Progress 09/01/03 to 08/31/07
Outputs
In Objective one, 36 gilts were exposed to androgen receptor agonists (testosterone or DHT), antagonist (flutamide) or a combination of both and vehicle from day 13 to estrus. Treatment with testosterone or DHT alone increased (P<.05) mean concentrations of FSH in serum and this effect was blocked by co-treatment with flutamide. The mean concentrations of estradiol and androstenedione were increased (P<.05) at two hours after injection of testosterone and testosterone plus flutamide; but not DHT, probably due to the role of testosterone as a substrate for estradiol and androstenedione. Treating gilts with DHT increased the subsequent ovulation rate (P<.06) but decreased embryonic survival and these effects were negated when co-treated with flutamide. In Objective 2, 120 gilts, 60 in each of two experiments, received daily injections of the androgen receptor agonists and antagonists as in Objective 1 except ovarian characteristics were evaluated in both experiments on
days 17 and 19. In Experiment 1, follicular health status (healthy, H; moderately atretic, MA; or very atretic, VA) was determined histologically. In Experiment 2, amounts of follicle-stimulating hormone receptor (FSHR) and luteinizing hormone receptor (LHR) mRNAs were examined. Numbers of H follicles were influenced (P<.05) by treatment and day of follicular evaluation (there was no interaction). Treatment with DHT increased (P<.05) the numbers of H follicles relative to control gilts on d 17 and 19. DHT administration from d 13 to 16 diminished (P<.05) the amounts of LHR mRNA in H follicles from d 17. The effects of DHT on numbers of H follicles and LHR mRNA were not observed in gilts receiving DHT + F. Flutamide treatment alone from d 13 to d16 also decreased the amounts of LHR mRNA on d 17. Treatment with androgens and(or) F did not influence numbers of total (H + MA + VA), MA, or VA follicles, estradiol concentrations in follicular fluid, and amounts of FSHR mRNA. Less (P<.05)
numbers and percentages of H follicles, and amounts of FSH mRNA were observed on d 17 than on d 19. By contrast, numbers and percentages of MA follicles were greater on d 17 than on d 19, those of VA follicles were not different between days. Results of this experimentation indicate that androgen treatment of gilts increases ovulation rate, in part, by stimulation of FSH secretion. Treatment with DHT during the follicular phase of the estrous cycle did not induce changes in numbers of total follicles during the periods of follicular recruitment and selection, but rather increased the numbers of healthy follicles in association with decreased amounts of LHR mRNA.
Impacts
Activation of the androgen receptor with DHT increased ovulation rates in gilts. Previous use of exogenous testosterone also increased ovulation rate and increased litter size in sows. Although eventual commercialization of these discoveries has many regulatory considerations, the present experiment is mechanistic in nature. What was learned in this project was that treating gilts with the androgen DHT, increased secretion of follicle stimulating hormone and increased the total number of healthy follicles, without significantly changing recruitment of new follicles. In addition, a new and potential mechanism of these effects on follicular development might be a role for the gene/message coding for the receptor for luteinizing hormone (LHR). The role of decreasing amounts of LHR during follicular development in swine warrants further investigation. The ability of androgens to improve ovulation rate in gilts by stimulating the release of a hormone from the brain and
decreasing an intracellular signal within the ovary were two novel discoveries obtained from this experimentation. Understanding pathways and sequences by which hormones increase ovulation rate and fertility will allow for improved reproductive management and improved performance in farrowing operations.
Publications
- H. Cardenas, E. Jimenez and W. F. Pope. 2007. Dihydrotestosterone influenced numbers of healthy follicles and follicular amounts of Luteinizing Hormone Receptor mRNA during the follicular phase of the estrous cycle in gilts. (In preparation for submission)
- E. Jimenez, H. Cardenas and W. F. Pope. 2007. Effects of androgens on serum concentrations of gonadotrophins and ovarian steroids in gilts. (In preparation for submission)
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Progress 01/01/06 to 12/31/06
Outputs
In Aim 2a, sixty gilts (n=5) were ovariectomized on either day 17 or 19 of the estrous cycle (day 0 = 1st day of estrus) receiving one of six treatments; control (C), 10 mg of testosterone (T), 10 mg of 5-alpha-dihydrotestosterone (DHT), 1.5g of flutamide (F; an androgen receptor antagonist), T plus F and DHT plus F. Injections began on day 13 at 8:00 a.m. and continued daily up to, but not including, the day of surgery. At recovery, follicles (greater than 5 mm in diameter) were aspirated to obtain a sample of follicular fluid and then subjected to standard fixation and embedding procedures for subsequent morphological examination of follicular atresia. Follicles were classified as healthy, moderately atretic or very atretic based on this morphological examination. The follicular fluid was frozen (minus 20C) and later subjected to RIA procedures for purposes of determining the concentrations of estradiol. Data was analyzed using ANOVA and means compared using LSD.
