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Biomedical subjects

G E Lamming

Publications and source records attributed to G E Lamming.

At least 37 records · Page 2Linked to original sources
PubMed1998

The use of milk progesterone profiles to characterise components of subfertility in milked dairy cows.

Milk progesterone (P4) concentrations of 1682 postpartum (PP) dairy cows during 2503 lactations were used to define and quantify the incidence of atypical ovarian patterns and to assess their impact on reproductive performance. A total of 257 animals (10.94%) with their first significant luteal activity after day 44 PP were considered a result of delayed ovulation type I (DOVI). Prolonged luteal activity (P4 > 3 ng/ml for at least 19 days) observed in 170 (7.3%) and 161 (6.35%) animals during first and subsequent cycles was considered a result of the presence of a persistent corpus luteum (CL), respectively denoted as PCLI and PCLII. Following the demise of an oestrous cycle CL, a total of 322 (12.85%) animals showed a delayed ovulation Type II (DOVII) with P4 < 3 ng/ml for > 12 days. In 238 inseminated animals (9.92%) prolonged luteal activity was followed by the CL demise which may indirectly indicate the incidence of a late embryo to early foetal mortality (LEM). In this study animals during 794 (31.7%) lactations had at least one atypical ovarian pattern before insemination that, in comparison to those with typical P4 patterns, contributed to a delayed conception (88.2 vs. 106.2 days), higher number of services per conception (1.49 vs. 1.8), lower first service conception rate (60.9 vs. 43.7%) and a reduced total conception rate (92.6 vs. 82.1%), all of which were significantly different at P < 0.001. The incidence of PCLI and PCLII before insemination resulted in a higher level of LEM. Milk progesterone monitoring offers an accurate and objective measurement of factors associated with PP ovarian activity which will assist in investigating the genetic and environmental factors' affecting fertility.

Animals↗
PubMed1998

Ovine trophoblast interferon enhances MHC class I expression by sheep endometrial cells.

Type I interferons have a variety of important immunological functions, including effects on expression of class I molecules of the major histocompatibility complex (MHC). Interferon-tau (IFN-tau) is an important anti-luteolytic factor produced by the trophoblast of ruminants. Ovine endometrial cells were cultured with recombinant ovine IFN-tau and stained with monoclonal antibodies specific for ovine MHC class I molecules. The expression of MHC class I was then determined by immunocytochemical or immunofluorescent staining using microscopy or flow cytometry. IFN-tau was found to enhance the expression of MHC class I molecules on the endometrial cells, as did recombinant IFN-alpha. No significant effects on MHC class II expression were observed. These findings may have important implications for cellular interactions associated with immunological aspects of pregnancy.

Animals↗
PubMed1998

Role of early luteal phase progesterone in control of the timing of the luteolytic signal in cows.

The effects of the pattern and concentration of early luteal phase progesterone on subsequent prostaglandin F2 alpha release in response to exogenous oxytocin was investigated during simulated luteal phases in ovariectomized cows treated with progesterone and oestradiol in patterns designed to simulate the range of luteal phase concentrations that occur naturally. In the first experiment, three groups of four cows received different concentrations of early luteal phase progesterone to determine the effective concentration in terms of cycle control. The results show that a plasma progesterone concentration early in the luteal phase as low as 0.6 ng ml-1 was sufficient to affect the timing of the subsequent luteolytic signal. In the second experiment, an early (day 1), a normal (day 4) or a late (day 7) postovulatory increase in progesterone was recreated in three groups of four cows. Responsiveness to oxytocin in the early progesterone group developed 3 days earlier than in the normal progesterone group, demonstrating the ability of early progesterone to advance the luteolytic signal. However, in the late progesterone group, there was no delay in the development of responsiveness to oxytocin compared with the normal progesterone group, demonstrating that the luteolytic signal is programmed to occur by a given time, irrespective of the early progesterone pattern. This demonstrates that a factor other than the timing of the early luteal phase progesterone increase ultimately must control the timing of luteolysis in cows.

Analysis of Variance↗
PubMed1998

Endometrial oxytocin receptor and uterine prostaglandin secretion in mares during the oestrous cycle and early pregnancy.

