276. Sex difference in the effect of cortisol on the LH response of the pituitary to exogenous GnRH in hypothalamo-pituitary disconnected gonadectomised sheep

2005 ◽  
Vol 17 (9) ◽  
pp. 114
Author(s):  
C. A. Stackpole ◽  
I. J. Clarke ◽  
A. I. Turner ◽  
A. J. Tilbrook
Keyword(s):  
Sex Difference ◽  
Breeding Season ◽  
Sex Steroids ◽  
Present Experiment ◽  
Control Period ◽  
Plasma Concentrations ◽  
Saline Infusion ◽  
Sheep Model ◽  
Blood Samples ◽  
Lh Secretion

We have used the hypothalamo-pituitary disconnected (HPD) sheep model to investigate direct pituitary actions of cortisol to suppress LH secretion in response to exogenous GnRH. We previously observed that, during the non-breeding season, treatment with cortisol did not suppress the LH response to GnRH in HPD gonadectomised rams or ewes.1 In the present experiment, we tested the effect of cortisol on the LH response to exogenous GnRH in gonadectomised HPD sheep during the breeding season. Using a cross-over design, HPD gonadectomised Romney Marsh rams (n = 6) and ewes (n = 5) received a saline or cortisol (250 μg/kg/h) infusion for 30 h on each of two days, one week apart. All animals were treated with 125 ng i.v. injections of GnRH every 2 h during a 6h control period preceding the infusion and during the infusion. Jugular blood samples were taken during the control period and the first 6 h and last 6 h of the infusion (over 3 LH pulses). Mean plasma concentrations of LH and LH pulse amplitudes, driven by programmed GnRH injections, were similar in gonadectomised rams and ewes and there were no significant effects of saline infusion between the control periods or the saline infusion in either sex. The amplitude of LH pulses was significantly (P < 0.05) reduced in rams during the first 6 h of the cortisol infusion compared to the control period, but there were no effects of the cortisol infusion in ewes. These data show that, in the absence of sex steroids, there is a sex difference in the mechanism by which cortisol acts at the pituitary to reduce LH secretion in response to exogenous GnRH in HPD gonadectomized sheep during the breeding season. We conclude that the effect of cortisol to reduce secretion of LH involves an action on the pituitary, at least in gonadectomised rams. (1)Stackpole CA, Turner AI, Clarke IJ and Tilbrook AJ (2003) Biology of Reproduction 36(Supplement 1), 288.

scholarly journals Suppression of the secretion of luteinizing hormone due to isolation/restraint stress in gonadectomised rams and ewes is influenced by sex steroids

1999 ◽  
Vol 160 (3) ◽  
pp. 469-481 ◽  
Author(s):  
AJ Tilbrook ◽  
BJ Canny ◽  
MD Serapiglia ◽  
TJ Ambrose ◽  
IJ Clarke
Keyword(s):  
Sex Steroids ◽  
Restraint Stress ◽  
Testosterone Propionate ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Blood Samples ◽  
Release Device ◽  
Lh Secretion ◽  
Female Sheep

