flow (FBF) during the pre-ovulatory period and on luteal blood flow (LBF) during dioestrus in Holstein-Friesian heifers. Twelve animals were randomly divided into two groups and treated with either intramuscular injection of 100 μg GnRH or intravenous (IV) injection of 5000 IU hCG on Day 0 (oestrus, 48 h after administration of PGF(2α) ) to induce ovulation. Follicular size (FS), FBF and time of ovulation were recorded with colour Doppler sonography at 0, 1, 3, 6, 12 and 24 h after GnRH and hCG treatment. Luteal size (LS) and LBF were investigated on Day 9 and 12 after ovulation. Plasma samples were taken to determine total oestrogens (E(tot) ) and progesterone (P(4) ) after each examination. Ovulation occurred between 24 and 48 h after treatment in all animals. No difference (p > 0.05) was observed in FS between the two treatment groups. Follicular blood flow was higher in the hCG group than that was in GnRH group at 1 h after treatment (p < 0.01). Total oestrogens were also higher (p < 0.01) in the hCG group than GnRH group; however, this difference was only obvious at 12 h after treatment. No difference (p > 0.05) was observed in LS, LBF or P(4) levels on Day 9 and 12 between treatment groups. In conclusion, the results suggest that induction of ovulation with hCG and GnRH has a temporary effect on FBF and oestrogen levels while no effect on the size of corpora lutea, LBF and P(4) levels was observed.

Optimizing a new 5-day CIDR-CO-Synch timed artificial insemination program

The 7-day CO-Synch + CIDR protocol is a popular ovulation-synchronization program used by cow-calf producers to facilitate artificial insemination (AI). A progesterone- impregnated controlled internal drug release (CIDR) insert is placed intravaginally and an injection of gonadotropin-releasing hormone (GnRH) is given. After 7 days, prostaglandin F2α(PGF2α) is administered and the CIDR insert is removed. Between 58 and 72 hours after insert removal, cows are inseminated after another injection of GnRH to induce ovulation. Timed AI pregnancy rates generally have ranged from 40 to 60% when suckled cows are treated with the 7-day CO-Synch + CIDR protocol.

Male Hypogonadism: Childhood Diagnosis and Future Therapies

Male hypogonadism results from inadequate testicular function manifested by the impairment of both testosterone secretion and spermatogenesis. Hypogonadism has several etiologies. Hypogonadotropic hypogonadism (HH) results from hypothalamic–pituitary disorders leading to a complete or partial deficiency in gonadotropin-releasing hormone (GnRH) secretion from hypothalamic neurons, or gonadotropin secretion from anterior pituitary, or defects in GnRH receptor at the pituitary. All situations result in low or normal serum gonadotropin levels and low serum testosterone levels. Congenital HH can occur isolated (idiopathic HH) or in association with olfactory dysfunction (Kallmann’s syndrome). Gonadotropin deficiency can also occur with other pituitary hormone deficiencies. Most of the congenital isolated HH are still idiopathic. However, defects in more than ten genetic loci with multiple modes of inheritance, accounting for monogenic and occasionally oligogenic presentations were found in approximately 30% of cases. Acquired HH results from a hypothalamic–pituitary structural lesion as well as from tumors, trauma, autoimmunity or radiation. Hypergonadotropic hypogonadism is characterized by elevated serum gonadotropin levels due to testicular disorders, chromosomal abnormalities (Klinefelter syndrome), genetic syndromes as well as acquired conditions (autoimmunity, chemotherapy or radiation therapy). The main clinical feature of a male infant with hypogonadism is micropenis associated with or without cryptorchidism. The diagnosis of HH at childhood is difficult and usually postponed until adult age. At pubertal age, the differential diagnosis between the constitutional delay of growth and puberty, and HH is tricky and no hormonal test can consistently distinguish between these two disorders with 100% sensitivity and specificity; therefore, clinical follow-up is essential. Optimal management of male hypogonadism depends of the underlying etiology. Genetic tests are now available to detect genetic mutations in candidate genes essential for hypothalamic–pituitary axis function. Infants with micropenis require testosterone or dihydrotestosterone therapy to increase penile length. The first-line therapy for cryptorchidism is orchiopexy. Puberty should be induced with a low dose of testosterone and fertility could be achieved with chorionic gonadotropin hormone, recombinant luteinizing hormone and follicle stimulating hormone preparations or pulsatile GnRH injection. A small subset of HH patients may have a reversible phenotype enabling the withdrawal of medication in up to 10% of cases.

Central administration of growth hormone-releasing hormone and corticotropin-releasing hormone stimulate downstream movement and thyroxine secretion in fall-smolting coho salmon ( Oncorhynchus kisutch)

The ultimate signal triggering downstream migration in anadromous salmonids is unknown. A plasma surge of T 4 (T 4 surge) occurs during downstream migration in salmonids; however, the causal relationship between migratory behavior and the T 4 surge is not well known. We first examined the progression of smolt indicators (skin silvering, condition factor (CF), gill Na +, K +-ATPase (NKA) activity and plasma T 4 levels) in underyearling, fall-smolting coho salmon ( Oncorhynchus kisutch) from August to December. In November, the fish showed the characteristics of fully developed smolts, i.e. the skin completely covered with silvery scales, CF at a nadir, and peak NKA activity and plasma T 4 levels. Based on these results, we examined the effects of four neuropeptides, thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), growth hormone-releasing hormone (GHRH), and gonadotropin-releasing hormone (GnRH), on the downstream movement (negative rheotaxis) and T 4 surge in fully smoltified underyearling coho salmon. The experiment was run in circular-shaped channel tanks and the neuropeptide treatment was performed as intracerebroventricular (ICV) injections. ICV injection of GHRH and CRH stimulated both downstream movement and plasma T 4 level. TRH injection stimulated plasma T 4 level but suppressed downstream movement. GnRH injection had no effect. It is hypothesized that GHRH and CRH play key roles in triggering downstream migration of anadromous salmonids, and that the accompanying T 4 surge is a consequence of the neuroendocrine processes that trigger migration.

