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1.
Crossbred boars were used to evaluate the influence of exposure to 8 or 16 hr of light daily from 75 to 175 days of age on growth rate, testicular characteristics and endocrine function. At 160 days of age, concentrations of testosterone in serum (P<.10), the areas under plotted 12 hr testosterone profiles (P<.10) and the number (P<.05) and magnitude (P<.10) of testosterone secretory spikes were increased in boars exposed to 16 hr of light compared to boars in 8 hr light, but concentrations of LH in serum were similar in boars exposed to both treatments. Treatment with GnRH resulted in similar concentrations of LH in serum for both groups of boars. Testosterone in serum after GnRH-mediated LH release was greater at .5 (P<.05) and 1.0 (P<.10) hr following GnRH in boars exposed to 16 hr of light compared to boars at 8 hr, but concentrations of testosterone were similar for both treatments from 1.5 to 4.0 hr after GnRH. Growth rate and testicular and epididymal weights and sperm reserves at 175 days of age were not significantly altered by duration of photoperiod. Boars exposed to 8 hr of light had more hair per unit area than boars exposed to 16 hr of light. We conclude that exposure of prepubertal boars to longer daily photoperiods results in increased concentrations of testosterone in serum at 160 days of age.  相似文献   

2.
Effects of season and photoperiod on the anterior pituitary gland and testes were studied by responses to exogenous GnRH. Stallions were assigned to one of three treatments: 1) control, exposed to natural day length; 2) S-L, 8 h of light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984; or 3) S-S, 8:16 from July 16, 1982 until March 5, 1984. Approximately every 8 wk, stallions were administered GnRH (2 micrograms/kg BW) and blood was sampled at 20-min intervals for 2 h before and 8 h after GnRH administration. Concentrations of LH, FSH and testosterone were determined. Baseline concentrations (mean of pre-GnRH samples) of all hormones fluctuated seasonally (P less than .05), but only LH and testosterone displayed seasonal changes (P less than .05) in maximum response to GnRH (highest concentration above baseline after GnRH). The FSH response to GnRH was not affected (P greater than .05) by season, photoperiod or the season X treatment interaction. Exposure of S-L stallions to 16:8 in December resulted in early recrudescence of baseline concentrations of LH, FSH and testosterone. Maximum concentration of testosterone in response to GnRH was stimulated by 16:8, but the increase in baseline LH concentrations in S-L stallions was not associated with an increase in maximum LH response to GnRH. Seasonal patterns of baseline concentrations of FSH and testosterone and maximum LH response to GnRH in S-S stallions were similar to those for control stallions.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

3.
The effects of hemi-castration upon compensatory hypertrophy, serum gonadotropin and testosterone concentrations, testicular gonadotropin receptors and daily sperm production (DSP) were studied in 10 crossbred ram lambs. At 4 mo of age lambs were either hemi-castrated (HC; n = 5) or left intact (INT; n = 5). Blood samples were collected every 2 h for the first 24 h post-surgery, every 6 h for the next 24 h and then three times weekly for the following 14 wk. Serial blood samples (15-min intervals for 8 h) were collected during the 4th, 8th and 12th week following hemi-castration. Individual mean testicular and epididymal weights increased (P less than .05) 48 and 33% in HC compared with INT rams, respectively. Serum follicle stimulating hormone (FSH) increased (P less than .05) within 8 h after HC, reached peak concentrations within 1 wk and remained elevated for 4 wk before returning to concentrations of INT rams. Neither mean serum luteinizing hormone (LH) nor pulse patterns of LH or FSH were different (P greater than .05) between these two groups at any period examined. Serum testosterone (T) concentrations were lower (P less than .05) during the first 48 h post-surgery in HC rams, but by 1 wk concentrations were similar (P greater than .05) to those in INT rams. Remaining testes from HC and INT rams were removed at 7 mo of age, 3 mo after initial gonadal manipulation. On a per-testis basis there were more (P less than .05) LH and FSH receptors in HC than INT rams, respectively; however, concentrations of receptors were not different (P greater than .05).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

