CHARACTERIZATION OF CATIONIC AMINO ACID TRANSPORT SYSTEMS IN RAT ERYTHROCYTES: LACK OF EFFECT OF URAEMIA ON l-ARGININE INFLUX

1. Chronic renal failure (CRF) is associated with the abnormal regulation of nitric oxide (NO) synthesis at the systemic level. The transport of L-arginine, upregulated in blood cells from uraemic patients, modulates NO synthesis in this pathological condition. The model of partial nephrectomy in rats is widely accepted as a valid model of uraemia. Because there are no reports of L-arginine transport in blood cells from uraemic rats, the aim of the present study was to investigate L-arginine transport in red blood cells (RBCs) from these rats. 2. The kinetics of L-arginine transport in RBC and plasma and the amino acid profiles of RBC were investigated in control, sham-operated and subtotally nephrectomized rats. 3. L-Arginine transport was mediated via the cationic amino acid transport system y+ and a transport system with kinetics resembling the human system y+L. In control RBC, the apparent Ki for L-leucine inhibition of L-arginine transport via system y+L was 0.16 +/- 0.02 and 4.8 +/- 2 mmol/L in the presence of Li+ and Na+, respectively. 4. The Vmax values for L-arginine transport via system y+L and system y+ were similar in RBC from control sham-operated and uraemic rats. Moreover, L-arginine concentrations in plasma and RBC were not affected by uraemia. 5. The findings of the present study provide the first evidence that L-arginine transport in rat erythrocytes is mediated by two distinct cationic transport systems with characteristics of systems y+ and y+L, which accept neutral amino acids only in the presence of Li+. In contrast with previous studies in uraemic patients, plasma levels and maximal transport rates of L-arginine were not altered in this rat model of CRF.

Timing of follicular phase events and the postovulatory progesterone rise following synchronisation of oestrus in cows

In cows the timing of both ovulation and the subsequent postovulatory progesterone rise are critical to successful fertilisation and early embryo development. The aim of this study was to determine the degree of variability in the timing of ovulation relative to other follicular phase events and to determine how variations in the timing of follicular phase events contribute to the timing of the postovulatory progesterone rise. Plasma concentrations of progesterone, oestradiol and luteinising hormone (LH) and the timing of oestrus and ovulation were determined following induction of luteolysis were determined in 18 mature, non-lactating Holstein-Friesian cows. Four cows were excluded on the basis of abnormal reproductive function. In the remaining 14 cows oestrus occurred at 57.4+/-4.3h and the LH surge at 54.6+/-4.0h following luteolysis (progesterone <1ngmL(-1)) followed by a fall in circulating oestradiol concentration at 64.6+/-4.4h. Cows ovulated at 88.0+/-4.7h with the postovulatory progesterone rise (to >1ngmL(-1)) occurring 159+/-7.2h after luteolysis. There was considerable variation in the timing of ovulation following luteolysis (range 64-136h) onset of oestrus (range 24-40h) and onset of the LH surge (range 24-44h). Cows were then split on the basis of interval from progesterone fall to progesterone rise giving groups (n=7 per group) with intervals of 180.6+/-6.7 and 138.3+/-5.7h (P<0.001). Between groups, both the intervals from luteolysis to ovulation (98.3+/-6.9 vs 77.7+/-3.4h; P<0.05) and ovulation to progesterone rise (82.3+/-4.2 vs. 60.6+/-5.5h; P<0.01) were longer in late rise cows. There was no difference between groups in the interval from oestrus or LH surge to ovulation. In conclusion the results of this study further highlight the high variability that exists in the timing and interrelationships of follicular phase events in the modern dairy cow, reemphasising the challenges that exist in optimising mating strategies. However, the data do suggest that in cows with poor post ovulatory progesterone secretion, the key problem appears to be poor post ovulatory development rather than a delay in ovulation.

Timing of prostaglandin F(2alpha) release episodes and oxytocin receptor development during luteolysis in the cow

The timing of PGF(2alpha) release and the timing and extent of the rise in endometrial oxytocin receptors was determined in relation to the timing of the progesterone fall during luteolysis in cycling cows. In cows undergoing luteolysis (n = 6), measurement of PGF(2alpha) metabolite in hourly plasma samples collected during daily 10 h sampling periods identified a total of 2.2+/-0.5 PGF(2alpha) release episodes per animal, each of 4.0+/-0.4 h duration. In cows in which luteolysis was not observed (n = 4) no PGF(2alpha) release episodes were identified. In a further three cows in which additional repeated uterine biopsies were collected on days 15, 17, 19, 21 and 23, endometrial oxytocin receptors were initially undetectable (<15 fmol/mg protein) but had increased to 120+/-19 fmol/mg protein prior to the initiation of PGF(2alpha) release episodes. Receptor concentrations then continued to increase reaching peak concentrations of 651+/-142 after luteolysis had been completed.

