Circulating Progesterone Concentrations Research Articles

Effects of low versus physiologic plasma progesterone concentrations on ovarian follicular development and fertility in beef cattle

The objective of this study was to determine the effects of low versus physiologic plasma progesterone concentrations during the ovulatory wave on fertility in cattle. Suckled beef cows ( Bos taurus; n = 129) and pubertal heifers ( Bos taurus; n = 150) at random stages of the estrous cycle were given a luteolytic dose of prostaglandin F 2α (500 μg cloprostenol; PGF) twice, 11 d apart. Ten days after the second PGF treatment, cattle were given estradiol benzoate im (1.5 and 1.0 mg for cows and heifers, respectively) and a progesterone-releasing intravaginal device (Cue-Mate) with a single pod containing 0.78 g progesterone (Day 0). Cattle in the low-progesterone group (n = 148) received a luteolytic dose of PGF on Day 0, whereas those in the high-progesterone (i.e., physiologic plasma concentrations) group (n = 131) were allowed to retain their corpora lutea. On Day 8, the Cue-Mate was removed, and PGF was given to both groups. Fifty-four hours to 56 h later, cattle received 12.5 mg of porcine LH (pLH) im and were concurrently artificially inseminated. The dominant follicle in the low-progesterone group was larger (P < 0.001) than that in the high-progesterone group on the day of insemination (14.9 ± 0.3 mm vs. 12.7 ± 0.3 mm, mean ± SEM). At 7 d after ovulation, the low-progesterone group had a larger corpus luteum (24.5 ± 0.54 mm vs. 21.9 ± 0.64 mm, P < 0.01) and higher plasma progesterone concentration (4.0 ± 0.3 vs. 3.1 ± 0.2, P < 0.01) than that of the high-progesterone group. However, pregnancy rates did not differ (79 of 148, 53.4%, and 70 of 131, 53.4%) for low- and high-progesterone groups, respectively). In summary, low circulating progesterone concentrations during the growing phase of the ovulatory follicle resulted in a larger dominant follicle and a larger CL that produced more progesterone, with no significant effect on pregnancy rate.

Evaluation of models to induce low progesterone during the early luteal phase in cattle

Two experiments were designed to evaluate models for generation of low circulating progesterone concentrations during early pregnancy in cattle. In Experiment 1, 17 crossbred heifers (Bos taurus) were assigned to either prostaglandin F 2α (PGF 2α) administration on Days 3, 3.5, and 4 (PG3; n = 9) or to control (n = 8). Blood samples were collected from heifers from Days 1 to 9 for progesterone assay. Progesterone concentrations were decreased (P < 0.03) between 18 and 48 h after first PGF 2α treatment in heifers assigned to PG3 compared with that of controls. In Experiment 2, 39 crossbred heifers detected in estrus were inseminated (Day 0) and assigned to either (1) PGF 2α administration on Days 3, 3.5, and 4 (PG3; n = 10), (2) PGF 2α administration on Days 3, 3.5, 4, and 4.5 (PG4; n = 10), (3) Progesterone Releasing Intravaginal Device (PRID) insertion on Day 4.5 with PGF 2α administration on Days 5 and 6 (PRID + PGF 2α; n = 10), or (4) control (n = 9). Blood samples were collected daily until Day 15, and conceptus survival rate was determined at slaughter on Day 16. Progesterone concentrations during the sampling period in the PG3 and PG4 groups did not differ but were less than that of controls (P < 0.01). After an initial peak, progesterone concentrations in the PRID + PGF 2α group were similar to that of controls. More heifers in the PG4 group (6 of 10) had complete luteal regression than did those in the PG3 group (3 of 10). Conceptus survival rate on Day 16 did not differ between groups. There was a significant correlation between progesterone concentration on Days 5 and 6 and conceptus size on Day 16. In summary, treatment with PGF 2α on Days 3, 3.5, and 4 postestrus appeared to provide the best model to induce reduced circulating progesterone concentrations during the early luteal phase in cattle.

