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1.
Eight long-term ovariectomized pony mares were treated with either dihydrotestosterone (DHT) benzoate (400 micrograms/kg body weight) in safflower oil or an equivalent amount of oil every other day for 21 d to determine the effects of DHT on follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations in blood samples drawn once daily and after administration of three successive injections of gonadotropin releasing hormone (GnRH). The GnRH injections were given at 4-h intervals on the day following the last DHT or oil injection. Treatment with DHT benzoate did not alter (P greater than .10) concentrations of FSH or LH in daily blood samples relative to controls. The FSH and LH response, assessed by areas under the GnRH curves, decreased (P less than .05) from the first to third injection of GnRH when averaged over both groups of mares. There was no effect of DHT treatment on FSH response to GnRH. There was an interaction (P less than .05) between treatment and GnRH injection for LH areas; areas decreased (P less than .05) for DHT-treated mares from the first to third GnRH injection but were unchanged for control mares. It seems that DHT alone cannot mimic the stimulatory effects of testosterone on FSH production and secretion as observed in previous experiments with ovariectomized and intact mares. Moreover, because intact mares have been shown previously to respond to DHT treatment with an increase in GnRH-induced FSH secretion, it appears that some mechanism is lost in long-term ovariectomized mares, making them unresponsive to DHT treatment.  相似文献   

2.
In Exp. 1, 16 long-term ovariectomized pony mares were used to determine the effects of treatment with estradiol benzoate (EB) and dihydrotestosterone (DHT) benzoate alone, and in combination, on secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after three consecutive injections of gonadotropin releasing hormone (GnRH). Administration of EB alone, or in combination with DHT, every other day for 11 d reduced (P less than .05) concentrations of FSH and increased (P less than .05) concentrations of LH in daily blood samples, and increased (P less than .05) the secretion of both gonadotropins after administration of GnRH. Treatment with DHT alone had no effect (P greater than .10) on LH or FSH concentrations in daily blood samples and no effect on the LH response to exogenous GnRH. There was no interaction (P greater than .10) between DHT and EB treatment for any hormonal characteristic. In Exp. 2, the control mares and mares treated with DHT in Exp. 1 were equally allotted to treatment with vehicle or testosterone propionate (TP) every other day for six injections, and then GnRH was administered as in Exp. 1. Treatment with TP had no effect (P greater than .10) on LH or FSH concentrations in daily blood samples but increased (P less than .05) the FSH response to exogenous GnRH, confirming our findings in previous experiments. It is concluded that the TP-induced stimulation of FSH secretion after exogenous GnRH in ovariectomized mares may involve estrogens produced from aromatization of the injected androgen.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

3.
Twenty ovariectomized pony mares were used to determine if dihydrotestosterone propionate (DHTP) administration, with or without estradiol benzoate (EB) pretreatment, would have the same effects on follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion as testosterone propionate (TP) administration. All mares were given an initial injection of gonadotropin releasing hormone (GnRH) to characterize their LH and FSH response, and then two groups of mares (n = 4/group) were administered EB (22 micrograms/kg of body weight), two groups were administered vehicle (safflower oil) and a fifth group was administered TP (175 micrograms/kg of body weight) daily for 10 days. Following a second injection of GnRH, one group of EB-treated mares and one group of oil-treated mares were administered DHTP (175 micrograms/kg of body weight) daily for 10 days; the other EB- and oil-treated mares were administered oil and the TP-treated mares were continued on the same dose of TP for 10 days. A final injection of GnRH was then given. Treatment with EB increased (P less than .01) concentrations of LH in daily blood samples and increased (P less than .05) the LH response to exogenous GnRH. Administration of TP or DHTP reduced (P less than .05) both daily LH concentrations and the LH response to exogenous GnRH. Concentrations of FSH in daily blood samples were reduced (P less than .05) and the FSH response to exogenous GnRH was increased (P less than .05) by administration of EB alone, DHTP alone or TP.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

