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Biomedical subjects

D T Baird

Publications and source records attributed to D T Baird.

At least 163 records · Page 9Linked to original sources
PubMed1991

Effect of FSH on ovarian inhibin secretion in anoestrous ewes.

In Exp. 1, 7 Finn-Merino ewes which had one ovary autotransplanted to a site in the neck had jugular and timed ovarian venous blood samples collected at 10-min intervals for 2 h before and 3 h after injection of 5 micrograms NIAMDD-oFSH-S16. In Exp. 2, 8 Finn-Merino ewes with ovarian autotransplants had jugular and timed ovarian venous blood samples collected at 15-min intervals for 2 h before and 12 h after bolus injection of 40 micrograms NIAMDD-oFSH-S16 and infusion of oFSH-S16 at 6 micrograms/min for 4 h. In Exp. 2 the follicular population of the ovary was assessed by real-time ultrasound at the beginning and end of the experimental period. In both experiments the secretion rates of inhibin (1-3 ng/min) and oestradiol (0.5-8 ng/min) were similar to those observed during the luteal phase of the cycle in the breeding season, indicating significant follicular development in these animals. In Exp. 1 there was no change in the secretion of oestradiol or inhibin after the injection of FSH which resulted in a 25% increase (P less than 0.05) in the concentration of FSH in plasma. Inhibin secretion was pulsatile but there was no difference in inhibin pulse frequency before (1.6 +/- 0.2 pulses/h) or after (1.2 +/- 0.5 pulses/h) injection of FSH. In Exp. 2 injection of FSH resulted in an increase (P less than 0.001) in plasma concentrations of FSH in the sample taken 10 min after injection from a baseline of 1.2 +/- 0.2 ng/ml to a peak of 10.6 +/- 1.0 ng/ml (mean +/- s.e.m.).(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗
PubMed1991

Effect of steroid- and inhibin-free ovine follicular fluid on ovarian follicles and ovarian hormone secretion.

Treatment of ewes with steroid-free ovine follicular fluid (oFF) during the follicular phase of the oestrous cycle results in the immediate inhibition of the ovarian secretion of oestradiol, inhibin and androgens. An experiment was conducted to determine whether this effect of oFF was due to inhibin, or to direct inhibition of ovarian function by other factors in oFF. Eight ewes in which the left ovary and vascular pedicle had been autotransplanted to a site in the neck were studied during the breeding season. Luteal regression was induced in all animals by injection of cloprostenol (100 micrograms i.m.; PG) on Day 10 of the luteal phase. The animals were divided into two groups (n = 4) and treated with either steroid-free oFF (oFF; 3 ml s.c.; 3.2 microgram p1-26 alpha inhibin/ml) or steroid-free oFF in which the inhibin content had been reduced by greater than 90% (IFoFF; 3 ml s.c.; 0.3 microgram p1-26 alpha inhibin/ml) by affinity chromatography, 24 and 36 h after PG. Samples of ovarian and jugular venous blood were collected at (i) intervals of 4 h from 16 h before until 120 h after PG and (ii) intervals of 10 min from 48 to 52 h after injection of PG to investigate the pattern of pulsatile secretion of ovarian hormones. All ewes had previously been monitored during a normal PG-induced follicular phase. Injection of oFF resulted in an increase (P less than 0.05) in the concentration of inhibin in jugular venous plasma and a profound (P less than 0.001) and prolonged decrease in the peripheral concentration of follicle-stimulating hormone (FSH). Injection of IFoFF had no significant effect on peripheral concentrations of inhibin or FSH in the first 24 h after treatment; thereafter inhibin concentrations fell (P less than 0.01) progressively until 40 h and then increased (P less than 0.01) until 72 h after treatment. In both treatment groups, however, within 24-36 h of treatment the concentration of FSH increased 5-10-fold (P less than 0.001) to a peak that occurred within 48-60 h and then declined to basal concentrations within 72-84 h of treatment. The concentration of luteinizing hormone (LH) in jugular venous plasma increased in both groups after treatment (P less than 0.01), although the rise after injection of oFF only started after 24 h. Thereafter, there was a progressive increase in the concentration of LH, peaks occurring 48-60 h after treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Androgens↗
PubMed1991

Immunocytochemical localization of inhibin alpha-subunit in the human corpus luteum.