Circulating concentrations of 13,14-dihydro-15-ketoprostaglandin F2 alpha (PGFM) were measured before and after administration of oxytocin and after endometrial biopsy, with or without uterine flushing performed per vaginam, on days 10, 14 and 18 after ovulation in nine pregnant and nine cyclic mares. Concentrations of oxytocin receptor were measured in endometrial biopsy samples. Neither pregnancy status nor time after ovulation affected basal PGFM concentrations. PGFM concentrations were increased after oxytocin administration on each of the days studied in cyclic mares; on day 14 the mean response was 4.5 times higher than the mean response on days 10 and 18. In contrast, during pregnancy, responses to oxytocin administration occurred only on days 10 and 18. Marked increases in PGFM concentrations in response to endometrial biopsy occurred only on day 14 in cyclic mares and on day 18 in pregnant mares. Mean concentrations of oxytocin receptor were between 200 and 300 fmol mg-1 protein on day 10 in both pregnant and cyclic mares; in cyclic mares oxytocin receptor concentrations were increased approximately threefold on day 14 compared with days 10 and 18, but no such increase was evident during pregnancy. Total amounts of PGFM secreted after oxytocin treatment correlated with endometrial oxytocin receptor concentrations in cyclic (P < 0.001) but not in pregnant (P > 0.5) mares, and the same was true for PGFM release induced by endometrial biopsy (cyclic: P = 0.0025; pregnant: P > 0.5). The data support the hypothesis that endometrial concentrations of oxytocin receptor determine uterine prostaglandin F2 alpha secretion in cyclic mares and that endometrial oxytocin receptor concentrations are reduced in early pregnancy by a product of the conceptus. The increase in response of the pregnant uterus to oxytocin treatment or biopsy-flushing between days 14 and 18 was not due to an increase in the concentration of oxytocin receptors but presumably reflected increased receptor sensitivity.

Analysis of Variance↗
PubMed1998

Control of luteolysis in the one-humped camel (Camelus dromedarius).

Blood plasma concentrations of 13,14-dihydro-15-keto PGF2 alpha (PGFM) were measured in groups of mature non-pregnant and pregnant camels to study PGF2 alpha release patterns around the time of luteolysis and the timing of the signal for pregnancy recognition. Injection of each of four camels with 10 and 50 mg of PGF2 alpha showed clearly that five times the dose of exogenous hormone produced five times the amount of PGFM in peripheral plasma, thereby indicating that, as in other animal species, PGFM is the principal metabolite of PGF2 alpha in the camel. Serial sampling of three non-pregnant camels on each of days 8, 10 and 12, and three pregnant camels on day 10, after ovulation for 8 h showed a significant (P < 0.05) rise in mean plasma PGFM concentrations only on day 10 in the non-pregnant, but not the pregnant, animals. A single intravenous injection of 20, 50 or 100 iu oxytocin given to three groups of three non-pregnant camels on day 10 after ovulation did not increase their basal serum PGFM concentrations. However, daily treatment of six non-pregnant camels between days 6 and 15 (n = 3) or 20 (n = 3) after ovulation with 1-2 g of the prostaglandin synthetase inhibitor, meclofenamic acid, inhibited PGF2 alpha release and thereby resulted in continued progesterone secretion throughout the period of meclofenamic acid administration. These results showed that, as in other large domestic animal species, release of PGF2 alpha from, presumably, the endometrium controls luteolysis in the dromedary camel. Furthermore, reduction in the amount of PGF2 alpha released is associated with luteal maintenance and the embryonic signal for maternal recognition of pregnancy must be transmitted before day 10 after ovulation if luteostasis is to be achieved. However, the results also indicate that, in contrast to ruminants, the release of endometrial PGF2 alpha in the non-pregnant camel may not be controlled by the release of oxytocin.

Animals↗
PubMed1997

Estimation of genetic variation in the interval from calving to postpartum ovulation of dairy cows.

