Gonadotropin-releasing Hormone Group Research Articles

Endometrial Na +, K +-ATPase pump function and vasopressin levels during hysteroscopic surgery in patients pretreated with GnRH agonist

To investigate the effects of gonadotropin-releasing hormone (GnRH) analog pretreatment on endometrial Na+, K+-adenosine triphosphatase (ATPase) pump function and peripheral blood vasopressin levels, and their role in fluid absorption and mechanisms of hyponatremia in patients undergoing hysteroscopic endometrial ablation. Prospective, randomized, placebo-controlled study (Canadian Task Force classification I). University-affiliated hospital. Seventeen women with dysfunctional uterine bleeding. Nine women received a GnRH analog and eight received saline approximately 6 to 8 weeks before hysteroscopic ablation by electrosurgery. Both before randomization and immediately before surgery, endometrial biopsy samples were obtained and numbered consecutively without patient identification. Operative hysteroscopy was performed with glycine 1.5% mixed with 2% alcohol. The amount of irrigant and irrigant deficit; blood levels of albumin and ethanol; hematocrit and hemoglobin; changes in sodium levels; and central venous pressure were compared. The Na+, K+-ATPase pump activity was significantly increased in the GnRH analog group compared with the saline group and correlated with decreased estradiol levels (0.4 +/- 0.08 vs 0.26 +/- 0.06 micro mol/min/ml). Vasopressin levels were significantly lower in the GnRH group (3.2 +/- 0.9 vs 7.6 +/- 1.7 micro mol/L). Mean volume of irrigant used and operating time were similar in both groups. Volume deficit, decrease in protein, and hematocrit were less in GnRH than in the saline group. Blood ethanol levels, decrease in sodium, and irrigant deficit were significantly lower in GnRH group. Pretreatment with GnRH analogs may prevent the adverse effects of estradiol on endometrial Na+, K+-ATPase and creates a protective mechanism against iatrogenic hyponatremia, which is more critical in women than men in case of absorption of irrigating fluid. Moreover, created hypoestrogenism may enhance Na+, K+-ATPase activity in brain as well as endometrium, thus decreasing women's susceptibility to hyponatremic complications and brain damage. Suppressed vasopressin levels may be protective against fluid absorption in GnRH analog-treated patients.

Gonadal and pituitary responsiveness of stallions is not down-regulated by prolonged pulsatile administration of GnRH.

The objective of this study was to determine if prolonged pulsatile administration of homologous gonadotropin-releasing hormone (GnRH) at therapeutic or 5x therapeutic doses would cause down-regulation of the stallion's hypothalamic-pituitary-testicular axis. Fifteen stallions were randomly assigned to three treatment groups (n=5/group) and received a 0.5 ml subcutaneous dose of saline (group 1), 50 microg GnRH (group 2), or 250 microg GnRH (group 3) every 2 hours for 75 days. Weekly evaluations of follicle stimulating hormone, luteinizing hormone, and testosterone and monthly evaluations of daily sperm output and spermatozoal motility failed to demonstrate any decreased pituitary or gonadal responsiveness within or among treatment groups (P > 0.1) as a result of treatment with GnRH. Results of this study demonstrate that the hypothalamic-pituitary-testicularaxis of the stallion, unlike that of other domestic species, is remarkably refractory to GnRH-induced down-regulation.

Antibodies against different forms of GnRH distinguish different populations of cells and axonal pathways in a urodele amphibian, Taricha granulosa

Neurons immunoreactive to the peptide hormone gonadotropin-releasing hormone (GnRH) have been identified in the posterior diencephalon or anterior midbrain of diverse vertebrates. These cells are located caudal to the more well-characterized GnRH neurons in the nervus terminalis and septo-preoptic area, and are believed to express one or more of the nonmammalian forms of the GnRH. The present study utilized immunocytochemical techniques to determine whether the posterior GnRH group is present in a urodele amphibian, the newt Taricha granulosa. Antibodies directed against different molecular forms of GnRH were used to evaluate the immunological properties of GnRH-containing neurons in amphibians. An antibody selective for mammalian GnRH labeled perikarya in the nervus terminalis (terminal nerve) and septo-preoptic region, as described previously. Thick fibers that arise from terminal nerve and septo-preoptic neurons project mainly to the median eminence, medial pallium and habenula. An antibody selective for chicken GnRH II labeled cell bodies in the paraventricular organ and posterior tubercle of the caudal diencephalon, and thin fibers that project widely throughout the central nervous system. Region-specific staining with different GnRH antibodies supports the interpretation that different molecular forms of GnRH are expressed by neuroanatomically distinguishable systems.