The localization of inhibin alpha-subunit within the human corpus luteum was investigated. The antiserum used was raised in sheep against the first 1-23 amino acid sequence of the N-terminus of the human inhibin alpha-subunit. Using the avidin-biotin immunoperoxidase technique, intense immunostaining was localized within the granulosa-lutein cells of the corpus luteum, with absence of staining in the theca-lutein cells and surrounding ovarian tissue. Similar distribution of inhibin alpha-subunit immunostaining was observed in 12 corpora lutea obtained during the early, mid- and late-luteal phases and no changes in intensity were apparent at these different stages. Negative controls were obtained by applying antiserum which had been preabsorbed overnight with excess inhibin peptide in place of primary antiserum and also normal nonimmune sheep serum as a substitute for primary antiserum. These results provide further evidence that the human corpus luteum is a significant source of immunoreactive inhibin during the normal human menstrual cycle. The specific localization within the granulosalutein cells of the corpus luteum suggests that inhibin alpha-subunit production may originate from a discrete cell population within the human corpus luteum.

Corpus Luteum↗
PubMed1991

Inhibin and oestradiol in the control of FSH secretion in the sheep.

In the sheep both FSH and LH are necessary for development of large antral follicles. The secretion of FSH is controlled by the negative feedback effect of two ovarian hormones, oestradiol and inhibin, acting at the level of the anterior pituitary. Both are derived from the granulosa cells of large antral follicles which are present in sheep ovaries throughout the oestrous cycle. FSH stimulates growth and mitosis and so the fully differentiated granulosa cells of the large preovulatory follicles acquire receptors for LH, have maximal aromatase activity and produce large amounts of inhibin. The number of these large antral follicles (oestrogenic) which have the potential for ovulation corresponds to the ovulation rate specific for each particular breed of sheep. Over 90% of the oestradiol secreted by the ovaries is derived from these chosen follicles. In contrast, inhibin (and androstenedione) is also secreted by large antral follicles which have lost or not yet acquired maximal aromatase activity. The secretion of oestradiol by the preovulatory follicle(s) is dependent on the supply of androgen precursors produced by the theca which is stimulated by LH. When the concentration of progesterone falls at the end of the luteal phase the increased secretion of LH stimulates the progressive increase in secretion of oestradiol which occurs during the follicular phase. At this stage of the cycle there is a modest inconsistent rise in inhibin, the secretion of which is not stimulated by LH but is related to the increase in the number of large antral follicles. It is suggested that inhibin with its long half-life sets the overall level of negative feedback while oestradiol is responsible for the day-to-day fluctuations in the concentration of FSH which determines the number of ovulatory follicles. This dual control of FSH is adapted to monitor both the total number of large antral follicles in the ovaries (inhibin) and the number which are selected for ovulation (oestradiol).

Animals↗
PubMed1991

Gonadotrophic control of follicle growth in the ewe.

Preovulatory follicle growth in the ewe is dependent on FSH although no precise relationship appears to exist between plasma concentrations of FSH and the number of preovulatory follicles which develop or ovulation rate. This may be related to a hitherto unrecognized influence of pulsatile LH on the growth of large follicles. Preovulatory follicle growth is dependent on the presence of basal amounts of LH, but pulsatile LH, while being essential to supply an increase in androgen substrate to the granulosa cells of the follicle, may also play a role in reducing the responsiveness of many large follicles to FSH, in particular during the preovulatory phase when plasma concentrations of FSH are reduced. Thus selection of the preovulatory follicle(s) may involve a previously unrecognized interaction between FSH and pulsatile LH secretion in which pulses of LH act in a negative rather than positive manner.