Cardiovascular consequences of life-long exposure to dietary isoflavones in the rat

Dietary soy intake in man is proposed to provide cardiovascular protection, but it is not established whether this property is attributable to the soy protein per se or to associated dietary isoflavones. This investigation aimed to establish whether the dietary isoflavones in soy protein affect cardiovascular function. Ten days prior to mating, male and female Wistar rats were habituated to either a soy based isoflavone rich diet (plasma concentration 1.87 micromol l(-1) isoflavones) or the same diet after isoflavone elution (plasma isoflavone not detectable). Offspring were weaned onto and maintained on the same diet as their dam and sire for 6 months. Blood pressure, and constrictor and dilator responses in the aorta and mesenteric resistance arteries were assessed at 3 and 6 months of age. There was no effect of isoflavone removal from the diet on blood pressure, heart rate, aortic function or mesenteric artery contractile function, at either 3 or 6 months of age. Resistance mesenteric arteries from 6-month-old female rats fed the isoflavone rich diet demonstrated a modest increase in arterial distensibility compared with those fed the depleted diet, and mesenteric arteries from male and female rats fed the isoflavone rich diet showed increased sensitivity to acetylcholine. In summary, the isoflavone content of soy protein has no influence on blood pressure in healthy rats fed a diet based on soy protein, but influences small artery function.

ACTIVATION OF l-ARGININE TRANSPORT IN UNDIALYSED CHRONIC RENAL FAILURE AND CONTINUOUS AMBULATORY PERITONEAL DIALYSIS PATIENTS

1. Treatment with haemodialysis and continuous ambulatory peritoneal dialysis (CAPD) presents different pathophysiological profiles and it has been suggested that clinical outcome in chronic renal failure may depend on the mode of dialysis. The transport of L-arginine, a precursor of nitric oxide, into blood cells is increased in uraemic patients on haemodialysis. The present study was designed to investigate L-arginine transport into red blood cells (RBC) in uraemic patients not yet on dialysis and on CAPD therapy. 2. Eleven uraemic patients not yet on dialysis and 17 on CAPD were included in the study. L-Arginine transport into RBC and plasma and RBC amino acid profiles were analysed in these sets of patients. 3. L-Arginine transport via system y(+), but not y(+)L, into RBC, was significantly increased in undialysed uraemic patients (459 +/- 40 micromol/L per cell per h) and CAPD patients (539 +/- 61 micromol/L per cell per h) compared with controls (251 +/- 39 micromol/L per cell per h). High-pressure liquid chromatography measurements demonstrated low levels of plasma L-arginine in uraemic patients both on CAPD (54 +/- 3 micromol/L) and not yet on dialysis (80 +/- 6 micromol/L) compared with control subjects (146 +/- 14 micromol/L). 4. Our findings provide the first evidence that uraemic patients not yet on dialysis and on CAPD present with an activation of L-arginine transport via system y(+) into RBC associated with reduced plasma levels of L-arginine.

In vivo expression of interferon tau mRNA by the embryonic trophoblast and uterine concentrations of interferon tau protein during early pregnancy in the cow

In this study, we have measured uterine concentrations of interferon tau and intensity of embryonic interferon tau mRNA expression between day 14 and 18 in cows. While interferon tau concentrations rose dramatically (P < 0.001) from day 14 to 18, there was no significant increase in the intensity of expression of interferon tau mRNA by the trophoblast. When results were analyzed on the basis of embryo size, well elongated embryos (>10 cm) produced significantly (P < 0.001) more interferon tau than smaller embryos but showed similar levels of interferon tau mRNA expression. These results demonstrate that the increase in interferon tau concentrations responsible for the maternal recognition of pregnancy results from the increase in embryo size during elongation and not from any upregulation of mRNA expression.

Effect of post-mating GnRH analogue (buserelin) treatment on PGF2alpha release in ewes and ewe lambs

The objectives of this study were to determine the effects of buserelin or saline treatment on ovarian function (Experiment 1), plasma PGFM concentrations and oxytocin stimulated prostaglandin F(2alpha) (PGF(2alpha)) release (Experiment 2) in ewe lambs and ewes. Welsh Halfbred ewes (n=26) and ewe lambs (n=24) were mated to vasectomised rams at synchronised oestrus and on Day 12 post-mating each animal was injected intramuscularly either normal saline or 4 microg buserelin. In Experiment 1, plasma progesterone and oestradiol concentrations were determined in samples collected by jugular venepuncture 1h before and at 0, 2, 4, 6, 8, 24, 48 and 72 h after treatment (n=7 per treatment group). Progesterone concentrations increased (P<0.05) from 2 to 8h after buserelin treatment and returned to basal levels after 72 h, whereas oestradiol concentrations were maximal at 2h post-treatment and returned to basal levels after 24h (P<0.05). Oestradiol concentrations were lower (P<0.05) in buserelin-treated animals than controls at 72 h post-treatment. Basal and post-treatment progesterone concentrations were greater (P<0.05) in ewes than in ewe lambs but oestradiol levels were similar for both age groups. Ovulation rate, determined by laparoscopy on Day 14, was similar for both age groups (ewes 1.1; ewe lambs 1.0). Buserelin treatment induced accessory corpora lutea in ewes (4/7; 57%) but not in ewe lambs (0/7; 0%). In the Experiment 2, plasma PGFM concentrations were determined in samples collected at 20-min intervals for 6h on Day 14 and at 20-min intervals for 1h before and at 10-min intervals for 1h and then at 20-min intervals for a further 3h period after an intravenous injection of oxytocin (1IU/kg body weight) on Day 15 post-oestrus. In this experiment there were five ewe lambs and six ewes per treatment group. There was no effect of buserelin treatment or age on basal PGFM concentrations on either Day 14 or 15. Although peak PGFM concentrations tended to be lower in buserelin-treated animals, the difference was not significant (P>0.05). However, peak duration following oxytocin challenge on Day 15 post-mating was shorter (P<0.05) in control ewes compared with control ewe lambs. In conclusion, buserelin treatment given on Day 12 post-oestrus enhances luteal function more in ewes than ewe lambs and after a transitory increase, reduces oestradiol concentrations in both ewes and ewe lambs. However, buserelin treatment does not significantly attenuate the luteolytic signal.