Pulsatile gonadotrophin releasing hormone versus gonadotrophin treatment of hypothalamic hypogonadism in males

In this study, pulsatile gonadotrophin releasing hormone (GnRH) therapy and gonadotrophin therapy were compared for male patients with idiopathic hypothalamic hypogonadism. Thirty-six patients, 19 with this condition, and 17 with Kallmann's syndrome, were included in the study. Their mean age was 21.1 +/- 3.0 years (+/- SD). They were divided into two groups of similar age, number and testicular volume. Pulsatile GnRH therapy was started with 4 micrograms GnRH s.c. every 2 h using a portable pump and gonadotrophin therapy with weekly i.m. injections of 3 x 2500 IU human chorionic gonadotrophin (HCG). After 8-12 weeks of HCG treatment, 150 IU human menopausal gonadotrophin (HMG) 2-4 times weekly were added and the dose of HCG reduced if necessary. Testosterone concentrations increased significantly more (P < 0.03) in the gonadotrophin group than in the GnRH group (22.5 +/- 8.1 versus 16.8 +/- 5.5 nmol/l). The rise in oestradiol levels was also significantly higher (P < 0.001) in the gonadotrophin group than in the GnRH group (150 +/- 70 versus 88 +/- 59 pmol/l). Five patients developed gynaecomastia during gonadotrophin therapy. An increased testicular volume (TV) occurred more rapidly (P < 0.001) and was significantly more pronounced (P < 0.001) after GnRH therapy (delta TV = 8.1 +/- 2.0 ml) than with gonadotrophins (delta TV = 4.8 +/- 1.8 ml). Sperm counts were performed in 14 patients given GnRH and in 17 patients given gonadotrophins. Ten patients given GnRH had positive sperm counts, ranging from 1.5 to 14 x 10(6) spermatozoa/ml; eight of those given gonadotrophins also developed spermatogenesis (2-26 x 10(6)/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-dependent increases in plasma growth hormone following clonidine injection in luteal phase heifers

Gonadotropin releasing hormone (GnRH) was given to 109 cows and heifers during the course of 224 superovulations. Follicle stimulating hormone (FSH) was administered twice daily (5 or 6 mg) for 3.5 to 4 days beginning on any of Days 9 to 14 of the estrous cycle; prostaglandin (45 mg PGF2α or 750 ug cloprostenol) was given in a split dose on the fourth day. Donor cows and heifers were placed into four groups according to previous superovulation treatments, which consisted of one to three treatments or of no previous treatment. Every other cow or heifer within each of the four subgroups was treated with GnRH (200 μg i.m.) at standing estrus. Only donors that exhibited estrus within 32 to 72 h after the first prostaglandin treatment were used in the study. Animals were inseminated artificially 12 and 24 h after standing estrus was first observed.No differences were noted in the number of ovulations, total ova or transferable embryos recovered from the GnRH or control groups; however, two interactions were detected. Cows given GnRH had fewer palpable corpora lutea than control cows (P < 0.05), but this difference was not seen in heifers. The second interaction was that GnRH seemed to depress ovulation rate in donors not previously superovulated, but this effect was not observed with subsequent superovulations. Cows yielded more total ova than heifers (P < 0.01). There was no difference in return to estrus between GnRH and control groups after a second prostaglandin treatment at the time of embryo recovery. Most donors within each group resumed cycling between 5 and 12 d after embryo recovery.

Pattern of gonadotropin-releasing hormone (GnRH)-like stimuli sufficient to induce follicular growth and ovulation in ewes passively immunized against GnRH.