Animals↗
PubMed1990

Post-ovulatory contraception.

It is possible to prevent pregnancy after unprotected intercourse by suppressing ovulation, inhibiting fertilization or interfering with tubal transport and/or implantation of the early embryo. IUCDs probably prevent implantation by stimulating the release of prostaglandins from the endometrium but are not acceptable to many women. Post-coital contraceptive steroids, e.g. high-dose oestrogens, are associated with a relatively high incidence of side-effects and must be taken within 72 hours of coitus. As these agents are effective by creating a uterine environment unfavourable for implantation, it may be possible to use antigestagens or antioestrogens in this way. It is already known that an antigestagen in combination with a prostaglandin is a highly effective method of inducing abortion in very early pregnancy. The corpus luteum is essential for the maintenance of pregnancy and its destruction by a luteolytic agent should dislodge the implanting embryo. If an effective method of preventing implantation could be developed which was relatively free from side-effects, it should be possible to use it as a regular form of contraception to be taken only when the risk of pregnancy had occurred.

Contraceptives, Postcoital↗
PubMed1990

The effects of the antiprogestin mifepristone, in vivo, and progesterone in vitro on prolactin production by the human decidua in early pregnancy.

This study investigated the regulatory effect of progesterone on decidual prolactin (dPRL) production during early human pregnancy (6-7 weeks). Patients (n = 7) were treated with the antiprogestin-mifepristone (RU 486; 600 mg single oral dose) for 24-36 h before termination of pregnancy by curettage. Tissue was also obtained from patients without pretreatment in vivo (n = 8) and acted as controls. Decidual tissue was incubated in vitro with and without progesterone and mifepristone for 5 days and the medium changed daily. Prolactin production by decidua parietalis decreased over the period of incubation and was unaffected by addition of progesterone or mifepristone. However, in the group pretreated in vivo with mifepristone, the production of dPRL was markedly lower than in the control group. In contrast, the production of dPRL by decidua capsularis to which trophoblast was attached, was maintained at a constant level over 5 days of culture and was unaffected by pretreatment with mifepristone in vivo or its addition in vitro, or by progesterone. Prolactin was immunolocalized using avidin-biotin immunoperoxidase staining to decidualized cells within the decidua and the intensity of staining was reduced or absent in the decidua parietalis from the mifepristone group compared to controls, but was similar in decidua capsularis in both control and mifepristone groups, in good agreement with the in-vitro production of dPRL. Our findings suggest that the effect of progesterone may be only facilitative, maintaining decidual differentiation, and dPRL production might only be associated with the presence of progesterone-dependent differentiated decidual cells. Apart from progesterone, factors from trophoblast cells can maintain dPRL production during pregnancy.

Abortion, Induced↗
PubMed1990

Pharmacological 'rescue' of the corpus luteum results in increased inhibin production.

Inhibin production by the corpus luteum was investigated by undertaking pharmacological rescue of the corpus luteum with hCG in four healthy women. Blood samples were collected daily for two menstrual cycles. Starting 7 days after the LH surge in the second cycle, incremental doses of hCG (125-8000 IU) were administered daily for 7 days resulting in hCG levels comparable to those seen in normal pregnancy. Following hCG, the luteal phase was prolonged and there were significant increases in the plasma concentrations of inhibin (P less than 0.05), and oestradiol (P less than 0.05). The progesterone concentration was maintained at the mid-luteal phase peak and as a result was significantly higher than those on the equivalent days of the control cycle (P less than 0.05). It was concluded that rescue of the corpus luteum with physiological levels of hCG resulted in a significant output of inhibin, thus suggesting that the corpus luteum is a significant source of inhibin in early pregnancy.

Adult↗
PubMed1990

Circulating bioactive follicle stimulating hormone and immunoreactive inhibin levels during the normal human menstrual cycle.