The use of milk progesterone to monitor reproductive function in beef suckler cows

Milk progesterone analysis was used to monitor reproductive function in 134 autumn calving cross-bred suckler cows. Progesterone was measured in milk samples collected three times per week from around 4 week post-calving to around day 60 of pregnancy during 1st and 2nd lactation. The mean day of onset of luteal activity (OLA) was 40.7 +/- 1.1 with the distribution skewed towards a later return. Once cyclicity had been initiated the incidence of reproductive cycle problems (6.5%) was low, though animals with such problems (n = 14) exhibited a delayed interval to first service (P < 0.05), lower conception and calving rates (P < 0.001), increased services per pregnancy (P < 0.001) and a higher (P < 0.10) barren rate (14.3% versus 4.0%) compared to animals with normal cycles (n = 201). In conclusion, using milk progesterone analysis we found a relatively low incidence of reproductive cycle problems in beefxdairy suckler cows. However, while the incidence of cycle problems was low, those animals with problems showed significantly impaired reproductive function.

Metabolic variables and plasma leptin concentrations in dairy cows exhibiting reproductive cycle abnormalities identified through milk progesterone monitoring during the post partum period

We have used milk progesterone analysis to monitor reproductive function in lactating dairy cows and have then related this reproductive function to a variety of metabolic variables. Monitoring of cows (n = 41) during the period of onset of luteal function (first milk progesterone reading>5 ng/ml) revealed that delayed onset was associated with increased milk yield and greater loss of body weight and body condition but was not related to plasma metabolite or leptin concentrations. Further monitoring of reproductive function in these 41 cows and an additional 33 cows (total n = 74) during the mating period (from weeks 6 to 14 post partum) identified reproductive cycle abnormalities in 29 (39.2% of animals). The occurrence of cycle abnormalities was associated with increased milk yield (P < 0.05), elevated plasma beta hydroxybutyrate (P < 0.05) and reduced plasma leptin (P < 0.01) concentrations as well as a lower (P < 0.05) rate of gain of body weight and condition score but was not associated with plasma urea or glucose concentrations. Furthermore, cows exhibiting cycle abnormalities had a longer (P < 0.01) interval to first service and a smaller percentage had conceived by 100 days post partum (34.5% versus 66.7%; P < 0.01). These results provide further evidence that impaired reproductive function during the post partum period in dairy cows is caused by a poor energy status and not elevated urea concentrations. Reduced plasma leptin concentrations in animals suffering reproductive dysfunction further supports this view.

Relationships between maternal hormone secretion and embryo development on day 5 of pregnancy in dairy cows

In cattle, increasing early embryonic losses are associated with inadequate progesterone concentrations within the first three weeks of pregnancy. The aim of this study was to investigate the complex relationship between early maternal progesterone concentration and embryo development early within the first week of pregnancy, specifically, on day 5 post-oestrus in dairy cows. Twenty Holstein-Friesian cows at the end of lactation were inseminated at oestrus (day 0) and on day 5 post-oestrus cows were slaughtered and the reproductive tract flushed to determine the presence and stage of embryo development. Three cows that had failed to synchronise correctly were excluded from analysis while in the remaining 17 cows 11 (65%) were pregnant with embryos at the morula (n = 3), 9-16 (n = 3) and 8-cell (n = 5) stages of development. No differences in day 5 plasma progesterone concentrations or corpus luteum (CL) size or progesterone content were observed between pregnant (n = 11) and non-pregnant (n = 6) cows. In cows with embryos beyond the 8-cell stage of development (n = 6) plasma progesterone concentration (P < 0.001) and CL weight (P < 0.01) were higher and plasma insulin concentrations lower (P < 0.001) than in cows with 8-cell embryos (n = 5). In addition there was a negative relationship between plasma progesterone and plasma insulin in pregnant cows (R(2) = 0.65; P < 0.005). In cows with an embryo present in the oviduct, oviductal glucose concentrations were lower (P < 0.05) than in cows with no embryo present. These results confirm progesterone is not only directly associated with embryo development, but that it may indirectly modulate embryo development via changes in the oviductal environment. In summary, the association between maternal progesterone concentration and embryo development exists as early as day 5 of pregnancy in dairy cows.