The pattern of GnRH-like stimuli capable of inducing follicular growth, ovulation, and luteal function was evaluated in ewes passively immunized against GnRH. The estrous cycles of 30 regularly cyclic sheep were synchronized using vaginal pessaries impregnated with a synthetic progestogen. Animals were passively immunized against GnRH (groups 2-5, n = 6) or the carrier protein, keyhole limpet hemocyanin (KLH; group 1, n = 6), at the time of pessary removal (PR). Circhoral delivery of saline (groups 1, 2, and 5) or low amplitude GnRH agonist (des-Gly10 GnRH ethylamide [100 ng/hourly pulse]; groups 3 and 4) was initiated at PR and continued for 3 (groups 4 and 5) or 12 days (groups 1-3). In groups 4 and 5, the amplitude of the GnRH-like stimulus was increased to 800 ng/hourly pulse (stimulus-shift) during the 24-h period beginning 72 h after PR. The amplitude of the hourly stimulus was adjusted to 100 ng/pulse 96 h after PR and continued at that level to Day 12. The endocrine changes associated with follicle growth and maturation (serum concentrations of estradiol [E2] above 10 pg/ml), ovulation (surge-like secretion of LH and FSH), and normal luteal function (serum concentrations of progesterone [P] above 2 ng/ml) were evident in ewes passively immunized against KLH (group 1). In this group, the preovulatory surge of gonadotropins was noted 48.7 +/- 1.2 h after PR. These endocrine events were blocked by passive immunization against GnRH (group 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of gonadotropin-releasing hormone and gonadotropin therapy in male patients with idiopathic hypothalamic hypogonadism

To compare pulsatile gonadotropin-releasing hormone (GnRH) therapy with gonadotropin therapy in male patients with idiopathic hypothalamic hypogonadism. Prospective study. Patients had free choice between the two forms of therapy. Patients were treated on an outpatient basis in our department. Eighteen patients of matched age (mean [+/- SD] age: 21.1 +/- 3.0 years and 23.6 +/- 7.3 years) and similar testicular volume were treated in each group. Pulsatile GnRH therapy was started with 4 micrograms GnRH subcutaneously every 2 hours using a portable pump and gonadotropin therapy with 3 x 2,500 IU human chorionic gonadotropin (hCG) weekly injected intramuscularly. After 8 to 12 weeks of hCG treatment, 150 IU human menopausal gonadotropin two to four times weekly were added. Testosterone (T) and estradiol (E2) levels increased significantly higher (T: P less than 0.03; E2; P less than 0.001) in the gonadotropin group than in the GnRH group (T: 22.5 +/- 8.1 versus 16.8 +/- 5.5 nmol/L; E2: 150 +/- 70 versus 88. +/- 59 pmol/L). Five patients developed gynecomastia during gonadotropin therapy. The rise of testicular volume was significantly more pronounced (P less than 0.001) in the GnRH group (delta testicular volume = 8.1 +/- 2.0 mL) than in the gonadotropin group (delta testicular volume = 4.8 +/- 1.8 mL). Ten patients of the GnRH and 8 of the gonadotropin group had positive sperm counts, ranging from 1.5 to 26 x 10(6) spermatozoa/mL. The latter was achieved more rapidly in the GnRH group (12 +/- 1.6 versus 20 +/- 2.3 months: P less than 0.02). Endocrine and exocrine testicular function can be normalized by both forms of therapy. Gonadotropin therapy has more side effects. Gonadotropin-releasing hormone leads to a higher testicular volume and a more rapid initiation of spermatogenesis compared with gonadotropin therapy.

The effects of administration of gonadotrophins and estrogens on prenatal survival in gilts

