Effect of a long acting GnRH analogue or placebo on plasma LH/FSH, urethral pressure profiles and clinical signs of urinary incontinence due to Sphincter mechanism incompetence in bitches

In 23 bitches with urinary incontinence due to spaying, the effect of treatment with a long-acting formulation of leuprolide acetate on frequency of incontinence, plasma gonadotropin levels and urodynamic parameters was evaluated. In addition, the clinical effect was compared with that of treatment with alpha-adrenergics. Before treatment, the dogs' incontinent episodes occurred, on average, 4 times per day on up to 6 days per week. In the pre-trial after therapy with phenylpropanolamine (n=23) the episodes of incontinence decreased by 92%, in the double-blind study 5 weeks after GnRH-analogue (n=11) by 71%; and by 28% after the placebo (n=12). By the end of the study, nine of twenty-two leuprolide treated bitches responded completely to treatment and were continent for periods lasting 70-575 days after treatment. In another 10 dogs, response to therapy was partial and the frequency of incontinence was reduced by at least 50%. After therapy with placebo, one bitch had no episodes of incontinence for 412 days. Treatment with the GnRH-analogue significantly decreased the plasma gonadotropin levels but there was no correlation between the effect on gonadotropin levels and response to treatment. Treatment with leuprolide or placebo had no effect on urethral closure pressure regardless of the response to treatment. The hypothesis that the change of the plasma gonadotropin levels after spaying is the cause of reduced urethral closure function was not supported by the results of this study. A possible direct effect of GnRH-analogues on the bladder is discussed. Long acting GnRH analogues appear to be a well-tolerated alternative for urinary incontinence treatment, but they appear to be less effective than the alpha-adrenergics.     

Gonadotropin-releasing hormone immunization for the treatment of urethral sphincter mechanism incompetence in ovariectomized bitches

We have investigated GnRH immunization for the treatment of urethral sphincter mechanism incompetence in ovariectomized bitches. It has been reported that decreasing LH secretion through the use of GnRH agonists temporarily restores continence in some bitches. Therefore, decreasing the circulating LH concentrations by immunizing against GnRH might temporarily maintain continence in incontinent dogs. Sixteen incontinent dogs given phenylpropanolamine (PPA) to control incontinence were recruited for this study. Eleven dogs were immunized against GnRH (novel treatment group) at week 0, and nine dogs were vaccinated again 4 weeks later. Five dogs (standard treatment group) were vaccinated with a placebo twice at 4-week intervals. PPA was discontinued in the novel treatment group 2 weeks after revaccination, and standard-treatment dogs were given PPA for the duration of the study. Blood samples were collected before each treatment and at 6, 8, 10, 12, 16, 20, and 24 weeks and owners recorded episodes of incontinence throughout the study. Ten of the eleven dogs in the novel treatment group experienced side effects as a result of vaccination; two of these dogs experienced more severe side effects after the first vaccination and were withdrawn from the study as a result. Of the nine dogs that completed the vaccination series, four dogs remained continent after PPA was discontinued. For these four dogs, there was no difference in incontinent episodes when they were given PPA versus treatment with the vaccine. All nine novel-treatment dogs developed a GnRH antibody titer and experienced a significant decrease in circulating LH concentrations. In conclusion, GnRH immunization was effective in maintaining continence in four of the nine incontinent ovariectomized dogs, and in these dogs, treatment with the vaccine was comparable with treatment with PPA.     

Plasma FSH and LH in prepubertal Booroola ewe lambs

Basal plasma concentrations (four 30-min samples) and GnRH-induced release of gonadotrophins were measured every 15 days between 30 and 90 days and at 110 days of age in Merino ewe lambs from the prolific Booroola ('B') flock (n = 18-23), the medium prolificacy ('T') flock (n = 14-20), and the 'O' flock (n = 4-8) of low prolificacy. At ages of 30 and 45 days B ewe lambs had mean basal plasma FSH concentrations of 145 and 122 ng/ml which were significantly higher (P less than 0.01) than those seen in T (45 and 53 ng/ml), and O (39 and 38 ng/ml) flock ewes. Between 60 and 110 days of age there were no significant differences between genotypes. The increment in FSH concentrations above basal levels induced by the subcutaneous injection of 100 micrograms synthetic GnRH was only significantly (P less than 0.05) greater in B than T and O genotype ewe lambs at 110 days of age but not at other ages. The basal plasma FSH differences between the B, T and O genotypes at 30 and 45 days of age were not consistently related to the size of litter in which lambs were born. At 30 days of age the mean plasma LH concentration of B, T, and O flock lambs were 2.6 +/- 0.5, 1.2 +/- 0.6 and 0.7 +/- 0.8 ng/ml respectively. These differences were not significant. At later ages there were also no significant differences between the genotypes with respect to basal LH, and the increase in LH induced by exogenous GnRH was always similar for the three genotypes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of steroid administration on pituitary luteinizing hormone and follicle-stimulating hormone in ovariectomized pony mares in the early spring: pituitary responsiveness to gonadotropin-releasing hormone and pituitary gonadotropin content