4.
An experiment was conducted to determine whether partial neutralization of estrogens via active immunization alters testosterone propionate (TP)-induced increases in FSH secretion after GnRH administration in ovariectomized pony mares. Twenty mares were used in a 2 X 2 factorial arrangement of treatments (n = 5/group). Factor 1 was long-term active immunization against either bovine serum albumin (BSA) or estrone-17-oxime-BSA. Factor 2 was 11-d administration of either vehicle (vegetable oil) or TP (175 micrograms/kg BW). Plasma concentrations of FSH were not affected (P greater than .1) by either factor. As expected, the FSH response to exogenous GnRH was threefold greater (P less than .05) in BSA-immunized mares treated with TP than in BSA-immunized mares receiving oil. However, immunization against estrogens reduced (P less than .05) this TP-induced increase in FSH response by 52%. Plasma concentrations of LH were decreased (P less than .08) by TP; this effect was not altered (P greater than .1) by immunization against estrogen. The LH response to exogenous GnRH was not affected (P greater than .1) by either factor. We conclude that aromatization of testosterone to estrogen is partially responsible for the increased FSH response to exogenous GnRH in TP-treated mares. In contrast, suppression of LH concentrations by TP appears to involve only the androgenic effect of TP.  相似文献   

5.
Twelve long-term ovariectomized (OVX) pony mares were used to determine the effects of dexamethasone (DEX) or progesterone (PR) on concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in daily blood samples and after administration of gonadotropin releasing hormone (GnRH). All mares were subsequently administered dihydrotestosterone (DHT) to determine if DEX or PR treatment altered the FSH or LH response to this androgen. Daily blood sampling was started on day 1. After a pretreatment injection of GnRH on day 5, four mares were administered DEX at 125 micrograms/kg of body weight (BW), four mares were administered PR at 500 micrograms/kg of BW and four mares were administered vehicle. Injections were given subcutaneously in vegetable shortening daily through day 14. After a second injection of GnRH on day 15, all mares were administered DHT in shortening at 150 micrograms/kg of BW. Injections of DHT were given daily through day 24. A final injection of GnRH was given on day 25. Treatment of mares with DEX 1) reduced (P less than .01) daily LH secretion and briefly increased (P less than .05) daily FSH secretion and 2) increased (P less than .01) the FSH response to exogenous GnRH. Treatment of mares with PR had no effect on daily LH secretion but increased (P less than .05) daily FSH secretion and increased (P less than .01) the FSH response to exogenous GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

6.
Two experiments with steers were performed to determine the effects of 10 days of treatment with testosterone propionate (TP) on secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) after the administration of gonadotropin releasing hormone (GnRH). In Experiment 1, eight 15-month-old Holstein steers castrated at 12 months of age were used. In Experiment 2, eight beef-type steers between the ages of 12–18 months old and which had been castrated for 8–15 months were used. An initial injection of GnRH was followed by 10 daily injections of TP (175 ug/ kg of body weight) or safflower oil, and on the eleventh day a second injection of GnRH was given. Hormonal endpoints in long-term castrated steers (Experiment 2) were not altered by TP treatment. In contrast, TP treatment significantly suppressed FSH and LH concentrations in daily blood samples from Experiment 1 steers and significantly increased the response to GnRH. The lack of response in the long-term castrated steers (Experiment 2) to TP treatment is similar to the response observed in previous experiments with long-term ovariectomized cows. However, from the results of Experiment 1, it appears that the timing of castration influences the response to TP treatment.  相似文献   