In gilts ovulation occurs over a 4 to 8-hour period, with 70% of the ova being shed over a relatively short span of time. These oocytes supposedly give rise to more developed embryos at Days 10 to 12 which advance the uterine environment and reduce survival rates of less developed embryos because of an asynchronous environment. The aim of this experiment was to reduce embryo mortality by influencing the duration and pattern of ovulation. Crossbred gilts (n = 98) were bred at their first observed estrus after being exposed to boars at 200 days of age. Estrus detection was carried out daily at 0000, 0800 and 1600 hours. All gilts were artifically inseminated with fresh semen, with a minimum of 2.7 billion spermatozoa, at both 16 and 32 hours after detection of estrus. Gilts were randomly assigned to one of the following treatments at detection of estrus: 1) 500 IU (2ml) chorionic gonadotrophin (hCG) injected intravenously at the onset of estrus (n = 22); 2) 16 μg (4 ml) gonadotrophin releasing hormone (GnRH) injected intravenously at the onset of estrus (n = 25); 3) 11.5 μg estrogen added to the semen at the time of AI (n = 25); 4) control, untreated gilts (n = 26). All gilts were slaughtered at Day 30 of gestation (Day 0 = day of detected estrus). The mean (±SEM) number of ovulations in pregnant gilts per treatment was 13.0 ± 0.52, 12.6±0.51, 13.6±0.54 and 13.3±0.52, while the mean (±SEM) number of normal embryos per treatment was 10.3±0.67, 10.5±0.66, 10.3 ± 0.69 and 10.5 ± 0.67 for hCG, GnRH, estrogen and control groups, respectively, for an embryonic survival rate of 80 ± 4.2%, 83 ± 4.1%, 74 ± 4.3% and 79±4.2% in pregnant gilts. If nonpregnant gilts are included, the embryonic survival rate for treatments 1 to 4 was 76±7.0%, 73±6.5%, 60±6.5%, and 64±6.4%, respectively. There was no significant difference between treatments for any of these variables. There was no evidence that administration of hCG, or GnRH at the onset of estrus, or the addition of estrogen to semen improved embryonic survival in gilts by Day 30 in this experiment.

Effects of season, GnRH administration and lupin supplementation on the ovarian and endocrine responses of merino ewes treated with PMSG and FSH-P to induce superovulation

Administration of gonadotrophin releasing hormone (GnRH) 24 h after sponge withdrawal did not affect the numbers of corpora lutea (CL) or persistent large follicles (LF) in ewes superovulated with 400 I.U. pregnant mare serum gonadotrophin and 12 mg follicle stimulating hormone in spring (11.6 +/- 0.9 v. 13.0 +/- 0.9 CL and 0.8 +/- 0.9 v. 0.9 +/- 0.3 LF, for +GnRH and -GnRH ewes, respectively). However, it did increase the ovulatory response of ewes superovulated in autumn (15.8 +/- 1.2 v. 11.8 +/- 1.1 CL). The incidence of ewes with prematurely regressed CL was also greater in autumn than in spring (21/89 v. 5/88). Supplementary feeding with lupin grain in autumn had no effect on numbers of CL but did increase the incidence of ewes with LF (18/48 v. 7/46) and caused a marked reduction in the incidence of ewes with regressed CL (1/44 v. 20/45). For ewes treated in autumn, there were no effects of lupin supplementation or GnRH administration on peak oestradiol-17 beta (E2) or peak luteinizing hormone (LH) levels. However, when peak E2 concentrations in the plasma were adjusted for numbers of preovulatory follicles, higher concentrations were observed for ewes in the +lupin/-GnRH group (12.4 +/- 2.9 pg mL-1) than in other treatment groups (range 4.3 +/- 0.4 to 5.7 +/- 0.3 pg mL-1). Moreover, the time of the LH peak was advanced by both lupin supplementation and GnRH treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Involution, pathology and histology of the uterus in dairy cattle with retained placenta and uterine discharge following GnRH

Sixty Holstein cows were assigned to one of three groups to assess the effect of gonadotrophin releasing hormone (GnRH) and clinical grouping on uterine histology, bacterial isolation and involution. Twenty cows had retained placenta (RP), 22 uterine discharges (UD), and 18 were controls (C). Cows were palpated three times weekly from 15 to 50 days postpartum. On day 15, postpartum cows received either 200 μg GnRH or saline (i.m.). Uterine swabs and tissue samples were collected once each week from 15 to 50 days postpartum. Uterine discharge was examined three times weekly and assigned a value of: 1=clear, 2=flecked pus or cloudy, 3=thick, white purulent discharge and 4=thick, red-brown purulent discharge. Discharge score was significantly different between clinical groups and decreased over time post-partum in a linear manner. Initial discharge score was highest in UD cows (3.0) and lowest in C cows (1.7). RP cows were intermediate (2.7). Involution was not affected by clinical group or GnRH and was completed for uterine horns and cervix between 40 to 50 days postpartum. A heavy occurrence of diffuse lymphocytes was most prevalent in RP cows (54%) ( P < 0.01) and least prevalent in C cows (5.4%). The occurrence of focal lymphocytes was low across groups and was not affected by GnRH or clinical group. Neutrophils were most common ( P < 0.01) in cows injected with GnRH (58% vs 39% for saline treated). Only neutrophils decreased in number with time postpartum. Fibrosis was not affected by clinical group, treatment, or days postpartum. Corynebacterium pyogenes was more prevalent ( P < 0.05) in RP than UD or C cows (53%, 35%, and 12%, respectively). Injection of GnRH on day 15 postpartum did not alter involution, infection status or histology of the uterus in cows with RP or UD. However, the measured variables suggest that RP and UD constitute two distinctly different groups.