In this study we used an isolation/restraint stress to test the hypothesis that stress will affect the secretion of LH differently in gonadectomised rams and ewes treated with different combinations of sex steroids. Romney Marsh sheep were gonadectomised two weeks prior to these experiments. In the first experiment male and female sheep were treated with vehicle or different sex steroids for 7 days prior to the application of the isolation/restraint stress. Male sheep received either i.m. oil (control rams) or 6 mg testosterone propionate injections every 12 h. Female sheep were given empty s.c. implants (control ewes), or 2x1 cm s.c. implants containing oestradiol, or an intravaginal controlled internal drug release device containing 0.3 g progesterone, or the combination of oestradiol and progesterone. There were four animals in each group. On the day of application of the isolation/restraint stress, blood samples were collected every 10 min for 16 h for the subsequent measurement of plasma LH and cortisol concentrations. After 8 h the stress was applied for 4 h. Two weeks later, blood samples were collected for a further 16 h from the control rams and ewes, but on this day no stress was imposed. In the second experiment, separate control gonadectomised rams and ewes (n=4/group) were studied for 7 h on 3 consecutive days, when separate treatments were applied. On day 1, the animals received no treatment; on day 2, isolation/restraint stress was applied after 3 h; and on day 3, an i. v. injection of 2 microg/kg ACTH1-24 was given after 3 h. On each day, blood samples were collected every 10 min and the LH response to the i.v. injection of 500 ng GnRH administered after 5 h of sampling was measured. In Experiment 1, the secretion of LH was suppressed during isolation/restraint in all groups but the parameters of LH secretion (LH pulse frequency and amplitude) that were affected varied between groups. In control rams, LH pulse amplitude, and not frequency, was decreased during isolation/restraint whereas in rams treated with testosterone propionate the stressor reduced pulse frequency and not amplitude. In control ewes, isolation/restraint decreased LH pulse frequency but not amplitude. Isolation/restraint reduced both LH pulse frequency and amplitude in ewes treated with oestradiol, LH pulse frequency in ewes treated with progesterone and only LH pulse amplitude in ewes treated with both oestradiol and progesterone. There was no change in LH secretion during the day of no stress. Plasma concentrations of cortisol were higher during isolation/restraint than on the day of no stress. On the day of isolation/restraint maximal concentrations of cortisol were observed during the application of the stressor but there were no differences between groups in the magnitude of this response. In Experiment 2, isolation/restraint reduced the LH response to GnRH in rams but not ewes and ACTH reduced the LH response to GnRH both in rams and ewes. Our results show that the mechanism(s) by which isolation/restraint stress suppresses LH secretion in sheep is influenced by sex steroids. The predominance of particular sex steroids in the circulation may affect the extent to which stress inhibits the secretion of GnRH from the hypothalamus and/or the responsiveness of the pituitary gland to the actions of GnRH. There are also differences between the sexes in the effects of stress on LH secretion that are independent of the sex steroids.

scholarly journals Seasonal changes in the negative feedback regulation of the secretion of the gonadotrophins by testosterone and inhibin in rams

1999 ◽  
Vol 160 (1) ◽  
pp. 155-167 ◽  
Author(s):  
AJ Tilbrook ◽  
DM de Kretser ◽  
IJ Clarke
Keyword(s):  
Breeding Season ◽  
Negative Feedback ◽  
Plasma Concentrations ◽  
Feedback Regulation ◽  
Negative Feedback Regulation ◽  
Blood Samples ◽  
Vehicle Treatment ◽  
Breeding Seasons ◽  
Lh Secretion ◽  
Hypothalamic Level

Three experiments were conducted with castrated Romney Marsh rams (wethers) to investigate the ability of testosterone and inhibin to suppress the secretion of LH and FSH during the breeding and the non-breeding seasons. In Experiment 1, wethers (n=5/group) were treated every 12 h for 7 days with oil or 16 mg testosterone propionate (i.m.) and were then given two i.v. injections either of vehicle or of 0.64 microg/kg human recombinant inhibin A (hr-inhibin) 6 h apart. Blood samples were collected for 4 h before inhibin or vehicle treatment and for 6 h afterwards for the assay of LH and FSH. In Experiments 2 and 3 wethers underwent hypothalamo-pituitary disconnection (HPD) and were given 125 ng GnRH i.v. every 2 h. In Experiment 2, HPD wethers (n=3/group) were injected (i.m.) every 12 h with oil or testosterone and blood samples were collected over 9 h before treatment and 7 days after treatment. In Experiment 3, HPD (n=5/group) wethers were treated with vehicle or hr-inhibin, as in Experiment 1, after treatment with oil, or 4, 8 or 16 mg testosterone twice daily for 7 days. Blood samples were collected over 4 h before treatment with vehicle or hr-inhibin and for 6 h afterwards. Treatment of wethers with testosterone (Experiment 1) resulted in a significant decrease in the plasma concentrations of LH and number of LH pulses per hour but the magnitude of these reductions did not differ between seasons. Testosterone treatment had no effect on LH secretion in GnRH-pulsed HPD wethers in either season and treatment with hr-inhibin did not affect LH secretion in wethers or HPD wethers in any instance. Plasma concentrations of FSH were significantly (P<0.05) reduced following treatment with testosterone alone during the breeding season but not during the non-breeding season. FSH levels were reduced to a greater extent by treatment with hr-inhibin but this effect was not influenced by season. During the non-breeding season, the effect of hr-inhibin to suppress FSH secretion was enhanced in the presence of testosterone. These experiments demonstrate that the negative feedback actions of testosterone on the secretion of LH in this breed of rams occurs at the hypothalamic level and is not influenced by season. In contrast, both testosterone and inhibin act on the pituitary gland to suppress the secretion of FSH and these responses are affected by season. Testosterone and inhibin synergize at the pituitary to regulate FSH secretion during the non-breeding season but not during the breeding season.

