Jugular Venous Plasma Research Articles

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)

Catheterization of the caudal vena cava via the lateral saphenous vein in the ewe, cow, and gilt: an alternative to utero-ovarian and medial coccygeal vein catheters2

Current methods for obtaining venous blood from the reproductive organs of livestock often have a low rate of success or involve intensive surgical procedures that may impair ovarian function. Therefore, the caudal vena cava was catheterized via the lateral saphenous vein to determine the feasibility of using this method for chronic sampling of blood draining from the reproductive organs of ewes (n = 6), cows (n = 6), and gilts (n = 7). Blood samples were collected at 2-cm (ewes and gilts) or 5-cm (cows) intervals during insertion of catheters. Correct placement, defined as the position at which plasma concentrations of progesterone or estrogen were at least threefold greater than in jugular venous plasma, varied among species and among animals within species. It seemed, however, that a majority of catheters would be placed correctly if secured at 48 to 52 cm in ewes, 52 cm in gilts, and 90 to 100 cm in cows. Saphenous vein catheters were secured for sequential sampling of vena caval blood during the follicular phase of ewes (n = 25), cows (n = 4), and gilts (n = 5). Catheters remained patent for the duration of sampling in all individuals. Concentrations of estrogen in jugular and vena caval plasma were correlated (ewe P less than .0003; cow P less than .0001; gilt P less than .0001). Profiles of progesterone and estrogen revealed an episodic pattern of secretion in vena caval but not jugular plasma. Catheterization of the vena cava via the saphenous vein is a relatively simple and noninvasive method for obtaining blood containing uterine and ovarian hormones before their metabolism.

Effect of intra-ovarian infusion of oxytocin on plasma progesterone concentrations in pregnant ewes

The function of oxytocin receptors in the corpus luteum of pregnant ewes was investigated by infusing saline or oxytocin (100 ng/min) into the utero-ovarian artery of pregnant ewes (62 +/- 5 days, n = 12). During a 4-h infusion, plasma oxytocin (OT) concentration increased to 268 +/- 80 pg OT/ml in the OT-infused group and remained unchanged at 2.5 +/- 1.5 pg OT/ml in the saline-infused group. Progesterone concentration in jugular venous plasma (17 +/- 9 ng/ml) rapidly decreased during oxytocin infusion to 59 +/- 10% and 26 +/- 9% of control at 1.5 and 2 h, respectively; the utero-ovarian venous concentration of 64 +/- 38 ng/ml decreased by a similar magnitude during oxytocin infusion. Electron microscopy of corpora lutea, removed at the end of the experiments, showed no indication of luteolytic changes following oxytocin infusion. It was concluded that oxytocin markedly and rapidly reduces progesterone secretion in pregnant ewes.

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)

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)

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)

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)

Concentrations of oestradiol-17β in plasma and milk and progesterone in plasma during the oestrus cycle and in early pregnancy in goats

Pre-ovulatory peaks in oestradiol-17β concentrations were observed on days 1 or 2 and post-ovulatory peaks between days 4 and 7, both in jugular venous plasma and defatted milk, day 1 being the day of the onset of oestrus in the goats. Mean values of the magnitudes of these concentration peaks and of their timing (relative to oestrus) during the oestrus cycle did not differ significantly ( P>0·05) from those when the goats were mated and became pregnant. Pre-ovulatory oestradiol-17β peaks were invariably greater than the corresponding post-ovulatory peaks, as were peak concentrations in plasma relative to those in defatted milk collected on the same day. Mean intervals between the pre- and post-ovulatory peaks in oestradiol-17β concentrations were respectively 4·2 days for plasma and 4·0 days for defatted milk. Concentrations of oestradiol-17β in jugular venous plasma and defatted milk were strongly correlated: rank correlation coefficients for the three goats studied were 0·871, 0·668 and 0·739. It is suggested that in goats, as in cattle, ovarian follicular oestradiol-17β secretion approaching pre-ovulatory level is restored by 4 days after oestrus and its rapid decline after this time may be due to the inhibitory influence of the rapidly rising plasma progesterone concentration.