The induction of a delayed post-ovulatory progesterone rise in dairy cows: a novel model

A delayed rise in post-ovulatory progesterone is associated with poor embryo development in the cow, although the underlying cause of this aberrant luteal function is poorly understood. The objective of this study was to develop a novel model, in which a delayed progesterone rise could be induced by manipulating the dynamics of the follicular phase. Luteolysis was induced in 20 dairy cows in the presence of either a larger follicle > 10 mm (LF, n = 11) or a smaller follicle < 10 mm (SF, n = 9) and transrectal ultrasonography was performed to determine follicle and CL growth and timing of ovulation. Plasma progesterone and oestradiol were analysed 3x daily. Cows were slaughtered on either day 4 (n = 4 per group) or day 7 (SF, n = 5; LF, n = 7) after ovulation. The pre-ovulatory follicle was larger in the LF group than the SF group at luteolysis (13.5 +/- 0.4 mm versus 6.7 +/- 0.7 mm, P < 0.001) and ovulation (16.7 +/- 0.3 mm versus 13.6 +/- 0.6 mm, P < 0.001). The LF group experienced a shorter follicular phase and ovulated 36 h earlier than the SF group (P < 0.001). At luteolysis, plasma oestradiol concentrations were greater in the LF group (P < 0.001), although peak concentrations were not different (P > 0.05). Moreover, higher progesterone concentrations were observed in the LF group during the early luteal phase (P < 0.05). Luteal weights were positively correlated with plasma progesterone concentrations on day 5 (P < 0.05) but not day 8. In conclusion, a model has been developed which has shown that the dynamics of follicle development during the pre-ovulatory period is an important determinant of subsequent CL development and function.

Endometrial Oxytocin Receptor Concentration and Activity in Prepubertal Ewe Lambs

We have measured endometrial oxytocin receptor concentrations during prepuberty in ewe lambs, and have investigated the effect of progesterone on the activity of these receptors. In the first study, oxytocin receptor concentrations were undetectable in 2-week prenatal lambs but had increased immediately following birth and were then maintained throughout prepubertal life. Despite the presence of oxytocin receptors animals showed no prostaglandin F(2alpha) (PGF(2alpha)) release in response to exogenous oxytocin challenge at either 3 or 5 months of age. In a second study in 4-month-old ewe lambs treatment with exogenous progesterone resulted in the appearance of PGF(2alpha) release in response to oxytocin after 10 days of treatment. Thus, during the prepubertal life, ewe lambs possess the prerequisites of a luteolytic mechanism in that they have a dormant population of oxytocin receptors in which progesterone can induce oxytocin-stimulated PGF(2alpha) release.

Effects of time of progesterone supplementation on embryo development and interferon-tau production in the cow

We have investigated the effects of the timing of progesterone supplementation on early embryo development in mature, non-lactating Holstein-Friesian cows. Animals were inseminated 72 h (day 1) and 96 h following prostaglandin injection and were either left as untreated controls (n=6) or received progesterone supplementation from either days 5 to 9 (early; n=6) or from days 12 to 16 (late; n=6). Daily plasma samples were collected until day 16, when cows were slaughtered and reproductive tracts recovered and flushed to collect embryos and to measure interferon-tau activity. Both early and later progesterone supplementation resulted in marked increases in plasma progesterone (P<0.01). Early, but not late, progesterone supplementation resulted in a fourfold increase in trophoblast length (P<0.01) and a sixfold increase in uterine concentration of interferon-tau (P<0.05). The results demonstrate that progesterone supplementation during the postovulatory rise, but not later in the luteal phase, increases embryo development and interferon-tau production.

Endocrine and paracrine control of follicular development and ovulation rate in farm species

Productivity in farm species is controlled by many factors, including ovulation rate. In cattle, single ovulations occur most frequently and in sheep (and goats) the number of ova released can range from one to many depending upon the breed, whilst the pig is polyovular. The processes of recruitment and selection determine the number of ovulatory follicles in all these species with FSH and subsequently LH playing major roles. GnRH-agonist models in which endogenous gonadotrophin secretion is suppressed and exogenous LH and/or FSH are administered at specific concentrations in defined patterns, are useful in all three species for elucidating the precise roles of specific hormones in stimulating follicular development. Differences in the hypothalamic-pituitary-ovarian feedback response lead to the differences in the number of ovulatory follicles, as does the pool of antral follicles from which the ovulatory ones are selected. Precocious development of follicles is also associated with more ovulations, as is the case with the Booroola due to the single gene acting through bone morphogenetic proteins (BMPs). It is well established that ovulation rate can also be influenced by exogenous hormone administration and by environmental factors such as nutrition. It has become apparent that these nuritional effects are mediated by a direct action at the level of the ovary, involving insulin, insulin-like growth factors (IGF) I and II and their binding proteins among other factors. These factors can also affect the quality of the oocyte and consequently embryo development and survival. Recently, the regulation of follicular angiogenesis has been shown to be important for the development of ovulatory follicles, particularly vascular endothelial growth factor (VEGF) which is produced primarily by the granulosa cells within the ovary and can be stimulated by gonadotrophins. Administration of VEGF has been shown to stimulate pre-antral follicular growth and increase the number of pre-ovulatory follicles. In summary both extra- and intra-ovarian factors are involved in the control of ovulation rate. Manipulation of the angiogenic process may also provide new opportunities for regulating the quality and number of follicles that ovulate.