4.
The objective of the present study was to determine if postpubertal boars (12-13 months of age; 156 +/- 8 kg) with large testes had altered hypothalamic control of secretion of luteinizing hormone (LH). Seven boars with the highest estimated 150 d, paired testis weights from a line selected for large testes (769 +/- 60 g = mean weight of excised testes) and 8 boars from a control group (control, 544 +/- 20 g) were tethered in stalls and fitted with indwelling jugular catheters. Males were bled when they were intact, 14 days after castration and during administration of sodium pentobarbital anesthetic (subsequent to castration) to block secretion of endogenous LH-releasing hormone (LHRH). Blood samples were collected at 12-min intervals for 6 hr before and 1 hr after intravenous injection of LHRH in intact and castrated males. During anesthesia, LHRH was administered 4 times at 1-hr intervals and blood samples were collected every 6 min. All samples were analyzed for concentrations of LH and pooled samples were analyzed for concentrations of 17-beta estradiol (E2) and testosterone (T). In intact and castrated males, mean concentrations of LH, frequency and amplitude of pulses of LH, and concentrations of E2 and T were not different between boars of the two groups (P greater than .10). Response to exogenous LHRH was less (P less than .05) in intact males with large testes than in corresponding males from the control group (P less than .05). Fourteen days after castration, males that had larger testes before castration had less of a response to LHRH than males from the control group (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

5.
Thirteen crossbred boars were immunized at 1 mo of age against either testosterone-3-oxime-equine serum albumin (treated boars) or equine serum albumin (control boars) to test the hypothesis that active immunization against testosterone stimulates testicular growth and development in the prepubertal boar. All boars were injected with the appropriate antigen at 2, 3, 4, 5 and 6 mo of age and were slaughtered at 14 mo of age. Active immunization against testosterone resulted in an increase (P less than .05) in tritiated-testosterone binding by plasma within 60 d after the primary immunization; the degree of binding decreased by 6 mo but remained elevated (P less than .05) relative to controls through 12 mo of age. There was no effect of treatment on body weights through 12 mo of age. Concentrations of testosterone in plasma were higher (P less than .05) in testosterone-immunized boars than in controls; this increase was likely due to antibody binding rather than increased testosterone secretion because (1) concentrations of androgen in testicular parenchyma at slaughter were not altered by treatment and (2) plasma concentrations of estrogens were generally not affected by treatment. Concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were markedly suppressed in testosterone-immunized boars during the time when concentrations of these gonadotropins were high in control boars (greater than 3 mo of age). In spite of suppression of average LH and FSH concentrations, testicular weights, daily sperm production rates and seminal characteristics were similar for the two groups of boars at slaughter. (ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

6.
Three studies were conducted to determine the effects of exogenous melatonin (M) on changes in scrotal circumference (SC), fertility and reproductive hormone concentrations of rams. Rams were initially housed in barns with controlled photoperiod and given 16 wk of long (16L:8D) or short (8L:16D) days. In Studies I and II, implants of M were given for 40 to 80 d beginning at maximal SC. Results showed that implanted rams had greater (P less than .05) blood M concentrations than nonimplanted controls. However, M did not prevent testicular regression. In Study III, M was given to rams after testicular regression had occurred. Rams were implanted with M weekly for 6 or 4 wk, followed by a withdrawal period of 4 wk (6:4, 4:4 respectively). Results showed that M (6:4) stimulated (P less than .05) testicular growth compared with nonimplanted controls. Treatment of rams with M for 8 mo did not affect LHRH-induced LH release (P greater than .05), but it reduced basal and LHRH-induced testosterone release (P less than .05). Reproductive performance of rams in Studies I and III was compared with that of nonimplanted rams. Fertility of M-treated rams in the spring from Studies I and III (86% to 91%) was similar to that in autumn (93%). Fertility of rams from Studies I and III exceeded (P less than .05) that of nonimplanted rams in April (59% to 62%). Net lamb production from ewes mated in the spring was greater if rams were treated with M and(or) photoperiod.  相似文献   