These experiments tested the hypothesis that administration of steroid hormones to ovariectomized (OVX) mares during the vernal transition to the breeding season would influence LH and FSH secretion. Circulating gonadotropin concentrations, response to exogenous GnRH, and pituitary gonadotropin content were monitored. Experiments 1 and 2 were conducted, beginning 10 March, and 3 February, respectively, utilizing a total of 30 long-term OVX pony mares. In experiment 1, mares were administered vehicle (n = 5) or estradiol-17 beta (E2, n = 5, 5 mg/3 ml sesame oil), twice daily for 16 days. Blood samples were collected daily for assessment of circulating LH and FSH concentrations. On Day 10 of treatment, 400 micrograms GnRH were administered to all mares. LH increased significantly over days of treatment in the estradiol-treated group, but pituitary response to GnRH tended to be less than in control mares. Circulating FSH tended to decline over days of treatment in estradiol-treated mares, and the pituitary response to GnRH was significantly reduced. Pituitary LH, but not FSH, was increased on Day 16 of treatment with estradiol. In experiment 2, 20 OVX mares received, twice daily, vehicle (n = 5), E2, n = 5; 5 mg), progesterone (P4, n = 5; 100 mg), or progesterone plus estradiol (P4/E2, n = 5; 100 + 5 mg). Treatment continued for 14 days. GnRH (100 micrograms) challenges were administered on Days 6 and 13 of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of a GnRH cytotoxin on reproductive function in peripubertal male dogs

Methods for long-term or permanent disruption of reproductive function via nonsurgical techniques are needed for a variety of species, including companion animals. In a previous study, we demonstrated the ability of a cytotoxin (pokeweed antiviral protein-PAP) conjugated to d-Lys(6)-GnRH, to disrupt reproductive function in adult male dogs. The objective of the present study was to examine the ability of a d-Lys(6)-GnRH-PAP conjugate to disrupt reproductive function in peripubertal male dogs. Peripubertal male dogs (n=15; approximately 16-32 weeks old) were treated with d-Lys(6)-GnRH-PAP as follows: dogs (n=7; Group I) received GnRH-PAP (0.1 mg/kg SQ) with a second treatment (0.25 mg/kg) 20 weeks later. An additional group (n=3; Group II) of peripubertal dogs was treated with GnRH-PAP (0.25 mg/kg) twice (20 weeks apart). Control dogs (n=5) received d-Lys(6)-GnRH analog (0.0045 mg/kg SQ) without PAP. Efficacy was assessed by monitoring testis size, serum concentrations of testosterone and LH, as well as LH release subsequent to a GnRH (5 microg/kg) stimulus. Dogs in Group I (n=5) that did not respond to the initial two treatments were given a third GnRH-PAP injection (0.25 mg/kg), 12 months after the initial treatment. The initial GnRH-PAP treatment in peripubertal male dogs did not affect testis growth, LH release or serum testosterone concentrations; however, administration of a higher dose of GnRH-PAP after puberty resulted in a marked and rapid decline in testis size, serum testosterone concentrations and LH responsiveness to GnRH stimulation in 9 of 10 dogs. Suppression of reproductive function was maintained in treated dogs for 18-50 weeks; four dogs had suppression of reproductive activity through the end of the study. In conclusion, GnRH-PAP given after puberty markedly suppressed reproductive activity. Due to variability in the response and duration of suppression after treatment with GnRH-PAP, more research is required to determine its efficacy for nonsurgical sterilization of the male dog.     