Effects of circulating progesterone and insulin on early embryo development in beef heifers

The aims of this study were to determine the effect on early embryo development of feeding a diet formulated to enhance circulating insulin concentrations and secondly to investigate the association between early embryo development and maternal progesterone concentrations in beef heifers. The study was carried out in 32 Simmental x Holstein Friesian heifers 22-25 months of age weighing 506+/-7kg and in condition score 3.1+/-0.1. Animals were fed two diets that were isoenergetic and isonitrogenous, but that would encourage either propionate (diet A) or acetate (diet B) production in the rumen. The rationale was that propionate would induce a greater insulin release in response to feeding. Animals were fed a 50:50 mix of the two diets for 14 days at 0.8x maintenance, with straw provided ad libitum. Animals were then fed one of the experimental diets for 3 weeks prior to synchronisation of oestrus and insemination and for a further 16 days following mating. All heifers were blood sampled daily from oestrus synchronisation and eight animals on each diet underwent daily transrectal real-time ultrasonography to determine the day of ovulation. All heifers were slaughtered at Day 16 after mating. While feeding of diet A (propionic) caused a significant (P<0.05) increase in the plasma insulin to glucagons ratio differences in insulin were not significantly different. This is probably due to the fact that insulin concentrations were quite high as the heifers used in the present study were in good body condition making further increases in insulin difficult to achieve. Diet did not affect size of ovulatory follicle (DIET A: 15.1+/-0.7mm; diet B: 14.6+/-0.7mm), day of ovulation (diet A: 3.5+/-0.2 days; diet B: 3.4+/-0.2 days), mean plasma progesterone concentration (diet A: 4.7+/-0.4ng/ml; diet B: 5.2+/-0.3ng/ml), corpus luteum weight (diet A: 6.0+/-0.2g; diet B: 6.0+/-0.2g) or pregnancy rate (diet A: 81.3%; diet B: 81.3%). However, the proportion of well-elongated (>10cm) embryos on Day 16 was higher in animals fed diet A than in those fed diet B (84.6% versus 38.5%; P<0.05). While progesterone concentration did not differ between pregnant and non-pregnant heifers, progesterone did show an earlier post-ovulatory rise in heifers with well-elongated (>10cm) embryos with levels in these animals significantly higher on Days 4 and 5 than in heifers with small (<10cm) embryos at slaughter. This study demonstrated an enhancement in early embryo development in animals fed a diet generating an increased insulin:glucagon ratio that was not related to circulating maternal progesterone concentrations. However, across diets, enhanced embryo development was associated with elevated plasma progesterone on Days 4 and 5 following mating.

Attenuation of PGF2alpha release in ewes infused with the oxytocin antagonist L-368,899

We have investigated the effects of systemic administration of the oxytocin antagonist (OTA) L-368,899 on luteolytic PGF(2alpha) release in ewes. In the first study, carried out in four ovariectomized ewes primed with progesterone to induce responsiveness to oxytocin, 3-h i.v. infusions of 3, 10 and 30 microg/kg/min OTA, carried out on days 12, 14, 16 and 18 in a Latin Square design, resulted in a significant attenuation of the oxytocin induced increase in PGFM concentration at all doses (OTA 139+/-8.3% of pre-oxytocin baseline; control 206.8+/-18.7%; P<0.005). In a further study, continuous infusion of cyclic ewes (n=6) with 10 microg/kg/min OTA from day 13 to day 17 of the cycle resulted in a reduction in both the frequency (OTA 1.0+/-0.4/ewe; control 2.2+/-0.2/ewe; P<0.05) and amplitude (OTA 31.8+/-11.0 pg/ml; control 68.8+/-10.4 pg/ml; P<0.05) of endogenous PGFM episodes compared to control ewes (n=5) measured during daily 8-h sampling windows on days 14-17. This reduction in PGFM concentrations was accompanied by a modest extension in the day of luteolysis (progesterone <0.5 ng/ml) to day 17.5+/-0.4 in the OTA treated group compared with day 16.4+/-0.5 in the control group (P=0.07). The results demonstrate that treatment with OTA caused a significant reduction in episodes of increased PGFM concentration during the period of luteolysis and may provide an approach by which to reduce early pregnancy failure.