scholarly journals Influence of sex and gonadal status of sheep on cortisol secretion in response to ACTH and on cortisol and LH secretion in response to stress: importance of different stressors

2002 ◽  
Vol 173 (1) ◽  
pp. 113-122 ◽  
Author(s):  
AI Turner ◽  
BJ Canny ◽  
RJ Hobbs ◽  
JD Bond ◽  
IJ Clarke ◽  
...  
Keyword(s):  
Sex Differences ◽  
Sex Difference ◽  
Restraint Stress ◽  
Cortisol Response ◽  
Blood Samples ◽  
Response To Stress ◽  
Lh Secretion ◽  
Gonadal Status ◽  
Major Mediator

There are sex differences in the response to stress and in the influence of stress on reproduction which may be due to gonadal steroids but the nature of these differences and the role of the gonads are not understood. We tested the hypotheses that sex and the presence/absence of gonads (gonadal status) will influence the cortisol response to injection of ACTH, insulin-induced hypoglycaemia and isolation/restraint stress, and that sex and gonadal status will influence the secretion of LH in response to isolation/restraint stress. Four groups of sheep were used in each of three experiments: gonad-intact rams, gonadectomised rams, gonad-intact ewes in the mid-luteal phase of the oestrous cycle and gonadectomised ewes. In Experiment 1 (n=4/group), jugular blood samples were collected every 10 min for 6 h; after 3 h, two animals in each group were injected (i.v.) with ACTH and the remaining two animals were injected (i.v.) with saline. Treatments were reversed 5 days later so that every animal received both treatments. Experiment 2 (n=4/group) used a similar schedule except that insulin was injected (i.v.) instead of ACTH. In Experiment 3 (n=5/group), blood samples were collected every 10 min for 16 h on a control day and again 2 weeks later when, after 8 h of sampling, all sheep were isolated and restrained for 8 h. Plasma cortisol was significantly (P<0.05) elevated following injection of ACTH or insulin and during isolation/restraint stress. There were no significant differences between the sexes in the cortisol response to ACTH. Rams had a greater (P<0.05) cortisol response to insulin-induced hypoglycaemia than ewes while ewes had a greater (P<0.05) cortisol response to isolation/restraint stress than rams. There was no effect of gonadal status on these parameters. Plasma LH was suppressed (P<0.05) in gonadectomised animals during isolation/restraint stress but was not affected in gonad-intact animals, and there were no differences between the sexes. Our results show that the sex that has the greater cortisol response to a stressor depends on the stressor imposed and that these sex differences are likely to be at the level of the hypothalamo-pituitary unit rather than at the adrenal gland. Since there was a sex difference in the cortisol response to isolation/restraint, the lack of a sex difference in the response of LH to this stress suggests that glucocorticoids are unlikely to be a major mediator of the stress-induced suppression of LH secretion.

scholarly journals Plasma concentrations of prolactin in brushtail possums (Trichosurus vulpecula) in different physiological states

