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1.
A radioimmunoassay (RIA) based on anti-equine prolactin antiserum and radioiodinated canine prolactin was used to assess the dose response of plasma prolactin to thyrotropin releasing hormone (TRH) in mares in the nonbreeding season (winter) and in mares in estrus in the breeding season (summer). Mares were administered TRH intravenously and blood samples were collected via jugular catheters at −15, 0, 15, 30, 45, 60, 90, 120, 180 and 240 min relative to injection. Doses of TRH were 0, .08, .40, 2.0 and 10.0 mg per mare (n = 3 per dose within each season). The prolactin response was assessed by absolute hormonal concentrations before and after TRH injection and by net area under the curve. Prolactin concentrations in plasma before injection of TRH were higher (P < .01) in estrous mares in summer than in anestrous mares in winter (4.8 vs 1.3 ng/ml). Moreover, there was a greater (P < .01) response to TRH injection in estrous mares than in anestrous mares. Based on areas under the curve, there was an effect of season (P < .01) and of TRH dose (P < .01) as well as a season-dose interaction (P < .01). In general, there was little or no prolactin response to any dose of TRH in anestrous mares in winter when pre-TRH concentrations were low. In contrast, there was an increase in the prolactin response with increasing doses of TRH up to 2.0 mg in estrous mares in summer; 2.0 and 10.0 mg of TRH resulted in similar prolactin secretion. We conclude 1) that prolactin secretion in the horse is stimulated by TRH as has been reported for other species and 2) that prolactin concentrations and the TRH-induced secretion of prolactin are greater in estrous mares in summer than in anestrous mares in winter.  相似文献   

2.
Pituitary and serum from 86 male or female horses of various reproductive states were collected in the normal breeding season (summer) and in the nonbreeding season (winter) at a commercial slaughterhouse. Concentrations of prolactin (PRL), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay. Concentrations of pregnant mare serum gonadotropin and reproductive steroids in serum and gross appearance of the reproductive tract and gonads were used to catagorize reproductive state. Concentrations of PRL were higher (P less than .01) in summer than in winter in pituitary and serum of mares, stallions and geldings. In summer, mares had higher (P less than .01) concentrations of PRL in serum than stallions. In mares, concentrations of LH in pituitary were higher (P less than .05) in summer than in winter. Concentrations of LH in serum were higher (P less than .01) in summer than in winter in mares and geldings, higher (P less than .01) in mares than in stallions in summer, higher (P less than .01) in geldings than in stallions in summer and higher (P less than .01) in mares with low serum progesterone (P) concentrations than in mares with high P concentrations in summer. Concentrations of FSH in pituitary and serum did not differ between summer and winter for any type of horse.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

3.
In two successive years, the pattern of secretion of thyroxine was compared in seasonally anestrous mares and a subpopulation of mares that exhibited estrous cycles during the nonbreeding season. Blood samples were collected two or three times per week between October and April from a total of 15 mares that exhibited estrous cycles during the nonbreeding season and 21 anestrous mares. Monthly mean concentrations of thyroxine during the period from October through April were greater (p<0.05) in cycling versus anestrous mares. However, it remains to be determined whether continuation of estrous cycles during the nonbreeding season and elevated concentrations of thyroxine are causally related.  相似文献   