Increased nitric oxide synthesis in uraemic platelets is dependent on L-arginine transport via system y(+)L

Bleeding tendency in uraemic patients seems to be related to alterations in the activity of the L-arginine-nitric oxide (NO) signalling pathway in platelets. We have reported previously that L-arginine influx into human platelets is mediated by the high-affinity cationic amino acid transport system y(+)L. In the present study we examined the dependency of nitric oxide synthase (NOS) activity on L-arginine transport in platelets isolated from healthy controls and uraemic patients on haemodialysis. We investigated basal and ADP-stimulated NOS activity, as reflected by the conversion of L-[(3)H]arginine to L-[(3)H]citrulline, in platelets obtained from healthy controls and uraemic patients on haemodialysis. To determine whether NOS activity depended on L-arginine transport, we analysed the effects of competitive inhibitors of L-arginine transport via system y(+)L on NOS activity. Basal NOS activity was increased from 0.21+/-0.06 to 0.7+/-0.2 pmol/10(8) platelets ( n=9, P<0.05) in uraemic patients. Stimulation by ADP (10 micro M) significantly increased NOS activity (inhibitable by L-NAME) in control platelets (252%) but failed to increase further the elevated NOS activity in uraemic platelets. Homocysteine and L-leucine, competitive inhibitors of system y(+)L, markedly inhibited NOS activity in uraemic platelets. These observations indicate that platelets from uraemic patients on haemodialysis generate more NO than control platelets and that entry of L-arginine via system y(+)L is most likely rate-limiting for platelet NO production in chronic renal failure.

Follicle growth, corpus luteum function and their effects on embryo development in postpartum dairy cows

Absent or irregular ovarian cycles in lactating dairy cows are caused by failure to ovulate the dominant follicle at the appropriate time. The follicle then either regresses or develops into a cyst. This process can be triggered by a variety of metabolic and disease factors that act at the hypothalamus and pituitary gland to inhibit pulsatile LH secretion and the LH surge, and at the ovary to reduce follicular growth and oestradiol production. Cows of poor energy status have low circulating concentrations of insulin-like growth factor I (IGF-I). Predisposing factors include calving difficulties, inappropriate diet, reduced intake of dry matter and a high rate of body condition score loss. Various stressors predispose the follicle to cyst development by inhibiting the LH surge and ovulation; these include common infections, such as mastitis. Even when ovulation does occur, poor follicular development may result in production of an inadequate corpus luteum. The timing of the increase in progesterone in the early luteal phase (days 4-5) appears to be a key determinant of fertility, probably because it alters the secretory activity of the reproductive tract, thus influencing embryonic growth and interferon-tau production. A period of negative energy balance after calving can reduce fertility even though metabolic parameters have apparently improved at the time of service.

Activation of L-arginine transport in peripheral blood mononuclear cells in chronic renal failure

Transport of LL-arginine, the precursor for nitric oxide (NO) synthesis, has been investigated in human peripheral blood mononuclear cells (PBMCs) obtained from healthy volunteers and chronic renal failure patients. Chronic renal failure patients were either on treatment by haemodialysis or continuous ambulatory peritoneal dialysis (CAPD). Saturable influx of L-arginine in PBMCs was mediated by the cationic amino acid transport systems y(+) and y(+)L. Initial rates of L-arginine transport (2 microM) via system y(+) were significantly increased in chronic renal failure patients, whereas transport via system y(+)L was unaffected. The increase in L-arginine transport via system y(+) was: 1.7-fold in uraemic patients on CAPD, 4.3-fold in uraemic patients pre-haemodialysis and 2.6-fold post-haemodialysis. When the intracellular PBMCs amino acid profile was analysed in chronic renal failure patients and control subjects, L-lysine and L-arginine concentrations were significantly increased in pre-haemodialysis uraemic patients and restored to normal values by haemodialysis and CAPD. The present study provides the first evidence that system y(+) mediates the increased transport of L-arginine in PBMCs from patients with chronic renal failure. The increased activity of system y(+) may provide the necessary supply of L-arginine to sustain NO synthesis in PBMCs exposed to increased levels of circulating cytokines in chronic renal failure.

Expression of oxytocin, oestrogen and progesterone receptors in uterine biopsy samples throughout the oestrous cycle and early pregnancy in cows