Basal and estradiol-induced release of gonadotropins in dairy cows with naturally occurring ovarian cysts

A study was conducted to identify relationships between serum sex steroid concentrations and release of gonadotropins in dairy cows with ovarian cysts. Cows with ovarian cysts were grouped according to sex steroid profiles as being under estrogenic (n = 6) or low steroid (n = 6) influence. All cows were submitted to a sampling and treatment protocol to 1) record basal pulsatile release of gonadotropins and 2) determine whether luteinizing hormone (LH) or follicle stimulating hormone (FSH) was released after sequential administration of exogenous estradiol and gonadotropin releasing hormone (GnRH) treatments were given 30 h apart. Basal LH was higher in the estrogen-influence group (P < 0.05). There were no differences between groups in basal FSH concentrations or frequency and amplitude of pulsatile LH or FSH release. Only one of the twelve cows, an individual from the low steroid group, had a preovulatory-like surge of gonadotropins after exogenous estradiol. All cows released LH and FSH in response to GnRH treatment, with no differences between groups. These results show that 1) there is considerable variation in pulsatile release of gonadotropins in cows with ovarian cysts, even among individuals with similar sex steroid profiles, and 2) suggest that a factor in the persistence, and perhaps initiation, of the cystic condition is refractoriness to the positive feedback effect of estradiol on gonadotropin release.     

The effect of a GnRH agonist on follicular dynamics and response to FSH stimulation in prepubertal calves

Endocrine control of follicular growth was determined by observing the left ovary of prepubertal calves previously treated with a potent GnRH agonist for 13 days. The ovarian response to hormonal stimulation was determined using the right ovaries of the same animals. Three-month-old crossbred calves were assigned to one of the two following treatment groups: 1) saline control for 13 days, with purified porcine FSH for the last 3 days (n = 5); and 2) GnRHa for 13 days, with purified porcine FSH for the final 3 days (n = 5). The left ovaries were removed from all calves after 10 days, and the right ovaries were removed at the end of treatment. Plasma concentrations of FSH, LH and oestradiol-17 beta were followed up during the GnRHa and pFSH treatments. The maximum macroscopic diameter of the F1 follicle, as determined by daily ultrasonography, did not differ between GnRHa-treated calves (from 6.6 to 10.4 mm) and the saline control calves (from 6.7 to 10.3 mm). Histological analysis of the ovaries showed that the number of follicles > 0.40 mm in diameter varied greatly for calves of the two groups (from 11 to 220 at 10 days). GnRHa significantly increased the mean number of follicles (total and nonatretic) of size class > 5.4 mm as compared to saline control calves (P < 0.05). The FSH treatment significantly increased the mean number of follicles 3.00-5.4 and > 5.4 mm in diameter (P < 0.05), with no change in the number of follicles smaller than 3.00 mm. The rate of atresia of large follicles (3.01-5.40 mm) was significantly reduced by purified porcine FSH treatment in both groups (P < 0.05). In no case did the GnRHa induce ovulation or luteinization of follicles. The LH and FSH concentrations increased transiently after GnRHa treatment on the first day, but afterwards, both hormones increased to only one sixth of what was observed after the initial GnRHa injection treatment. This increase in LH and FSH was observed 1 h after GnRHa treatment on each consecutive day of the experiment and were significantly different in the control group (0 h versus 1 h versus 2 h x saline control versus GnRH agonists groups; P < 0.01). During the superovulatory treatment, FSH concentrations peaked at around 0.70 ng.mL-1 in both saline- and GnRHa-treated groups on the first day but on the last day of surovulatory treatment, FSH concentrations were higher in GnRHa agonist-treated calves than in the control calves (day 11 versus day 12 versus day 13 x saline control versus GnRH agonist treatment groups; P < 0.01). LH profiles were unchanged by surovulatory treatment. Concentrations of oestradiol-17 beta increased significantly over the three days (P < 0.001) of the superovulatory treatments in both groups (P < 0.01). These results indicate that GnRH agonist treatment allows recruited antral follicles to pursue their growth during the early selection process via sustained FSH and LH secretion allowing more than a single large follicle to maintain their growth without going to atresia.     