2006 ◽  
Vol 190 (2) ◽  
pp. 295-305 ◽  
Author(s):  
J L Crawford ◽  
B P Thomson ◽  
M F Beaumont ◽  
D C Eckery
Keyword(s):  
Breeding Season ◽  
Post Partum ◽  
Mammalian Species ◽  
Plasma Concentrations ◽  
Oestrous Cycle ◽  
Brushtail Possum ◽  
Blood Samples ◽  
Lh Surge ◽  
Time Determination ◽  
First Time

Prolactin (Prl) has been implicated in reproduction in many mammalian species and is illustrated by the distinctive patterns of secretion during the breeding season, the oestrous cycle and lactation. The recent development of a homologous RIA for measuring the circulating Prl concentrations in brushtail possums has facilitated the reliable measurement of Prl in plasma during different physiological states in this species for the first time. Determination of Prl concentrations during lactation involved the collection of weekly blood samples from eight female possums from the time of parturition through either one or two consecutive lactational cycles. Prl was at baseline levels during early lactation (weeks 0–14 post-partum), and then increased markedly to maximum concentrations at weeks 19–21 before returning to nadir levels at a time coincident with the weaning of pouch young (weeks 23–27). The profile of Prl secretion over the oestrous cycle and in particular at the time of the preovulatory LH surge was obtained from 14 possums during the reproductive cycle, in which preovulatory follicle development and ovulation were monitored by laparoscopy. There was no distinct daily pattern of Prl secretion during the oestrous cycle; however, in 3/4 possums in which a typical preovulatory LH surge was measured, a biphasic preovulatory Prl surge was also observed. The preovulatory Prl surge commenced 2–6 h prior to, and had returned to baseline close to the onset of, the preovulatory LH surge, and a second surge of Prl occurred concomitantly with the delayed preovulatory FSH surge. Seasonality of Prl levels was established from weekly blood samples collected from six barren female possums, and concentrations of Prl were lower during the breeding season compared to the non-breeding season. Additionally, a circadian pattern of Prl secretion was evident in both female and male possums, with Prl levels higher in the morning compared to the afternoon. In conclusion, interpretation of endogenous secretory patterns suggests that Prl may be important during late lactation and at impending ovulation, but the involvement of the circannual rhythm of Prl in the regulation of seasonality in the brushtail possum remains to be determined.

Effects of continuous infusions of 4-hydroxyoestradiol and oestradiol on plasma LH-levels in the ovariectomized ewe

1984 ◽  
Vol 107 (3) ◽  
pp. 328-336 ◽  
Author(s):  
G. Emons ◽  
C. Brack ◽  
R. Chatelain ◽  
H. H. Abel ◽  
S. Isedor ◽  
...  
Keyword(s):  
Plasma Concentrations ◽  
Low Doses ◽  
Total Period ◽  
Blood Samples ◽  
Central Target ◽  
Target Sites ◽  
Negative Effect ◽  
The Right ◽  
Lh Secretion ◽  
Different Doses

Abstract. Ovariectomized ewes were infused over a period of 12 h at constant rates with different doses of the catecholoestrogen 4-hydroxyoestradiol (4-OHE2) or the primary oestrogen oestradiol (E2) via a catheter placed in the right atrium. Blood samples were drawn every hour for a total period of 48 h starting 1 h before the beginning of the steroid infusion. Luteinizing hormone (LH), 4-OHE2 and E2 concentrations were measured in these samples by specific radioimmunoassays. Infusions of low doses E2 (0.5 μg/h) or 4-OHE2 (2 μg/h) caused only a suppression of LH-secretion. At doses of 1 μg E2/h or 5 μg 4-OHE2/h this negative effect was followed by inconsistent elevations of plasma LH. Beyond this threshold dose, E2 at infusion rates of 2, 5 and 10 μg/h and 4-OHE2 at infusion rates of 10, 25 and 50 μg/h produced the negative effect and massive LH-surges. At still higher infusion rates (E2: 20 μg/h, 4-OHE2: 100 μg/h) lower elevations of plasma LH levels were observed. 4-OHE2 had to be infused at 4–5 times higher rates than E2 to obtain comparable plasma concentrations of either oestrogen. Under this condition the effects of 4-OHE2 and E2 were similar indicating that 4-OHE2 has the same potency as E2 at central target sites.