Effects of GnRH on superovulated cattle

Gonadotropin releasing hormone (GnRH) was given to 109 cows and heifers during the course of 224 superovulations. Follicle stimulating hormone (FSH) was administered twice daily (5 or 6 mg) for 3.5 to 4 days beginning on any of Days 9 to 14 of the estrous cycle; prostaglandin (45 mg PGF 2α or 750 ug cloprostenol) was given in a split dose on the fourth day. Donor cows and heifers were placed into four groups according to previous superovulation treatments, which consisted of one to three treatments or of no previous treatment. Every other cow or heifer within each of the four subgroups was treated with GnRH (200 μg i.m.) at standing estrus. Only donors that exhibited estrus within 32 to 72 h after the first prostaglandin treatment were used in the study. Animals were inseminated artificially 12 and 24 h after standing estrus was first observed. No differences were noted in the number of ovulations, total ova or transferable embryos recovered from the GnRH or control groups; however, two interactions were detected. Cows given GnRH had fewer palpable corpora lutea than control cows (P < 0.05), but this difference was not seen in heifers. The second interaction was that GnRH seemed to depress ovulation rate in donors not previously superovulated, but this effect was not observed with subsequent superovulations. Cows yielded more total ova than heifers (P < 0.01). There was no difference in return to estrus between GnRH and control groups after a second prostaglandin treatment at the time of embryo recovery. Most donors within each group resumed cycling between 5 and 12 d after embryo recovery.

Gonadotropin Releasing Hormone-Induced Secretion of Luteinizing Hormone during the Milk-Ejection Reflex in the Postpartum Beef Cow2

A study was conducted to determine the effect of the milk-ejection reflex on exogenous gonadotropin releasing hormone (GnRH)-induced release of luteinizing hormone (LH) after short-term calf removal. Twenty-four postpartum multiparous beef cows were assigned randomly to groups arranged in a 2(3) factorial arrangement. Factors consisted of two levels of suckling [suckled (S) or nonsuckled (NS)], treatment with GnRH [saline (C) or 200 micrograms GnRH] and days postpartum (d 1 and 14). Dams were isolated from their calves for 4 h on d 1 and 14 postpartum. At the end of 4 h dams were reunited with their calves in S + C and S + GnRH groups, while dams of calves in NS + C and NS + GnRH groups remained separated an additional 2 h. Cows were injected iv with saline or GnRH following the 4-h isolation period, 5 min after calves had begun suckling or nuzzling the udder. Sera from jugular blood samples collected 15 min prior to the end of the 4-h isolation period, immediately prior to injection (0 h) and at 15 min intervals thereafter for 120 min were analyzed for LH. Serum concentrations of LH in control cows did not differ due to suckling or stage of the postpartum period and averaged 2.3 +/- .1 ng/ml. Pituitary response to GnRH was determined by computing the rate of LH release. Rate of LH release (ng LH.ml-1.min-1) in response to GnRH on d 14 was greater (P less than .001) than on d 1 in both suckled and nonsuckled groups (S + GnRH, 37.1 +/- 3.9 vs 18.3 +/- 5.0; NS + GnRH, 34.7 +/- 5.9 vs 14.5 +/- 1.1). However, GnRH-induced release of LH did not differ between suckled and nonsuckled cows on either d 1 or 14 postpartum. These data indicate that response of the bovine pituitary to GnRH during the postpartum period is not influenced by the act of suckling but is enhanced with time after parturition.

