Glycosylation and immunocytochemistry of binucleate cells in pronghorn (Antilocapra americana, Antilocapridae) show features of both Giraffidae and Bovidae

Although the pronghorn (Antilocapra americana) resembles an antelope, its nearest relatives are the giraffe and okapi. In this study we have examined the placentae of 6 pronghorns using lectin- and immunocytochemistry to identify giraffid and bovid features. Binucleate cells (BNC) of the placenta exhibited features intermediate between those of the giraffe and bovine; Dolichos biflorus agglutinin binding - strong in the bovine BNC and absent in the giraffe - was evident in only a subpopulation of BNC while binding to blood vessels, as in the giraffe. Binding of Phytolacca americana agglutinin resembled that of the giraffe and okapi whereas many other glycans were found in all four clades. PAG antigens were similar to bovine and okapi but not giraffe. In summary, although the pronghorn outwardly resembles an antelope, placental BNC show giraffid features. Although each clade has its own individual characteristics, there are far more similarities than differences between them, emphasizing the common ancestry of all four clades.

Technical note: Validation of a chemical pregnancy test in dairy cows that uses whole blood, shortened incubation times, and visual readout

Chemical pregnancy testing is an alternative to traditional methods of pregnancy diagnosis (either manual palpation or ultrasound) in postpartum dairy cows and heifers. The objective was to validate a chemical pregnancy test that confers the advantages of using whole blood, rapid incubation times, and visual readout. Blood and milk samples were collected from Holstein dairy cows [n=320; 162±62 (mean ± SD) d in milk] on a confinement farm in northeast Missouri at 28 d after artificial insemination (AI). The samples were assayed for pregnancy-associated glycoproteins (PAG) by using a rapid visual test as well as traditional plasma- and milk-based tests. Transrectal ultrasonography diagnosis for pregnancy at 35 to 38 d after AI was the reference (gold) standard for all PAG tests. One hundred fifty-nine cows were diagnosed as pregnant by the reference standard (pregnancies per AI=49.7%). The tests were ELISA and either optical density (OD; measured with a microtiter plate reader; plasma, milk, and rapid visual tests) or visual readout (rapid visual test) were used to diagnose pregnancy. When OD was used, the percentage of pregnant cows classified correctly (sensitivity) for the plasma, milk, and rapid visual tests were 97±1, 96±2, and 95±1% (±SE), respectively. The sensitivity of the rapid visual test when assessed visually was 98±1%. The specificity (proportion of nonpregnant cows classified correctly) for the plasma, milk, and rapid visual was 94±2%, 94±2%, and 93±2% when an OD was used. When read visually, the specificity of the rapid visual test was lesser (85±3%) because some cows with faint visual signals yielded false positive diagnosis. The overall accuracy (proportion of pregnant and nonpregnant cows diagnosed correctly) was similar for all tests (plasma, milk, rapid visual OD, and rapid visual; 96±1, 95±1, 94±1, and 92±2%, respectively). In a second experiment, lactating Holstein cows (n=291) from 4 commercial confinement dairy farms in western Kentucky were tested 25 to 95 d after AI using the rapid visual test. The OD of the rapid visual test followed the known profile for PAG in circulation during the first trimester of pregnancy. The conclusion is that the rapid visual test has equal sensitivity and accuracy as existing PAG tests. A slightly lower specificity was found when the rapid visual test was read visually.

Behavioral and physiological changes around estrus events identified using multiple automated monitoring technologies