Dynamic progesterone responses to simulation of a natural pulse of a metabolite of prostaglandin F 2α in heifers

The effects of prostaglandin F 2α (PGF) on circulating progesterone concentration were studied in four groups ( n = 4) of Holstein heifers 9 d after ovulation. The progesterone response to simulation of a pulse of 13,14-dihydro-15-keto-PGF (PGFM) by a 2-h intrauterine (IU) infusion of 0.5 mg of PGF was compared with the response to a PGF-bolus IU injection of 4 mg. The beginning of infusion and time of injection were designated Minute 0. Progesterone concentration did not change significantly between Minute 0 and Hour 48 in control or IU vehicle-treated groups. In the PGF-bolus group, progesterone concentration increased ( P < 0.05) between Minutes 0 and 10 and then decreased. In the PGF-infusion group, simulation of a PGFM pulse was not associated with an initial transient increase in progesterone. The first significant decrease ( P < 0.05) in progesterone began at Minute 20 and continued until Hour 1. The progesterone concentration then began to rebound ( P < 0.05) at Hour 1 and peaked at Hour 3 at almost the same concentration as at the start of PGF infusion. The progesterone again decreased after Hour 3 and increased again between Hours 24 and 48. In summary: (1) an initial transient increase in progesterone was not detected in association with an individual simulated pulse of PGF, indicating that the frequently reported pronounced transient increase after a bolus luteolytic dose of PGF is a nonphysiological response and (2) simulation of a PGFM pulse resulted in a distinct transient rebound in progesterone beginning at Hour 1 of the PGF infusion.

Effect of fixed-time embryo transfer on reproductive efficiency in high-producing repeat-breeder Holstein cows

The aim of the present study was to compare a synchronization of time of ovulation protocol for fixed-timed embryo transfer (FTET) with the usual administration of a single dose of prostaglandin associated with detection of estrus. Also, the effect of the presence of CL at the beginning of FTET protocol was evaluated. Lactating Holstein cows ( n = 651) with three previous artificial inseminations were classified according to presence or absence of a corpus luteum (CL). Cows with a CL were randomly assigned to two additional treatments and submitted to embryo transfer after detection of estrus (PGF-Estrus) or FTET (FTET-CL). Cows without CL were allocated to the FTET-NoCL treatment. On a random day of the estrous cycle (Day 0), cows in the PGF-Estrus treatment ( n = 229) were treated with 150 μg d-cloprostenol (PGF) i.m. followed by detection of estrus from Day 1 through Day 5 after PGF. Embryos were transferred 6–8 days after estrus detection. Cows in the FTET-CL ( n = 208; presence of CL) and FTET-NoCL ( n = 214; absence of CL) treatments received a norgestomet ear implant plus 2 mg estradiol benzoate (EB) and 50 mg progesterone i.m. on Day 0. On Day 8, the implant was removed and 400 IU eCG, 150 μg d-cloprostenol and 1 mg estradiol cypionate i.m. were administered. No detection of estrus was performed and Day 10 was arbitrarily considered as the estrus day. Ultrasonographic exams were performed in all recipients and only cows with a single CL ≥ 15 mm or multiple CL received a fresh or frozen–thawed embryo on Day 17. Pregnancy was diagnosed by ultrasonography at 30 and 60 days of pregnancy. When FTET and PGF-Estrus were compared, the proportion of cows receiving an embryo (recipients transferred-to-treated rate) was greater in the FTET-CL (75.0% (156/208) than in PGF-Estrus (34.5%, 79/229; P < 0.0001) treatment. Pregnancy rate (60 days) was also greater in FTET-CL (29.3%, 61/208) when compared to PGF-Estrus (16.2%, 37/229; P = 0.001). However, no differences were found in pregnancy loss [PGF-Estrus = 11.9% (5/42), FTET-CL = 9.0% (6/67); P = 0.62] and circulating progesterone concentration at embryo transfer [PGF-Estrus = 4.02 ± 0.52 ng/mL ( n = 25), FTET-CL = 3.33 ± 0.32 ng/mL ( n = 27); P = 0.25] among these treatments. The presence of CL at the beginning of FTET protocol resulted greater transferred-to-treated rate [FTET-CL = 75.0% (156/208) vs. FTET-NoCL = 61.2% (131/214); P = 0.003], but showed no effect on pregnancy rate at 60 days [FTET-CL = 29.3% (61/208) vs. FTET-NoCL = 22.9% (49/214); P = 0.13], pregnancy loss [FTET-CL = 9.0% (6/67) vs. FTET-NoCL = 2.0% (1/50); P = 0.15] and circulating progesterone concentration at ET [FTET-CL = 3.33 ± 0.32 ng/mL ( n = 27) compared to FTET-NoCL = 3.44 ± 0.40 ng/mL ( n = 2 9); P = 0.82]. In conclusion, the protocol for synchronization of time of ovulation using norgestomet ear implant, EB and eCG increased recipients transferred-to-treated and pregnancy rates in high-producing repeat-breeder Holstein cows. Also, recipients without CL at the beginning of the time of ovulation synchronization treatment resulted in similar pregnancy rate as recipients with CL submitted to FTET protocol. Thus, the suggested protocol allowed the performance of FTET, without the need for detection of estrus, simplifying the reproductive management and increasing the reproductive efficiency in repeat-breeder Holstein recipients.