Progesterone does not affect the amount of mRNA for gonadotropins in the anterior pituitary gland of ovariectomized ewes

To evaluate the effect of progesterone on the synthesis and secretion of gonadotropins, ovariectomized ewes either were treated with progesterone (n = 5) for 3 wk or served as controls (n = 5) during the anestrous season. After treatment for 3 wk, blood samples were collected from progesterone-treated and ovariectomized ewes. After collection of blood samples, hypothalamic and hypophyseal tissues were collected from all ewes. Half of each pituitary was used to determine the content of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the number of receptors for gonadotropin-releasing hormone (GnRH). The amounts of mRNA for LH beta subunit, FSH beta subunit, alpha subunit, growth hormone, and prolactin were measured in the other half of each pituitary. Treatment with progesterone reduced mean serum concentrations of LH (p less than 0.001) but ot FSH (p greater than 0.05). Further, progesterone decreased (p less than 0.05) the total number of pulses of LH. We were unable to detect pulsatile release of FSH. Hypothalamic content of GnRH, number of receptors for GnRH, pituitary content of gonadotropins and mRNA for LH beta subunit, FSH beta subunit, alpha subunit, growth hormone, and prolactin were not affected (p greater than 0.05) by treatment with progesterone. Thus, after treatment with progesterone, serum concentrations of LH (but not FSH) are decreased. This effect, however, is not due to a decrease in the steady-state amount of mRNA for LH beta or alpha subunits.     

Effects of gonadotropin-releasing hormone administration on the pituitary-gonadal axis in male and female dogs before and after gonadectomy

GnRH-stimulation tests were performed in 14 female and 14 male client-owned dogs of several breeds, before and 4 to 5 mo after gonadectomy. The aim of the study was to obtain more insight into the pituitary-gonadal axis in intact and neutered dogs and to establish reference values. Basal plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations were increased significantly after gonadectomy in both bitches and male dogs. In both males and females ranges of the basal plasma FSH concentrations, before and after gonadectomy, did not overlap as opposed to the overlap in ranges of the basal plasma LH concentrations. Before gonadectomy basal plasma LH concentrations were lower and basal plasma FSH concentrations were higher in bitches than in male dogs. After gonadectomy these basal values did not differ significantly. GnRH administration before gonadectomy resulted in an increase in plasma LH and FSH concentrations in both genders. GnRH administration after gonadectomy produced an increase only in plasma LH concentrations in both genders, and a just significant increase in plasma FSH in castrated male dogs. GnRH administration before gonadectomy resulted in a significant increase in plasma testosterone concentration in both genders. In males ranges of basal and GnRH-stimulated plasma testosterone concentrations before and after gonadectomy did not overlap. Basal plasma estradiol concentrations were significantly higher in intact males than in castrated males and their ranges did not overlap. The basal estradiol concentrations in bitches before and after ovariectomy were not significantly different. At 120 min after GnRH administration, ranges of plasma estradiol concentration of intact and ovariectomized bitches no longer overlapped. In conclusion, basal plasma FSH concentration appears to be more reliable than basal plasma LH concentration for verification of neuter status in both male and female dogs. The basal plasma testosterone concentration appears to be reliable for verification of neuter status in male dogs. The plasma estradiol concentration at 120 min after GnRH administration can be used to discriminate between bitches with and without functional ovarian tissue.     

Antagonistic and agonistic GnRH analogue treatment of precocious puberty: tracking gonadotropin concentrations in urine

BACKGROUND: The pharmacodynamics of gonadotropin-releasing hormone (GnRH) agonists includes an initial 'flare-up' of the pituitary-gonadal axis, followed by reduced luteinizing hormone (LH) secretion. The question is if combining a short-acting antagonist with a long-acting agonist can diminish gonadotropin flare-up. METHODS: To achieve quick downregulation in patients with recently diagnosed central precocious puberty (CPP, 7 patients) or short stature with short predicted final height (3 patients), we combined the GnRH antagonist cetrorelix (3 subcutaneous injections every 72 h) at the beginning of GnRH agonist treatment (leuprorelin or triptorelin) in 6 patients and compared the effect to 4 patients treated solely with GnRH agonist. To monitor effects, we measured LH and FSH concentrations in urine collected from initial morning urination during the first month of treatment. RESULTS: In both treatment groups, gonadotropin flare-up could be detected in urine levels increased due to the flare-up phenomenon which was of short duration (<5 days) in the majority (5 of 6) of combined-treated patients and in the minority (1 of 4) of patients treated by agonist alone. During the first 10 days of treatment, mean LH concentration measured in urine was significantly lower in 4 CPP patients treated by the combined therapy compared to 3 CPP patients treated by the agonist only (mean LH combined therapy: 10.4 +/- 2.8 vs. 20.1 +/- 11.0 mU/ml in the agonist-only group, mean +/- SEM, p < 0.05). Significant correlations between stimulated serum LH in GnRH test prior to treatment and maximum urine LH after initiating GnRH analogue treatment (r = 0.547, p = 0.043), as well as basal serum LH and basal urine LH (r = 0.685, p = 0.014) were found. CONCLUSION: Combined GnRH agonist and antagonist treatment led to rapid gonadotropin suppression. Also, urine measurements of LH and FSH seemed suitable for monitoring gonadotropin-inhibiting or -stimulating properties of GnRH analogues in individual patients. However, a controlled trial of a larger patient cohort is required to decide which treatment is the most effective.     