scholarly journals Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

1980 ◽  
Vol 33 (2) ◽  
pp. 213 ◽  
Author(s):  
RJ Rodgers ◽  
IJ Clarke ◽  
JK Findlay ◽  
Ainslie Brown ◽  
IA Cumming ◽  
...  
Keyword(s):  
Breeding Season ◽  
Area Under The Curve ◽  
Ovarian Vein ◽  
Blood Samples ◽  
Serial Blood ◽  
Area Unit ◽  
And Control ◽  
Lh Secretion

The levels of plasma LH and FSH were measured in serial blood samples taken at 15-min intervals for 6 h from ewes that had remained fertile after grazing oestrogenic pasture (clover-fertile ewes), from ewes that were permanently affected by clover disease (clover-infertile ewes) and from normal ewes. Two flocks of ewes from different locations were studied. In flock I, tonic LH secretion (total area under the curve of LH concentration versus time, 1 area unit = 1 ng ml- 1 x 1 h) was significantly (P < 0'05) greater in clover-infertile ewes (10'4 area units) during anoestrus than in ewes that had remained fertile after prolonged grazing of oestrogenic clover (5·4 area units). Tonic LH and FSH secretions during the breeding season and FSH secretion during anoestrus were not significantly different. In flock 2, LH levels during the breeding season were significantly (P < 0'05) elevated in clover-infertile ewes (10' 9 area units) compared to normal ewes (5' 4 area units) that had never grazed oestrogenic clover. LH secretion in clover-infertile ewes (7. 8 area units) was intermediate to that found in infertile and control ewes. Concentrations of FSH, progesterone and ovarian vein oestradiol-17 P (Ez) during the breeding season were similar in the three groups.

Effect of follicular fluid and inhibin immunoneutralization on FSH-induced preovulatory follicle growth in the ewe

1991 ◽  
Vol 131 (3) ◽  
pp. 401-409 ◽  
Author(s):  
A. S. McNeilly ◽  
W. Crow ◽  
B. K. Campbell
Keyword(s):  
Follicular Fluid ◽  
Plasma Concentrations ◽  
Potential Interaction ◽  
Preovulatory Follicle ◽  
Follicle Growth ◽  
Sheep Model ◽  
Fluid Concentration ◽  
Lh Secretion ◽  
Infusion Period

ABSTRACT The potential direct ovarian effects of immunoneutralization of inhibin, which increases, and follicular fluid treatment, which inhibits, follicle development in normal ewes was investigated in a sheep model in which endogenous FSH and LH secretion was suppressed thus removing any potential effects of treatment-induced alterations in endogenous FSH or LH secretion. Eighteen Welsh Mountain ewes were treated with two agonist implants containing 3·3 mg buserelin giving a total of 6·6 mg buserelin per animal. During week 5 of treatment all ewes were given a 72-h continuous infusion of ovine FSH (5 μg/h) starting at 09.00 h. Six ewes were treated with antiserum to the 1–26α peptide fragment of porcine inhibin 0 h and 24 h after the start of the FSH infusion, and a further six ewes were treated with charcoal-stripped ovine follicular fluid (oFF) as a source of inhibin, at 09.00 and 17.00 h throughout the 72 h of FSH infusion. The plasma concentrations of both FSH and LH were significantly reduced in all ewes after 5 weeks of treatment with buserelin, and no large follicles > 2·5 mm in diameter were present. Treatment with inhibin antiserum or oFF had no effect, compared with control ewes, on the plasma concentrations of either FSH or LH during the FSH infusion period. After 72 h of FSH infusion there was no difference in the number of small follicles (<2·5 mm in diameter) or large follicles (> 2·5 mm in diameter) or the size of the largest follicles between control ewes and ewes treated with either inhibin antiserum or oFF. However, large oestrogenic follicles from ewes treated with oFF secreted significantly (P<0·01) more testosterone in vitro and had a significantly (P<0·01) higher follicular fluid concentration of testosterone than both control ewes and ewes treated with inhibin antiserum. These results show that the effects of inhibin immunization in increasing follicle growth and oFF in inhibiting follicle growth in normal sheep are not related to a direct effect of these treatments on the ovary, but are mediated by the effects of treatment on the plasma concentrations of FSH. The effect of oFF in increasing thecal androgen production suggests an increase in thecal sensitivity to LH. In the sheep model used in the present study, pulsatile LH secretion was abolished and large follicles were induced to develop under the influence of FSH in the presence of only basal concentrations of LH. The results suggest a potential interaction between oFF components and pulsatile LH secretion in modulating FSH-induced preovulatory follicle growth through an alteration in thecal sensitivity to LH. Journal of Endocrinology (1991) 131, 401–409