7.
Five lighthorse mares were actively immunized against gonadotropin releasing hormone (GnRH) conjugated to bovine serum albumin (BSA) to study the involvement of GnRH in luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion following ovariectomy (OVX) and after administration of testosterone propionate (TP). Five mares immunized against BSA served as controls. Immunizations were started on November 1, and OVX was performed in June (d 1). All mares were treated with TP from d 50 to 59 after OVX. On the day of OVX, concentrations of LH were lower (P less than .05) in GnRH-immunized mares than in BSA-immunized mares and were generally nondetectable; FSH concentrations were reduced (P less than .05) by 50% in GnRH-immunized mares relative to BSA-immunized mares. In contrast to BSA-immunized mares, plasma concentrations of LH or FSH did not increase after OVX in GnRH-immunized mares. The LH response to GnRH analog (less than .1% cross-reactive with GnRH antibodies) on d 50 was reduced (P less than .05) by 97% in GnRH-immunized mares relative to BSA-immunized mares, whereas the FSH response was similar for both groups. Treatment with TP for 10 d reduced (P less than .01) the LH response and increased (P less than .01) the FSH response to GnRH analog in BSA-immunized mares, but it had no effect (P greater than .1) on the response of either gonadotropin in GnRH-immunized mares.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

8.
Ten stallions were used to determine if the stallion responds to administration of testosterone propionate (TP) with an increase in follicle stimulating hormone (FSH) secretion after administration of gonadotropin releasing hormone (GnRH) as has been previously observed for geldings and intact and ovariectomized mares. Five stallions were treated with TP (350 μg/kg of body weight) in safflower oil every other day for 11 days; control stallions received injections of safflower oil. The response to GnRH (1.0 μg/kg of body weight) was determined for all stallions before the onset of treatment (GnRH I) and at the end of treatment (GnRH II). Blood samples were also withdrawn daily from 3 days prior to treatment through GnRH II. Treatment with TP decreased (P<.10) concentrations of FSH in daily blood samples. However, treatment with TP did not affect (P>.10) the GnRH-induced secretion of FSH. Concentrations of luteinizing hormone (LH) decreased (P<.05) in daily blood samples averaged over both groups of stallions and were lower (P<.10) in TP-treated stallions than in controls during the latter days of treatment. We conclude that TP administration to stallions does not alter the FSH response to GnRH as has been observed for geldings and for mares of several reproductive states.  相似文献   

9.
Hourly pulses of gonadotropin-releasing hormone (GnRH) or bi-daily injections of estradiol (E2) can increase luteinizing hormone (LH) secretion in ovariectomized, anestrous pony mares. However, the site (pituitary versus hypothalamus) of positive feedback of estradiol on gonadotropin secretion has not been described in mares. Thus, one of our objectives involved investigating the feedback of estradiol on the pituitary. The second objective consisted of determining if hourly pulses of GnRH could re-establish physiological LH and FSH concentrations after pituitary stalk-section (PSS), and the third objective was to describe the declining time trends of LH and FSH secretion after PSS. During summer months, ovariectomized pony mares were divided into three groups: Group 1 (control, n = 2), Group 2 (pulsatile GnRH (25 μg/hr), n = 3), and Group 3 (estradiol (5 mg/12 hr), n = 3). All mares were stalk-sectioned and treatment begun immediately after stalk-section. Blood samples were collected every 30 min for 8 h on the day before surgery (DO) and 5 d post surgery (D5) to facilitate the comparison of gonadotropin levels before and after pituitary stalk-section. Additionally, jugular blood samples were collected every 12 hr beginning the evening of surgery, allowing for evaluation of the gonadotropin secretory time trends over the 10 d of treatment. On Day 10, animals were euthanized to confirm pituitary stalk-section and to submit tissue for messenger RNA analysis (parallel study). Plasma samples were assayed for LH and FSH by RIA. Mean LH secretion decreased from Day 0 to Day 5 in Groups 1 and 3, whereas LH secretion tended (P < 0.08) to decrease in Group 2 mares. On Day 5, LH was higher (P < 0.01) in Group 2 (17.26 ± 3.68 ng/ml; LSMEANS ± SEM), than either Group 1 (2.65 ± 4.64 ng/ml) or group 3 (4.28 ± 3.68 ng/ml). Group 1 did not differ from Group 3 on Day 5 (P < 0.40). Similarly, mean FSH levels decreased in all groups after surgery, yet Group 2 mares had significantly (P < 0.001) higher FSH concentrations (17.66 ± 1.53 ng/ml) than Group 1 or Group 3 (8.34 ± 1.84 and 7.69 ± 1. 63 ng/ml, respectively). Regression analysis of bi-daily LH and FSH levels indicated that the time trends were not parallel. These findings indicate: 1) Pituitary stalk-section lowered LH and FSH to undetectable levels within 5 d after surgery, 2) pulsatile administration of GnRH (25 μg/hr) maintained LH and FSH secretion, although concentrations tended to be lower than on Day 0, and 3) E2 did not stimulate LH or FSH secretion.  相似文献   