Data on the interval from calving to the commencement of luteal activity of postpartum dairy cows were obtained for 1737 lactations of 1137 British Friesian cows in 11 commercial herds and 1 experimental herd between 1975 and 1982. The interval from calving to commencement of luteal activity was measured using progesterone concentrations of milk samples that were collected three or more times per week from shortly after calving to approximately 100 DIM of the following gestation. Genetic models were fitted using REML and accounting for known genetic relationships. Estimates of heritability and repeatability were 0.28 and 0.28, respectively, for the untransformed data; 0.21 and 0.26, respectively, for log-transformed data; and 0.13 and 0.26, respectively, after reciprocals were considered. In all cases, the heritability was significantly different from 0, and, of three scales, the log transformation had the greater likelihood. The likelihood of the transformation was closely related to the magnitude of the coefficient of skewness, and the power transformation with maximum likelihood was between 0.35 and 0.30, for which heritability was 0.19. The geometric mean interval was 25.6 d; coefficient of variation was 37%; and herds, years, parity, and season all had significant effects upon the interval to commencement of luteal activity. The postpartum interval grew longer by 2.2% with each parity [confidence interval 95% (1.1%, 3.0%)] and showed seasonal variation. Cows calving during spring took 1.21 times longer to commencement of luteal activity than did cows calving during autumn [95% confidence interval (1.13, 1.29)]. Genetic regression on PTA of the sire for milk, fat, and protein yields and for fat and protein percentages and on a national economic index were carried out using a subset of animals during 721 lactations. The regression was positive for fat percentage, but not significantly different from 0 for others. The magnitude of the heritability estimate in this study indicates that the postpartum interval to commencement of luteal activity may be useful for selecting cattle for improved fertility because shorter intervals have been postulated to be correlated with higher reproductive efficiency.

Animals↗
PubMed1996

Inter-breed variation in the postpartum ewe response to continuous low dose infusion of GnRH.

During the nonbreeding season the pituitary and ovarian responses to a subcutaneous GnRH infusion were investigated in acyclic, lactating Mule ewes which exhibit a deep seasonal anestrus and in Finn x Dorset ewes in which seasonal anestrus is ill-defined. Each breed received 10 d of progestagen priming before being subdivided into 3 groups. In Group L + G, 5 lactating ewes received GnRH (250 ng/h sc) for 96 h; in Group D + G, 5 dry ewes received GnRH (250 ng/h sc) for 96 h; in Group L, 5 lactating ewes received saline vehicle for 96 h. The infusions began when lactating and dry ewes were approximately 28 d and 120 d post partum, respectively. Blood samples were collected for LH, progesterone and estradiol analysis. Estrous behavior was monitored between Day -4 and Day +7. On Day +7 the reproductive tract was also examined. In the Mule ewes the mean plasma LH concentration increased (P < 0.05) following minipump insertion in each treatment group, although mean LH levels were greater (P < 0.05) in Group D + G, than in either Group L + G or Group L. Following the GnRH infusion, mean plasma estradiol levels increased (P < 0.05) in Group D + G but not in Group L + G. A preovulatory LH surge and subsequent ovulation occurred in 5 5 , 2 5 and 0 5 ewes from Group D + G, L + G and L, respectively, and estrus was recorded in 5 5 , 1 5 and 0 5 of these ewes, respectively. The LH surges began earlier (P < 0.05) (43.2 +/- 6.8 h vs 77.0 +/- 1.0 h) and the ovulation rate was greater (2.2 +/- 0.37 vs 1.00 +/- 0.00) in Group D + G than Group L + G. In the Finn x Dorset ewes mean LH concentrations increased (P < 0.05), to a similar level following minipump insertion in Groups D + G and L + G, but not Group L. The elevated LH levels were accompanied by increased (P < 0.05) plasma estradiol levels in Group D + G, but not in Group L + G. The GnRH infusion culminated in an LH surge and estrous behavior in 5 5 , 1 5 and 0 5 ewes from Groups D + G, L + D and L, respectively. The interval to the LH surge was similar between Group D + G (48.4 +/- 6.6 h) and Group L + G (46.0 h). Ovulation was evident in those ewes which exhibited an LH surge plus one additional ewe from Group L + G. The mean ovulation rate was greater in Group D + G (4.00 +/- 1.05) than in Group L + G (1.5 +/- 0.50). These data show that continuous GnRH infusion can consistently induce out of season breeding in the nonlactating Mule and Finn x Dorset ewe but can not break combined seasonal and lactational anestrous in these breeds. Further, between-breed differences are evident in the site along the hypothalamic-pituitary-ovarian axis at which reproduction is compromised in ewes at the same chronological stage post partum.