scholarly journals Pulsatile secretion of LH in the ram: a re-evaluation using a discrete deconvolution analysis

1992 ◽  
Vol 133 (1) ◽  
pp. 75-85 ◽  
Author(s):  
M.-P. Laurentie ◽  
R. Garcia-Villar ◽  
P.-L. Toutain ◽  
J. Pelletier
Keyword(s):  
Plasma Concentration ◽  
Concentration Profile ◽  
Plasma Concentrations ◽  
Deconvolution Analysis ◽  
Blood Samples ◽  
Before And After ◽  
Quiescence Period ◽  
The Mean ◽  
Rate Profile ◽  
Lh Secretion

ABSTRACT The purpose of the present experiment was to characterize LH secretion pulsatility in rams by analysing the instantaneous secretion rate profile obtained by deconvoluting the plasma concentration profile. Plasma LH concentration profiles were obtained by collecting blood samples every 6 min for 24 h during two different sessions separated by an interval of 15 days. Individual kinetic parameters of ovine LH (oLH) were determined following i.v. injection of oLH. By deconvoluting the plasma concentration profile, it was shown that a pulse has an effective duration of only 20·41±7·69 (s.d.) min whereas the mean duration estimated from measurement of plasma concentrations was 61·00 ± 15·16 min. The number of pulses was similar before and after deconvolution (7·80±1·99 vs 9·70 ± 3·44 pulses/24 h respectively). Using deconvolution the calculated production rate was 2·26 ± 0·94 μg/kg per 24 h, about 50% of this production being located in the pulses. Statistical analysis of pulsatility revealed that pulse occurrence was a non-periodic event and that the amplitude of LH pulses and the associated amount of LH released were correlated with the duration of the preceding quiescence period, but had no statistically significant influence on the duration of the following quiescence period. Journal of Endocrinology (1992) 133, 75–85

The testis is not the major source of circulating follistatin in the ram

1996 ◽  
Vol 149 (1) ◽  
pp. 55-63 ◽  
Author(s):  
A J Tilbrook ◽  
D M de Kretser ◽  
F R Dunshea ◽  
R Klein ◽  
D M Robertson ◽  
...  
Keyword(s):  
Breeding Season ◽  
Jugular Vein ◽  
Plasma Concentrations ◽  
Testicular Tissue ◽  
Blood Samples ◽  
Gonadotrophin Releasing Hormone ◽  
Physiological Dose ◽  
Significant Uptake ◽  
Breeding Seasons ◽  
Matched Samples