10.
Thirty-five ovariectomized pony mares were used to study the relationships among luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) concentrations in blood (secretion), in pituitary (storage) and in blood after secretagogue administration, as well as the content of gonadotropin releasing hormone (GnRH) in hypothalamic areas, under various conditions of steroidal and nonsteroidal treatment. Five mares each were treated daily for 21 d with vegetable shortening (controls), testosterone (T; 150 micrograms/kg of body weight, BW), dihydrotestosterone (DHT; 150 micrograms/kg BW), estradiol (E2; 35 micrograms/kg BW), progesterone (P4; 500 micrograms/kg BW), dexamethasone (DEX; 125 micrograms/kg BW) or charcoal-stripped equine follicular fluid (FF; 10 ml). Secretagogue injections (GnRH and thyrotropin releasing hormone, TRH, at 1 and 4 micrograms/kg of BW, respectively) were given one d prior to treatment and again after 15 d of treatment. Relative to controls, treatment with T, DHT and DEX reduced (P less than .05) LH secretion, storage and response to exogenous GnRH, whereas treatment with E2 increased (P less than .05) these same characteristics. Treatment with P4 reduced (P less than .05) only LH secretion. Treatment with T, DHT, E2 and DEX reduced (P less than .05) FSH secretion, whereas treatment with P4 increased (P less than .05) it and FF had no effect (P greater than .1). All treatments increased (P less than .05) FSH storage, whereas only treatment with T and DHT increased (P less than .05) the FSH response to exogenous GnRH. Other than a brief increase (P less than .05) in PRL secretion in mares treated with E2, secretion of PRL did not differ (P greater than .1) among groups. Only treatment with E2 increased (P less than .01) PRL storage, yet treatment with T or DHT (but not E2) increased (P less than .05) the PRL response to exogenous TRH. Content of GnRH in the body and pre-optic area of the hypothalamus was not affected (P greater than .1) by treatment, whereas treatment with T, E2 and DEX increased (P less than .1) GnRH content in the median eminence. For LH, secretion, storage and response to exogenous GnRH were all highly correlated (r greater than or equal to .77; P less than .01). For FSH, only storage and response to exogenous GnRH were related (r = .62; P less than .01). PRL characteristics were not significantly related to one another. Moreover, the amount of GnRH in the median eminence was not related (P greater than .1) to any LH or FSH characteristic.  相似文献   

11.
Six pony geldings were actively immunized against GnRH conjugated to bovine serum albumin (BSA) to study 1) the relative dependency of LH and FSH storage, secretion and response to GnRH analog on GnRH bioavailability and 2) the effects of reduced GnRH bioavailability on GnRH storage in the hypothalamus. Five geldings were immunized against BSA. Geldings were immunized in December and 4, 8, 14, 20, 26 and 32 wk later. Ponies immunized against GnRH had increased (P less than .01) GnRH binding in plasma within 6 wk. By June, plasma concentrations of LH and FSH in ponies immunized against GnRH had decreased (P less than .02) by 86 and 59%, respectively, relative to ponies immunized against BSA. The LH response to an injection of GnRH analog, which did not bind to anti-GnRH antibodies, was reduced (P less than .005) by 90% in ponies immunized against GnRH relative to ponies immunized against BSA. In contrast, the FSH response to GnRH analog was similar (P greater than .1) for both groups. Immunization against GnRH reduced (P less than .05) weight of the anterior pituitary (AP) by 31%, LH content in AP by 91% and FSH content in AP by 55% relative to ponies immunized against BSA. There was no effect of GnRH immunization on prolactin characteristics or on GnRH concentrations in the median eminence, preoptic area or body of the hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