Oestradiol-17β in testis and jugular venous plasma of intact and hemi-castrated prepubertal lambs and in jugular venous plasma of castrated prepubertal lambs

An assay procedure comprising plasma oestrogen extraction into ether, separation of phenolic steroids (oestrogens) from non-phenolic matter, separation of oestrogens by chromatography on Sephadex LH20 and their radioimmunoassay (RIA), using oestrogen-specific antiserum, has shown sub-capsular, testis venous plasma, pooled from intact and hemi-castrated, prepubertal lambs to contain concentrations of oestradiol-17β in the range 80–120 pg/ml. By this same procedure, jugular plasma of these lambs contained significant ( P < 0.05) concentrations of oestradiol-17β ranging up to 4.2 pg/ml. Jugular venous plasma of castrated lambs collected at 4 and 9.6 weeks of age also contained significant concentrations of oestradiol-17β (0.46 pg/ml and 1.03 pg/ml respectively). It is concluded that the testis is an important source of the oestradiol-17β present in the systemic plasma of prepubertal lambs but that another source may also exist. The Sephadex LH20 chromatography and RIA revealed the presence in plasma, both testis and jugular venous, of significant concentrations of RIA- reactive material which had greater chromatographic mobility than oestrone (and oestradiol-17β).

Inhibin Concentrations in Ovarian and Jugular Venous Plasma and the Relationship of Inhibin with Follicle-Stimulating Hormone and Luteinizing Hormone during the Ovine Estrous Cycle*

A heterologous RIA for ovine inhibin was developed which was sufficiently sensitive and specific to describe the peripheral concentrations of immunoreactive inhibin (iINH) during the estrous cycle of the ewe and to examine the effects of cautery of ovarian follicles on concentrations of iINH in ovarian and jugular venous plasma. Parallel logit-log dose-response lines were observed among ovine follicular fluid, ewe plasma, and pure native ovine (31 kDa) and bovine (31 kDa) inhibin. iINH could not be detected in ovariectomized ewe plasma, and there was no apparent cross-reactivity with a variety of structurally related and unrelated hormones and peptides, except a monomeric form of the alpha-subunit of INH, iINH in follicular fluid was 10(4)-fold higher than that in ovarian venous plasma, which was 3-fold higher than that in peripheral plasma. Cautery of the follicles resulted in a 35% reduction in iINH and an 81% reduction in estrogen concentrations in the ovarian vein within 10 min. During the estrous cycle, iINH and FSH were inversely related in samples taken over 30 h in the luteal phase (r = -0.69; P less than 0.001) and in the pre- and postovulatory phases (r = -0.45; P less than 0.001). iINH and LH were not related in the luteal phase, but were weakly positively correlated in the follicular phase (r = 0.31; P less than 0.01). iINH and estrogen concentrations in the follicular phase were also weakly correlated (r = 0.30; P less than 0.001). Furthermore, iINH concentrations rose in the follicular phase and decreased within 3-6 h of the preovulatory surges of LH and FSH, reaching a nadir around the time of the second rise in FSH 24-48 h later. It is concluded that 1) large antral follicles are a major source of peripheral iINH during the ovine estrous cycle; 2) iINH levels increase in the follicular phase with the growth of the dominant follicle and may be inhibited by the preovulatory surge of gonadotropin; 3) the fall in inhibin after the LH surge may be responsible for the second rise in FSH; and 4) the inverse relationship between FSH and iINH is consistent with the hypothesis that inhibin is involved in the feedback regulation of FSH.