This study included 2 objectives. The first objective was to describe estrus-related changes in parameters automatically recorded by the CowManager SensOor (Agis Automatisering, Harmelen, the Netherlands), DVM bolus (DVM Systems LLC, Greeley, CO), HR Tag (SCR Engineers Ltd., Netanya, Israel), IceQube (IceRobotics Ltd., Edinburgh, UK), and Track a Cow (Animart Inc., Beaver Dam, WI). This objective was accomplished using 35 cows in 3 groups between January and June 2013 at the University of Kentucky Coldstream Dairy. We used a modified Ovsynch with G7G protocol to partially synchronize ovulation, ending after the last PGF2α injection (d 0) to allow estrus expression. Visual observation for standing estrus was conducted for four 30-min periods at 0330, 1000, 1430, and 2200h on d 2, 3, 4, and 5. Eighteen of the 35 cows stood to be mounted at least once during the observation period. These cows were used to compare differences between the 6h before and after the first standing event (estrus) and the 2wk preceding that period (nonestrus) for all technology parameters. Differences between estrus and nonestrus were observed for CowManager SensOor minutes feeding per hour, minutes of high ear activity per hour, and minutes ruminating per hour; twice daily DVM bolus reticulorumen temperature; HR Tag neck activity per 2h and minutes ruminating per 2h; IceQube lying bouts per hour, minutes lying per hour, and number of steps per hour; and Track a Cow leg activity per hour and minutes lying per hour. No difference between estrus and nonestrus was observed for CowManager SensOor ear surface temperature per hour. The second objective of this study was to explore the estrus detection potential of machine-learning techniques using automatically collected data. Three machine-learning techniques (random forest, linear discriminant analysis, and neural network) were applied to automatically collected parameter data from the 18 cows observed in standing estrus. Machine learning accuracy for all technologies ranged from 91.0 to 100.0%. When we compared visual observation with progesterone profiles of all 32 cows, we found 65.6% accuracy. Based on these results, machine-learning techniques have potential to be applied to automatically collected technology data for estrus detection.

Effect of subluteal concentrations of progesterone on luteinizing hormone and ovulation in lactating dairy cows

Two experiments were conducted to determine if administration of progesterone within a low, subluteal range (0.1-1.0 ng/mL) blocks the luteinizing hormone (LH) surge (experiments 1 and 2) and ovulation (experiment 2) in lactating dairy cows. In experiment 1, progesterone was administered to cycling, lactating dairy cows during the luteal phase of the estrous cycle using a controlled internal drug release (CIDR) device. CIDRs were pre-incubated in other cows for either 0 (CIDR-0), 14 (CIDR-14) or 28 days (CIDR-28). One group of cows received no CIDRs and served as controls. One day after CIDR insertion, luteolysis was induced by two injections of prostaglandin (PG) F(2alpha) (25 mg) at 12 h intervals. Two days after the first injection, estradiol cypionate (ECP; 3 mg) was injected to induce a LH surge. Concentrations of progesterone after luteolysis were 0.11, 0.45, 0.78 and 1.20 ng/mL for cows treated with no CIDR, CIDR-28, CIDR-14, and CIDR-0, respectively. LH surges were detected in 4/4 controls, 4/5 CIDR-28, 2/5 CIDR-14 and 0/5 CIDR-0 cows following ECP. In experiment 2, progesterone was administered to cycling, lactating, Holstein cows during the luteal phase of the estrous cycle as in experiment 1. Luteolysis was induced as in experiment 1. The occurrence of an endogenous LH surge and ovulation were monitored for 7 days. Concentrations of progesterone after luteolysis were 0.13, 0.30, 0.70 and 1.20 ng/mL for cows treated with no CIDR, CIDR-28, CIDR-14 and CIDR-0, respectively. LH surges and ovulation were detected in 5/5 controls, 3/7 CIDR-28, 0/5 CIDR-14 and 0/5 CIDR-0 cows. It was concluded that low concentrations of progesterone can reduce the ability of either endogenous or exogenous estradiol to induce a preovulatory surge of LH and ovulation.

Effect of a single injection of progesterone on ovarian follicular cysts in lactating dairy cows

The objective of this experiment was to evaluate the effect of a single injection of progesterone on the lifespan of ovarian follicular cysts and to examine the fate of follicles that mature following treatment. Lactating Holstein and Jersey cows with ovarian follicular cysts were identified by rectal palpation. The ovaries of cystic cows were then examined by transrectal ultrasonography three times weekly to monitor formation of new follicular cysts. Cows with newly formed follicular cysts were treated either with a single injection of progesterone (200 mg, IM, n = 11) or corn oil vehicle (n = 7). Venous blood samples were collected daily for quantification of progesterone. Blood sampling and ultrasonography continued until ovulation or a new follicular cyst formed. Treatment reduced the lifespan of the cyst by 12 days, from 29.8 +/- 2.3 days in control cows to 17.2 +/- 1.8 days in progesterone-treated cows (P = 0.01). Progesterone treatment also tended to alter the frequency of subsequent follicular events. Ovulation occurred in 4/11 cows that were treated with progesterone whereas none of the vehicle treated cows ovulated (P = 0.07). In conclusion, a single injection of 200mg of progesterone, administered early in the life of an ovarian follicular cyst, shortened its lifespan and in some cases was followed by ovulation of a new follicle.