521. EFFECT OF KISSPEPTIN ON REPRODUCTIVE FUNCTION IN SEASONALLY ACYCLIC RED DEER HINDS

A preliminary study was conducted to examine whether the marked inhibition of ovulation in seasonally acyclic red deer could be overcome by use of kisspeptin to stimulate gonadotrophin release in these animals. After 14 days progesterone priming with intravaginal CIDR-G devices, non-lactating and lactating hinds (n = 8 in both cases) received 0.50 µmol murine kisspeptin-10 in saline solution delivered intravenously in 30 hours, either continuously or as 4-hourly boluses, and lactating hinds (n = 8) received saline solution intravenously as controls. Kisspeptin treatment caused an elevation (P &lt; 0.05) of the mean plasma LH concentration at 2 h (0.36 + 0.237 versus 0.11 + 0.006 ng/ml, treated versus controls, respectively). Two weeks later there was a tendency (Chi-square = 9.286, 4 d.f., P = 0.054) for an increase in occurrence of medium and larger sized ovarian follicles in treated hinds. However, no ovulations resulted from the infusions and there was no effect on timing of the onset of ovulatory activity during the subsequent breeding season, as determined from circulating progesterone concentrations. It is concluded that kisspeptin stimulates the reproductive axis in seasonally acyclic red deer hinds, however the dose or mode of administration required to produce ovulations may be higher than what is effective for sheep in an equivalent reproductive state.

Interrelationships among morphology, echotexture, and function of the bovine corpus luteum during the estrous cycle

It has been suggested that ultrasound image attributes are a potential indicator of physiological and functional status of the corpus luteum (CL) in several species, including cattle. The aims of this study were to evaluate CL morphological, functional and echotextural characteristics, and also to investigate the hypothesis that those attributes are correlated and change similarly throughout an estrous cycle. Ovaries of crossbred ( Bos taurus taurus × Bos taurus indicus) heifers were evaluated using ultrasonography daily throughout an interestrus interval using a B-mode, real-time ultrasound machine equipped with a 5 MHz linear-array rectal transducer, during a natural estrous cycle (Experiment 1; n = 12) or during a shortened cycle, with luteolysis induction 10 d after estrus (Experiment 2; n = 6). Blood samples were collected for assay of plasma progesterone concentrations. Corpora lutea areas were measured and daily images of each CL were videotaped and digitized for computer-assisted analysis using custom-developed software. In Experiment 1, area of luteal tissue increased until a maximum value 10 d after estrus ( P < 0.001), followed by a plateau phase, and then a decline beginning 14 d after estrus. Luteal tissue area was highly correlated to plasma progesterone concentrations ( r = 0.86; P < 0.001). When luteolysis was induced in Experiment 2, loss of CL function (decrease in plasma progesterone concentrations to metestrous values) preceded tissue regression by 48 h (24 h compared with 72 h; P < 0.001). The mean pixel value of ultrasound images did not change in Experiment 1 ( P > 0.70), but a day effect on this attribute was observed in Experiment 2 ( P = 0.052). In contrast, mean pixel value was correlated to plasma progesterone concentrations in Experiment 1 ( r = −0.63; P < 0.05), but not in Experiment 2 ( r = −0.28; P > 0.10). In regard to CL heterogeneity, defined as the standard deviation of the mean pixel value of the luteal tissue, a time effect was observed following both natural (Experiment 1; P < 0.009) and luteolysis-induced (Experiment 2; P < 0.05) estrous cycles ( P < 0.05). Moreover, this variable was correlated with plasma progesterone concentrations ( r = −0.71 and −0.58 in Experiments 1 and 2, respectively; P < 0.01), indicating that CL images were more heterogeneous during metestrus and after luteolysis (functional regression). In summary, morphological and echotextural attributes were correlated with CL function and underwent similar changes during the estrous cycle. Luteal tissue heterogeneity, assessed by ultrasonography, is considered a potential indicator of CL functional status, because it is correlated to circulating progesterone concentrations.