4.
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   

5.
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   

6.
Studies were conducted to determine the specificity and cause of altered pituitary hormone secretion when ewes ingest endophyte-infected (Acremonium coenophialum) GI-307 tall fescue (toxic fescue). Plasma concentrations of prolactin (PRL) but not growth hormone (GH) or thyroid stimulating hormone (TSH) in ewes grazing toxic fescue were significantly lower (P < .01) than concentrations measured in ewes grazing orchardgrass (OG). Comparing hormone secretory responses of ewes grazing each grasstype, ewes on toxic fescue released less PRL following thyrotropin releasing hormone (TRH) challenge than ewes on OG. TSH responses to TRH were not affected by grasstype. At this dose of TRH, GH secretion was not significantly affected in either group of ewes. In a separate study, dopamine hydrochloride (DA) was infused into control ewes to define the effect of a pure dopamine agonist on basal and TRH-stimulated secretion of PRL, GH and TSH. DA depressed both basal and TRH-stimulated secretion of PRL without affecting the basal concentrations or responses of GH or TSH. Based on the assumption that the active agent in toxic fescue responsible for the observed hypoprolactinemia was a dopaminergic agonist, haloperidol (HAL), a DA receptor blocking drug, was administered to ewes grazing toxic fescue or OG. HAL evoked significant PRL secretion unaccompanied by any GH or TSH effect in both toxic fescue and OG ewes. Administration of HAL resulted in a gradual increase over 4 hr in PRL in toxic fescue ewes and prolonged the duration of the PRL response to TRH. No differences in circulating plasma concentrations of DA, epinephrine or norepinephrine were measured in ewes on troxic fescue or OG.

Alterations in pituitary hormone secretion due to toxic factors in fescue were confined to PRL. Hormone secretory responses to TRH and HAL suggest that the effects on PRL are mediated through dopamine-like activity in toxic fescue.  相似文献   


7.
Fifty-four lactating Holstein cows were used to define relationships between stage of lactation and environmental measures on thyrotropin releasing hormone (TRH)-induced secretion of triiodothyronine (T3, thyroxine (T4) and prolactin. Mean black globe temperatures were -.3, 20.6, and 25.5C for winter, spring, and summer months, respectively. The circulating hormone responses of T3, T4 and prolactin were significantly affected by season, sampling time and there was a season by sampling time interaction. T4 response was affected by stage of lactation, while prolactin responses differed by stage of lactation across the three seasons. Both T3 and T4 responses were lowest in winter and may indicate greater utilization rates to meet metabolic demands. T3 responses peaked near 3 hr post TRH, while T4 increased to the end of the 7 hr sampling period. Prolactin responses to TRH increased from winter through summer and were responsive to changes in ambient temperature and photoperiod. T4 response increased with advancing stage of lactation and could be due to changes in metabolic activity and clearance. Spring TRH-induced prolactin response decreased with advancing lactation whereas, the response increased as lactation progressed during the summer. Monthly milk yield was affected by stage of lactation and lactation number. Early lactation cows produced most milk and milk yield peaked in third lactation. Differential responses to TRH may reflect alterations in milk yield during different stages of lactation.  相似文献   

8.
Ten lighthorse stallions were used to determine 1) whether prolactin (PRL) and cortisol responses previously observed after acute exercise in summer would occur in winter when PRL secretion is normally low, 2) whether subsequent treatment with a dopamine receptor antagonist, sulpiride, for 14 d would increase PRL secretion and response to thyrotropin-releasing hormone (TRH) and exercise, and 3) whether secretion of LH, FSH, and cortisol would be affected by sulpiride treatment. On January 11, blood samples were drawn from all stallions before and after a 5-min period of strenuous running. On January 12, blood samples were drawn before and after an i.v. injection of GnRH plus TRH. From January 13 through 26, five stallions were injected s.c. daily with 500 mg of sulpiride; the remaining five stallions received vehicle. The exercise and secretagogue regimens were repeated on January 27 and 28, respectively. Before sulpiride injection, concentrations of both cortisol and PRL increased (P less than .05) 40 to 80% in response to exercise; concentrations of LH and FSH also increased (P less than .05) approximately 5 to 10%. Sulpiride treatment resulted in (P less than .05) a six- to eightfold increase in daily PRL secretion. The PRL response to TRH increased (P less than .05) fourfold in stallions treated with sulpiride but was unchanged in control stallions. Sulpiride treatment did not affect (P greater than .05) the LH or FSH response to exogenous GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