Influence of repeated low doses of gonadotrop in releasing hormone on postpartum interval and serum luteinizing hormone in Brahman cross cows

Two experiments were conducted to examine the effects of repeated low-dose injections of gonadotropin releasing hormone (GnRH) 30 to 40 d post partum on reproductive characteristics in multiparous suckled Brahman cross cows. In Experiment I, 39 cows were injected (i.v.) with GnRH (5 μg/injection) at 2-h intervals for either 0 (control), 6, 12, or 24 h at 30 to 37 d post partum. GnRH injections for short periods (6h) increased the number of cows exibiting estrus within 45 d of treatment, but cows injected for 24 h failed to exhibit estrus during this period. The period from treatment to first estrus was shorter in the 6-h GnRH group compared to the control group. Injections for 6h significantly (P < 0.05) increased in serum luteinizing hormone (LH) concentrations 1 d after GnRH treatment. In Experiment II we examined the effect of i.v. GnRH injections (5 μg/injection at 2-h intervals) for 6h in a larger group of cows (n = 70). The days from treatment to first estrus were reduced (P < 0.05) in GnRH-treated cows; however, first-service conception rates were significantly lower (P < 0.01) in treated compared to control cows (46.4 and 80.0%, respectively). The results led us to believe that GnRH injections for short periods reduce postpartum interval to first estrus, but fertility at first estrus is lowered.

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 × 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 μg 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.

Administration of GnRH in vivo stimulates progesterone and inhibits androgen accumulation by ovarian follicles isolated from pubertal rabbits

A single i.v. injection of gonadotropin releasing hormone (GnRH) to pubertal female rabbits led to an ovulatory pulse of LH but no ovulations resulted. By contrast, 5 i.v. injections over 6 h led to 1–3 ovulations in 5 of 8 animals treated. Twenty-four hours after the initial injection animals were killed and follicles isolated. Large follicles > 1 mm dia, from both GnRH treated groups released more progesterone during the control incubation period than those from saline treated. Small follicles < 1 mm dia, from the same GnRH groups accumulated 3–6 times more progesterone than those from saline treated when stimulated with luteinizing hormone (LH). Testosterone accumulation by small and large follicles was not affected by one injection of GnRH but was depressed in follicles from rabbits treated with 5 injections of GnRH. A single injection of GnRH enhanced the ability of small and large follicles to release estradiol which was depressed 30% in the presence of LH. Multiple GnRH injections depressed estradiol accumulation by small and large follicles. These data suggest the administration of GnRH in vivo can have stimulatory as well as inhibitory effects on subsequent follicular steroid release and accumulation in vitro.

The influence of semen quality, as determined by percent intact acrosomes, on fertilization rates in superovulated cows

Gonadotropin releasing hormone (GnRH) was given to 109 cows and heifers during the course of 224 superovulations. Follicle stimulating hormone (FSH) was administered twice daily (5 or 6 mg) for 3.5 to 4 days beginning on any of Days 9 to 14 of the estrous cycle; prostaglandin (45 mg PGF2α or 750 ug cloprostenol) was given in a split dose on the fourth day. Donor cows and heifers were placed into four groups according to previous superovulation treatments, which consisted of one to three treatments or of no previous treatment. Every other cow or heifer within each of the four subgroups was treated with GnRH (200 μg i.m.) at standing estrus. Only donors that exhibited estrus within 32 to 72 h after the first prostaglandin treatment were used in the study. Animals were inseminated artificially 12 and 24 h after standing estrus was first observed.No differences were noted in the number of ovulations, total ova or transferable embryos recovered from the GnRH or control groups; however, two interactions were detected. Cows given GnRH had fewer palpable corpora lutea than control cows (P < 0.05), but this difference was not seen in heifers. The second interaction was that GnRH seemed to depress ovulation rate in donors not previously superovulated, but this effect was not observed with subsequent superovulations. Cows yielded more total ova than heifers (P < 0.01). There was no difference in return to estrus between GnRH and control groups after a second prostaglandin treatment at the time of embryo recovery. Most donors within each group resumed cycling between 5 and 12 d after embryo recovery.

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.