Role of progesterone in regulating uteroovarian venous concentrations of PGF2 α and PGE2 during the estrous cycle and early pregnancy in ewes

The role of progesterone in regulation of uteroovarian venous concentrations of prostaglandins F₂ α (PGF₂α) and E₂ (PGE₂) during days 13 to 16 of the ovine estrous cycle or early pregancy was examined. At estrus, ewes were either mated to a fertile ram or unmated. On day 12 postesturus, ewes were laparotomized and a catheter was inserted into a uteroovarian vein. Six mated and 7 unmated ewes received no further treatment. Fifteen mated and 13 unmated ewes were ovariectomized on day 12 and of these, 7 mated and 5 unmated ewes were given 10 mg progesteron sc and an intravaginal pessary containing 30 mg of progesterone. Uteroovarian venous samples were collected every 15 min for 3 h on days 13 to 16 postestrus. Mating resulted in higher mean daily concentrations of PGE₂ in the uterovarian vein than in unmated ewes. Ovariectomy prevented the rise in PGE₂ with day in mated ewes but had no effect in unmated ewes. Progesterone treatment restored PGE₂ in ovariectomized, mated ewes with intact embros. Mating had no effect on mean daily concentrations of PGF₂α or the patterns of the natural logarithm (ln) of the invariance of PGF₂α. Ovariectomy resulted in higher mean concentrations and ln invariances of PGF₂α on day 13 and lower mean concentrations and ln invariances of PGF₂α on days 15 and 16. Replacement with progesterone prevented these changes in patters of mean concentrations and ln variances of PGF₂α following ovariectomy. It is concluded that progesterone regulates the release of PGF₂α from the uterus, maintaining high concentrations while also preventing the occurrence of the final peaks of PGF₂α which are seen with falling concentrations of progesterone. This occurs in both pregnant and non-pregnant ewes. Progesterone is also needed to maintain increasing concentrations of PGE₂ in mated ewes.     

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.     

Plasma gonadotropin and progesterone concentrations during the estrous cycle of Finn, Suffolk and Targhee ewes

Hormonal profiles during the estrous cycle of Finn, Suffolk and Targhee ewes were compared in six ewes of each breed. Blood samples were drawn by venipuncture at 8-h intervals from onset to onset of consecutive estrous periods. Number of corpora lutea (CL) and ovarian follicles >/=3 mm in diameter on Day 10 (estrus = Day 0) were observed using endoscopy. Estrous cycle length was 14.9, 15.6 and 16.4 d (P<0.01) in Finn, Suffolk and Targhee ewes, respectively. Finns had more (P<0.001) CL (3.5) than Suffolks (2.0) and Targhees (1.8), but luteal phase progesterone concentrations were similar among breeds in peak level and area under the curve. In Finn ewes, the amplitude of the preovulatory LH surge was lower (P<0.01) and tended to occur later in estrus; otherwise LH levels and patterns were similar among breeds. A coincident follicle stimulating hormone (FSH) preovulatory surge occurred in most ewes, the amplitude of which was related to that of luteinizing hormone (LH); r = 0.67, P<0.01. Plasma FSH levels and patterns were similar in Finn, Suffolk and Targhee ewes and most ewes had three to four secretory episodes. Follicles >/=3 mm averaged 1.8, 1.0 and 1.2 (P>0.1) in Finn, Suffolk and Targhee ewes, respectively. Results indicate that the higher ovulation rate of the Finn ewe is not elicited by increased FSH levels at any stage of the estrous cycle.     

Circulating concentrations of oxytocin during the estrous cycle and early pregnancy in sheep

Plasma concentrations of oxytocin and progesterone have been measured by radioimmunoassay in jugular venous blood obtained daily from 5 sheep during 2 estrous cycles and in early pregnancy.Concentrations of oxytocin were relatively high (15–30 pg/ml) during the luteal phase of the cycle, but fell at estrus (to 1–17 pg/ml). A fall in oxytocin was also observed on day 15 of pregnancy, when, as expected, progesterone levels remained high. It is suggested that raised basal levels of oxytocin are unlikely to cause the increasing uterine release of prostaglandin F_2α which occurs at the end of the estrous cycle.     

Uterine secretion of prostaglandin F2 alpha in response to oxytocin in ewes: changes during the estrous cycle and early pregnancy.