7.
Considerable variation exists in the serum levels of gonadotropins in boars; this results in differential testicular function. Boars (Chinese Meishan, European White composite, and crosses of the two breeds) selected for high and low circulating FSH concentrations were used to define possible differences in pituitary sensitivity to GnRH and GnRH antagonist and gonadal and adrenal responses. After a 2-h pretreatment sampling period, boars were injected with GnRH or GnRH antagonist and repetitively sampled via jugular cannula for changes in serum concentrations of FSH, LH, testosterone, and cortisol. In response to varying doses of GnRH or GnRH antagonist, FSH, LH, or testosterone changes were not different in high- or low-FSH boars. Declines in LH after GnRH stimulation were consistently faster in boars selected for high FSH. Chinese Meishan boars had considerably higher cortisol concentrations than White composite boars (132.2 +/- 28.5 vs 67.4 +/- 26.8 ng/mL, respectively; P < .01). When select high- and low-gonadotropin Meishan:White composite crossbreds were sampled, cortisol levels were elevated but comparable between the two groups (126.5 +/- 13.7 vs 131.4 +/- 13.4 ng/mL, respectively). After GnRH antagonist lowered LH concentrations, administration of hCG resulted in increased testosterone and cortisol concentrations. Although testosterone concentrations remained high for 30 h, cortisol concentrations returned to normal levels within 10 h after hCG injection. The mechanism by which boars selected for high gonadotropins achieve increased levels of LH and FSH may not be due to differences in pituitary sensitivity to GnRH but to differences in clearance from the circulation.  相似文献   

8.
The effects of unilateral castration (UC) and induced unilateral cryptorchidism (UCR) on basal plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, and on the responses of these hormones to gonadotropin releasing hormone (GnRH), were investigated in bulls altered at 3, 6 or 9 months of age. Blood plasma was collected before and after GnRH (200 micrograms) stimulation approximately 1 year following gonadal manipulation. Neither mean baseline concentrations nor GnRH-induced increases in plasma testosterone were altered (P greater than .1) by hemicastration or UCR (P greater than .1). Both mean baseline LH and GnRH-induced LH release were greater (P less than .05) in bulls altered at 3 months of age than in bulls altered at 9 months of age. UC increased (P less than .05) plasma LH response to GnRH over that observed in intact bulls, but not above that in UCR bulls. UCR had no detectable effect on either baseline concentrations or GnRH-stimulated LH release. FSH was increased (P less than .05) in hemicastrates, while UCR had a variable effect on peripheral FSH: FSH was reduced (P less than .05) in UCR animals altered at 3 months of age but increased (P less than .05) in UCR bulls altered at both 6 and 9 months of age when compared to FSH in intact bulls. The results indicate that, compared with intact bulls, UC bulls release increased amounts of both gonadotropins but similar amounts of testosterone in response to GnRH stimulation. UCR had a variable effect on FSH release and did not alter either LH or testosterone.  相似文献   