Source of ovarian inhibin secretion during the oestrous cycle of the sheep

The source of inhibin secretion by the ovary in the sheep at different stages of the oestrous cycle was investigated by in-vivo cannulation of the ovarian veins. Twenty-four Scottish Blackface ewes were allocated to four groups of six ewes, i.e. those operated on during the luteal phase (day 10), and those operated on during the follicular phase 24-30, 36 and 60 h following an injection of 125 micrograms cloprostenol on day 10 of the luteal phase. Samples of jugular and timed ovarian venous blood were collected under anaesthesia before and after enucleation of the corpus luteum. Ovaries were then removed and follicles dissected out. Following injection of cloprostenol, luteal regression occurred as indicated by a fall in the secretion of progesterone. The concentration of inhibin in jugular venous plasma and its ovarian secretion rate were similar at all stages of the follicular phase and during the luteal phase. In contrast, the secretion rate of oestradiol rose from 2.86 +/- 0.73 pmol/min during the luteal phase to 8.70 +/- 2.24 pmol/min 24 h after injection of cloprostenol (P less than 0.05). Following enucleation of the corpus luteum the secretion rate of progesterone fell from 809 +/- 270 pmol/min to 86 +/- 30 pmol/min (P less than 0.001). There was also a smaller, artifactual fall in the secretion rate of oestradiol following enucleation of the corpus luteum, which was of similar size to a fall seen in the secretion rate of inhibin. This resulted in a significant (P less than 0.001) fall in the ratio of progesterone to inhibin, while the oestradiol to inhibin ratio remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between uterine secretion of prostaglandin F2 alpha induced by oxytocin and endogenous concentrations of estradiol and progesterone at three stages of the bovine estrous cycle.

The purpose of this experiment was to determine whether differences among cows in the ability of oxytocin to stimulate uterine secretion of prostaglandin F2 alpha (PGF2 alpha) were related to the endogenous ovarian steroid environment. Sexually mature heifers were treated with oxytocin (.33 IU/kg BW) at three stages of the estrous cycle: early (d 3 to 5; n = 5), middle (d 10 to 11; n = 5) or late (d 16 to 17; n = 5). To assess uterine responsiveness to oxytocin, concentrations of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) were quantified in jugular venous plasma samples collected at 1/2-h intervals for 8 h postinjection. The ovarian steroid environment at the time of injection was estimated by measuring the concentrations of progesterone and estradiol in jugular venous plasma samples collected at 4-h intervals for 12 h immediately prior to injection. Concentrations of PGFM increased immediately following injection of oxytocin either early or late in the estrous cycle. The response was much less during the middle of the estrous cycle. The magnitudes of response, early and late in the estrous cycle, were similar and greater than that observed during the middle of the estrous cycle (P less than .05). There was a positive relationship (R2 greater than .8; P less than .05) between magnitude of the response to oxytocin and ratio of estradiol to progesterone both early and late in the estrous cycle. Thus, individual differences in uterine secretion of PGF2 alpha in response to oxytocin were related to stage of the cycle and to differences in the endogenous ovarian steroid environment within each stage of the estrous cycle.

Progesterone in uterine and arterial tissue and in jugular and uterine venous plasma of sheep.

Concentrations of progesterone in uterine and arterial tissue and in uterine and jugular venous plasma were determined. Blood was collected on Days 4 and 9 postestrus from the jugular vein and the first and last venous branches draining each uterine cornu; uterine tissue and arteries were subsequently collected. Progesterone was greater (p less than 0.05) in the cranial third than in the middle or caudal thirds of the uterine horn adjacent to the corpus luteum (CL)-bearing ovary or in any third of the contralateral horn. Progesterone in uterine arterial segments adjacent to the CL-bearing ovary was higher (p less than 0.05) than in contralateral segments. Progesterone was higher (p less than 0.05) in blood from the first venous branch of the cranial third of the uterine cornu adjacent to the ovary with the CL, than in the last branch of the caudal third, or contralateral horn, or in jugular blood. When oviductal veins were resected on Day 9 postestrus, progesterone in the first vein draining the cranial third of the uterine cornu adjacent to the CL-containing ovary was not different (p greater than 0.05) 48 h after resection than in the same vessel in the opposite horn or in jugular blood. We concluded that progesterone and other ovarian products may be delivered to the uterus locally.