To examine the relationship between circulating levels of bioactive FSH (B-FSH) and immunoactive inhibin and oestradiol we studied five women during ovulatory cycles. Daily blood samples were collected from each subject during one menstrual cycle. B-FSH was measured using a modified, highly sensitive in-vitro rat granulosa cell bioassay. The inclusion of IGF-1 (10 micrograms/l) and transferrin (50 mg/l) in the assay system enhanced granulosa cell responsiveness to FSH and resulted in increased assay sensitivity. Inhibin was measured by a heterologous radioimmunoassay (RIA) using an antibody raised against 31 kDa bovine inhibin. Bioactive FSH (B-FSH) levels were closely correlated to those of immunoactive FSH (I-FSH, r = 0.79, P less than 0.001) throughout the cycle. Peak levels of B-FSH were observed during the early follicular phase (day -13, 44.7 +/- 9.6 IU/l, mean +/- SEM) and during the midcycle surge (35.2 +/- 6.2 IU/l); lowest levels occurring during the luteal phase (nadir 3.9 +/- 0.27 IU/l). Plasma oestradiol levels increased significantly during the follicular phase (P less than 0.001) to a peak on day -1 and were negatively correlated with B-FSH during the late follicular phase (day -8 to -1; r = -0.45, P less than 0.02). There was no change in the concentration of inhibin (range 55.3-72.3 U/l) during the follicular phase until day -2 after which an increase to a midcycle peak of 139 +/- 10.6 U/l was observed. No correlation was observed between inhibin and B-FSH during the follicular phase. A second increase in the concentration of inhibin was seen during the luteal phase; peak levels occurred by day 6 (311 +/- 25.8 U/l), remained elevated until day 12, and were negatively correlated with B-FSH (r = -0.53, P less than 0.001). No correlation was observed between oestradiol and inhibin or B-FSH during the luteal phase. We conclude that (1) oestradiol secretion from the growing follicle is primarily responsible for the negative feedback regulation of B-FSH resulting in a change from peak levels in the early follicular phase to basal levels in the late follicular phase; (2) significant and sustained increase in peripheral inhibin concentrations occur mostly during the luteal phase; and (3) regulation of FSH secretion by inhibin occurs primarily in the luteal phase. These results suggest a temporal relationship between oestradiol and inhibin in the negative feedback regulation of FSH in vivo.

Adult↗
PubMed1990

Pretreatment with mifepristone (RU 486) reduces interval between prostaglandin administration and expulsion in second trimester abortion.

The effect of pretreatment with mifepristone on prostaglandin-induced abortion was investigated in a double-blind randomized trial involving 100 women in the second trimester of pregnancy. The women were randomly allocated to receive either 600 mg oral mifepristone or placebo tablets 36 h before the administration of gemeprost pessaries. The median interval between administration of prostaglandin and abortion was significantly shorter in the mifepristone group (6.8 h) compared with the placebo group (15.8 h). The women pretreated with mifepristone required significantly fewer gemeprost pessaries to induce abortion and experienced significantly less pain than the women who had received placebo.

Abortifacient Agents↗
PubMed1990

The pattern of ovarian inhibin, estradiol, and androstenedione secretion during the estrous cycle of the ewe.