12.
Seventeen seasonally anovulatory light horse mares were treated daily, starting January 5 (d 1), for 28 d with GnRH analog (GnRH-A; 50 ng/kg BW) and(or) thyrotropin-releasing hormone (TRH; 5 microg/kg BW) in a 2 x 2 factorial arrangement of treatments to test the hypothesis that combined treatment may stimulate follicular growth and development. Ovaries were examined via ultrasonography and jugular blood samples were collected every 3 d. Frequent blood samples were collected after treatment injections on d 1, 2, 4, 7, 11, 16, and 22; on d 29, all mares received an i.v. mixture of GnRH, TRH, sulpiride, and EP51389 (a growth hormone secretagogue) to assess pituitary responsiveness. No consistent effects (P > 0.1) of treatment were observed for plasma LH, FSH, prolactin, or thyroxine concentrations in samples collected every 3 d. The only effect on ovarian follicle numbers was a reduction in number of follicles 11 to 19 mm in diameter due to TRH treatment (P = 0.029). No mare ovulated during treatment. On the days of frequent sampling, mean LH (P = 0.0001) and FSH (P = 0.001) concentrations were higher in mares receiving GnRH-A and tended to increase from d 1 through 7. In contrast, mean prolactin (P = 0.001) and thyroid-stimulating hormone (P = 0.0001) concentrations were high in mares receiving TRH on d 1 but rapidly decreased thereafter. When mares were administered the secretagogue mixture on d 29, the LH response was greater (P = 0.0002) in mares that had previously received GnRH-A but the FSH response was not affected (P > 0.1); the prolactin response was greater (P = 0.014) and the TSH response was smaller (P = 0.0005) in mares that had previously received TRH. Surprisingly, an immediate growth hormone response to EP51389 was absent in all mares. In conclusion, daily GnRH-A treatment stimulated plasma LH and FSH concentrations immediately after injection; although no long-term elevation in preinjection concentrations was achieved, the responses gradually increased over time, indicating a stimulation of gonadotropin production and storage. Daily treatment with TRH stimulated plasma TSH and prolactin concentrations, but the response diminished rapidly and was minimal within a few days, indicating a depletion of pituitary stores and little or no stimulation of production. There was no beneficial effect of adding TRH treatment to the daily GnRH-A regimen.  相似文献   

13.
The effect of adrenocorticotropin hormone (ACTH) on plasma cortisol and on gonadotropin releasing hormone (GnRH)-induced release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone was determined in nine Holstein bulls and 12 Holstein steers. Treatments consisted of animals receiving either GnRH (200 micrograms, Group G), ACTH (.45 IU/kg BW, Group A) or a combination of ACTH followed 2 h later by GnRH (Group AG). Group G steers and bulls had elevated plasma LH and FSH within .5 h after GnRH injection and plasma testosterone was increased by 1 h after GnRH injection in bulls. In Group A, plasma cortisol was elevated by .5 h after ACTH injection in both steers and bulls, but plasma LH and FSH were unaffected. In Group A bulls, testosterone was reduced after ACTH injection. In Group AG, ACTH caused an immediate increase in plasma cortisol in both steers and bulls, but did not affect the increase in either plasma LH or FSH in response to GnRH in steers. In Group AG bulls, ACTH did not prevent an increase in either plasma LH, FSH or testosterone in response to GnRH compared with basal concentrations. However, magnitude of systemic FSH response was reduced compared with response in Group G bulls, but plasma LH and testosterone were not reduced. The results indicate that ACTH caused an increase in plasma cortisol, but did not adversely affect LH or FSH response to GnRH in steers and bulls. Further, while testosterone was decreased after ACTH alone, neither ACTH nor resulting increased plasma cortisol resulted in decreased testosterone production in the bull after GnRH stimulation.  相似文献   