Corpus luteum size and plasma progesterone concentration in cows

It is often assumed that a larger corpus luteum will produce more progesterone and generate higher circulating plasma concentrations. The aim of the study was to determine whether the size of the corpus luteum does actually determine circulating plasma progesterone concentrations. Data were collated from a number of studies on various aspects of luteal function in non-lactating dairy cows to allow comparisons to be made between corpus luteum weight and plasma progesterone concentration across the luteal phase. In these studies oestrous cycles had been synchronised and animals slaughtered on day 5, day 8 or day 16 following oestrus. Both corpus luteum weight and plasma progesterone concentration increased between day 5 and day 8. Plasma progesterone concentration but not luteal weight also increased between day 8 and day 16. On day 5 there was a strong relationship between corpus luteum weight and plasma progesterone ( R 2 = 0.64; P < 0.001). However, no such relationship was present on day 8 or day 16. These results indicate that while during the early stage of corpus luteum development a relationship between size and progesterone is present, by day 8 of the cycle, the size of the corpus luteum is no longer of importance in determining circulating progesterone concentrations.

Plasma progesterone concentrations during early pregnancy in spring- and autumn-bred ewes

The objective of this experiment was to measure blood progesterone concentrations during early gestation to determine if the apparent reproductive failure in ewes bred out-of-season is due to a failure to conceive or embryonic loss. Blood samples were collected from spring- ( n = 61) and autumn-bred ewes ( n = 29) from Days 8 to 39 post-oestrus. Serum progesterone concentrations were analysed to ascertain whether ewes were ovulating and failing to maintain pregnancy, or conception was failing. Following pregnancy diagnosis 62 days after ram introduction, ewes were categorised as; no display of oestrus, mated but then identified as non-pregnant, or pregnant. A majority of spring-bred ewes that failed to display oestrus had silent oestrus (86%) and 66% of those ewes had abnormally short-lived corpora lutea. Circulating progesterone concentrations during dioestrus in ewes that had ovulated and displayed oestrus were unaffected by season. Similarly, progesterone concentrations during dioestrus did not differ between pregnant and mated non-pregnant ewes. The results indicated that while early luteylosis, low progesterone secretion from corpora lutea and embryo mortality did occur, these were in only a small proportion of ewes. Progesterone concentrations indicated that a majority of mated non-pregnant ewes had elevated progesterone concentrations necessary for the production of at least one viable embryo/foetus. This may be indicative to the failure of maternal recognition of pregnancy, and it is recommended that events surrounding this stage of pregnancy (Days 12–14) be examined more closely in ewes during the non-breeding season.

Mixed-breed twin production by contralateral direct-transfer of male embryos to beef cow recipients bred to GnRH-based, fixed-time AI

Two experiments were conducted to develop protocols for the use of fixed-time artificial insemination and embryo transfer (TAI and TET, respectively) to increase beef cattle productivity. Suckled beef cows were given GnRH (100 µg im) on Day − 10, and PGF (25 mg im) on Day − 3, with TAI on Day 0 (66 h later), and assigned to either embryo recipient (ER) or no embryo (NR) treatments on Days 6 or 7. Semen from Gelbvieh (GB) beef sires was used for TAI; sexed-male in vivo developed Holstein embryos (HO) were placed nonsurgically (TET) into the uterine horn contralateral to the corpus luteum. In Experiment 1, ovarian status of cows ( n = 111; 69 ± 11 d postpartum; mean ± SD on Day 0) in Groups I and II was presynchronized with a single PGF treatment on Day − 24; Groups II and III received GnRH concurrent with TAI, and ER ( n = 78) were selected from all groups on Days 6 or 7. Neither presynchronization nor GnRH affected rates of recipient selection, Day 45 pregnancy (43.2, 43.2, and 54.0% for Groups I, II and III, respectively), or calving (40.5, 37.8, and 43.2%). However, treatment with GnRH increased HO-birth rate (8.0, 14.0 and 24.0%; P < 0.05). In Experiment 2, cows ( n = 99, 113 ± 10 d postpartum) were assigned on Day 7 to NR and ER, with and without hCG (2500 IU im), following a TAI protocol (as per Group III in Experiment 1). Treatment with hCG increased reproductive rate (1.16 vs 1.44 calves/calving; P < 0.05), but had no significant effect on rates of Day 45 pregnancy (45.3 vs 41.3%), calving (31.2 vs 37.0%) or HO-births (20.0 vs 26.0%). In summary, GnRH-based synchronization rates were 71.2% (based on circulating progesterone concentrations that were < 1.0 ng/mL on Day 0 and ≥ 1.0 ng/mL on Day 7); TET did not affect GB-birth rate, but more calves were produced by ER than NR cows (1.43 vs 1.02 calves/calving; P < 0.01); and weaned calf production was 53% greater for twin- than singleton-suckled cows (392 ± 25 vs 256 ± 11 kg/dam; mean ± SEM, P < 0.05). Therefore, GnRH-based TAI and TET protocols for mixed-breed twin production increased beef cow productivity.