Journal Article↗
PubMed1996

Pattern of 11 beta-hydroxysteroid dehydrogenase type 1 messenger ribonucleic acid expression in the ovine uterus during the estrous cycle and pregnancy.

The present study was designed to examine the pattern and cellular localization of 11 beta-hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) gene expression in the ovine uterus during pregnancy and at 3 mo postpartum. High levels of 11 beta-HSD1 mRNA were detected in the endometrium from Days 60 to 143 (term = 145 days), and the levels did not change significantly during that time. The level of 11 beta-HSD1 mRNA in the endometrium was always much higher than that in the myometrium, in which the mRNA was not readily detectable throughout pregnancy; at 3 mo postpartum, 11 beta-HSD1 mRNA became undetectable in both endometrium and myometrium. Within the endometrium, intense immunoreactive 11 beta-HSD1 was localized exclusively to the luminal epithelium, and the intensity of 11 beta-HSD1 immunostaining closely followed the level of 11 beta-HSD1 mRNA. To determine whether the level of endometrial 11 beta-HSD1 mRNA was related to the status of ovarian function, tissues from non-pregnant animals at different stages of their reproductive cycle were also examined. It was found that 11 beta-HSD1 mRNA was undetectable in the endometrium of cycling animals up to Day 9 of the estrous cycle but was detectable thereafter. Taken together, these results demonstrate that within the ovine uterus the endometrium is always the dominant site of 11 beta-HSD1 gene expression in relation to the myometrium. Furthermore, the expression of 11 beta-HSD1 mRNA in the endometrium is closely related to the status of the reproductive cycle. The mRNA for 11 beta-HSD1 is highly expressed only during pregnancy and in non-pregnant animals during the late luteal phase. Since circulating levels of progesterone are elevated during both of these periods, the present findings suggest a progesterone effect on uterine 11 beta-HSD1 gene expression.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1996

The effect of oxytocin and oestradiol on the action of conceptus secretory protein in progesterone-treated ovariectomized ewes.

In intact cyclic ewes intrauterine infusion of conceptus secretory proteins results in the suppression of both endometrial oxytocin receptor concentrations and oxytocin-induced prostaglandin F2 alpha release. However, similar infusion in progesterone-treated ovariectomized ewes, while suppressing endometrial oxytocin receptors, does not fully inhibit oxytocin-induced prostaglandin F2 alpha release. To examine whether this anomaly resulted from an inadequate simulation of the luteal phase in the ovariectomized ewe treated with progesterone alone, the effects of additional treatment with two other ovarian hormones, oestradiol-17 beta and oxytocin, was investigated. Rather than permitting conceptus secretory protein to successfully inhibit oxytocin-induced prostaglandin F2 alpha release, treatment with oestradiol-17 beta in addition to progesterone actually resulted in an advancement in the timing of release. However, treatment with oxytocin, alone or in combination with oestradiol, permitted the full inhibition of oxytocin-induced prostaglandin F2 alpha release. To confirm that this effect did not result from the action of oxytocin alone, independently of the action of conceptus secretory protein, a second experiment was undertaken using a similar protocol but without the infusion of conceptus secretory protein. In this situation, oxytocin-induced prostaglandin F2 alpha release was only partially inhibited suggesting that both luteal oxytocin and conceptus secretory proteins are necessary to facilitate the full inhibition of luteolysis during early pregnancy in the ewe.

Animals↗
PubMed1996

Regulation of oxytocin, oestradiol and progesterone receptor concentrations in different uterine regions by oestradiol, progesterone and oxytocin in ovariectomized ewes.