Effect of vitamin A deficiency upon gonadotropin response to gonadotropin-releasing hormone

There is a monotypic change in basal serum gonadotropin levels following retinol treatment of chronically vitamin A-deficient (VAD) male rats. The present study was undertaken to investigate the hypothesis that the specific increase in serum follicle-stimulating hormone (FSH) represents a change in gonadotrope responsiveness to gonadotropin-releasing hormone (GnRH). To this end, a test dose of GnRH was given to VAD rats pre-, 5 days post-, and 10 days postreplacement of vitamin A (PVA). In VAD rats, basal serum FSH and luteinizing hormone (LH) levels were higher than those of controls. Increased LH/testosterone ratios, both in basal levels and in the secretory response to GnRH, suggested Leydig cell hyporesponsiveness in VAD animals. Both the FSH and LH responses to GnRH were maximal at 1 h, declining thereafter. Although the absolute increments in FSH and LH 1 h after GnRH in VAD rats were greater than in controls, the percent increase in FSH tended to be lower in VAD rats and to increase after vitamin A replacement. The specific enhancement of FSH release PVA became evident only when assessing total secretion of FSH and LH after GnRH. Luteinizing hormone response to GnRH increased PVA, but not significantly, while FSH secretion after GnRH increased both 5 and 10 days PVA, times during which basal FSH levels were also increasing. These changes in FSH secretion could not be attributed either to increases in endogenous GnRH or to changes in testosterone or estradiol levels. Basal serum androgen binding protein levels, elevated in VAD animals, did not respond to the acute increases in FSH after GnRH and remained high PVA, suggesting no acute change in Sertoli cell function. Thus, the PVA increase in FSH secretion unmasks a partial inhibition of the gonadotrope present in the retinol-deficient, retinoic acid-fed male rat.     

Influence of the degree of stimulation of the pituitary by gonadotropin-releasing hormone on the action of inhibin and testosterone to suppress the secretion of the gonadotropins in rams

This experiment determined if the degree of stimulation of the pituitary gland by GnRH affects the suppressive actions of inhibin and testosterone on gonadotropin secretion in rams. Two groups (n = 5) of castrated adult rams underwent hypothalamopituitary disconnection and were given two i.v. injections of vehicle or 0.64 microg/kg of recombinant human inhibin A (rh-inhibin) 6 h apart when treated with i.m. injections of oil and testosterone propionate every 12 h for at least 7 days. Each treatment was administered when the rams were infused i.v. with 125 ng of GnRH every 4 h (i.e., slow-pulse frequency) and 125 ng of GnRH every hour (i.e., fast-pulse frequency). The FSH concentrations and LH pulse amplitude were lower and the LH concentrations higher during the fast GnRH pulse frequency. The GnRH pulse frequency did not influence the ability of rh-inhibin and testosterone to suppress FSH secretion. Testosterone did not affect LH secretion. Following rh-inhibin treatment, LH pulse amplitude decreased at the slow, but not at the fast, GnRH pulse frequency, and LH concentrations decreased at both GnRH pulse frequencies. We conclude that the degree of stimulation of the pituitary by GnRH does not influence the ability of inhibin or testosterone to suppress FSH secretion in rams. Inhibin may be capable of suppressing LH secretion under conditions of low GnRH.     