134 EFFECT OF ELEVATED CIRCULATING PROGESTERONE CONCENTRATION ON DEVELOPMENT OF IN VITRO PRODUCED BOVINE ZYGOTES IN VIVO

Elevated concentrations of circulating progesterone in the immediate post-conception period have been associated with an increase in embryonic growth rate, interferon-tau production, and pregnancy rate in cattle and sheep. Much of this effect is likely mediated via downstream effects of progesterone-induced changes in gene expression in the tissues of the uterus. However, whether or not progesterone has a direct effect on the embryo also is unknown and, at least in vivo, in single ovulating animals, is difficult to assess. Using state-of-the-art endoscopic techniques, the objective of this study was to examine the effect of elevated progesterone on the development of IVP zygotes transferred to the oviducts of cattle with high or normal circulating progesterone concentrations. Simmental heifers (n = 14) were synchronized using a combination of 2 injections of a prostaglandin F2α analogue administered 11 days apart and gonadotropin-releasing hormone. Only animals exhibiting a clear standing oestrus (= day 0) were used. In order to produce animals with divergent progesterone concentrations, half of the animals received a PRID on day 3 of the oestrous cycle, which was left in place until embryo recovery. All animals were blood sampled daily from days 0 to 7. Cleaved embryos were transferred using endoscopy to the ipsilateral oviduct of each recipient on day 2 and recovered by non-surgically flushing the oviduct and the uterus on day 7. The number of embryos developing to the morula/blastocyst stage was recorded at recovery and following overnight culture in CR1aa medium. Data were analyzed by chi-square analysis. Insertion of a PRID on day 3 resulted in a significant elevation in progesterone concentrations from day 4 (2.36 ± 0.16 ng mL–1 v. 0.54 ± 0.10 ng mL–1, P &lt; 0.001) until day 6 (1.98 ± 0.22 ng mL–1 v. 0.95 ± 0.17 ng mL–1; P &lt; 0.01). The recovery rate was lower in animals that received a PRID (P &lt; 0.05). However, there was no effect of progesterone on the proportion of embryos developing to the morula/blastocyst stage. These results suggest that elevated concentrations of progesterone do not affect the ability of the early embryo to reach the blastocyst stage in vivo and that the reported positive effect of high progesterone levels in terms of fertility are manifested after day 8. Table 1. Effect of elevated progesterone concentration on development of in vitro produced bovine zygotes in vivo

Luteal Characteristics and Progesterone Production on Day 5 of the Bovine Oestrous Cycle

In this study we have examined luteal function in non-lactating and late lactation dairy cows on day 5 of the cycle, during the period of the post-ovulatory progesterone rise. Comparison of luteal progesterone content and in vitro synthetic capacity with circulating plasma progesterone demonstrated that circulating progesterone concentration is a function of total luteal activity rather than the activity of individual units of tissue. Incubation of luteal tissue in vitro demonstrated stimulatory activity of LH and IGF-I, and to a greater degree IGF-II, on luteal progesterone synthesis. Finally the study showed no effect of double ovulation on luteal function. Occurrence of double ovulation in 35% of animals was not associated with any difference in luteal function or plasma progesterone concentrations.