Evidence for involvement of prostaglandins in central alpha adrenergic activity and LH release in sheep

Circhoral pulsatile releases of immunoreactive luteinising hormone (LH) and prostaglandin F 2α (PGF 2α) occur synchronously into the jugular vein in ovariectomised sheep. Following a 4-hour control period, intra-carotid injections of phentolamine or intramuscular injections of phenoxybenzamine were given to ovariectomised sheep and the pulsatile release of LH and PGF 2α was monitored for a further 6 to 8 hours. Phenoxybenzamine caused a fall in LH and PGF 2α in jugular venous plasma. Phentolamine also reduced LH significantly but in this case a marked rise in PGF 2α as measured by radioimmunoassay (RIA) occurred after very high doses of phentolamine. Interpretation of the latter results was complicated by the fact that phentolamine at high dose levels interfered with the RIA of PGF 2α in plasma. Experiments were repeated in ovariectomised sheep with cannulae placed in the lateral ventricles of the brain for sampling cerebrospinal fluid (CSF). In contrast to the previously observed rise in jugular venous PGF 2α following high doses of phentolamine, a fall in CSF levels of immunoreactive PGF 2α occurred following intracarotid phentolamine or phenoxybenzamine in 3 out of 7 experiments, while no change was observed in the remaining 4 animals. Phentolamine did not reduce LH significantly in animals with intraventricular cannulae. The work provides support for the view that circhoral pulses of immunoreactive PGF 2α in sheep are neural in origin and may be related to sympathetic neurotransmission.

Concentrations of LH and oestradiol-17β in plasma of the dairy cow during the post-partum acyclic period

AbstractThe concentrations of LH and oestradiol-17β were measured in samples of jugular venous plasma collected frequently during an 8-h period from six acyclic cows between 21 and 27 days post partum. Fluctuations in oestradiol-17β concentrations were detected. Although the mean concentrations of oestradiol were similar whether ovulation occurred within 1 week of sampling or not, the amplitude of the fluctuations in oestradiol concentrations was greater in the three cows which ovulated within 1 week of the period of sampling. Increases in the concentration of LH were frequently followed by increases in the concentrations of oestradiol.

Direct venous-arterial transfer of 125I-radiolabelled relaxin and tyrosine in the ovarian pedicle in sheep.

125I-labelled relaxin and tyrosine were infused into the ovarian vein to investigate transfer to branches of the ovarian artery at the ovarian pedicle in sheep. The ovarian arteries supply the ovary, the oviduct, and the tip of the uterine horn. An exchange of relaxin (n = 24) and tyrosine (n = 18) was observed in blood samples collected from all branches of ovarian arteries. This is expressed as a ratio of radioactivity greater than 1 between jugular venous blood plasma and arterial blood plasma. The average ratio (+/- s.d.) over the total infusion period of 1 h was 1.42 (+/- 0.35) for relaxin and 1.69 (+/- 0.38) for tyrosine with maximal values up to 4.9 and 2.9, respectively. Of the total amount of substance infused (348 pmol/h), 0.22% of the relaxin and 1.19% of the tyrosine reached the adjacent arteries directly. From these investigations it is concluded that molecules with a molecular weight of approximately 6000 can be transferred directly from veins to arteries at the ovarian pedicle, and the efficiency of this exchange does not only depend on molecular size.

Progesterone-binding protein in the corpus luteum, blood and lymph of sheep

A protein which binds progesterone but not cortisol was found in luteal cytosol, utero-ovarian venous plasma, ovarian lymph and jugular venous plasma of sheep. The protein was isolated from other steroid-binding activities present in luteal cytosol and plasma by de-adsorption from hydroxyapatite with 40 mM phosphate. In all cases, it bound progesterone at 4°C with an equilibrium affinity constant of the order of 10 6 l/mol, but did not bind cortisol. After chromatography on hydroxyapatite and Sephadex G-200, the protein obtained from utero-ovarian venous plasma had lost much of its steroid-binding activity, but migrated as a monomer of molecular weight 64 000 in polyacrylamide gel. Bovine luteal cytosol is reported to contain two proteins which bind progesterone similarly. In ruminants, these proteins may participate in the biosynthesis and secretion of progesterone from luteal cells and its transport in blood.

Inhibin secretion by the sheep ovary.