9.
Six insulin-sensitive and 6 insulin-insensitive mares were used in a replicated 3 by 3 Latin square design to determine the pituitary hormonal responses (compared with vehicle) to sulpiride and thyrotropin-releasing hormone (TRH), 2 compounds commonly used to diagnose pituitary pars intermedia dysfunction (PPID) in horses. Mares were classified as insulin sensitive or insensitive by their previous glucose responses to direct injection of human recombinant insulin. Treatment days were February 25, 2012, and March 10 and 24, 2012. Treatments were sulpiride (racemic mixture, 0.01 mg/kg BW), TRH (0.002 mg/kg BW), and vehicle (saline, 0.01 mL/kg BW) administered intravenously. Blood samples were collected via jugular catheters at −10, 0, 5, 10, 20, 30, 45, 60, 90, and 120 min relative to treatment injection. Plasma ACTH concentrations were variable and were not affected by treatment or insulin sensitivity category. Plasma melanocyte-stimulating hormone (MSH) concentrations responded (P < 0.01) to both sulpiride and TRH injection and were greater (P < 0.05) in insulin-insensitive mares than in sensitive mares. Plasma prolactin concentrations responded (P < 0.01) to both sulpiride and TRH injection, and the response was greater (P < 0.05) for sulpiride; no effect of insulin sensitivity was observed. Plasma thyroid-stimulating hormone (TSH) concentrations responded (P < 0.01) to TRH injection only and were higher (P < 0.05) in insulin-sensitive mares in almost all time periods. Plasma LH and FSH concentrations varied with time (P < 0.05), particularly in the first week of the experiment, but were not affected by treatment or insulin sensitivity category. Plasma GH concentrations were affected (P < 0.05) only by day of treatment. The greater MSH responses to sulpiride and TRH in insulin-insensitive mares were similar to, but not as exaggerated as, those observed by others for PPID horses. In addition, the reduced TSH concentrations in insulin-insensitive mares are consistent with our previous observation of elevated plasma triiodothyronine concentrations in hyperleptinemic horses (later shown to be insulin insensitive as well).  相似文献   

10.
Concentrations of serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) were determined after the administration of freshly reconstituted thyrotropin-releasing hormone (TRH), reconstituted TRH that had been previously frozen, or thyrotropin (TSH) to 10 mature dogs (6 Greyhounds and 4 mixed-breed dogs). Thyrotropin-releasing hormone (0.1 mg/kg) or TSH (5 U/dog) was administered IV; venous blood samples were collected before and 6 hours after administration of TRH or TSH. Concentrations of the T4 and T3 were similar (P greater than 0.05) in serum after administration of freshly reconstituted or previously frozen TRH, indicating that TRH can be frozen at -20 C for at least 1 week without a loss in potency. Concentrations of T4, but not T3, were higher after the administration of TSH than they were after the administration of TRH (P less than 0.01). Concentrations of T4 increased at least 3-fold in all 10 dogs given TSH, whereas a 3-fold increase occurred in 7 of 10 dogs given freshly reconstituted or previously frozen TRH. Concentrations of T4 did not double in 1 dog given freshly reconstituted TRH and in 1 dog given previously frozen TRH. Concentrations of T3 doubled in 5 of 10, 2 of 10, and 5 of 10 dogs given TSH, freshly reconstituted TRH, or previously frozen TRH, respectively. Results suggested that concentrations of serum T4 are higher 6 hours after the administration of TSH than after administration of TRH, using dosage regimens of 5 U of TSH/dog or 0.1 mg of TRH/kg.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