Relationship between endogenous progesterone and follicular dynamics in lactating dairy cows with ovarian follicular cysts

Two experiments were conducted to examine circulating concentrations of progesterone (P4) in cows with ovarian follicular cysts (OFCs) and to relate differing levels of P4 to subsequent follicular events. In experiment 1, peripheral concentrations of P4 were determined in cows diagnosed with OFCs. Nonpregnant, lactating Holstein and Jersey cows (n = 32) were diagnosed as having OFCs by rectal palpation. Ovarian follicular cysts were then examined by transrectal ultrasonography to confirm the presence of OFCs (follicle diameter, >/=17 mm; absence of luteal tissue). At confirmation, a blood sample was collected for quantification of P4. The concentration of P4 at confirmation was classified as low (<0.1 ng/ml), intermediate (0.1-1.0 ng/ml), or high (1.0-2.0 ng/ml). More OFCs were associated with intermediate (66%) than with either low (28%) or high (6%) concentrations of P4. In experiment 2, the fate of follicles (diameter, >/=10 mm) that formed in the presence of an OFC was determined and related to circulating concentrations of P4 during follicular development. Follicles (n = 59) that formed in the presence of an OFC ovulated (n = 19), formed a cyst (n = 30), or underwent normal growth and regression (NGR; n = 10). Endogenous P4 in the 7-day period during follicular development was classified as low (if P4 dropped to <0.1 ng/ml for 1 day or longer), intermediate (if P4 averaged between 0.1 and 1.0 ng/ml and never dropped to <0.1 ng/ml), or high (if P4 averaged >1.0 ng/ml and never dropped to <0.1 ng/ml). In the presence of intermediate P4, 75% of observed follicles formed cysts, compared with 10% that ovulated and 15% that experienced NGR. In the presence of low P4, 53%, 41%, and 6% of follicles ovulated, formed a follicular cyst, or experienced NGR, respectively. Thus, an association between intermediate P4 and the formation of OFCs was established.

Direct inhibitory effect of progesterone on oxytocin-induced secretion of prostaglandin F(2alpha) from bovine endometrial tissue

The effect of progesterone on oxytocin-induced secretion of prostaglandin (PG) F(2alpha) from bovine endometrial tissue explants was examined. Endometrial tissue from the late luteal phase were preincubated for 20 h in control medium. Explants were then treated for 6 h with control medium, oxytocin (10(-7) M), progesterone (10(-5) M), or both hormones. Oxytocin increased the medium concentration of 13,14-dihydro-15-keto-PGF(2alpha), whereas progesterone completely suppressed the stimulatory effect of oxytocin. In experiment 2, isolated endometrial epithelial cells were incubated with progesterone (10(-5) M), oxytocin (10(-7) M), and combinations of these hormones with or without actinomycin D (1 ng/ml). Only oxytocin stimulated secretion of PGF(2alpha), and this response was suppressed by progesterone. Oxytocin induced a rapid increase in intracellular concentrations of Ca(2+) detected within 1 min of exposure of epithelial cells from the same cows. Progesterone pretreatment diminished this response. In experiment 3, direct effects of progesterone (2 nM-20 microM) on binding of (3)H-oxytocin to the membrane preparation from epithelial cells were determined by saturation analysis. Oxytocin binding was suppressed by progesterone at every dosage tested. Progesterone is capable of suppressing the ability of oxytocin to induce endometrial secretion of PGF(2alpha). This effect appears to be mediated through a direct interference in the interaction of oxytocin with its own receptor.

Ovarian follicular cysts in dairy cows: an abnormality in folliculogenesis

Ovarian follicular cysts are a major reproductive problem in lactating dairy cows. The primary physiological defect leading to the formation of ovarian follicular cysts is a failure of the hypothalamus to trigger the preovulatory surge of luteinizing hormone (LH) in response to estradiol. The factor responsible for this hypothalamic defect may be progesterone. Intermediate levels of progesterone have been shown to prevent ovulation and promote persistence of dominant follicles in normal cycling cows. Recently, we found that 66% of cows with ovarian follicular cysts had progesterone concentrations in an unusual, intermediate range (0.1-1.0 ng/mL) at the time of their detection. A majority of new follicles (76%) that develop in the presence of these intermediate progesterone concentrations became cysts. Only 10% ovulated. Based on these observations, a novel model for the formation and turnover of ovarian follicular cysts is proposed.