An in-vitro bioassay for inhibin based on FSH content or release by rat pituitary cells was validated for measuring inhibin activity in ovine plasma and lymph. Dose-dependent increases in inhibin activity were detected in peripheral plasma of 4 ovariectomized ewes 1 min after i.v. injections of ovine follicular fluid, and the half-life of inhibin in plasma for 2 ewes was 45 and 50 min, respectively. Inhibin was detected in ovarian lymph but not in ovarian or jugular venous plasma, even after treatment of ewes with PMSG to induce folliculogenesis. Destruction of visible follicles (greater than 0.5 mm diameter) on the ovaries of 4 PMSG-treated ewes by electrocautery was followed by a rapid and sustained decline in secretion of inhibin in ovarian lymph for up to 4 h. Ovarian lymph flow rates were either unchanged or slightly increased after cautery. Oestrogen concentrations in peripheral venous plasma declined within 15-30 min of cautery, but concentrations remained well above baseline. There was a significant decrease in peripheral progesterone concentrations in these same samples, but not until 2-3 h after cautery. FSH in peripheral plasma was depressed or non-detectable in PMSG-treated ewes and neither FSH nor LH concentrations in peripheral plasma were significantly altered up to 4 h after cautery of ovarian follicles. It is concluded that (a) antral follicles (greater than 0.5 mm) are the source of inhibin present in ovarian lymph, and (b) the ovarian lymphatic system is a route by which inhibin could reach the peripheral circulation, particularly in the luteal phase when ovarian lymph flow rates are high.

Hormone responses to exogenous GnRH pulses in post-partum dairy cows.

Nine Friesian dairy cows were treated with 2.5 micrograms GnRH i.v. at 2-h intervals for 48 h commencing between Days 3 and 8 post partum. Hormone concentrations were measured in jugular venous plasma. An episodic pattern of LH release was induced in all animals and there was no significant change in amplitude during treatment. However, cows treated between Days 7 and 8 ('late') showed higher LH episode peaks than did those treated between Days 3 and 6 ('early'). Plasma FSH concentrations showed a less clear episodic pattern in response to GnRH injection. The mean height of FSH responses to GnRH tended to be higher in the 'early' group than in the 'late' group, as did mean FSH concentrations during the pretreatment sampling period. Although clear episodic changes were not observed, GnRH treatment induced a rapid sustained rise in plasma oestradiol-17 beta concentrations, indicating the responsiveness of ovarian follicles to gonadotrophin stimulation early in the post-partum period. There was no difference in oestradiol-17 beta concentrations between the 'early' and 'late' groups during the treatment period. Only one cow exhibited preovulatory-type LH, FSH and oestradiol-17 beta surges during the 96-h post-treatment sampling period. It is concluded that: (1) responsiveness to GnRH pulses increases significantly and FSH responsiveness tends to decrease with time post partum, (2) ovarian follicles are able to secrete oestradiol-17 beta in response to GnRH-induced LH and FSH release during the early post-partum period and there is no time-dependent change in responsiveness; and (3) the lack of preovulatory surges, except in one cow, may reflect a temporary defect in the positive-feedback mechanism by which high concentrations of oestradiol-17 beta induce preovulatory gonadotrophin release.

Radioimmunoassay of cortisol in peripheral blood plasma of buffaloes peripartum

Changes in the concentration of cortisol were observed in the jugular venous plasma of pregnant buffaloes on days 30, 15, 5, 2 and 1 prepartum, at partum, at regular 6-hr intervals up to 72 hr postpartum and on days 4, 6, 10, 18, 34 and 50 postpartum. A radioimmunoassay (RIA) procedure for cortisol standardized in the laboratory was used. Mean plasma cortisol levels showed little fluctuation (P<0.05) between days 30 and 2 prepartum with the values ranging from 1.28 ± 0.23 to 1.46 ± 0.13ng/ml. A small (but nonsignificant) rise in the hormone level was observed one day prepartum followed by a sharp increase to a high mean value of 3.78±0.36 ng/ml (P<0.05) at parturition. A sharp decline (P<0.05) to a low mean value was recorded within 6 hr postpartum followed by marked fluctuations in the hormone level up to 72 hr postpartum. The hormone levels subsequently varied narrowly between 1.74±0.39 and 2.01±0.27 ng/ml up to 50 days postpartum.