11.
A series of experiments was performed to determine the factor(s) responsible for an apparent inhibition of GH secretion in mares administered the GH secretagogue EP51389 in combination with GnRH, thyrotropin-releasing hormone (TRH), and sulpiride. Experiment 1 tested the repeatability of the original observation: 10 mares received EP51389 at 10 microg/kg BW; five received TRH (10 microg/kg BW), GnRH (1 microg/kg BW), and sulpiride (100 microg/kg BW) immediately before EP51389, and five received saline. The mixture of TRH, GnRH, and sulpiride reduced (P = 0.0034) the GH response to EP51389, confirming the inhibitory effects. Experiment 2 tested the hypothesis that sulpiride, a dopamine antagonist, was the inhibitory agent. Twelve mares received EP51389 as in Exp. 1; six received sulpiride before EP51389 and six received saline. The GH responses in the two groups were similar (P > 0.1), indicating that sulpiride was not the inhibitory factor. Experiment 3 tested the effects of TRH and(or) GnRH in a 2 x 2 factorial arrangement of treatments. Three mares each received saline, TRH, GnRH, or the combination before EP51389 injection. There was a reduction (P < 0.0001) in GH response in mares receiving TRH, whereas GnRH had no effect (P > 0.1). Given those results, Exp. 4 was conducted to confirm that TRH was inhibitory in vivo as opposed to some unknown chemical interaction of the two compounds in the injection solution. Twenty mares received TRH or saline and(or) EP51389 or saline in a 2 x 2 factorial arrangement of treatments. Injections were given separately so that the two secretagogues never came in contact before injection. Again, TRH reduced (P < 0.0001) the GH response to EP51389. In addition, TRH and EP51389 each resulted in a temporary increase in cortisol concentrations. Experiment 5 tested whether TRH would alter the GH response to GHRH itself. Twelve mares received porcine GHRH at 0.4 microg/kg BW; six received TRH prior to GHRH and six received saline. After adjustment for pretreatment differences between groups, the GHRH-induced GH response was completely inhibited (P = 0.068) by TRH. Exp. 6 was a repeat of Exp. 5, except geldings were used (five per group). Again, pretreatment with TRH inhibited (P < 0.0001) the GH response to GHRH. In conclusion, TRH inhibits the GH response not only to EP51389 but also to GHRH in horses, and in addition to its known secretagogue action on prolactin and TSH it may also stimulate ACTH at the dosage used in these experiments.  相似文献   

12.
An experiment was conducted to determine the effects of high vs low body condition scores (BCS) produced by restricted feeding on reproductive characteristics, hormonal secretion, and leptin concentrations in mares during the autumnal transition and winter anovulatory period. Mares with BCS of 6.5 to 8.0 were maintained on pasture and/or grass hay, and starting in September, were full fed or restricted to produce BCS of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) by December. All but one mare with high BCS continued to ovulate or have follicular activity during the winter, whereas mares with low BCS went reproductively quiescent. Plasma leptin concentrations varied widely before the onset of restriction, even though all mares were in good body condition. During the experiment, leptin concentrations gradually decreased (P < 0.0001) over time in both groups, but were higher (P < 0.009) in mares with high vs low BCS after 6 wk of restriction, regardless of initial concentration. No differences (P > 0.1) between groups were detected for plasma concentrations of LH, FSH, TSH, GH, glucose, or insulin in samples collected weekly; in contrast, plasma prolactin concentrations were higher (P < 0.02) in mares with high BCS, but also decreased over time (P < 0.008). Plasma IGF-I concentrations tended (P = 0.1) to be greater in mares with high vs low BCS. The prolactin response to sulpiride injection on January 7 did not differ (P > 0.1) between groups. During 12 h of frequent blood sampling on January 12, LH concentrations were higher (P < 0.0001), whereas GH concentrations (P < 0.0001) and response to secretagogue (EP51389; P < 0.03) were lower in mares with high BCS. On January 19, the LH response to GnRH was higher (P < 0.02) in mares with high BCS; the prolactin response to TRH also was higher (P < 0.01) in mares with high BCS. In conclusion, nutrient restriction resulting in low BCS in mares resulted in a profound seasonal anovulatory period that was accompanied by lower leptin, IGF-I, and prolactin concentrations. All but one mare with high BCS continued to cycle throughout the winter or had significant follicular activity on the ovaries. Although leptin concentrations on average are very low in mares with low BCS and higher in well-fed mares, there is a wide variation in concentrations among well-fed mares, indicating that some other factor(s) may determine leptin concentrations under conditions of high BCS.  相似文献   