This study examined the expression patterns of oxytocin and steroid receptors in the bovine endometrium during the oestrous cycle and early pregnancy to elucidate their respective roles in the regulation of luteolysis and the maternal recognition of pregnancy. In Expt 1, uterine biopsies were collected from four cows throughout three oestrous cycles each, to provide daily samples. In Expt 2, uterine tissue was collected on days 12, 14, 16 and 18 of the oestrous cycle (n = 20) or early pregnancy (n = 16). Oxytocin receptor, oestrogen receptor alpha and progesterone receptor mRNAs were localized by in situ hybridization, and localization of oestrogen receptor and progesterone receptor was confirmed by immunocytochemistry. All three receptors showed time- and cell-specific expression patterns. Oestrogen receptor alpha increased in all regions at oestrus but high concentrations were also found in the luminal epithelium during the mid-luteal phase and in the deep glands throughout the oestrous cycle. Progesterone receptor expression was higher in the stroma than it was in the types of epithelial cell, and increased expression was observed at oestrus and during the early luteal phase. The cyclical upregulation of oxytocin receptors in the luminal epithelium on about day 16 was not related to preceding changes in the endometrial expression of either oestradiol alpha or progesterone receptors. During early pregnancy, oxytocin receptor expression was suppressed. Oestrogen receptor a concentrations increased in the non-pregnant cows and decreased in the pregnant cows between days 16 and 18, but these changes followed rather than preceded the upregulation of oxytocin receptors in the non-pregnant cows. It is concluded that the initial upregulation of oxytocin receptors in the luminal epithelium, which triggers luteolysis, is not associated directly with changes in expression of oestrogen receptor alpha.

Expression of the insulin-like growth factor (IGF) system in the bovine oviduct at oestrus and during early pregnancy

Early mammalian embryo development in vitro can be enhanced by co-culture with oviductal cells and by the addition of insulin-like growth factors (IGFs). This study examined the expression patterns of the oviductal IGF system in cattle in relation to the number of days after oestrus and the presence or absence of embryos. Oviducts were collected from: (i) 66 nulliparous heifers on day 3, day 6 or day 16 after insemination and from (ii) ten non-pregnant, lactating cows on day 0 or day 1 of the oestrous cycle. Oviducts were coiled, frozen whole and sectioned for in situ hybridization. Expression patterns of mRNAs encoding IGF-I, IGF-II, type 1 IGF receptor (IGF-1R), and the IFG binding proteins (IGFBP)-1, -3 and -5 were determined from autoradiographs. Separate measurements were made for the mucosa and muscle layers of the infundibulum, ampulla and isthmus. None of the parameters measured differed between heifers with or without the presence of an embryo. mRNAs encoding IGF-I and IGF-1R were present in the mucosa and muscle of all three oviductal regions, and the highest value of IGF-I mRNA was measured in heifers on day 3. IGF-II mRNA was expressed predominantly in the muscle wall. IGFBP-1 mRNA was not detectable, whereas mRNAs encoding IGFBP-3 and -5 were expressed in both the muscle and mucosa. IGFBP-3 expression was higher in cows on day 0 and day 1 of the oestrous cycle than in heifers on day 3, day 6 and day 16 after insemination. A peak of IGFBP-5 expression was reached on day 6. Locally or systemically produced IGFs, regulated by IGFBPs, may act directly on the embryo or indirectly via modulation of oviductal secretions and muscular activity to influence the success of early embryo development.

Expression of the insulin-like growth factor (IGF) system in the bovine oviduct at oestrus and during early pregnancy

Early mammalian embryo development in vitro can be enhanced by co-culture with oviductal cells and by the addition of insulin-like growth factors (IGFs). This study examined the expression patterns of the oviductal IGF system in cattle in relation to the number of days after oestrus and the presence or absence of embryos. Oviducts were collected from: (i) 66 nulliparous heifers on day 3, day 6 or day 16 after insemination and from (ii) ten non-pregnant, lactating cows on day 0 or day 1 of the oestrous cycle. Oviducts were coiled, frozen whole and sectioned for in situ hybridization. Expression patterns of mRNAs encoding IGF-I, IGF-II, type 1 IGF receptor (IGF-1R), and the IFG binding proteins (IGFBP)-1, -3 and -5 were determined from autoradiographs. Separate measurements were made for the mucosa and muscle layers of the infundibulum, ampulla and isthmus. None of the parameters measured differed between heifers with or without the presence of an embryo. mRNAs encoding IGF-I and IGF-1R were present in the mucosa and muscle of all three oviductal regions, and the highest value of IGF-I mRNA was measured in heifers on day 3. IGF-II mRNA was expressed predominantly in the muscle wall. IGFBP-1 mRNA was not detectable, whereas mRNAs encoding IGFBP-3 and -5 were expressed in both the muscle and mucosa. IGFBP-3 expression was higher in cows on day 0 and day 1 of the oestrous cycle than in heifers on day 3, day 6 and day 16 after insemination. A peak of IGFBP-5 expression was reached on day 6. Locally or systemically produced IGFs, regulated by IGFBPs, may act directly on the embryo or indirectly via modulation of oviductal secretions and muscular activity to influence the success of early embryo development.