Induction of estrus with intramuscular injections of GnRH or PMSG in lactating goats (Capra hircus ) primed with a progestagen during seasonal anestrus

In Experiment 1, goats in seasonal anestrus (n=154) were treated with sponges impregnated with 1 of 2 types of progestagen (MAP or FGA) followed by PMSG (400 IU im) 48 h before sponge removal. The type of progestagen used had no effect on kidding, abortion, pseudogestation, multiple births, stillbirths, number of live births per doe or gestation length. In Experiment 2, lactating goats (n=24) in seasonal anestrus were treated with progestagen sponges (MAP). At sponge removal they received one of the following treatments: 1 injection of PMSG (400 IU im), 1 injection of GnRH (125 mug im; GnRH-1), or 2 injections of GnRH (125 mug/injection im; GnRH-2) at a 48 h interval. Serum samples were taken at 6-h intervals for 96 h, starting 12 h after sponge removal. Heterologous radioimmunoassays were validated for the measurements of goat FSH, LH, E(2) and P(4). The onset of estrus (P=0.004), mean doe receptivity (P=0.0006), maximum preovulatory E(2) concentrations (P=0.0001) and LH peak concentrations (P=0.08) occurred significantly later for GnRH-1 and GnRH-2 than for PMSG treatment. The PMSG treatment induced a preovulatory LH peak in a greater number of goats (P=0.05) and gave a higher gestation rate than GnRH-1 and GnRH-2 treatments (57 vs 0 vs 12%; P=0.03). It is likely that the GnRH treatments administered did not reactivate the hypothalamo-pituitary-gonadal axis. Thus, intramuscular injections of GnRH in lactating goats primed with a progestagen were not as effective in regulating reproductive performance during seasonal anestrus as were injections of PMSG.     

Androgen and progesterone effects on follicle-stimulating hormone and luteinizing hormone secretion in anestrous mares

Anestrous lighthorse mares were treated in December with dihydrotestosterone (DHT; 150 micrograms/kg of body weight), progesterone (P; 164 micrograms/kg), both DHT and P (DHT+P), testosterone (T; 150 micrograms/kg), or vehicle (n = 4/group). Daily blood sampling was started on Day 1, and on Day 4 all mares were administered a pretreatment injection of gonadotropin-releasing hormone (GnRH) and were bled frequently to characterize the responses of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) concentrations. Treatment injections were given on Day 4 and then daily through Day 17. On Day 18, all mares were again administered GnRH and were bled frequently. Treatment of mares with DHT, P, or T increased (p less than 0.01) plasma concentrations of these steroids to approximately 1.5 ng/ml during the last 10 days of treatment. There was no effect (p greater than 0.10) of treatment on LH or FSH concentrations in daily blood samples. Relative to the pretreatment GnRH injection, mares treated with T or DHT+P secreted approximately 65% more (p less than 0.01) FSH in response to the post-treatment GnRH injection; FSH response to the second GnRH injection was not altered (p greater than 0.10) in control mares or in DHT- or P-treated mares. There was no effect of any steroid treatment on LH secretion after administration of GnRH (p greater than 0.10). Averaged over all mares, approximately 94 times more FSH than LH was secreted in response to injection of GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of in vivo administration of testosterone propionate on in vitro production of follicle-stimulating hormone and luteinizing hormone by pituitaries of pony mares

The in vitro incorporation of [3H]leucine into immunoprecipitable follicle-stimulating hormone (FSH) and luteinizing hormone (LH) was assessed for pituitaries from pony mares treated with testosterone propionate (TP) or oil (controls). Mares were treated every other day with TP (n = 4) at 350 micrograms/kg of body weight or with an equivalent volume of oil (n = 4). One day following the sixth injection of TP, each mare received an intravenous injection of gonadotropin releasing hormone (GnRH) at 1.0 micrograms/kg body weight and was bled frequently for 4 h. Treatment of mares with TP reduced FSH (P less than 0.05) and LH (P less than 0.01) concentrations in daily blood samples and increased (P less than 0.01) the amount of FSH secreted in response to GnRH compared with control mares. Incorporation of [3H]leucine into immunoprecipitable FSH was also greater (P less than 0.01) in pituitaries from TP-treated mares compared with control mares on both a per mg tissue and per anterior pituitary basis. The amount of LH secreted after GnRH, the amount left in the pituitary and the incorporation of [3H]leucine into LH were not affected by treatment. These results confirm earlier conclusions drawn from indirect evidence that androgens increase the production of FSH in the mare.     