13.
The purpose of this study was to validate a thyroid-stimulating hormone (TSH) assay in a model of equine hypothyroidism. Thyrotropin-releasing hormone (TRH) stimulation tests were performed in 12 healthy adult mares and geldings, aged 4 to greater than 20 years. before and during administration of the antithyroid drug propylthiouracil (PTU) for 6 weeks. Serum concentrations of equine TSH, total and free thyroxine (T4), and total and free triiodothyronine (T3) were measured. Before PTU administration, mean +/- standard deviation baseline concentrations of TSH were 0.40 +/- 0.29 ng/mL. TSH increased in response to TRH, reaching a peak concentration of 0.78 +/- 0.28 ng/mL at 45 minutes. Total and free T4 increased from 12.9 +/- 5.6 nmol/L and 12.2 +/- 3.5 pmol/L to 36.8 +/- 11.4 nmol/L and 23.1 +/- 5.9 pmol/L, respectively, peaking at 4-6 hours. Total and free T3 increased from 0.99 +/- 0.51 nmol/L and 2.07 +/- 1.14 pmol/L to 2.23 +/- 0.60 nmol/l and 5.78 +/- 1.94 pmol/L, respectively, peaking at 2-4 hours. Weekly measurements of baseline TSH and thyroid hormones during PTU administration showed that total and free T, concentrations fell abruptly and remained low throughout PTU administration. Total and free T4 concentrations did not decrease dramatically until weeks 5 and 4 of PTU administration, respectively. A steady increase in TSH concentration occurred throughout PTU administration, with TSH becoming markedly increased by weeks 5 and 6 (1.46 +/- 0.94 ng/mL at 6 weeks). During weeks 5 and 6 of PTU administration, TSH response to TRH was exaggerated, and thyroid hormone response was blunted. Results of this study show that measurement of equine TSH in conjunction with thyroid hormone measurement differentiated normal and hypothyroid horses in this model of equine hypothyroidism.  相似文献   

14.
Eight seasonally anestrous mares were administered intravaginal polyurethane sponges on December 15 and then weekly thereafter until February 1. Control mares received no sponges or genital contact. Sponge insertion caused an immediate surge in follicle-stimulating hormone (FSH) concentrations in jugular plasma in 50% of treated mares whereas no control mares had surges in FSH (P less than .05). The effect of treatment on luteinizing hormone (LH) concentrations was much less dramatic and only three treated mares appeared to have positive responses. Sponge-treated mares exhibited positive responses in FSH concentrations 11 times out of 32 mare-days and control mares zero out of 28 (P less than .05). The magnitude of the FSH response decreased rapidly with successive responses. Sponge insertion induced estrus in four of eight treated mares; no control mares exhibited estrus (P less than .05). Sponge insertion also increased ovarian size and the incidence of large follicles. When all mares were fed altrenogest for 14 d beginning February 1, there was no beneficial effect of sponge treatment on number of mares exhibiting estrus or on pregnancy rate. These data confirm earlier speculations that sponge treatment causes surges in gonadotropins and increased ovarian size in approximately 50% of anestrous mares. However, sponge treatment does not appear to provide a practical means of preparing mares for progestogen synchronization during the nonbreeding season.  相似文献   

15.
Serum concentrations of thyrotropin (TSH), prolactin, thyroxine, and 3,5,3'-triiodothyronine in 15 euthyroid dogs and 5 thyroidectomized and propylthiouracil-treated dogs after thyrotropin-releasing hormone (TRH) administration were measured. Although thyroidectomized and propylthiouracil-treated dogs had higher (P less than 0.01) base-line concentrations of TSH in serum than did euthyroid dogs, concentrations of TSH after TRH administration varied at 7.5, 15, and 30 minutes with 14 of 45 samples obtained from healthy dogs having lower TSH concentrations than before TRH challenge. Similarly, concentrations of 3,5,3'-triiodothyronine in the serum of euthyroid dogs 4 hours after TRH administration were similar (P less than 0.05) to concentrations before TRH challenge. Although the mean concentration of thyroxine in serum was elevated (P less than 0.05) 4 hours after administration of TRH to euthyroid animals, as compared with base-line levels, the individual response was variable with concentrations not changing or decreasing in 4 dogs. Therefore, the TRH challenge test as performed in the current investigation was of limited value in evaluating canine pituitary gland function. Although mean concentrations of TSH in serum were higher (P less than 0.05) in euthyroid dogs after TRH administration, the response was too variable among individual animals for accurate evaluation of pituitary gland function. Concentrations of prolactin in the sera of dogs after TRH administration, confirmed previous reports that exogenously administered TRH results in prolactin release from the canine pituitary and indicated that the TRH used was biologically potent.  相似文献   