Quantitative analysis of changes in endometrial gland morphology during the bovine oestrous cycle and their association with progesterone levels

This study describes a digital technique for uterine morphometry and its application to endometrial structure during the bovine oestrous cycle. Neither the number nor the size of uterine gland ducts changed during the cycle but a reduction in total endometrial area from days 0 to 8 after oestrus led to an increase in the proportion of the endometrium occupied by gland ducts (gland duct density). This effect on day 8 was maintained to day 16. When endometrial morphology was related to circulating progesterone concentrations on days 5 and 8 of the luteal phase, no relationships were found on day 5, but on day 8, a high progesterone concentration was associated with an increased number of gland ducts. Furthermore, in animals slaughtered on day 8, a high progesterone concentration on day 5 was associated with decreased gland duct size, though a simultaneous decrease in endometrial area led to an increase in gland duct density. The results suggest that contrary to expectation, endometrial glands do not grow and regress during the oestrous cycle, although cyclic changes in endometrial area controlled by progesterone lead to changes in gland duct density.

Luteal Characteristics and Progesterone Production on Day 5 of the Bovine Oestrous Cycle

In this study we have examined luteal function in non-lactating and late lactation dairy cows on day 5 of the cycle, during the period of the post-ovulatory progesterone rise. Comparison of luteal progesterone content and in vitro synthetic capacity with circulating plasma progesterone demonstrated that circulating progesterone concentration is a function of total luteal activity rather than the activity of individual units of tissue. Incubation of luteal tissue in vitro demonstrated stimulatory activity of LH and IGF-I, and to a greater degree IGF-II, on luteal progesterone synthesis. Finally the study showed no effect of double ovulation on luteal function. Occurrence of double ovulation in 35% of animals was not associated with any difference in luteal function or plasma progesterone concentrations.

Impaired Progesterone Production in Nr5a2+/− Mice Leads to a Reduction in Female Reproductive Function1

NR5A2 is an orphan nuclear receptor involved in cholesterol metabolism and embryogenesis. The high level of expression of NR5A2 in the ovary and its involvement in the regulation of steroidogenic gene expression also suggest a role for this transcription factor in female reproductive function. In vivo evidence for a role for NR5A2 in fertility, however, is still lacking. In order to address this possibility, we used Nr5a2+/- mice to demonstrate that heterozygosity for a null mutation of Nr5a2 leads to a decreased fertility in females. Our results indicate that although Nr5a2+/- mice display normal follicular development, ovulation, and estrogen production, they exhibit altered luteal function. More specifically, we show that the reduced reproductive ability of Nr5a2+/- females arises from a reduction in circulating progesterone concentrations and can be rescued by exogenous progesterone supplementation. This study therefore provides the first in vivo evidence for a role of NR5A2 in reproductive function and steroidogenesis.

Uterine epithelial changes during placentation in the viviparous skink Eulamprus tympanum

We used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to describe the complete ontogeny of simple placentation and the development of both the yolk sac placentae and chorioallantoic placentae from nonreproductive through postparturition phases in the maternal uterine epithelium of the Australian skink, Eulamprus tympanum. We chose E. tympanum, a species with a simple, noninvasive placenta, and which we know, has little net nutrient uptake during gestation to develop hypotheses about placental function and to identify any difference between the oviparous and viviparous conditions. Placental differentiation into the chorioallantoic placenta and yolk sac placenta occurs from embryonic Stage 29; both placentae are simple structures without specialized features for materno/fetal connection. The uterine epithelial cells are not squamous as previously described by Claire Weekes, but are columnar, becoming increasingly attenuated because of the pressure of the impinging underlying capillaries as gestation progresses. When the females are nonreproductive, the luminal uterine surface is flat and the microvillous cells that contain electron-dense vesicles partly obscure the ciliated cells. As vitellogenesis progresses, the microvillous cells are less hypertrophied than in nonreproductive females. After ovulation and fertilization, there is no regional differentiation of the uterine epithelium around the circumference of the egg. The first differentiation, associated with the chorioallantoic placentae and yolk sac placentae, occurs at embryonic Stage 29 and continues through to Stage 39. As gestation proceeds, the uterine chorioallantoic placenta forms ridges, the microvillous cells become less hypertrophied, ciliated cells are less abundant, the underlying blood vessels increase in size, and the gland openings at the uterine surface are more apparent. In contrast, the yolk sac placenta has no particular folding with cells having a random orientation and where the microvillous cells remain hypertrophied throughout gestation. However, the ciliated cells become less abundant as gestation proceeds, as also seen in the chorioallantoic placenta. Secretory vesicles are visible in the uterine lumen. All placental differentiation and cell detail is lost at Stage 40, and the uterine structure has returned to the nonreproductive condition within 2 weeks. Circulating progesterone concentrations begin to rise during late vitellogenesis, peak at embryonic Stages 28-30, and decline after Stage 35 in the later stages of gestation. The coincidence between the time of oviposition and placental differentiation demonstrates a similarity during gestation in the uterus between oviparous and simple placental viviparous squamates.