The regulation of oxytocin, oestradiol and progesterone receptors in different uterine cell types was studied in ovariectomized ewes. Animals were pretreated with a progestogen sponge for 10 days followed by 2 days of high-dose oestradiol to simulate oestrus. They then received either low-dose oestradiol (Group E), low-dose oestradiol plus progesterone (Group P) or low-dose oestradiol, progesterone and oxytocin (via osmotic minipump; Group OT). Animals (three to six per time-point) were killed following ovariectomy (Group OVX), at oestrus (Group O) or following 8, 10, 12 or 14 days of E, P or OT treatment. In a final group, oxytocin was withdrawn on day 12 and ewes were killed on day 14 (Group OTW). Oxytocin receptor concentrations and localization in the endometrium and myometrium were measured by radioreceptor assay, in situ hybridization and autoradiography with the iodinated oxytocin receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin. Oestradiol and progesterone receptors were localized by immunocytochemistry. Oxytocin receptors were present in the luminal epithelium and superficial glands of ovariectomized ewes. In Group O, endometrial oxytocin receptor concentrations were high (1346 +/- 379 fmol [3H]oxytocin bound mg protein-1) and receptors were also located in the deep glands and caruncular stroma in a pattern resembling that found at natural oestrus. Continuing low-dose oestradiol was unable to sustain high endometrial oxytocin receptor concentrations with values decreasing significantly to 140 +/- 20 fmol mg protein-1 (P < 0.01), localized to the luminal epithelium and caruncular stroma but not the glands. Progesterone treatment initially abolished all oxytocin receptors with none present on days 8 or 10. They reappeared in the luminal epithelium only between days 12 and 14 to give an overall concentration of 306 +/- 50 fmol mg protein-1. Oxytocin treatment caused a small increase in oxytocin receptor concentration in the luminal epithelium on days 8 and 10 (20 +/- 4 in Group P and 107 +/- 35 fmol mg protein-1 in Group OT, P < 0.01) but the rise on day 14 was not affected (267 +/- 82 in Group OT and 411 +/- 120 fmol mg protein-1 in Group OTW). In contrast, oestradiol treatment was able to sustain myometrial oxytocin receptors (635 +/- 277 fmol mg protein-1 in Group O and 255 +/- 36 in Group E) and there was no increase over time in Groups P, OT and OTW with values of 61 +/- 18, 88 +/- 53 and 114 +/- 76 fmol mg protein-1 respectively (combined values for days 8-14). Oestradiol receptor concentrations were high in all uterine regions in Group O. This pattern and concentration was maintained in Group E. In all progesterone-treated ewes, oestradiol receptor concentrations were lower in all regions at all time-points. The only time-related change occurred in the luminal epithelium in which oestradiol receptors were undetectable on day 8 but developed by day 10 of progesterone treatment. Progesterone receptors were present at moderate concentrations in the deep glands, caruncular stroma, deep stroma and myometrium in Group O. Oestradiol increased progesterone receptors in the luminal epithelium, superficial glands, deep stroma and myometrium. Progesterone caused the loss of its own receptor from the luminal epithelium and superficial glands and decreased its receptor concentration in the deep stroma and myometrium at all time-points. There was a time-related loss of progesterone receptors from the deep glands of progesterone-treated ewes between days 8 and 14. These results show differences in the regulation of receptors between uterine regions. In particular loss of the negative inhibition by progesterone on the oxytocin receptor by day 14 occurred only in the luminal epithelium, but is unlikely to be a direct effect of progesterone as no progesterone receptors were present on luminal epithelial cells between days 8 and 14.

Animals↗
PubMed1995

Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH.

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 +/- 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day -5 and Day +7 and estrous behavior was monitored between Day -4 and Day +7. Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 +/- 0.03 vs 0.46 +/- 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 +/- 3.0 vs 56.3 +/- 4.1 h) and was of greater magnitude (32.15 +/- 3.56 vs 18.84 +/- 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 +/- 0.15 and 1.33 +/- 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.

Journal Article↗
PubMed1995

Control of endometrial oxytocin receptors and prostaglandin F2 alpha production in cows by progesterone and oestradiol.

We have investigated changes in endometrial oxytocin receptor concentrations and prostaglandin F2 alpha release in response to exogenous oxytocin treatment in ovariectomized cows treated with progesterone and oestradiol, and made comparisons with similar treatment in cyclic cows. In long-term ovariectomized cows, endometrial oxytocin receptors were present (300 fmol mg-1 protein), but no prostaglandin F2 alpha was released in response to oxytocin treatment until after the administration of progesterone. Subsequent administration of a concentration of oestradiol sufficient to induce oestrus resulted in the downregulation of these receptors and the loss of oxytocin responsiveness, which did not reappear within 20 days in the absence of further hormone treatment. When induced oestrus was followed by further treatment with luteal phase concentrations of progesterone and oestradiol, both oxytocin receptors and oxytocin-stimulated release of prostaglandin F2 alpha reappeared by day 16 after oestrus, in a pattern similar to that seen during the luteal phase of cyclic cows. These results demonstrate how progesterone and oestradiol control the development and responsiveness of endometrial oxytocin receptors in cows, and provide a valuable model in which to investigate further the precise control of the oxytocin receptor in this species.