16.
Short-term patterns of growth hormone (GH) secretion and factors affecting it were studied in mares and stallions. In Exp. 1, hourly blood samples were collected from three mares and three stallions in summer and winter. Although GH concentrations varied in a pulsatile manner in all horses, there was no effect of sex or season (P greater than .1) on plasma GH concentrations and no indication of a diurnal pattern of GH secretion. In Exp. 2, 10-min blood samples were drawn for 8 h from 12 mares; after 6 h, porcine GH-releasing hormone (GHRH) was administered i.v. at 0, 45, 90, or 180 micrograms/mare (three mares per dose). Pulsatile secretion of GH occurred in all mares and averaged 2.4 +/- .3 peaks/6 h; amplitudes were variable and ranged from 2.6 to 74.4 ng/mL. Eight of nine mares responded within 20 min to GHRH injection, but there was no difference (P greater than .1) among the three doses tested. In Exp. 3, plasma GH concentrations in stallions increased (P less than .05) 8- to 10-fold after 5 min of acute physical exercise or exposure to an estrual mare. Restraint via a twitch (5 min) and epinephrine administration (3 mg i.v.) also increased (P less than .05) plasma GH concentrations by approximately fourfold. In Exp. 4 and 5, administration of either .4, 2, or 10 mg of thyrotropin-releasing hormone (TRH) or 100 or 500 mg of sulpiride (a dopamine receptor antagonist) increased (P less than .01) plasma prolactin concentrations but had no effect (P greater than .1) on GH concentrations during the same period of time.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

17.
Effects of thyrotropin releasing hormone (TRH) on serum levels of thyroid hormones were studied in 12 Thoroughbred mares. Significant increases (P<0.05) of serum T4 levels occurred as early as 2 hours and peaked at 4–10 hours after intravenous injection of 0.5 – 5 mg TRH. Following injection of 0.5, 1, 3 and 5 mg of TRH the serum levels of T4 were increased 2.25, 2.42,2.42 and 3.67 fold, respectively, over pre-injection levels. Serum levels of T3 were also significantly increased (P<0.05) at 1 or 2 hours and peaked at 2 to 4 hoursafter injection. The mean peak increase of T3 levels were 2.87, 3.21, 3.10 and 3.10 fold over pre- injected in level in 0.5, 1, 3,5 mg treated horses, respectively. These results suggest that TRH can be an alternative to heterologous TSH for the equine thyroid function test. The recommended dosage is 1–3 mg, and most appropriate time to collect post-TRH blood sample is between 4–6 hours. Serum levels of T4 and T3 should increase 2–3 fold from baseline in normal horses.  相似文献   

18.
On December 11, 1974, 15 seasonally anestrous mares were assigned at random to 1 of 3 experimental groups: outdoor-control, indoor-control, or indoor light-treated (a 16-hour photo-period). This experiment was terminated on April 21, 1975. The five mares in the indoor light-treated group ovulated 59.0+/-6.9 days later, which was 74 days earlier (P less than 0.01) than 2 of the 5 outdoor-controls (the other 3 ovulated after April 21 during a subsequent experiment) and 50 days earlier (P less than 0.05) than the indoor-controls. Durations of the 1st estrus for the 3 groups of mares were 13.3+/-3.6, 8.4+/-2.0, and 6.0+/-1.0 days for the indoor light-treated, indoor-control, and outdoor-control groups, respectively. The indoor light-treated mares averaged 4.2 estrous cycles before April 21, the indoor-control mares averaged 1.4 estrous cycles, and 2 of 5 outdoor-control mares ovulated 1 time during the experiment. The peripheral blood luteinizing hormone (LH), estradiol, and progesterone concentrations were minimal during winter anestrous. The hormone changes normally associated with estrous cycle activity in mares--maximal estradiol and luteinizing hormone concentrations near ovulation and maximal progesterone concentration during diestrus--were observed in all mares beginning at the 1st estrus. Hair loss was observed earlier in the light-treated mares, than in either of the other groups. In conclusion, a 16-hour photo-period initiated in early December for anestrous brood mares caused endocrinologically normal estrous cycles to begin within 2 months. This may allow breeding and foaling considerably earlier than normally expected.  相似文献   