Corpus luteum size and function following single and double ovulations in non-lactating dairy cows

Data was collated from a number of studies on various aspects of luteal function in non-lactating dairy cows to allow comparisons to be made between single and double ovulating animals. In these studies, estrous cycles had been synchronized and animals slaughtered on day 5 or 8. The overall incidence of double ovulations was 28.3%. Double ovulation was associated with smaller individual corpora lutea but no difference in total weight of luteal tissue or any aspect of luteal tissue function or plasma concentrations of progesterone. Furthermore, in a sub set of animals, there was no difference in preovulatory follicle characteristics or plasma concentrations of estradiol around ovulation. These results demonstrated a high incidence of double ovulation in non-lactating cows that had no influence on circulating progesterone concentrations.

Progesterone and the distribution of pituitary gonadotropin isoforms in cattle

The objective of the present study was to determine the relative proportion of gonadotropin isoforms in bovine pituitary glands affected by progesterone. Twelve postpubertal heifers (Swiss-Zebu) were assigned to three groups ( n = 4): intact animals in the luteal phase of the estrous cycle (diestrus group); ovariectomized heifers with (OVXP) or without progesterone treatment (OVX). Prior to pituitary gland collection, a blood sample was taken from each animal to determine the circulating progesterone concentration. Pituitary protein extractions processed by chromatofocusing were eluted with a pH gradient ranging from 10.5 to 3.5. The LH and FSH eluent was grouped on the basis of the following three criteria: (1) as either a basic (pH ≥7.5), neutral (pH 7.4–6.5) and acid (pH ≤6.4); (2) according to the pH unit (pH ≥10.5–3.5); (3) on the basis of distinct isoforms 12 peaks of which (A–L) were identified for LH and 11 (I–XI) for FSH. The analysis by range of pH and by pH of elution in the OVX and OVXP groups showed no difference in the LH and FSH isoform ratio, but diestrus cattle differs having a greater ratio ( p < 0.05) of basic LH isoforms (87.5 ± 0.4%) and lesser ratio ( p < 0.05) of acid isoforms (5.4 ± 0.7%). In the diestrus group, the ratio of acid FSH isoform increased (62.1 ± 1.7%), while neutral isoforms decreased (5.7 ± 0.4%, P < 0.05). The analysis by isoform type of LH revealed a greater proportion of isoforms C (pH 9.4) and E (pH 9.0) in the groups with circulating progesterone when compared to the OVX group. The heterogeneity of FSH was quantitatively similar in most isoforms in the three groups, with the exception of the predominant isoform (VIII, pH 4.9) that was more abundant in the diestrus group ( p < 0.05). These results indicate that progesterone with other gonad factors influence the pituitary glicosylation altering the relative proportions of gonadotropin isoforms.

Luteal blood flow and progesterone production in mares

The temporal relationships between blood flow in the corpus luteum (CL) and circulating progesterone concentrations were studied in 20 mares. Retrospective inspection of plasma progesterone concentrations indicated that a precipitous decrease occurred during Days 15–17 (Day 0 = ovulation) and was defined as the luteolytic period. Mean percentage of CL with color-Doppler signals for blood flow was maximum on Day 10 (77.3%), and Days 10–14 (49.8%) were defined as the preluteolytic period. The cross-sectional area of the CL decreased progressively from Day 4 (9.0 cm 2) to Day 19 (1.5 cm 2). Progesterone reached maximum concentration on Day 8 (12.8 ng/ml) and thereafter CL area and plasma progesterone decreased in parallel until the onset of luteolysis. During the luteolytic period, the decrease in plasma progesterone was about sixfold greater than during the preluteolytic period, whereas the decrease in CL area and in percentage of CL with blood-flow area were about twofold greater. There was no indication that an acute increase or decrease in luteal blood flow occurred prior to the precipitous decrease in plasma progesterone.