Timing of onset of somatotropin supplementation on reproductive performance in dairy cows

The objective of this field trial was to determine whether delaying the start of recombinant bovine somatotropin (rbST) supplementation from 9 to 10 wk postpartum to 17 to 18 wk postpartum would improve reproductive performance in lactating dairy cows. Cows from nine herds (n = 798 cows; 766 Holsteins, 32 Jerseys) were assigned at random to receive rbST supplementation at 14-d intervals beginning during wk 9 to 10 (n = 399) or wk 17 to 18 (n = 399) after calving. Effects of herd, season of calving, parity, and onset of rbST supplementation (9 to 10 wk vs. 17 to 18 wk) on days to first service and days open were determined. In primiparous but not multiparous cows, there tended to be fewer days to first service and fewer days open when onset of rbST supplementation was delayed. Percentages of cows pregnant at 150, 200, and 250 d postpartum were also examined. Time of onset of rbST did not affect percentages of multiparous cows pregnant at 150, 200, and 250 d postpartum. However, there appeared to be a slight tendency for percentages of pregnant primiparous cows to be greater at 200 and 250 d postpartum for those receiving rbST supplementation beginning at 17 to 18 wk compared to those receiving rbST starting at 9 to 10 wk. In conclusion, delaying the start of rbST supplementation to wk 17 to 18 postpartum had no beneficial effect on reproductive performance of multiparous cows but tended to improve some measures of reproductive performance in primiparous cows.

Trends in reproductive performance in Southeastern Holstein and Jersey DHI herds

Trends in average days open and services per conception from 1976 to 1999 were examined in 532 Holstein and 29 Jersey herds from 10 Southeastern states. Three-year averages for eight intervals (time) were calculated (first: 1976 to 1978; eighth: 1997 to 1999). Milk, fat, fat-corrected milk, and number of cows increased across time. Herds of both breeds had linear, quadratic, and cubic effects of time on days open and services per conception. For 1976 to 1978, respective averages of days open and services per conception were 122 +/- 2.8 d and 1.91 +/- 0.08 for Jerseys, 124 +/- 0.7 d and 1.91 +/- 0.02 for Holsteins. Days open increased nonlinearly to 152 +/- 2.8 d for Jerseys and 168 +/- 0.7 d for Holsteins by 1997 to 1999, resulting in a breed x time interaction. Services per conception also increased nonlinearly, reaching 2.94 +/- 0.04 services for both breeds in 1994 to 1996, changing only slightly after 1996. Fat-corrected milk and number of cows had small but significant effects. Five subregions (one to three states) differed in mean days open and services per conception, but changes in those measures across time among subregions were similar. Days to first service increased by 16 (Holsteins) and 18 d (Jerseys) during the last five 3-yr periods, associated with increasing days open. Estrus detection rates generally declined from 1985 to 1999, associated inversely with services per conception. Reduced reproductive performance in Southeastern dairy herds is of concern. Multiple strategies are needed to attenuate further declines.

Cellular mechanisms by which oxytocin mediates ovine endometrial prostaglandin F2alpha synthesis: role of G(i) proteins and mitogen-activated protein kinases