An experiment was conducted in order to determine the pattern of, and the relationships between, the secretion of inhibin, estradiol, and androstenedione by the ovary and the concentration of LH, FSH, and PRL during the estrous cycle of sheep. The estrous cycles of 6 Finn-Merino ewes in which the left ovary had been autotransplanted to the neck were synchronized by two injections of cloprostenol (100 micrograms im) a potent analog of prostaglandin F2 alpha (PG) given 14 days apart. The ewes had ovarian and jugular venous blood samples taken at four hourly intervals from 42 h before the second PG injection until day 6 of the following cycle. All animals responded to PG with the preovulatory LH surge occurring within 58 +/- 2 h (mean +/- SEM). The concentration of FSH in jugular venous plasma fell (P less than 0.001) after the induction of luteolysis and then exhibited 3 peaks, the first coincident with the LH surge, the second on day 1, and the third on day 6. After injection of PG the secretion rates of inhibin, estradiol, and androstenedione increased (P less than 0.05) within 4-8 h. After this increase in the early follicular phase the secretion rate of estradiol continued to rise until the time of the LH surge (P less than 0.001). Although the secretion of androstenedione and inhibin increased in the 36 h before the LH surge the magnitude of this rise was less marked than for estradiol and was not statistically significant. Within 4-8 h of the start of the LH surge the secretion of estradiol and androstenedione declined rapidly reaching barely detectable levels within 16 h (P less than 0.001). In contrast the secretion of inhibin increased after the LH surge reaching a broad peak (P less than 0.05) of approximately 16-h duration, coincident with the second peak of FSH. From days 2-6 mean secretion of inhibin remained relatively stable at 2-6 ng/min although considerable variation was observed in individual profiles. The rate of estradiol secretion increased steadily from its nadir on day 1 to a broad peak centered around day 3 (3-6 ng/min, P less than 0.001) followed by a decline until by day 6 the estradiol secretion rate was less than 1 ng/min (P less than 0.01). The secretory profile for PRL showed a close relationship with estradiol secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Androstenedione↗
PubMed1990

Expression of TGF-beta isoforms during first trimester human embryogenesis.

We have studied the expression of the genes encoding transforming growth factors (TGFs) beta 1, beta 2 and beta 3 in human embryos ranging from 32 to 57 days post-coitum, using in situ hybridization. The spatial and temporal pattern of expression of each gene is distinct, though each occasionally overlaps. TGF-beta 1 is expressed in haematopoietic, endothelial and osteogenic tissues. TGF-beta 2 and TGF-beta 3 are expressed in a wide variety of mesenchymal tissues including areas of chondrogenic activity. TGF-beta 2 is also found in several epithelial and in the ventral nervous system. The differential transcript distributions are broadly similar to those seen in mouse embryos suggesting that there is conservation of TGF-beta gene regulatory sequences and developmental function across this species boundary.

Bone and Bones↗
PubMed1990

Effects of passively immunizing ewes against inhibin and oestradiol during the follicular phase of the oestrous cycle.

Passive immunization was used to investigate the importance of inhibin and oestradiol in the control of FSH production during the follicular phase of the oestrous cycle in the sheep. Four groups of five mature Scottish Blackface ewes were injected with normal sheep plasma (control), antiserum to the 1-26 alpha peptide fragment of porcine inhibin, antiserum to oestradiol-17 beta, or a combination of the two antisera, 24 h following cloprostenol-induced luteal regression. There was no difference in the concentration of LH in jugular venous plasma between the control and inhibin-immunized groups following the injection of normal sheep plasma or inhibin antiserum, with both groups exhibiting normal LH surges. In both the groups immunized against oestradiol, the basal concentration of LH rose by 25-30% (P less than 0.05) during the 96-h period following injection, while the LH surge and consequent formation of a corpus luteum was inhibited. In all three immunized groups there was a significant (P less than 0.001) rise in the concentration of FSH starting 3.8-4.8 h after the injection of antiserum. The duration of the rise was similar in the groups injected with oestradiol antiserum alone (43.6 +/- 12.8 h) or in combination with inhibin antiserum (40.6 +/- 11.7 h), but was significantly (P less than 0.05) shorter in the group immunized against inhibin alone (17.0 +/- 0.5 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The effect of a potent gonadotrophin-releasing hormone antagonist on ovarian secretion of oestradiol, inhibin and androstenedione and the concentration of LH and FSH during the follicular phase of the sheep oestrous cycle.