Experiment 1 was conducted to determine when the ovine uterus develops the ability to secrete prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin and how development is affected by pregnancy. Pregnant and nonpregnant ewes received an injection of oxytocin (10 IU, i.v.) on Day 10, 13, or 16 postestrus. Jugular venous blood samples were collected for 2 h after injection for quantification of 13,14-dihydro-15-keto-PGF2 alpha (PGFM). In nonpregnant ewes, concentrations of PGFM increased following oxytocin on Day 16 but not on Day 10 or 13. Concentrations of PGFM did not increase following treatment on Day 10, 13, or 16 in pregnant ewes. Therefore, the ability of oxytocin to induce uterine secretion of PGF2 alpha develops after Day 13 in nonpregnant but not in pregnant ewes. Experiment 2 was conducted to precisely define when uterine secretory responsiveness to oxytocin develops. Pregnant and nonpregnant ewes received oxytocin on Day 12, 13, 14, or 15. In nonpregnant ewes, concentrations of PGFM increased following treatment on Days 14 and 15, but not earlier. Peripheral concentrations of progesterone showed that uterine secretory responsiveness to oxytocin developed prior to the onset of luteal regression. As in experiment 1, the increase in concentrations of PGFM following administration of oxytocin was much lower in pregnant than in nonpregnant ewes; however, some pregnant ewes did respond to oxytocin with an increase in PGFM. In experiment 3, pregnant ewes received an injection of oxytocin on Day 18, 24, or 30 postmating. Concentrations of PGFM increased following oxytocin on Days 18 and 24. The conceptus appears to delay and attenuate the development of uterine secretory responsiveness to oxytocin.     

PGE receptor characteristics on porcine luteal cells during the estrous cycle and early pregnancy.

This study examined the affinities and concentrations of prostaglandin E (PGE) receptors on porcine luteal cells during the estrous cycle and early pregnancy. Corpora lutea (CL) were obtained from nonpregnant gilts at days 9 (n = 4), 12 (n = 3), and 14 (n = 6); three gilts possessed red, vascular CL and three gilts had white nonvascular CL) of the estrous cycle, and days 9 (n = 4), 12 (n = 3), 14 (n = 5), and 30 (n = 5) of pregnancy. The CL were dissociated enzymatically to disperse single cells and the red blood cells were removed by elutriation. The luteal cells were assayed for specific PGE binding by displacement analysis with use of [3H] PGE2 and varying concentrations of unlabeled PGE2. The specific binding of [3H] PGE2 to luteal cells decreased (p < 0.05) from days 9 to 14 of the estrous cycle, but only decreased (p < 0.05) from days 9 to 12 of pregnancy. Specific binding was higher (p < 0.05) on day 14 of pregnancy than the comparable stage of the estrous cycle. The affinities of PGE receptors decreased (p < 0.05) only on the luteal cells dissociated from red, vascular CL of day 14 nonpregnant gilts compared with those of other days of the estrous cycle and pregnancy. The number of PGE receptors on porcine luteal cells was similar (p > 0.05) in pregnant and nonpregnant gilts, but decreased (p < 0.05) on days 12-14 postestrus. During early pregnancy, it was evident that high affinity PGE receptors are sustained on porcine luteal cells; however, the role of the PGE receptors in maternal recognition of pregnancy remains speculative.     

Estrogen and progesterone concentrations in bovine milk during the estrous cycle

Estrogen and progesterone concentrations in milk during the estrous cycle were estimated in 18 normally cycling Holstein dairy cows. The estrogen and progesterone concentrations in milk during the estrous cycle followed the pattern described for them in blood in the corresponding period. During most of the estrous cycle, estrogen concentration remained at approximately 200 pg/ml and reached a proestrous peak of 360 +/- 127 pg/ml on day 19. The progesterone concentration in milk during the estrous cycle increased to a peak on day 13 (45.5 +/- 6.6 ng/ml) and thereafter declined towards estrus. Estrus detection/prediction based on milk progesterone concentrations appears feasible in view of the significant differences in milk progesterone concentrations between the early luteal (post-ovulatory), luteal and rapid follicular growth periods of the estrous cycle.     

Effect of trilostane on PGE, PGF2alpha, estradiol-17beta, and progesterone secretion and pregnancy of 90-day ovariectomized pregnant ewes

Ninety-day pregnant sheep were ovariectomized and received vehicle or trilostane every 12 h through 132 h, starting at 72 h postovariectomy. All trilostane-treated ewes aborted (P < or = 0.05) between 36 and 50 h after initiation of treatment. Profiles of progesterone in jugular venous blood differed (P < or = 0.05) and was lower (P < or = 0.05) in trilostane-treated ewes. Profiles of estradiol-17beta in jugular venous plasma of trilostane-treated ewes differed (P < or = 0.05) from controls. Estradiol-17beta increased after the first two treatments, followed by a return 2 h later to pretreatment levels (P > or = 0.05), which was followed by a sustained increase (P < or = 0.05) in estradiol-17beta. Profiles of PGF2alpha in inferior vena cava plasma of trilostane-treated ewes differed and were greater (P < or = 0.05) and occurred with the sustained increase in estradiol-17beta and the onset of most of the abortions. Profiles of PGE in inferior vena cava plasma between control and trilostane-treated 90-day pregnant ewes did not differ (P > or = 0.05). It is concluded that abortions occur at midpregnancy in sheep when the estradiol-17beta : progesterone ratio changes sufficiently to cause a sustained increase in estradiol-17beta and PGF2alpha but without changing placental secretion of PGE.     