Alteration of gonadotrophin and steroid hormone release, and of ovarian function by a GnRH antagonist in gilts

This study examined the impact of the gonadotrophin-releasing hormone (GnRH) antagonist Antarelix on LH, FSH, ovarian steroid hormone secretion, follicular development and pituitary response to LHRH in cycling gilts. Oestrous cycle of 24 Landrace gilts was synchronised with Regumate (for 15 days) followed by 800 IU PMSG 24h later. In experiment 1, Antarelix (n=6 gilts) was injected i.v. (0.5mg per injection) twice daily on four consecutive days from day 3 to 6 (day 0=last day of Regumate feeding). Control gilts (n=6) received saline. Blood was sampled daily, and every 20 min for 6h on days 2, 4, 6, 8 and 10. In experiment 2, gilts (n=12) were assigned to the following treatments: Antarelix; Antarelix + 50 microg LHRH on day 4; Antarelix + 150 microg LHRH on day 4 or control, 50 microg LHRH only on day 4. Blood samples were collected daily and every 20 min for 6h on days 2, 4 and 6 to assess LH pulsatility. Ovarian follicular development was evaluated at slaughter.Antarelix suppressed (P<0.05) serum LH concentrations. The amount of LH released on days 4-9 (experiment 1) was 8.80 versus 36.54 ngml(-1) (S.E.M.=6.54). The pattern of FSH, and the preovulatory oestradiol rise was not affected by GnRH antagonist. Suppression of LH resulted in a failure (P<0.05) of postovulatory progesterone secretion. Exogenous LHRH (experiment 2) induced a preovulatory-like LH peak, however in Antarelix treated gilts the LH surge started earlier and its duration was less compared to controls (P<0.01). Furthermore, the amount of LH released from day 4 to 5 was lower (P<0.01) in Antarelix, Antarelix + 50 and Antarelix + 150 treated animals compared to controls. No differences were estimated in the number of LH pulses between days and treatment. Pulsatile FSH was not affected by treatment. Mean basal LH levels were lower (P<0.05) after antagonist treatment compared to controls. Antarelix blocked the preovulatory LH surge and ovulation, but the effects of Antarelix were reduced by exogenous LHRH treatment. The development of follicles larger than 4mm was suppressed (P<0.05) by antagonist treatment.In conclusion, Antarelix treatment during the follicular phase blocked preovulatory LH surge, while FSH and oestradiol secretion were not affected. Antarelix failed to alter pulsatile LH and FSH secretor or pituitary responsiveness to LHRH during the preovulatory period.     

Comparative response of rams and bulls to long-term treatment with gonadotropin-releasing hormone analogs

The objective was to compare the relative response between rams and bulls in characteristics of LH, FSH and testosterone (T) secretion, during and after long-term treatment with GnRH analogs. Animals were treated with GnRH agonist, GnRH antagonist, or vehicle (Control) for 28 days. Serial blood samples were collected on day 21 of treatment, and at several intervals after treatment. Injections of natural sequence GnRH were used to evaluate the capacity of the pituitary to release gonadotropins during and after treatment. Treatment with GnRH agonist increased basal LH and T concentrations in both rams and bulls, with a greater relative increase in bulls. Endogenous LH pulses and LH release after administration of GnRH were suppressed during treatment with GnRH agonist. Treatment with GnRH antagonist decreased mean hormone concentrations, LH and T pulse frequency, and the release of LH and T after exogenous GnRH, with greater relative effects in bulls. Rams previously treated with antagonist had a greater release of LH after administration of GnRH compared with control rams, while rams previously treated with agonist showed a reduced LH response. Bulls previously treated with agonist had reduced FSH concentrations and LH pulse amplitudes compared with control bulls while bulls previously treated with antagonist had greater T concentrations and pulse frequency. The present study was the first direct comparison between domestic species of the response in males to treatment with GnRH analogs. The findings demonstrated that differences do occur between rams and bulls in LH, FSH and testosterone secretion during and after treatment. Also, the consequences of treatment with either GnRH analog can persist for a considerable time after discontinuation of treatment.     