Animals↗
PubMed1995

Progesterone inhibition of the development of the luteolytic signal in cows.

Mated cows that subsequently undergo luteolysis have significantly lower plasma concentrations of progesterone than do cows in which pregnancy is maintained. Two groups of ovariectomized cows were treated with progesterone and oestradiol to recreate luteal phases exhibiting the extremes of plasma concentrations of progesterone (6.0 +/- 0.4 and 12.4 +/- 0.8 ng ml-1) normally seen in intact cows. The effect of this difference in progesterone on the development of the luteolytic signal was determined by monitoring the basal and oxytocin-stimulated plasma concentrations of the principal metabolite of prostaglandin F2 alpha' PGFM on days 12-16 of the simulated luteal phases. Basal PGFM concentrations were similar in the low and high progesterone groups on all days. The mean plasma concentration of PGFM showed a larger increase following oxytocin in the low progesterone group on days 13 and 14 (P < 0.05) and on days 15 and 16 (P < 0.1). These results demonstrate that a low plasma concentration of progesterone results in the development of a stronger luteolytic signal, and provide an explanation for the fact that cows with lower plasma concentrations of progesterone are more prone to embryo loss.

Animals↗
PubMed1995

Local action of trophoblast interferons in suppression of the development of oxytocin and oestradiol receptors in ovine endometrium.

Luteolysis in sheep is associated with uterine secretion of pulses of prostaglandin F2 alpha (PGF2 alpha) due to the action of luteal oxytocin on endometrial oxytocin receptors. For pregnancy to become established inhibition of oxytocin receptors is important as an antiluteolytic mechanism. The maternal recognition of pregnancy in cattle and sheep involves production, by the trophoblast, of a type 1 interferon (IFN-tau) that suppresses uterine development of oxytocin receptors and the generation of luteolytic episodes of PGF2 alpha. The action of IFN-tau in surgically prepared unilaterally pregnant ewes was investigated. Finn-Dorset ewes were anaesthetized on day 6 or 7 of the oestrous cycle and one uterine horn was surgically isolated at the uterine bifurcation from the body of the uterus. Ewes were mated at the subsequent oestrus either by a fertile or by a vasectomized ram and killed on day 13 or 16 after mating. On day 16, in the non-pregnant ewes, there was no measurable uterine IFN-tau but there were high concentrations of oxytocin receptors in both horns. In the pregnant ewes on day 16 after mating, the oxytocin receptor concentration was 45 +/- 11 fmol mg-1 protein in the pregnant horn and 585 +/- 131 fmol mg-1 in the non-pregnant horn. Antiviral activity was 5.8 x 10(7) +/- 5.2 x 10(7) U ml-1 in the pregnant horn and 2.9 x 10(3) +/- 1.2 x 10(3) U ml-1 in the non-pregnant horn. Thus, 16 days after mating, the pregnant horn exhibited high antiviral activity but oxytocin receptors were suppressed, while in the same endocrine environment (characteristic of pregnancy) there were low IFN-tau and high oxytocin receptor concentrations in the isolated horn equivalent to those expected at the onset of luteolysis. In situ hybridization to ovine mRNA encoding the oxytocin receptor and autoradiographic studies using the 125I-labelled oxytocin antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin both showed that the large amount of oxytocin receptor message and binding sites in the endometrium of the isolated horn were localized in the luminal epithelium. Immunocytochemical studies showed that there was a suppression of oestradiol receptors in the pregnant horn but high concentrations equivalent to those at oestrus were present in the isolated horn. The content of progesterone receptors was low in the stromal tissue only in both horns, a pattern of localization similar to that seen in the late luteal phase and in early pregnancy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Effect of the level of oestradiol on oxytocin-induced prostaglandin F2 alpha release in the cow.