Concentration of prostaglandins F in uterine venous plasma of anesthetized mares during the estrous cycle and early pregnancy

Prostaglandins F were quantitated by radioimmunoassay in uterine venous plasma of anesthetized mares on day 7 of estrus, days 2, 6, 10, 14 or 18 of diestrus and days 10, 14 or 18 of pregnancy. The PGF concentration was greater (P<.01) at day 14 of diestrus than at all other days studied. The concentrations at days 10 and 18 of diestrus and at days 10, 14 and 18 of pregnancy were greater (P<.05) than at day 7 of estrus and days 2 and 6 of diestrus. PGF concentrations at days 10 and 14 were greater (P<.01) for diestrous than for pregnant mares.     

Uterine contractile activity in mares during the estrous cycle and early pregnancy

Transrectal ultrasonography was used to quantitate uterine contractile activity during the estrous cycle and early pregnancy in pony mares (nonbred, n = 9; pregnant, n = 16). Continuous 1-min scans of longitudinal sections of the uterine body were videotaped, and uterine activity scores (1=minimal activity, 5=maximal activity) were assigned to each tape segment. There was a tendency (P<0.06) for a main effect of reproductive status (nonbred versus pregnant), a main effect of day (P<0.0001), and a reproductive status by day interaction (P<0.006). Uterine activity scores were higher (P<0.05) in pregnant mares on Days 1, 11, 12, and 17 (Day 0=day of ovulation) than in nonbred mares. Maximal activity in pregnant mares occurred on Days 11 to 14 during the reported period of maximal embryo mobility. Activity scores decreased (P<0.05) between the day prior to and the day of fixation (mean = Day 15) of the embryonic vesicle. Activity scores were maintained at an intermediate level for several days following fixation before declining to minimal levels by 7 d postfixation. A postovulatory decrease (P<0.04) in activity scores was observed in nonbred mares, but not in pregnant mares, between Days 0 and 1 followed by a progressive increase (P<0.03) between Days 2 and 4. Maximal activity in nonbred mares occurred during the late luteal phase (Days 13 to 14), corresponding temporally to the reported onset of luteolysis.     

Follicular development during early pregnancy and the estrous cycle of the sow

The objective of this study was to monitor and compare follicle populations and follicular development in pregnant and nonpregnant sows from Day 3 to Day 20 after breeding. Twenty-four sows were paired within parity on the day of artificial insemination and were randomly allocated within pair for insemination with either killed (n=12) or live spermatozoa (n=12). All the sows were artificially inseminated with the pooled ejaculate of the same boar. From Day 3 through Day 20 post estrus, ovarian follicles were scanned daily by ultrasonography. Ultrasound images were recorded on videotape and were retrospectively analyzed. Follicles were mapped to indentify the existence of follicular waves. The follicles were then classified as small (< 3 mm), medium (3-5 mm), or large (>/=5 mm). Pregnancy diagnosis was performed on Day 21 by ultrasonography. Pregnant sows maintained a constant proportion of the follicle population in the small, medium and large follicle categories. However, in the nonpregnant sows, the proportion of follicles in the various size categories remained constant until Day 15. Thereafter, the proportion of small follicles decreased (P < 0.05) from Day 15 to 20, and the proportions of medium and large follicles increased (P < 0.05). The predictability of pregnancy status on Day 20 based on follicle populations in any of the 3 follicle categories was low. Moreover, there was no evidence of follicular waves during the estrous cycle or early pregnancy. In conclusion, the proportion of small follicles decreased while medium and large follicle increased from Day 15 through Day 20 of the estrous cycle, but not during a similar stage of pregnancy. This latter finding concurs with follicle recruitment from the pool of small follicles for ovulation following PGF2alpha secretion to induce luteolysis, which reduces progesterone concentrations and thereby allows for the stimulation of the pool of small follicles by gonadotropins.     

Blood constituents during the estrous cycle and early pregnancy in dairy cows

The objective of this study was to determine if maternal platelet count, white blood cell count or other blood constituents undergo sustained alterations in concentration following fertilization. Blood samples from 17 Holstein females were collected over an 18-d period starting at estrus. Blood was analyzed for levels of platelets, white blood cells, red blood cells, hemoglobin and hematocrit. Results were analyzed for differences between nonpregnant and pregnant groups. Analysis of variance revealed a day-by-group interaction in the platelet count (P<0.01). White blood cell count showed both a day-by-group interaction and a difference between days (P<0.01). Red blood cell count, hematocrit and hemoglobin levels resulted in no significant difference between the two groups (P>0.05). While statistically significant differences were observed in platelet and white blood cell count, neither of these were sustained over a period longer than 2 d.