By selective removal and replacement of LH stimulation we sought to examine the relative importance of inhibin and oestradiol in controlling FSH secretion, and the role of LH in the control of ovarian hormone secretion, during the follicular phase of the oestrous cycle. Eight Finn-Merino ewes which had one ovary removed and the other autotransplanted to a site in the neck were given two injections of a gonadotrophin-releasing hormone (GnRH) antagonist (50 micrograms/kg s.c.) in the follicular phase of the cycle 27 h and 51 h after luteal regression had been induced by cloprostenol (100 micrograms i.m.). Four of the ewes received, in addition, i.v. injections of 2.5 micrograms LH at hourly intervals for 23 h from 42 to 65 h after GnRH antagonist treatment. Ovarian jugular venous blood samples were taken at 10-min intervals for 3 h before and 5 h after the injection of antagonist (24-32 h after cloprostenol) and from 49 to 53 h after antagonist (74-78 h after cloprostenol). Additional blood samples were taken at 4-h intervals between the periods of intensive blood sampling. The GnRH antagonist completely inhibited endogenous pulsatile LH secretion within 1 h of injection. This resulted in a marked decrease in the ovarian secretion of oestradiol and androstenedione (P less than 0.001), an effect that was reversible by injection of exogenous pulses of LH (P less than 0.001). The pattern of ovarian inhibin secretion was episodic, but removal or replacement of stimulation by LH had no effect on the pattern or level of inhibin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstenedione↗
PubMed1990

Pulsatile secretion of inhibin, oestradiol and androstenedione by the ovary of the sheep during the oestrous cycle.

The pattern of pulsatile secretion of inhibin, oestradiol and androstenedione by the ovary at different stages of the oestrous cycle in sheep was studied in five Finn-Merino ewes in which the left ovary had been auto-transplanted to the neck. The ewes had jugular venous blood samples collected at 4-hourly intervals from 42 h before the induction of luteolysis by i.m. injection of cloprostenol (100 micrograms) on day 10 of the oestrous cycle, until day 3 of the following cycle. There were five periods of intensive blood sampling, when both ovarian and jugular venous blood samples were collected, as follows: (a) mid-luteal phase, before the second injection of cloprostenol on day 10 (15-min intervals for 6 h); (b) early follicular phase, 24 h after the second injection of cloprostenol (10-min intervals for 4 h); (c) late follicular phase, 48 h after the second injection of cloprostenol (10-min intervals for 4 h); (d) after the LH surge on day 1 of the cycle, 76 h after the second injection of cloprostenol (10-min intervals for 4 h); (e) early luteal phase on day 3 of the cycle, 120 h after the second injection of cloprostenol (10-min intervals for 3 h). Plasma was collected and the samples assayed for LH, FSH, progesterone, oestradiol, androstenedione and inhibin. The ovarian secretion rates for oestradiol, androstenedione and inhibin were calculated. All ewes responded normally to the luteolytic dose of cloprostenol with the preovulatory surge of LH occurring within 56.4 +/- 1.6 h (mean +/- S.E.M.) followed by the establishment of a normal luteal phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstenedione↗
PubMed1990

Ovine follicular fluid suppresses the ovarian secretion of androgens, oestradiol and inhibin.