14.
Nutritionally induced anovulatory cows were ovariectomized and used to determine the relationships between dose, frequency, and duration of exogenous gonadotropin-releasing hormone (GnRH) pulses and amplitude, frequency, and concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum. In Experiment 1, cows were given pulses of saline (control) or 2 micrograms of GnRH infused i.v. during a 0.1-, 1.25-, 5-, 10-, or 20-min period. Concentrations of LH and FSH during 35 min after GnRH infusion were greater than in control cows (P < 0.01), and FSH concentrations were greater when GnRH infusions were for 10 min or less compared with 20 min. In Experiment 2, the effect of GnRH pulse frequency and dose on LH and FSH concentrations, pulse frequency, and pulse amplitude were determined. Exogenous GnRH (0, 2, or 4 micrograms) was infused in 5 min at frequencies of once every hour or once every 4th hr for 3 d. There was a dose of GnRH x frequency x day effect on LH and FSH concentrations (P < 0.01), indicating that gonadotropes are sensitive to changes in pulse frequency, dose, and time of exposure to GnRH. There were more LH pulses when GnRH was infused every hour, compared with an infusion every 4th hr (P < 0.04). Amplitudes of LH pulses were greater with increased GnRH dose (P < 0.05), and there was a frequency x dose x day effect on FSH pulse amplitude (P < 0.0006). We conclude that LH and FSH secretion in the bovine is differentially regulated by frequency and dose of GnRH infusions.  相似文献   

15.
Four groups of mares, representing anestrus (AN; n = 8), early transition (ET; n = 7), late transition (LT; n = 8) and estrus (EST; n = 12) were used to examine release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) after a bolus injection of gonadotropin releasing hormone (GnRH) during the transition from anestrus into the breeding season. Estrous mares received GnRH on d 2 or 3 of estrus in the cycle immediately preceding slaughter. Anestrous, ET and LT mares received GnRH exactly 1 wk prior to slaughter. A single injection of GnRH (Sigma LHRH, L-0507, 2.0 micrograms/kg body weight in .9% saline, iv) was given to each mare. Blood samples were collected at -2, h, -1 h, directly prior to GnRH, then 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300, 360, 420 and 480 min post-injection. Maximum release of LH and FSH was observed within 30 min after injection of GnRH. Except for the LH response in EST mares, concentrations of both hormones had returned to pre-injection baseline levels within 8 h. Group means for area under the curve (AUC) of concentrations of LH in serum, and the maximum amount (MAX) of LH quantified in serum, post-GnRH, increased (P less than .05) progressively from AN to the breeding season. The AUC and MAX responses for FSH showed a reverse pattern, decreasing (P less than .05) from AN to the breeding season.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

16.
Ovarian function in 91 dairy cows with cystic ovarian disease was assessed by rectal palpation and by plasma hormone analysis before and after treatment. Plasma analysis showed that 84% of the cysts were correctly classified clinically and only these cows are considered further. Luteinised cysts occurred in 59 cows whereas only 18 had non-luteinised cysts. The mean plasma concentrations of luteinising hormone (LH), follicular stimulating hormone (FSH), progesterone, oestradiol and testosterone were not significantly different when compared with values at relevant stages of the oestrous cycle in normal cows. Success of treatment with progesterone, a synthetic prostaglandin, human gonadotrophin (HCG), or gonadotrophin releasing hormone (GnRH) was not dependent upon prior hormone concentrations, except for the prostaglandin which required active luteal tissue. LH and FSH concentrations in cows with luteinised cysts were not significantly different before and after successful treatment with GnRH or progesterone. Normal luteal function was not always established after treatment of non-luteinised cysts with GnRH.  相似文献   