9.
Thirty-six Landrace x Large White cross boars were selected from litters with either high or low estimated breeding values for 150-d paired testis weight. Blood samples were taken via jugular venipuncture at eight ages (42, 56, 70, 84, 98, 112, 126 and 140 d). At each sampling age, nine blood samples were taken at 30-min intervals. Luteinizing hormone (LH) was determined on the individual serum samples. Serum samples from each boar at each age were pooled and concentrations of follicle-stimulating hormone (FSH), estradiol-17 beta (E2) and testosterone (T) were determined. Paired testis width, testis length and body weight were measured at 98, 112, 126 and 140 d of age. Backfat probe, weights of excised testes and histological data on testes were obtained at 140 d of age. Boars with high testis weight (HTW) were heavier (P less than .05), had higher adjusted backfat probes (P less than .01) and had consistently larger in situ testis measurements (P less than .01) than did low testis weight (LTW) boars. Boars with HTW had heavier (P less than .01) testes and epididymides at 140 d of age. They also had a higher percentage of seminiferous tubules in which spermatogenesis was present (P less than .05), a larger percentage of tubules with a lumen (P less than .05) and tubules had a larger mean diameter (P less than .01) than did those of boar with LTW. Adjustment of in situ testis measurements and excised testis weights for body weight reduced line differences by less than 20%. A rise in LH concentrations occurred at approximately 100 d of age. Boars with HTW had higher (P less than .05) and more variable (P less than .01) LH concentrations than did boars with LTW. Boars with HTW also had higher maximum concentrations of LH during the pubertal rise (P less than .01) and these concentrations tended to reach maximum levels at younger ages. Concentrations of T increased in a fashion that was nearly linear with age (P less than .01) and tended to be higher for the boars with HTW (P less than .10). Concentrations of E2 changed little from 42 to 84 d of age but increased steadily thereafter. Boars with HTW had a more rapid increase in E2 concentrations than did boars with LTW (P less than .05).(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

10.
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   

11.
A synthetic progestogen (altrenogest) was fed to 24 Yorkshire X Duroc boars to determine effects on body growth, serum testosterone, and testicular characteristics. Boars from six litters (blocks) were allotted randomly to one of four treatment groups at 12 wk of age. Treatment groups were: controls, altrenogest fed for 3 wk, altrenogest fed for 6 wk and altrenogest fed for 9 wk. Treatment began at 15 wk of age at a daily dose of 20 mg X boar-1. Although there were no differences among treatment groups for gain and feed intake, boars fed altrenogest for 6 and 9 wk tended to consume more feed and were less (P less than .05) efficient than boars fed altrenogest for 3 wk or controls. Boars fed altrenogest for 3, 6 and 9 wk maintained lower (P less than .05) peripheral serum testosterone concentrations than controls from 15 to 24 wk of age. However, serum testosterone increased after altrenogest withdrawal in the 3- and 6-wk treatment groups but did not reach control concentrations by 24 wk. Boars fed altrenogest for 9 wk maintained serum testosterone below 1 ng/ml during the treatment period. Despite lower concentrations of serum testosterone in altrenogest-treated boars, backfat thickness was similar to controls, perhaps suggesting a slight anabolic effect of altrenogest on nutrient partitioning. Testicular weights and volumes at 24 wk decreased (P less than .001) linearly with increased duration of altrenogest feeding. Serum testosterone and estradiol in testicular venous effluent at castration were lower (P less than .01) in altrenogest-treated boars than in controls. These data demonstrate that feeding altrenogest inhibits both testicular growth and steroidogenesis of boars without altering body growth or backfat thickness.  相似文献   

12.
Seven sows were placed into one of two environmental chambers at 22 C, 5 d prior to farrowing. On day 9 of lactation, one chamber was changed to 30 C (n = 4) and the other remained at 22 C (n = 3). On days 24 and 25, blood samples were collected every 15 min for 9 hr and 7 hr, respectively. On day 24, thyrotropin releasing hormone (TRH) and gonadotropin releasing hormone (GnRH) were injected iv at hour 8. On day 25 naloxone (NAL) was administered iv at hour 4 followed 2 hr later by iv injection of TRH and GnRH. Milk yield and litter weights were similar but backfat thickness (BF) was greater in 22 C sows (P less than .05) compared to 30 C sows. Luteinizing hormone (LH) pulse frequency was greater (P less than .003) and LH pulse amplitude was less (P less than .03) in 22 C sows. LH concentrations after GnRH were similar on day 24 but on day 25, LH concentrations after GnRH were greater (P less than .05) for 30 C sows. Prolactin (PRL) concentrations were similar on days 24 and 25 for both groups. However, PRL response to TRH was greater (P less than .05) on both days 24 and 25 in 30 C sows. Growth hormone (GH) concentrations, and the GH response to TRH, were greater (P less than .0001) in 30 C sows. Cortisol concentrations, and the response to NAL, were less (P less than .03) in 30 C sows. NAL failed to alter LH secretion but decreased (P less than .05) PRL secretion in both groups of sows. However, GH response to NAL was greater (P less than .05) in 30 C sows. Therefore, sows exposed to elevated ambient temperature during lactation exhibited altered endocrine function.  相似文献   