Abstract The aims of this study were to determine the plasma concentrations of follistatin in rams and to assess if the testis contributes to circulating follistatin and if there is uptake or production of follistatin by the head in rams. Catheters were inserted in the carotid artery, jugular vein and spermatic vein of intact rams during the non-breeding season (experiment 1; n=5) and breeding season (experiment 2; n=4). In experiment 1, blood samples were collected from 5 rams every 10 min for 4 h, commencing 20–60 min after surgery. After 2 h of sampling 1 μg gonadotrophin-releasing hormone (GnRH) was injected intravenously. In experiment 2, blood samples were collected from 4 of the rams used in experiment 1 by venipuncture 30 and 15 min before surgery and every 15 min throughout surgery. Commencing 1 h after surgery, matched samples were taken from each of the vessels every 10 min for 4 h (1–4 h after surgery), then every hour for 20 h (4–24 h after surgery) and then every 10 min for 4 h (24–28 h after surgery). In both experiments, follistatin secretion was non-pulsatile and there were no significant differences between the concentrations of follistatin in any of the vessels. There was a significant (P<0·05) increase in the concentrations of follistatin in each of the vessels throughout the 4 h of 10-min sampling in both experiments. In experiment 2 plasma concentrations of follistatin in the jugular vein were significantly (P<0·05) lower before surgery than at other stages of the experiment. During the non-breeding season (experiment 1) the concentrations of follistatin in all vessels were about 2-fold higher (P<0·001) than during the breeding season (experiment 2). Concentrations of follistatin were measured in the testicular tissue of the ram, bull, monkey and rat and were found to be 13·6, 2·1, 2·5, 0·8 ng/g testis respectively. In experiment 3, blood samples were collected every 15 min for 4 h from castrated rams (n=6) in the absence of treatment with testosterone propionate (TP) and after 7 days of treatment with a physiological dose of TP during the breeding and non-breeding seasons. There was no effect of stage of breeding season or TP on the plasma concentrations of follistatin and these concentrations in the castrated rams were similar to the concentrations in the intact rams in experiment 2. In experiment 4, the function of Leydig cells was stimulated by administration of human chorionic gonadotrophin but this had no effect on plasma concentrations of follistatin. These experiments show that the concentrations of follistatin in the plasma of rams are measurable, that the testis is not the major contributor to circulating follistatin and that there is no significant uptake or production of follistatin by the head in rams. It appears that the contribution of the testis to circulating follistatin may vary with the stage of the breeding season, being greater during the non-breeding season than the breeding season. The gonadotrophins and testosterone do not appear to have a direct effect on the secretion of follistatin in rams. The increase in concentrations of circulating follistatin during surgery and more frequent blood sampling suggest a stress-related effect on the production of follistatin. Journal of Endocrinology (1996) 149, 55–63

PLASMA CONCENTRATIONS OF LUTEINIZING HORMONE, FOLLICLE-STIMULATING HORMONE AND PROGESTERONE DURING THE BREEDING SEASON IN EWES IMMUNIZED AGAINST ANDROSTENEDIONE OR TESTOSTERONE

1979 ◽  
Vol 81 (3) ◽  
pp. 249-259 ◽  
Author(s):  
N. D. MARTENSZ ◽  
R. J. SCARAMUZZI
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Breeding Season ◽  
Bovine Serum ◽  
Luteal Phase ◽  
Follicle Stimulating Hormone ◽  
Plasma Concentrations ◽  
Biologically Active ◽  
Active Fraction ◽  
Lh Secretion

Levels of plasma LH, FSH and progesterone during the breeding season were measured by radioimmunoassay in control ewes and ewes actively immunized against androstenedione-11α-hemisuccinyl–bovine serum albumin or testosterone-3(O-carboxymethyl)oxime–bovine serum albumin. Immunization against androstenedione resulted in normal oestrous cycles with raised plasma LH and progesterone levels and a reduction in the concentration of FSH during the luteal phase. It is tentatively suggested that androstenedione, or its metabolites, could modify the oestrogenic control of LH secretion and facilitate the release of FSH in the ewe. Immunization against testosterone prevented oestrus and resulted in markedly increased levels of LH without alteration of the FSH concentration. Since evidence of increased binding of oestradiol-17β was found in the ewes immunized against testosterone, these results cannot be attributed solely to a reduction in the biologically active fraction of testosterone.

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