17.
Changes in numbers of ovarian follicles and coincident secretion of pituitary gonadotropins were characterized in suckled, anovulatory beef cows injected iv with 500 ng of luteinizing hormone-releasing hormone (LHRH) every 2 h for 48 or 96 h, starting 21.4 +/- .4 d after parturition. Two hours after the last injection, all cows were ovariectomized. Compared with saline-injected controls, LHRH had no effect on baseline or overall concentrations of luteinizing hormone (LH) in serum (P greater than .10), but increased (P less than .05) frequency and decreased (P less than .05) amplitude of LH pulses. Luteinizing hormone-releasing hormone increased (P less than .05) baseline concentration of follicle stimulating hormone (FSH) in serum and frequency of FSH pulses, but decreased (P less than .05) pulse amplitude. Overall concentrations of FSH increased 20% (P less than .10). Exogenous LHRH did not affect diameter of the two largest follicles or numbers of follicles 1.0 to 3.9 mm, 4.0 to 7.9 mm or greater than or equal to 8.0 mm in diameter. These data suggest that increasing the frequency of episodic LH and FSH pulses in postpartum cattle by intermittent administration of LHRH did not increase mean circulating levels of LH, or alter size and numbers of ovarian follicles within the 96-h period of injections. Thus, induction of ovulation in anovulatory cows treated with low-dose injections of LHRH cannot be explained on the basis of an increase in mean concentrations of LH or numbers of antral follicles within 96 h after initiation of injections.  相似文献   

18.
Sequential samples of blood were drawn via jugular catheters every 15 min for 24 h from four mares in each of five reproductive states: intact anestrous mares in winter, intact diestrous mares in summer, intact estrous mares in summer, ovariectomized mares in winter and ovariectomized mares in summer. Estrous mares were sampled on d 4 or 5 of estrus and diestrous mares on d 10 or 11 of diestrus. Each sample of plasma was assessed for concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) in two independent radioimmunoassays. A computer program was developed that determined peak hormone concentrations based on assay sensitivity, assay variability and repeatability of peaks in both independent assays. Peaks in LH and FSH were observed for mares in all five reproductive states, except for FSH concentrations in estrous mares. High frequency peaks of short duration were observed only in ovariectomized mares. Low frequency peaks of relatively long duration were observed in both intact and ovariectomized mares in both seasons. With the exception of estrous mares, there was variation among mares in the patterns of LH and(or) FSH within any one group; all estrous mares exhibited high, variable LH concentrations and low, constant FSH concentrations. In general, peaks in both gonadotropins occurred simultaneously. Ovariectomized mares exhibited more (P less than .05) peaks/24 h than intact mares for both gonadotropins. Ovariectomized mares also exhibited more (P less than .05) FSH peaks/24 h in summer than in winter.  相似文献   

19.
The present experiment characterized the pituitary responsiveness to exogenous GnRH in the first 10 d after ovulation following commercially available deslorelin acetate implantation at the normal dosage for hastening ovulation in mares. Twelve mature, cyclic mares were assessed daily for estrus and three times weekly for ovarian activity starting May 1. Mares achieving a follicle at least 25 mm in diameter or showing signs of estrus were checked daily thereafter for ovarian characteristics. When a follicle >30 mm was detected, mares were administered either a single deslorelin acetate implant or a sham injection and then assessed daily for ovulation. On d 1, 4, 7, and 10 following ovulation, each mare was challenged i.v. with 50 microg GnRH, and blood samples were collected to characterize the LH and FSH responses. The size of the largest follicle on the day of treatment did not differ (P = 0.89) between groups. The number of days from treatment to ovulation was shorter (P < 0.001) by 2.0 d for the treated mares indicating a hastening of ovulation. The size of the largest follicle present on the days of GnRH challenge was larger in the treated mares on d 1 (P = 0.007) but smaller on d 10 (P = 0.02). In addition, the interovulatory interval was longer (P = 0.036) in the treated mares relative to controls by 4.4 d. Concentrations of FSH in plasma of the treated mares were lower (P < 0.05) than control concentrations from d 3 to 12; LH concentrations in the treated mares were lower (P < 0.05) relative to controls on d 0 to 5, d 7, and again on d 20 to 23. Progesterone values were the same (P = 0.99) for both groups from 2 d before ovulation though d 23. There was an interaction of treatment, day, and time of sampling (P < 0.001) for LH and FSH concentrations after injection of GnRH. Both the LH and FSH responses were suppressed (P < 0.009) in the treated mares relative to controls on d 1, 4, and 7; by d 10, the responses of the two groups were equivalent. In conclusion, deslorelin administration in this manner increased the interovulatory interval, consistently suppressed plasma LH and FSH concentrations, and resulted in a complete lack of responsiveness of LH and FSH to GnRH stimulation at the dose used during the first 7 d after the induced ovulation. Together, these results are consistent with a temporary down-regulation of the pituitary gland in response to deslorelin administered in this manner.  相似文献   