Oxytocin stimulates a rapid increase in ovine endometrial prostaglandin (PG) F2alpha synthesis. The overall objective of these experiments was to investigate the cellular mechanisms by which oxytocin induces endometrial PGF2alpha synthesis. The objective of experiment 1 was to determine whether G(i) proteins mediate oxytocin-induced PGF2alpha synthesis. Uteri were collected from four ovary-intact ewes on Day 14 postestrus. Caruncular endometrial explants were dissected and subjected to in vitro incubation. Pertussis toxin, an inhibitor of G(i) proteins, had no effect on the ability of oxytocin to induce PGF2alpha synthesis (P > 0.10). The objective of experiment 2 was to determine whether any of the three mitogen-activated protein kinases (MAPKs), extracellular signal regulated protein kinase (ERK1/2), c-Jun N-terminal/stress-activated protein kinase (JNK/SAPK), or p38 MAPK, mediate oxytocin-induced PGF(2alpha) synthesis. Eleven ovary-intact ewes were given an injection of oxytocin (10 IU; i.v.; n = 5) or physiological saline (i.v.; n = 6) on Day 15 postestrus. Uteri were collected 15 min after injection and caruncular endometrium was dissected. Endometrial homogenates were prepared and subjected to Western blotting. Membranes were probed for both total and phosphorylated forms of all three classes of MAPK. All classes of MAPK were detected in ovine endometrium, but oxytocin treatment had no effect on the expression of these proteins (P > 0.10). ERK1/2 was the only phosphorylated MAPK detected and its concentrations were higher in oxytocin-treated ewes (P < 0.01). The objective of experiment 3 was to further investigate the role of ERK1/2 during oxytocin-induced PGF2alpha synthesis. Uteri were collected from four ovary-intact ewes on Day 14 postestrus. Caruncular endometrial explants were dissected and subjected to in vitro incubation. PD98059, a specific inhibitor of ERK1/2 activity, blocked the ability of oxytocin to stimulate PGF(2alpha synthesis in a dose-dependent manner (P < 0.05). These results indicate that the ovine oxytocin receptor is not coupled to G(i) proteins. These results indicate that oxytocin induces phosphorylation of ERK1/2 and that this MAPK appears to mediate oxytocin-induced PGF2alpha synthesis in ovine endometrium.

Effect of oxytocin on expression of cytosolic phospholipase A2 mRNA and protein in ovine endometrial tissue in vivo

The induction of endometrial prostaglandin (PG) F2alpha synthesis by oxytocin is dependent upon activation of phospholipase (PL) A2 and mobilization of arachidonic acid. The objective of this study was to determine if oxytocin stimulates PGF2alpha synthesis by inducing synthesis of cytosolic PLA2 (cPLA2). In Experiment 1, 15 ovariectomized ewes were given progesterone and estradiol to simulate an estrous cycle. Ewes were then given an injection of oxytocin on Day 14 of the simulated estrous cycle. Jugular blood samples were collected and assayed for 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM). Uteri were collected at 0, 7.5, 25, 90, or 240 min postinjection (n = 3 ewes/time point). Total RNA was isolated from caruncular endometrium and subjected to dot-blot analysis. Oxytocin induced a rapid and transient increase in serum PGFM (P < 0.01). However, endometrial concentrations of cPLA2 mRNA did not change following oxytocin administration (P > 0.10). In Experiment 2, 11 ovary-intact ewes were given oxytocin (n = 5) or saline (n = 6) on Day 15 after estrus. Jugular blood samples were collected and assayed for serum concentrations of PGFM. Uteri were collected at 15 min postinjection. Homogenates were prepared from caruncular endometrium and subjected to Western blot analysis. Concentrations of PGFM were higher in oxytocin treated ewes compared to saline treated ewes at 15 min postinjection (P < 0.01). Endometrial concentrations of cPLA2 protein were greater in the cytosolic than in the microsomal fraction (P < 0.01). Oxytocin did not affect the amount of cPLA2 protein in either fraction (P > 0.10). In conclusion, oxytocin did not effect expression of either cPLA2 mRNA or protein in ovine endometrium. Oxytocin may stimulate PGF2alpha synthesis by activating cPLA2 protein that is already present in an inactive form.

Effects of progesterone and estradiol on uterine secretion of prostaglandin f(2alpha)in response to oxytocin in ovariectomized sows