13.
Influence of day length on seasonal endocrine responses were studied using stallions (seven per group). Treatments included 1) control, with natural day length; 2) 8 h light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984 (S-L); or 3) 8:16 from July 16, 1982 until March 5, 1984 (S-S). Blood was sampled hourly for 5 h every 4 wk; sera were pooled within horse, and luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone were quantified. Blood was collected every 20 min for 24 h every 8 wk and 2 wk before and after the December light shift. Samples were assayed for LH. Stallions in all groups underwent seasonal changes (P less than .05) in concentrations of LH, FSH, testosterone and basal concentrations of LH and amplitude of LH pulses. Season X treatment (P less than .05) reflected on early recrudescence of LH, FSH and testosterone concentrations in S-L stallions followed by earlier regression. Except for FSH hormone concentrations were depressed in S-S stallions. Number of LH pulses per 24 h was unaffected by season, treatment or their interaction. Mean amplitude of LH pulses was affected (P less than .05) by season X treatment; maximal values occurred in April vs February for control and S-L stallions, and minimal values occurred in December vs April. The season X treatment interaction (P less than .05) similarly affected basal concentrations of LH. Thus, seasonal changes in concentrations of LH, FSH and testosterone can be driven by photoperiod. Increased peripheral concentrations of LH during seasonal recrudescence of reproductive function apparently results from more LH secreted per discharge without an increased frequency of LH discharges.  相似文献   

14.
Mean concentrations and the occurrence of pulsatile release of luteinizing hormone (LH) were determined in 14-wk-old crossbred boars (50.5 +/- 1.5 kg) after bilateral or unilateral castration at 10 wk of age. Blood was collected at 10-min intervals for 5 h. Then gonadotropin releasing hormone (GnRH; 40 micrograms) was given and sampling was continued at 5-min intervals for 1 h. Compared with intact boars, bilateral castration increased (P less than .001) mean LH (982 +/- 56 vs 389 +/- 56 pg/ml), pulsatile releases of LH (7.0 +/- .6 vs 2.0 +/- .6 pulses/5 h) and LH pulse amplitude (617 +/- 29 vs 360 +/- 58 pg/ml). Unilaterally castrated boars did not differ from intact boars in any of the above measures of LH secretion. Testis weight increased more between 10 and 14 wk of age in the unilateral castrates than in the intact boars (432 +/- 42 vs 245 +/- 34%; P less than .05). Thus, compensatory hypertrophy occurred within 4 wk of castration. Plasma testosterone was lower for bilateral castrates than for intact animals (.1 +/- .8 vs 3.6 +/- .9 ng/ml; P less than .05) while unilateral castrates (3.8 +/- 1.0 ng/ml) and intact boars did not differ. Plasma estradiol concentrations in bilateral and unilateral castrates were not different from levels found in intact boars (1.8 +/- 1.8, 8.8 +/- 2.1 and 6.0 +/- 1.8 pg/ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