Ovariectomy during the luteal phase influences secretion of prolactin, growth hormone, and insulin-like growth factor-I in the bitch

A decline in circulating progesterone concentration plays an important role in the ethiopathogenesis of pseudopregnancy in the bitch. Because growth hormone (GH) and prolactin (PRL) are essential for normal mammogenesis and the secretion of these hormones is influenced by changes in the circulating progesterone concentration, the purpose of this study was to investigate the effects of mid-luteal phase ovariectomy on the 6-h pulsatile plasma profiles of GH and PRL and the basal plasma concentrations of GH, PRL, and insulin-like growth factor-I (IGF-I) in six beagle bitches. Ovariectomy was followed by only mild or covert signs of pseudopregnancy. The sharp decrease of the plasma progesterone concentration was accompanied by decreased basal plasma concentrations of GH and IGF-I and a rise in basal plasma PRL concentration. GH and PRL were secreted in a pulsatile fashion both prior to and after ovariectomy. The mean basal plasma GH concentration was significantly higher before ovariectomy than on days 1 and 7 after ovariectomy. The mean area under the curve above the zero level (AUC 0) for GH was significantly higher before than at 7 days after ovariectomy. The mean area under the curve above basal level (AUC b) and the frequency of GH pulses at 7 days after ovariectomy were significantly higher than before and 1 day after ovariectomy. Both the mean basal plasma PRL concentration and the mean AUC 0 for PRL increased after ovariectomy. In conclusion, ovariectomy of bitches in the mid-luteal phase stops progesterone-induced GH release from the mammary gland, as evidenced by the lowering of basal plasma GH levels, the recurrence of GH pulsatility, and the lowering of circulating IGF-I levels. The sudden lowering of plasma progesterone concentration is probably a primary cause of a prolonged increase in PRL secretion. These observations underscore the importance of similar, albeit less abrupt, hormonal changes in the cyclical physiological alterations in the mammary gland and in the development of pseudopregnancy.

Does injection of prostaglandin F 2α (PGF 2α) cause ovulation in anestrous Western White Face ewes?

In a previous study in our laboratory, treatment of non-prolific Western White Face (WWF) ewes with PGF 2α and intravaginal sponges containing medroxyprogesterone acetate (MAP) on ∼Day 8 of a cycle (Day 0 = first ovulation of the interovulatory interval) resulted in ovulations during the subsequent 6 days when MAP sponges were in place. Two experiments were performed on WWF ewes during anestrus to allow us to independently examine if such ovulations were due to the direct effects of PGF 2α on the ovary or to the effects of a rapid decrease in serum concentrations of progesterone at PGF 2α-induced luteolysis. Experiment 1: ewes fitted with MAP sponges for 6 days ( n = 12) were injected with PGF 2α ( n = 6; 15 mg im), or saline ( n = 6) on the day of sponge insertion. Experiment 2: ewes received progesterone-releasing subcutaneous implants ( n = 6) or empty implants ( n = 5) for 5 days. Six hours prior to implant removal, all ewes received a MAP sponge, which remained in place for 6 days. Ewes from both experiments underwent ovarian ultrasonography and blood sampling once daily for 6 days before and twice daily for 6 days after sponge insertion. Additional blood samples were collected every 4 h during sponge treatment. Experiment 1: 4–6 (67%) PGF 2α-treated ewes ovulated ∼1.5 days after PGF 2α injection; these ovulations were not preceded by estrus or a preovulatory surge release of LH, and resulted in transient corpora hemorrhagica (CH). The growth phase was longer ( P < 0.05) and the growth rate slower ( P < 0.05) in ovulating versus non-ovulating follicles in PGF 2α-treated ewes. Experiment 2: in ewes given progesterone implants, serum progesterone concentrations reached a peak (1.72 ng/mL; P < 0.001) on the day of implant removal and decreased to basal concentrations (<0.17 ng/mL; P < 0.001) within 24 h of implant removal. No ovulations occurred in either the treated or the control ewes. We concluded that ovulations occurring after PGF 2α injection, in the presence of a MAP sponge, could be due to a direct effect of PGF 2α at the ovarian level, rather than a sudden decline in circulating progesterone concentrations.