Gonadotropin secretion and pituitary responsiveness to GnRH in mares with granulosa-theca cell tumor

Granulosa-theca cell tumors (GTCTs) are able to secrete variable amounts of sex steroids and immunoreactive inhibin (ir-INH). Although the pituitary appears to be affected by the presence of a GTCT, pituitary responsiveness to exogenous GnRH has not been examined. The aims of the present study were to: (i) assess the plasma hormone concentrations of ir-INH, gonadotropins and sex steroids in eight mares with GTCT and (ii) assess the responsiveness of pituitary gonadotroph cells to exogenous GnRH stimulus both before and after tumor removal. In seven mares, the contralateral ovary was firm, small and inactive. Histopathological observations of the tumors confirmed the presumptive diagnosis of a GTCT. Four mares, judged to be in vernal transition period (n=2) and in the breeding season (n=2), were used as controls. A single intravenous injection of 40 microg of GnRH agonist was given to each mare and blood samples were collected every 15 min from 2 h before to 4 h after injection. In four GTCT mares, this procedure was repeated 20 (n=2) and 90 (n=2) days after tumors removal. All plasma samples were analyzed for concentrations of ir-INH, LH, FSH, estradiol-17beta (E2), testosterone (T) by RIA and progesterone (P) by EIA. Results showed that E2 levels were significantly higher (P<0.001) in control animals compared to E2 levels in GTCT mares before and after surgery. P and T concentrations were not statistically different between the groups. Baseline levels of ir-INH were greater (P<0.05) in GTCT mares before surgery than in control mares, and decreased to undetectable levels after neoplasia ablation. Baseline FSH did not differ between control and GTCT animals either before or after the ovaries were removed. LH baseline values appeared to be higher for affected mares, but the difference was not statistically significant. Maximum release (MR) and area under the gonadotrophin release curve (AUC) after the GnRH challenge for both the gonadotrophins were similar between the groups.     

FSH and LH plasma levels in bitches with differences in risk for urinary incontinence

To determine whether the height of the plasma gonadotropin levels after spaying is associated with urinary incontinence, the concentrations of plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) were determined once in 191 intact and 308 spayed bitches. The bitches were grouped according to their risk for urinary incontinence and the medians of their respective gonadotropin levels were compared. For intact anestrous bitches, the FSH- and LH-plasma concentrations were 5.2 (4, 8) ng/mL (median (Q1, Q3)) and 0.5 (0.5-0.5) ng/mL, respectively. In the first year after spaying, the gonadotropin concentrations rose significantly, then stabilised at a level around 10 times those of intact bitches (FSH 62.5 (44, 91) ng/mL; LH 6.1(4, 11) ng/mL). The plasma gonadotropin concentrations of long-term spayed (>12 months) continent bitches (n=209) were higher (FSH 66.8 (46, 104) ng/mL; LH 6.5 (4, 11) ng/mL) than in spayed incontinent bitches (n=60) (FSH 51.5 (38, 74) ng/mL; LH 5.5 (3, 8) ng/mL), the latter also had a higher body weight. Multiple regression analysis showed that the FSH-plasma concentration and not the body weight was decisive for the occurrence of urinary incontinence. The results of this study suggest that levels of gonadotropins are associated, directly or indirectly in the pathophysiology of urinary incontinence after spaying.     

Pituitary and ovarian responses of post-partum acyclic beef cows to continuous long-term GnRH and GnRH agonist treatment

Post-partum acyclic beef cows received continuous long-term treatment with GnRH (200 or 400 ng/kg body wt/h) or the GnRH agonist buserelin (5.5 or 11 ng/kg body wt/h) using s.c. osmotic minipumps which were designed to remain active for 28 days. All treatments increased circulating LH concentrations whereas FSH remained unchanged. Ovulation and corpus luteum (CL) formation as judged by progesterone concentrations greater than or equal to 1 ng/ml occurred in 0/5 control, 4/5 200 ng GnRH, 4/4 400 ng GnRH, 4/5 5.5 ng buserelin and 3/5 11 ng buserelin cows. The outstanding features of the progesterone profiles were the synchrony, both within and across groups, in values greater than or equal to 1 ng/ml around Day 6, and the fact that most CL were short-lived (4-6 days). Only 3 cows, one each from the 400 ng GnRH, 5.5 ng buserelin and 11 ng buserelin groups, showed evidence of extended CL function. Cows failed to show a second ovulation which was anticipated around Day 10 and this could have been due to insufficient FSH to stimulate early follicular development, or the absence of an endogenously driven LH surge. The highest LH concentrations for the respective groups were observed on Days 2 and 6 and by Day 10 LH was declining, although concentrations did remain higher than in controls up to Day 20.(ABSTRACT TRUNCATED AT 250 WORDS)