Thirty ovariectomized sows were used in an experiment designed to determine whether the ability of the porcine uterus to release prostaglandin (PG) F(2alpha) in response to oxytocin is regulated by progesterone (P(4)) and estradiol (E(2)). Sows were assigned to one of four treatment groups: 1) no steroids (ovariectomized controls; n = 8), 2) E(2) (n = 8), 3) P(4) (n = 7), or 4) E(2) + P(4) (n = 7). P(4) and E(2) were administered so as to mimic the normal temporal changes that occur in these hormones during the estrous cycle. A group of intact sows (n = 9) was included for comparison. All sows received an injection of oxytocin (30 IU, i.v.) on Days 12, 15, and 18 postestrus. Jugular venous blood samples were collected from 60 min before through 120 min after injection of oxytocin for quantification of 13,14-dihydro-15-keto-PGF(2alpha) (PGFM). Preinjection baseline concentrations of PGFM, the magnitude of the PGFM response above baseline, and area under the PGFM response curve (AUC) were calculated for each sow on each day and compared among treatment groups by ANOVA. Among the ovariectomized sows receiving steroid replacement, baseline concentrations of PGFM were low on Day 12 postestrus in all four groups. On Days 15 and 18, baseline concentrations remained low in the two groups that did not receive P(4) but increased in those that did. Both the magnitude of the response to oxytocin and AUC were small on Day 12 postestrus in all 4 groups. By Day 15, the magnitude of the response and AUC increased in the group that received both P(4) and E(2) but remained low in the other three groups. By Day 18, responses to oxytocin were greater in both groups that received P(4) than in those that did not. Baseline concentrations were similar in intact sows and in those that received both P(4) and E(2) on all three days examined. The magnitude of the response and the AUC were greater in the ovariectomized sows receiving P(4) and E(2) replacement than in the intact control sows on Days 15 and 18 postestrus. From these results, we conclude that P(4) and E(2) interact to control the time when the uterus begins to secrete PGF(2alpha) in response to oxytocin and the amount of PGF(2alpha) secreted.

Expression of a cytosolic phospholipase A2 by ovine endometrium on days 11-14 of a simulated oestrous cycle

Oxytocin stimulates the synthesis and secretion of PGF2 alpha from uterine tissues in vivo and in vitro late in the ovine oestrous cycle. The synthesis of eicosanoids is dependent upon the availability of free arachidonic acid which is released through the activity of arachidonate releasing phospholipases. In the present study, the following hypothesis was tested: the ovine endometrium expresses a cytosolic phospholipase A2 (cPLA2) and expression or activity of cPLA2 increases as uterine secretory responsiveness to oxytocin develops late in the oestrous cycle. Endometrial tissue was collected from cyclic ewes on day 15 of the oestrous cycle for the preparation of tissue homogenates and isolation of mRNA to determine whether ovine endometrium expressed a cPLA2. A 110 kDa band was detected by western blotting, indicating the presence of a putative ovine cPLA2. A 834 bp fragment of the ovine cPLA2 shared 87% homology with human and mouse cDNA, and northern blot hybridization analysis indicated a single 3.4 kb transcript. A total of 20 ewes were ovariectomized and treated with progesterone and oestrogen to simulate the oestrous cycle to determine whether the expression or activity of ovine cPLA2 changed during the onset of uterine secretory responsiveness to oxytocin in vivo. On days 11-14 (n = 5 per day) of a simulated oestrous cycle, caruncular endometrium was evaluated for expression of ovine cPLA2 mRNA and protein and the synthesis of PGF2 alpha in response to melittin (a potent stimulator of PLA2 activity). Immunoreactive cPLA2 and cPLA2 mRNA were observed on all days and did not increase during the development of uterine responsiveness to oxytocin in vivo. Similarly, melittin increased the synthesis of PGF2 alpha irrespective of day, indicating the presence of a functional cPLA2 on all days examined. These data indicate that the ovine endometrium expresses a functional cPLA2 and that ample concentrations of cPLA2 are present by day 11 of a simulated oestrous cycle.

Cellular mechanisms by which oxytocin mediates uterine prostaglandin F2 alpha synthesis in bovine endometrium: role of calcium

The objective of these experiments was to determine the role of Ca2+ during oxytocin-stimulated prostaglandin (PG) F2 alpha release from bovine endometrial tissue in vitro. Uteri were collected from dairy cows on the day after spontaneous luteal regression. Caruncular endometrial explants were dissected and incubated in vitro to determine phospholipase C activity or PGF2 alpha release. A23,187 (a calcium ionophore) and maitotoxin (an activator of voltage-gated L-type calcium channels) stimulated release of PGF 2 alpha in a concentration-dependent manner (P < 0.05). Thapsigargin (induces accumulation of Ca2+ in the cytoplasm by inhibiting endoplasmic reticulum Ca2+/ATPase pumps) stimulated release of PGF2 alpha in a concentration-dependent manner as well (P < 0.13). Oxytocin (10(-6) M), AIF4- (a nonspecific activator of G-proteins; 10(-5) M), A23,187 (10(-5) M), and melittin (a stimulator of phospholipase A2; 10(-4) M) stimulated PGF2 alpha release when explants were incubated in Ca(2+)-free medium (P < 0.10); however, oxytocin, A23,187, or melittin were unable to stimulate PGF2 alpha release when explants were incubated in Ca(2+)-free medium containing the calcium chelator EGTA (P < 0.10). This treatment did not prevent oxytocin or AIF4- from stimulating phospholipase C activity (P < 0.08). CoCl2 (a nonspecific Ca2+ channel blocker) and methoxyverapamil (a specific voltage-gated L-type Ca2+ channel blocker) prevented oxytocin from stimulating PGF2 alpha release (P < 0.05). Our results suggest that both extracellular and intracellular Ca2+ may be required for oxytocin to stimulate PGF2 alpha secretion in bovine endometrial tissue.