Unless otherwise indicated, all statistical differences were at least P<.05. Data will be discussed in the following order; number of follicles, percentage of follicles and concentration of follicular estradiol. The numbers of healthy follicles were affected by day and treatment. Treating gilts with DHT, but not T, increased the number of healthy follicles and co-treatment with F blocked this DHT effect. This is consistent with Aim 1. The number of follicles greater than or equal to 5 mm increased from day 17 to 19, 14.9 to 19.0, respectively. The numbers of moderately atretic follicles were affected only by day of examination, decreasing from 7.5 to 3.0 from day 17 to 19, respectively. There were no effects on the numbers of very atretic follicles. The percentage of healthy follicles was not affected by treatment but did increase from day 17 to 19, 61.8 to 75.0 %, respectively. Conversely, the proportion of moderately atretic follicles decreased from day 17 to 19, 29.0 to 12.1 %,
respectively. There were no effects on the percentage of very atretic follicles. Follicular concentrations of estradiol were not affected by treatment but did increase from day 17 to 19, 176 to 347 ng/ml, respectively. In conclusion of Aim 2a, utilizing a sample size of five gilts, treatment with an androgen receptor agonist, DHT, increased the number of healthy follicles without a concomitant change in the number of atretic follicles when examined on day 17 and 19. Regarding the final experimentation of this grant, Aim 2b, the animal aspect of this objective has recently been completed and expression of selected genes will be compared in the forthcoming months.
Impacts
Activation of the androgen receptor with DHT increased ovulation rates in gilts. Previous use of exogenous testosterone also increased ovulation rate and increased litter size in sows. Although eventual commercialization of these discoveries has many regulatory considerations, the present experiment is mechanistic in nature. Eventually, as more is learned about the role of the androgen receptor in ovarian and uterine activity, it is hopeful that a significant impact on swine reproductive performance can be realized.
Publications
- Jimenez, E., H. Cardenas and W.F. Pope. 2006. Administration of androgens increase serum concentrations of FSH in gilts. J. Anim. Sci. 84 (Suppl 2): 307 (abstract).
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Progress 01/01/05 to 12/31/05
Outputs
In Aim 1, thirty six gilts had a jugular vein cannulated and were assigned to one of six treatments: control (C; corn oil), 10 mg of testosterone (T), 10 mg of 5-alpha-dihydrotestosterone (DHT), 1.5 g of flutamide (F; an androgen receptor antagonist), T plus F and DHT plus F, per day. Beginning on d 13 (d 0= 1st d of estrus), injection of hormones were given daily at 8:00 AM and blood samples were collected every h continuing until d 0. Gilts were mated with two different boars. On d 11, corpora lutea (CL) and blastocysts were counted following ovariohysterechtomy. Serum concentrations of LH were determined hourly, FSH every 2 h and progesterone every 12 h. Data were analyzed using ANOVA and means compared using the PDIFF option of SAS. Duration of the estrous cycle was shortened (P<.05) in gilts treated with T and T plus F (18.8 and 18.7 d, respectively) as compared with gilts in the C group (20.3 d). Treating gilts with DHT numerically increased (25.0; P= .06) the
number of CL versus gilts receiving corn oil (21.0). Embryonic survival was negatively (P<.05) affected in gilts treated with androgens but this effect was negated when gilts were co-treated with androgens plus flutamide. Treatment of gilts with either T or DHT increased (P<.05) the mean concentrations of FSH (1.8 or 1.7 ng/ml, respectively) as compared with gilts treated with corn oil (1.3 ng/ml). Treatment with DHT plus F resulted in FSH concentrations that were not different than the C group and were less (P<.05) than the DHT group. This antagonistic effect of flutamide was also evident with T treatments. The mean concentration of LH in serum was greater (P<.05) only on d 13 in gilts treated with DHT versus T (treatment X d interaction; P<.05). There were no effects of treatments on serum concentrations of progesterone. Results indicated that one mechanism associated with the increase of ovulation rate in gilts treated with T or DHT might be stimulation of FSH secretion. Follicles
have been collected from Aim 2a and are presently being analyzed.
Impacts
This is the first demonstration that exogenous androgens act on the androgen receptor to increase FSH secretion in gilts. This effect on increasing endogenous FSH secretion alone, or with other factors, causes an increase in follicular development and ovulation rate in gilts. Utilizing this new information to improve follicular growth could significantly impact fecundity of animals, specifically, embryonic survival and litter size.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
This past year, blood samples were collected from 36 pigs, every hour from day 12 to estrus. The nearly 8,000 serum samples are being analyzed for LH, FSH, testosterone, estradiol, DHT, progesterone and adrostendione. Various steroid and gonadotropin assays are being conducted concurrently, To date, the assays for progesterone, DHT and testosterone have been completed. The LH analysis is 10% completed.
Impacts
A major component of litter size in pigs is ovulation rate and embryonic mortality. Use of exogenous androgens has been demonstated to increase ovulation rate, to improve the percentage of embryos surviving to day 12 and to increase litter size. This research is just beginning to investigate how the treatment of pigs with androgens affects the secretion of the gonadotrophins, follicle stimulating hormone and luteinizing hormone.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
In an attempt to better understand how exogenous androgens increase ovulation rate in pigs, blood samples will be taken frequently from gilts treated with androgens, or an androgen blocker, and analysed for changes in FSH and LH. This experimentation is in the beginning stages and no conclusions can be made at this time.
Impacts
A major component of litter size in pigs is ovulation rate and embryonic mortality. Use of exogenous androgens has been demonstated to increase ovulation rate, to improve the percentage of embryos surviving to day 12 and to increase litter size. This research is just beginning to investigate how the treatment of pigs with androgens affects the secretion of the gonadotrophins, follicle stimulating hormone and luteinizing hormone.
Publications
- No publications reported this period
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