19.
Prolactin may play multiple roles in equine reproduction. Prolactin appears to be associated with seasonal reproduction, and fluctuating prolactin levels during the estrous cycle suggest that it may play a role in estrous cyclicity as well. The purpose of this research was to investigate the activity of prolactin during the follicular phase of the estrous cycle. In experiment 1, prolactin concentrations were determined from plasma samples collected at least every other day throughout the estrous cycle. Periovulatory (ovulation ± 1 day) prolactin concentrations were compared with concentrations during early diestrus (days 2−10 postovulation). In experiment 2, prolactin concentrations were measured in follicular fluid collected from 74 follicles of various sizes. Follicles were grouped into small (≤20 mm), medium (21−35 mm), and large (>35 mm) size categories. Prolactin concentrations increased during the periovulatory period in cycling mares. This periovulatory surge was superimposed on baseline prolactin concentrations that varied with season. Prolactin was present in significant quantities in the follicular fluid. Follicular fluid prolactin concentrations were lowest in small follicles and increased in medium and large follicles. Concentrations did not differ between medium and large follicles. Follicular fluid prolactin concentrations were lower in autumnal follicles compared with summer follicles of comparable size. It is possible that the short-term surge in circulating prolactin around ovulation could be linked to the significant levels of prolactin in follicular fluid. Ovulation releases a relatively large volume of fluid into the peritoneum. The prolactin in this fluid could be a contributor to the periovulatory prolactin surge.  相似文献   

20.
Two experiments studied the effects of pretreatment with estradiol benzoate before treatment with a dopamine antagonist on prolactin secretion and reproductive traits in mares during (1) the seasonal anovulatory period and (2) the normal breeding season. Experiment 1 was performed in winter with 17 mares selected for low follicular activity. Nine mares received estradiol benzoate injections every other day for a total of 10 injections; 8 mares received similar injections of vehicle. Ten days after onset of injections, all mares were placed on daily injections of sulpiride (250 mg) for 35 days or until ovulation. Plasma prolactin concentrations were higher (P < .001) in mares receiving estradiol than in controls for all assessments from days 12 through 36. Plasma luteinizing hormone (LH) concentrations were also increased (P < .05) by estradiol treatment from days 14 to 23. Mean day of first ovulation was 73.6 for control mares and 29.0 for estradiol-treated mares (P = .016). Estradiol treatment greatly enhanced prolactin secretion in response to sulpiride and increased LH secretion in seasonally anovulatory mares, which together hastened the date of first ovulation by an average of 45 days. Experiment 2 was designed to assess the efficacy of a long-acting, single-injection microparticle preparation of another dopamine antagonist, domperidone, for increasing prolactin secretion in cyclic mares in the summer. The experimental design and procedures used in experiment 1 were repeated, except that a single 3-g domperidone-microparticle injection was administered on day 11 rather than 45 days of sulpiride injections. Day 0 was the first day of estrus for each mare. Prolactin concentrations were higher (P < .05) in mares receiving estradiol than in control mares from days 12 through 25 and after a thyrotropin-releasing hormone injection on d 21. Estrous cycle traits (time to ovulation and time of luteal regression) were not affected (P > .1) by treatment. Estradiol enhanced the prolactin response to a single injection of 3 g domperidone in cyclic mares in the summer in a manner similar to the estradiol enhancement of prolactin secretion in response to daily sulpiride injections in anovulatory mares in winter. Thus, the single injection of domperidone could possibly replace the daily sulpiride injections used in experiment 1 to induce ovulation in seasonally anovulatory mares; this needs to be tested in future experiments.  相似文献   

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