20.
Eight mature light-breed stallions with normal testes size, sperm output and semen quality were used to evaluate response to 3 GnRH challenge regimens in the summer in southeast Texas. Gonadotropin releasing hormone (50 μg) was administered intravenously once to each of eight stallions after three days of sexual rest (50 μg GnRH-1X). The same stallions were administered either 5μg GnRH intravenously once hourly for three injections (5 μg GnRH-3X) and 15μg GnRH intravenously once (15μg GnRH-1X) one and two weeks later. Blood samples were collected prior to and at intervals after GnRH administration. Plasma was immediately separated from blood samples and was frozen until assayed for LH, FSH, estradiol and testosterone concentrations. Percentage changes in hormone concentrations from pre-treatment values (baseline) were analyzed by paired studient'st-test to detect significant rises in hormone concentrations. Group mean percentage changes in hormone concentrations were analyzed by analysis of variance to compare responses among treatments. A computerized peak-detection algorithm (PC Pulsar) was used to detect peaks in LH and testosterone concentrations following 5 μg GnRH-3X and 15 μg GnRH-1X treatment.No differences (P>0.10) were detected in percentage change from baseline concentration for LH, FSH, or testosterone at one or two hours after administration of any of the three regimens of GnRH. When more frequent sampling intervals were analyzed for 5 μg GnRH-3X or 15 μg GnRH-1X treatments, no differences were detected in percentage change from baseline concentration for any hormone at 15, 30 or 60 minutes. Thereafter, percentage changes in concentrations of LH and FSH remained increased for 5μg GnRH-3X compared to 15 μg GnRH-1X treated stallions (P<0.05). Percentage changes in concentrations of testosterone were increased for 5μg GnRH-3X compared to 15 μg GnRH-1X treated stallions from 180–300 min (P<0.05), while no differences (P>0.10) were detected between 5 μg GnRH-3X and 15 μg GnRH-1X treated stallions for changes in concentrations of estradiol throughout the experiment.For 15 μg GnRH-1X treated stallions, maximum concentrations of LH in PC Pulsar-detected peaks occurred most commonly at 15 to 30 minutes (7/8 treatment periods) after GnRH injection. Maximum concentrations of testosterone in PC Pulsar-detected peaks occurred most commonly at 60–120 min (7/8 treatment periods) after GnRH injection.A protocol of blood sampling prior to, and 15, 30, 60 and 120 minutes after, intravenous administration of small doses of GnRH would be practical for challenge testing of stallions during the breeding season. In order to reduce cost of hormone assays, we suggest assay of the pre-challenge blood sample (baseline) could include LH, FSH, testosterone and estradiol concentrations (to assess overall hypothalamic-pituitary-testicularfunction), while only LH and testosterone concentrations need be determined after GnRH administration (to assess pituitary and testicular responsiveness). Assay for LH could be done on only the 15 and 30 minute post-GnRH samples, and assay for testosterone could be done on only the 60 and 120 minute post-GnRH samples. Failure to achieve approximately a 50% increase in LH concentration by 30 minutes after GnRH administration, and/or failure to achieve approximately a 100% increase in testosterone concentration by two hours after GnRH administration, could be further pursued either by treatment with increasing dosages of GnRH, or repeated administration of GnRH at hourly intervals, as has been suggested by other workers.  相似文献   

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