Mechanisms of FSH synthesis: what we know, what we don't, and why you should care

The pituitary gonadotropin hormones, FSH and LH, are key regulators of reproductive physiology. Though the two hormones are produced by the same cell type, often in response to the same endocrine and paracrine regulators, they sub-serve different biological functions and their synthesis and secretion are differentially regulated. This stems largely from differences in transcriptional, post-transcriptional, and post-translational regulation of their unique beta subunits. That is, both hormones are dimeric glycoproteins and share a common alpha subunit. Their unique beta subunits, however, derive from different genes encoding distinct proteins. Past and recent research indicates synthesis and release of the two hormones are subject to extensive and independent regulation. LH appears to be secreted predominantly via the regulated secretory pathway, whereas FSH release is largely constitutive. As such, investigations of FSH-beta subunit synthesis may lend direct insight into mechanisms underlying patterns of secreted FSH, more so than investigations of the LHbeta subunit. Here, we review recent investigations of transcriptional regulation of the FSH-beta subunit gene from different mammalian species, including humans. The results reveal both conserved and species-specific regulatory mechanisms that might contribute to inter-species variation in FSH release.

Roles of hCG in Advancing Follicular Growth to Ovulation after Concurrent Injections of PGF(2α) and GnRH in Postpubertal Holstein Heifers Bearing a CL.

A study was conducted to test the hypothesis that injecting Gonadotropin-releasing hormone (GnRH) concurrently with Prostaglandin F2 alpha (PGF2α) followed by an injection of human Chorionic Gonadotropin (hCG), would advance follicular growth to ovulation in Holstein heifers bearing a corpus luteum (CL). After manual examination of the CL, group 1 (PGF; n = 12) received an injection of PGF2α (25 mg, im). Group 2 (PGF + GnRH; n = 13) received an injection of GnRH (100 μg, im) immediately after an injection of PGF2α. Group 3 (PGF + GnRH + hCG; n = 12) received concurrent injections of PGF2α and GnRH followed with hCG (1500 IU, im) two days later. Follicular size and day of ovulation were monitored by daily ultrasonographic examination from days 1 to 10. Blood was collected on days-7, 0 (PGF2α administration), 2, and 7. Progesterone was not different (P > .05) on days-7, 0, and 2 between the experimental groups. However, it was higher (P < .005) in the PGF + GnRH + hCG group on day 7 compared to PGF + GnRH heifers, but not significantly higher than the PGF. Additionally, heifers in the PGF + GnRH + hCG group ovulated earlier (P < .05) than heifers in the PGF + GnRH and the PGF group. This data indicates that hCG advances follicular growth to ovulation in spite of high levels of progesterone when injected 48 h after concurrent treatments of GnRH and PGF2α on heifers bearing a CL.

Inherent capacity of the pituitary gland to produce gonadotropins is not influenced by the number of ovarian follicles ≥3 mm in diameter in cattle

We hypothesised that higher serum FSH concentrations in cattle with low v. high follicle numbers during follicular waves are caused by a different capacity of the pituitary gland to produce gonadotropins. Dairy cows with high (> or = 30; n = 5) and low (< or = 15; n = 5) follicle numbers were selected and serum concentrations of oestradiol and FSH during an oestrous cycle were measured. Cows were ovariectomised at oestrus and bled frequently up to 8 days after ovariectomy. After 33 days, cows were injected with gonadotropin-releasing hormone (GnRH) and bled intensively up to 8 h after GnRH injection. One day later, animals were injected with follicular fluid (FF) from bovine follicles and were bled intensively up to 2 days after the first injection. Serum concentrations of FSH and LH were measured. After 2 days, cows were killed and their pituitary glands collected. Prior to ovariectomy, serum oestradiol concentrations were similar between groups, whereas FSH concentrations were higher in cattle with low v. high numbers of follicles. No differences were detected in serum gonadotropin concentrations after ovariectomy, GnRH injection or FF challenge between groups. The results indicate that the inherent capacity of the pituitary gland to secrete gonadotropins does not differ between cattle with high v. low numbers of follicles during follicular waves.

Effect of some hormones on reproductive performance and some serum biochemical changes in synchronized black goats

In randomized block design, 58 indigenous black mountain goats were examined for the effect of different hormonal treatments in inducing oestrus on selected biochemical characteristics of blood serum that were (aspartate transaminase, AST. Alanine transaminase ALT, Akaline phosphatase, ALP, total protein, albumin and total cholesterol). The animals were randomly assigned into four groups according to their treatment. The control group (C) consisted of 10 females whereas the rest of the groups, each consisted of 12 females. The treatments included a double PGF2α (Dinoprost tromethamine) intramuscular injection (5 mg) at a time interval of 11 days plus an intramuscular injection of pregnant mare serum (PMSG) (400I. Uand 600I. U.) two days before second injection for (treatments, TI, T2) respectively. Treatment (T3) was as that of T1 except PMSG was not injected. T4 was treated as T3 plus an intramuscular injection of gonadotropin releasing hormone (GnRH) (12. 5µg) after 24 hours of second injection of PGF2α was added. The results indicated that oestrus was higher (P