15.
The objective of this study was to characterize correlated responses in testicular morphology and daily sperm production to divergent selection for testosterone production. Duroc boars from high and low lines (HTL and LTL, respectively) divergently selected over 10 generations for testosterone production in response to a GnRH challenge followed by random selection were used. Testicular tissues were sampled from all available males of generation 20 (HTL, n = 46; and LTL, n = 13). Volume densities for Leydig cells, seminiferous tubules, and Sertoli cells were estimated along with sperm production. The HTL boars had greater volume densities of Leydig cells than did LTL (P < 0.01). Volume density of seminiferous tubules tended to differ between lines (P < 0.07), but Sertoli cell volume densities did not differ (P < 0.27). Sperm production traits, adjusted for age, did not differ significantly between lines. Body, testicular, and epididymal weights were recorded for boars from HTL (n = 82) and LTL (n = 44) from generations 20 and 21. After adjustment for BW, average paired testicular weights for HTL and LTL were 417 and 457 g (P < 0.01), respectively. Epididymal weights, adjusted for BW, were heavier for HTL (P < 0.01) than for LTL. To demonstrate that the selection lines still differed for testosterone production, lines were evaluated in generation 21. Endogenous testosterone production of the HTL (n = 54) and LTL (n = 44) testosterone production line averaged 49.0 ng/mL and 27.8 ng/mL (P < 0.01), respectively. Plasma FSH concentrations did not differ between lines (P < 0.30). Selection for testosterone production in response to a GnRH challenge was an effective method of changing testosterone concentrations, testicular size, epididymal weight, and volume density of Leydig cells. However, daily sperm production per gram of testes was unchanged. Based on the results of this study, selection for testosterone production is not recommended as a method of increasing sperm production in pigs.  相似文献   

16.
The hormone GnRH has a stimulatory effect on gonadotropin synthesis and secretion. The objective of the first study was to evaluate concentrations of FSH and LH in plasma of boars after successive treatment with SB75, a GnRH antagonist. Thirteen boars greater than 1 yr of age (eight White Composite [WC] and five Meishan [MS]) were injected once daily with SB75 (10 microg/kg of body weight) for 4 d. Plasma concentrations of LH and testosterone (T) decreased after 1 h from the first dose of SB75. After 12 h of treatment, LH gradually returned to pretreatment concentrations, but T remained suppressed (< 2 ng/mL) until after the last injection of SB75. There was a modest, but significant, reduction in FSH during treatment with SB75. The prolonged inhibitory effect of SB75 on suppression of plasma T concentrations, in the presence of pretreatment concentrations of LH, implied direct effects of SB75 at the testis. In the second experiment, testicular tissue from adult boars was incubated in the presence of three doses of human chorionic gonadotropin (hCG; 0, .5, and 5 IU) with SB75 (250 ng/mL) or with Deslorelin, a GnRH agonist (500 ng/mL). Samples of media were collected every hour for 3 h, and concentrations of T and estrone (E1) were determined by RIA. Concentrations of T and E1 increased with time in response to treatment with hCG. Co-treatment with SB75 decreased media concentrations of T (P < .01) and E1 (P < .03) compared to controls (77.9 vs 85.7 +/- 2.0 and 4.7 vs 5.3 +/- .2 ng/g). In contrast, treatment with Deslorelin had no effect on the amount of T (P > .50) or E1 (P > .26) released with all dosages of hCG. These results indicate that a GnRH antagonist has a direct effect on the testis, decreasing amounts of T and E1 released from the Leydig cells; however, treatment with a GnRH agonist had no direct effect on release of these gonadal steroids. Thus, it remains unresolved whether the site of action of GnRH antagonist on testicular steroidogenesis is through a testicular GnRH receptor or through some other mechanism.  相似文献   

17.
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   

18.
Beef cows were used to determine if suckling influences release of LH via endogenous opioids at 28 +/- 4 d after parturition. Cows of similar weight and body condition (6.8 +/- .1, 1 = emaciated, 9 = obese) were assigned randomly to five groups (n = 6 to 7): 1) control-suckled/saline (suckled 15 min every 6 hr for 48 hr); 2) control-suckled/naloxone; 3) calf-removal/saline (calf removal for 52 hr); 4) calf-removal/naloxone; and 5) control-suckled/GnRH (Gonadotropin-Releasing Hormone). At 0 hr, saline was administered to all cows. This treatment was continued at 6 hr intervals for 24 hr. Either naloxone (0.5 mg/kg), GnRH (40 ng/kg) or saline was administered to cows in their respective groups every 6 hr during the ensuing 24-hr period in calf-removal groups, or immediately preceding each suckling episode in the control-suckled groups. Blood samples for analysis of luteinizing hormone (LH) were collected at 15-min intervals for 1 hr prior to and 3 hr after treatment at 0, 24, 36 and 48 hr. Cows were observed for estrus twice daily. All cows in the control-suckled/GnRH group released LH (P less than .05) in response to exogenous GnRH, indicating the presence of releasable quantities of the gonadotropin. Mean concentrations of LH were not effected (P greater than .05) by the control-suckled regime. However, calf-removal alone, or in combination with naloxone, increased (P less than .05) mean concentrations of LH by 48 hr.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