Production of recombinant ovine interferon tau using a Bombyx mori nuclear polyhedrosis baculovirus expression system

Ovine interferon tau (oIFN-tau) is an embryonic protein of critical importance in the establishment of pregnancy in the sheep. We have produced recombinant (r) oIFN-tau using a baculovirus expression system and demonstrated the biological activity of the protein produced. Bombyx mori larvae were infected with B. mori nuclear polyhedrosis virus (BmNPV), modified by inserting a cDNA coding for oIFN-tau downstream of the strong polyhedron promoter. Following infection, antiviral activity of the haemolymph rose to a maximum of 3.6 x 10(8) u/mL (equivalent to 3 mg roIFN-tau/mL) by day 5, when haemolymph was collected and stored frozen. Control haemolymph, collected from uninfected insects at an equivalent time, contained no antiviral activity. The roIFN-tau was partially purified by gel filtration column chromatography and the presence of roIFN-tau confirmed by western blotting. The biological activity of the partially purified roIFN-tau was tested in ewes. Treatment with roIFN-tau caused a significant delay in luteolysis confirming biological potency. The results demonstrate that this system can be successfully used to produce large quantities of roIFN-tau.

Milk production and composition, ovarian function, and prostaglandin secretion of dairy cows fed omega-3 fats

Four multiparous Holstein cows were used in a 4 x 4 Latin square experiment to study the effects of fat sources rich in omega-3 fatty acids on milk production and composition, follicular development, and prostaglandin secretion. All cows were fed a total mixed diet containing 60% grass silage and 40% concentrate. The four treatments were concentrates based either on Megalac, formaldehyde-treated whole linseed, a mixture (50:50, oil basis) of fish oil and formaldehyde-treated whole linseed, or no fat source in the concentrate but with 500 g per day of linseed oil being infused into the duodenum. Feed intakes and milk yield were similar among treatments. In general, the lowest digestibility was observed for the formaldehyde-treated whole linseed treatment. Feeding fish oil decreased milk fat and protein percentages. Alpha-linolenic acid increased from 1.0 to 13.9% of milk fatty acids with linseed oil infusion. This confirms the high potential to incorporate alpha-linolenic acid into milk, and suggests that the formaldehyde treatment had little effect to limit biohydrogenation in the rumen. Increasing the supply of alpha-linolenic acid to these cows did not result in an increase in the concentration of eicosapentaenoic acid in milk. Levels of 13,14-dihydro-15-keto-PGF2alpha in plasma were higher for cows receiving formaldehyde-treated linseed and fish oil. Increases in this metabolite in response to oxytocin challenge, tended to be lower for cows given linseed either as sole oil supplement in the diet or as a duodenal infusion of linseed oil. Follicle dynamics were similar among treatments. Larger corpora lutea (CL) were found with cows that received high levels of omega-3 fatty acids through the diet as formaldehyde-treated linseed or as a mixture of formaldehyde-treated linseed and fish oil, although CL were smaller when cows were infused with linseed oil into the duodenum. These results suggest that the improvement in gestation rate that was observed when feeding increased levels of alpha-linolenic acid in earlier work may partly result from lower levels of production of the dienoic prostaglandin PGF2alpha.

Modulation of sex hormone secretion in cows by acute infection with bovine viral diarrhoea virus

Bovine viral diarrhoea virus (BVDV) is a major pathogen of cattle and is responsible for considerable reproductive loss. In this study, the in vivo responses in six multiparous cows were investigated after a non-cytopathogenic BVDV challenge (strain Pe 515; 5 x 10(6) tissue culture infective dose 50) given 9 days before a synchronized ovulation. Six similar cows challenged with non-infectious culture medium served as controls. The experimental noncytopathogenic BVDV infection was followed by a viraemia and leucopenia at days 5-9 after challenge, but no other clinical signs of infection were detected. However, the BVDV infection altered endocrine function. Mean LH pulse frequency immediately before CIDR withdrawal was lower (P < or = 0.05) in the BVDV-infected (2.17 +/- 0.34 pulses per 8 h) compared with the sham-infected (4.83 +/- 1.04 pulses per 8 h) animals. At day 3 after CIDR withdrawal, plasma oestradiol concentrations remained high (P < 0.05) in the infected cows (2.19 +/- 0.51 pg ml(-1)) compared with the sham-infected controls (0.72 +/- 0.29 pg ml(-1)). However, there was no difference in the peak oestradiol concentration (BVDV: 2.31 +/- 0.29 versus sham: 2.34 +/- 0.41 pg ml(-1)). In addition, non-cytopathogenic BVDV significantly (P < 0.05) increased the duration of the interval between ovulation and onset of the postovulatory progesterone increase (values 1.0 ng ml(-1)) (BVDV: 3.0 +/- 0.26 versus sham: 4.0 +/- 0.26 days). The viral infection also significantly (P < 0.01) decreased mean plasma progesterone concentrations between day 3 and day 11 after ovulation (BVDV: 2.59 +/- 0.32 versus sham: 4.13 +/- 0.27 ng ml(-1)). These data show that non-cytopathogenic BVDV viraemias during the follicular phase can modulate the secretion of gonadotrophins and sex steroids, in particular progesterone, during a synchronized oestrous cycle. Therefore, viraemias during the follicular phase may reduce the fertility of cattle by disrupting the capacity of the ovulatory follicle to form a competent corpus luteum, thereby compromising early embryo development and maternal recognition of pregnancy.