We have investigated the effects of oestradiol-17 beta on the development of the luteolytic signal (prostaglandin F2 alpha (PGF2 alpha) release to an oxytocin challenge) using a steroid-treated ovariectomised cow model. Long-term ovariectomised cows were pre-treated with progesterone for 14 days followed by oestradiol-17 beta for 2 days to induce oestrus (day 0), and were then treated for a further 16 days with physiological doses of progesterone and oestradiol-17 beta to simulate a luteal phase. On day 11 oestradiol was either withdrawn (low group; n = 4), maintained (normal group; n = 4) or increased (high group; n = 4), generating mean (+/- S.E.M.) plasma concentrations of oestradiol from days 12-16 of 0.9 +/- 0.1, 2.3 +/- 0.4 and 3.7 +/- 0.2 pg/ml respectively. Basal and oxytocin-stimulated PGF2 alpha secretion was monitored by measuring concentrations of the principal metabolite of PGF2 alpha, 13,14-dihydro-15-keto PGF2 alpha (PGFM), in plasma samples collected before and after daily i.v. injection of 50 IU oxytocin from days 12-16. Basal PGFM was unaffected by the level of oestradiol treatment. In the normal group significant rises in plasma PGFM were seen following oxytocin on days 12, 13 and 14 (P < 0.05) as well as days 15 and 16 (P < 0.01). In the low group significant elevations in PGFM were only seen on days 15 and 16 (P<0.05), and were smaller (P<0.05) than those seen in the normal group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The oxytocin receptor, luteolysis and the maintenance of pregnancy.

During luteal regression episodic pulses of oxytocin secretion become coupled to the release of prostaglandin F2 alpha (PGF2 alpha) following synthesis of endometrial oxytocin receptors, but in early pregnancy the inhibition of oxytocin receptor formation by the conceptus prevents the development of the pulsatile pattern of PGF2 alpha release needed to achieve luteolysis. Oxytocin receptors are present on the luminal epithelium in ovariectomized and anoestrous ewes, in pregnant animals throughout most of gestation (day 21 to term) and in explants of endometrial tissue cultured in vitro. These receptors can be downregulated for a brief period by progesterone (10-12 days in sheep, 12-14 days in cattle). This period of inhibition can be extended by infusion of interferon tau (IFN-tau) (which probably inhibits oxytocin receptor gene transcription) or of oxytocin into the systemic circulation (which may act further downstream, possibly at the level of translation). Oxytocin receptors also develop on the caruncular stroma and deep glands at oestrus, but these need positive upregulation and appear dependent on an oestrogenic environment. Only epithelial receptors are needed to achieve a maximal PGF2 alpha response to an oxytocin challenge, but the presence of oxytocin receptors does not necessarily confer responsiveness as other factors may influence intracellular coupling mechanisms and precursor availability. The duration of the luteal phase is regulated by the time of the initial post-ovulatory rise in progesterone and the duration of exposure to progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Use of repeated biopsies to monitor endometrial oxytocin receptors in the cow.

A transcervical biopsy technique was used for the repeated collection of samples of bovine endometrium from individual cows to monitor the development of oxytocin receptors. The collection of biopsies from three cyclic cows at two-day intervals between days 13 and 17 after oestrus did not result in any shortening of the length of the cycle (mean +/- sem 22.0 +/- 0.5 days). Furthermore, the assay of serial blood samples from three cows around the time of biopsy on days 15 and 17 demonstrated that the technique did not induce any release of prostaglandin F2 alpha (PGF2 alpha). Oxytocin receptors were undetectable (< 20 fmol/mg protein) on days 13 and 15 of the cycle, increased to a mean of 121 +/- 16 fmol/mg protein on day 17 (before luteolysis), and were highest in samples collected at oestrus (498 +/- 84 fmol/mg protein). To determine whether a single biopsy of endometrium would give a representative measure of the concentration of uterine oxytocin receptors, the concentrations were determined in samples of caruncular and intercaruncular endometrium collected from the upper, middle and lower proportions of uteri from three oestrous animals at slaughter. The concentrations were similar in both types of tissue (caruncular 730 +/- 15 fmol/mg protein, intercaruncular 727 +/- 48 fmol/mg protein) and there were no differences between the three regions of the uterus.

Animals↗