An experiment was conducted to examine the effect of steroid-free ovine follicular fluid (oFF) on ovarian hormone secretion. Eight Merino x Finnish Landrace ewes in which the left ovary and vascular pedicle had been autotransplanted to a site in the neck were studied during the breeding season. Luteal regression was induced in all animals by injection of cloprostenol (100 micrograms, i.m.) on day 10 of the luteal phase. Four of the eight animals were treated with steroid-free oFF (3 ml, s.c.) in the early follicular phase, 24 and 36 h after injection of cloprostenol. Samples of both ovarian and jugular venous blood were collected at 4-h intervals from 20 h before until 96 h after injection of cloprostenol. Ovarian and jugular venous blood samples were also collected at 10-min intervals from 48 to 52 h after injection of cloprostenol to investigate the pattern of pulsatile secretion of ovarian hormones. Samples were assayed for oestradiol, androstenedione, testosterone and inhibin and the ovarian secretion rates calculated. Both injections of oFF resulted in a fourfold increase in the concentration of inhibin in jugular venous plasma within 4-8 h of administration (P less than 0.01) with concentrations remaining increased (P less than 0.05) until 56 h after cloprostenol (32 h after the first oFF injection). Following oFF injection there was a profound (100%; P less than 0.001) and prolonged decrease in the peripheral concentration of FSH until 60 h after cloprostenol at which time the concentration of FSH increased five- to sixfold (P less than 0.001) to a peak lasting 24 h. In contrast to FSH, the concentration of LH in jugular venous plasma rose immediately following oFF treatment and continued to increase, exhibiting a profile similar to that described for FSH. No preovulatory LH surge was detected in any of the oFF-treated ewes while untreated ewes had an LH surge within 58.0 +/- 1.2 (S.E.M.) h. Within 8 h of the first injection of oFF the ovarian secretion rate of oestradiol, androstenedione and inhibin began to decline to reach a nadir of less than 1 ng/min within 32-36 h (56-60 h after cloprostenol; P less than 0.01). Testosterone secretion, already barely detectable, did not change significantly following injection of oFF but remained low for 36 h following oFF and did not exhibit the increase observed over this period in controls. After injection of oFF the episodic secretion of oestradiol, androstenedione, testosterone and inhibin was markedly suppressed in spite of numerous pulses of LH.(ABSTRACT TRUNCATED AT 400 WORDS)

Androstenedione↗
PubMed1990

Ovarian secretion rates and peripheral concentrations of inhibin in normal and androstenedione-immune ewes with an autotransplanted ovary.

Active immunization of sheep against androstenedione results in an increase in ovulation rate that is associated with increased plasma levels of LH and progesterone, but not FSH. Although immunized ewes have more activated follicles the secretion rate of oestradiol is not increased. An experiment was conducted to examine the effect of androstenedione immunity on the ovarian secretion and peripheral plasma concentrations of inhibin. Merino ewes in which the left ovary had been autotransplanted to a site in the neck were divided into control (n = 5) and androstenedione-immune (n = 6) groups. Ovarian and jugular venous blood was collected every 10 min at two stages of the follicular phase, 21-27 h and 38-42 h after a luteolytic dose of an analogue of prostaglandin F2 alpha (PG), and every 15 min for 6 h on day 10 of the subsequent luteal phase. The ewes were monitored regularly for luteal function by measurement of the concentration of progesterone and preovulatory LH surges. The concentration of inhibin in jugular and ovarian venous plasma was determined by radioimmunoassay and ovarian secretion rates and peripheral concentrations are expressed as pg of 1-26 peptide fragment of the alpha chain. The ovarian secretion rate of inhibin tended to be greater in androstenedione-immune ewes at all stages of the oestrous cycle measured, with this difference being statistically significant (P less than 0.05) during the luteal phase (100 +/- 40 and 260 +/- 80 (S.E.M.) pg/min for control and immune groups respectively). The pattern of ovarian inhibin secretion exhibited pulsatile-like fluctuations which were not associated with LH pulses. Peripheral concentrations of inhibin were generally higher in immunized than in control ewes with this difference being significant (P less than 0.01) from day 4 to 14 of the luteal phase (59 +/- 5 and 110 +/- 7 ng/l for control and immune respectively). The ovarian secretion rate of immunoactive inhibin was greater (P less than 0.01) during the follicular phase than during the luteal phase in both groups of ewes, and peripheral concentrations of inhibin increased (P less than 0.001) following injection of PG in ewes from both treatment groups. We concluded that androstenedione immunity results in an increase in ovarian inhibin secretion, an effect that can probably be attributed to the greater number of large oestrogenic follicles present in the ovaries of these ewes.(ABSTRACT TRUNCATED AT 400 WORDS)

Androstenedione↗