19.
Prepubertal crossbred beef bulls served as controls or were actively immunized against the N-terminal, 30-amino acid synthetic fragment of porcine inhibin alpha, pI alpha (1-30). Antibody titers were detected in sera (greater than 40% B/BO in sera diluted 1,000-fold) but not in rete testis fluid of 390-d-old bulls. Serum FSH and inhibin remained static during a 5-h intensive bleed; inhibin was not acutely affected by a 15-fold LH rise and a threefold FSH rise induced by exogenous GnRH. Serum FSH, but not LH or testosterone, was consistently elevated (P less than .05) in immunized bulls compared with control bulls. Neither pituitary weight, pituitary gonadotropin content nor pituitary FSH/LH ratios were affected (P greater than .10) by pI alpha(1-30) active immunization. Testicular sperm density was greater (60 x 10(6) vs 45 x 10(6) sperm/g testis; P less than .10) in immunized bulls, but testes weight, epididymides weight and total daily sperm production remained unchanged. These results suggest that inhibin is important for regulation of FSH secretion and testicular function. Immunization with suitable inhibin vaccines may improve bull fertility.  相似文献   

20.
Immuno-peptides may have positive or negative effects on gonadal steroidogenesis, but few have been tested outside of rodent species or in vivo. In Exp. 1, thymulin, a secreted nonapeptide of the thymus, was incubated (1, 10, 100, or 1,000 ng/mL) with testicular minces (sampled at 3, 6, or 12 h) from Chinese Meishan boars of high gonadotropin/testicular steroidogenic function (n = 8) and White composite boars of European origin (n = 8 ) to test the hypothesis that thymulin could augment hCG stimulation of testicular androgen concentrations. Thymulin alone had few effects on androgen concentrations (testosterone, dehydroepiandrosterone+dehydroepiandrosterone sulfate [DHEA+DHEASO4]) in Meishan boar testicular incubates. In minces from White composites incubated with thymulin, testosterone concentrations were generally below control values (P<.05), but DHEA+DHEASO4 concentrations were unaffected. Thymulin had no effect on estrone concentrations in testicular incubates of White composite boars but stimulated estrone concentrations in Meishan testicular incubates. Thymulin plus hCG increased testosterone (3 and 6 h of incubation; P<.05) but not DHEA+DHEASO4 concentrations in White composite testicular incubates. Thymulin plus hCG did not alter androgen or estrogen concentrations from control values in Meishan testicular incubates. In Exp.2 with a protocol similar to that of Exp. 1 for testicular minces from White composite boars (n = 30), thymulin increased testosterone concentrations during the early incubation period (1 to 3 h; P<.05) and depressed testosterone concentrations at later times (6 h; P<.05). Thymulin synergized with hCG in stimulating increases in testosterone and DHEA+DHEASO4 concentrations (P<.05) but had no effect on estrone concentrations in vitro. Thymulin was tested in vivo in boars from three genetic lines selected for high, medium, or normal circulating LH concentrations (Meishan, select White composites, and control White composites, respectively). Injection of thymulin i.v. (4.4, 44.4, or 444.4 ng/kg BW) generally increased circulating testosterone concentrations (2 to 3 h later; P<.01), but the response was dependent on the boar's general circulating LH concentrations and dose of thymulin. Overall results from these studies support the hypothesis of a thymulin augmentation of LH stimulation of androgen increases in vitro and in vivo in the testis of boars.  相似文献   

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