Concentrations of oxytocin in the intercavernous sinus of mares during luteolysis: temporal relationship with concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha

The reproductive tracts of nine thoroughbred mares were examined by ultrasound to determine the day of ovulation (day 0). Mares were fitted with intercavernous sinus cannulae on the day before the start of sample collection of pituitary venous effluent rich in oxytocin. Intercavernous sinus blood samples were collected for at least 36 h at 5 min intervals beginning at noon on day 13 (n = 2), day 15 (n = 5) or day 16 (n = 2) after ovulation. Concentrations of oxytocin and 13,14-dihydro-15-keto prostaglandin F2 alpha (PGFM) in plasma were determined by radioimmunoassay. Three high-magnitude surges of PGFM (> 1 ng ml-1) were found in these samples. Three high magnitude pulses of oxytocin (> 200 pg ml-1) were also observed, one associated with each of the PGFM surges. In each of these cases, the oxytocin pulse appeared to follow or coincide with the onset of the PGFM surge. Lower magnitude pulses of both hormones were detected throughout the bleeding period in every mare. The average interval between these pulses was 122.3 min for oxytocin and 121.0 min for PGFM. The interval between pulses for individual mares varied from 90 to 199 min for oxytocin, and from 87 to 213 min for PGFM. However, there was no correlation between PGFM and oxytocin pulse intervals among mares. Within each mare, there was no discernable association between low magnitude pulses of oxytocin and PGFM. From these data, it was concluded that high-magnitude surges of PGF2 alpha are associated with similar surges of oxytocin from the posterior pituitary gland, and that PGF2 alpha may induce their secretion. The posterior pituitary gland also appears to secrete oxytocin in a pulsatile manner at a frequency of approximately 1 pulse every 2 h but these pulses do not appear to be associated with the low magnitude pulses of PGF2 alpha secreted from the uterus.

Oxytocin- and aluminium fluoride-induced phospholipase C activity and prostaglandin F2 alpha secretion during the ovine luteolytic period

A series of studies was conducted to characterize changes in components of the cell signalling cascade that mediates oxytocin-induced prostaglandin F2 alpha (PGF2 alpha) synthesis at the onset of luteolysis in sheep. In the first experiment, caruncular tissue was dissected from 20 ewes on days 12-15 of the oestrous cycle, and incubated for the measurement of phospholipase C (PLC) activity or secretion of PGF2 alpha. Activation of GTP-binding proteins with aluminium fluoride stimulated both inositol phosphate accumulation and PGF2 alpha secretion on all days examined. However, oxytocin did not stimulate PLC activity or PGF2 alpha accumulation until day 13. While the ability of oxytocin to stimulate PLC activity increased after day 13, oxytocin-induced PGF2 alpha secretion declined slightly from day 13 to 15, suggesting that cell signalling components downstream from PLC modulate the response to oxytocin after day 13. Oxytocin failed to stimulate PGF2 alpha synthesis on day 14 after oestrus. Secretion of endogenous luteal oxytocin may have rendered uterine tissues collected on day 14 refractory to oxytocin in vitro. Therefore, a second study was conducted in ovariectomized, steroid replaced ewes. Ovarian steroids were administered to mimic endogenous changes in progesterone and oestradiol. The temporal patterns of PGF2 alpha synthesis in response to oxytocin and pharmacological agents were similar to uterine tissues from cyclic ewes in the first experiment; however, the magnitude of the response was less. These data suggest that oxytocin receptors are absent or are not coupled to PLC until day 13 after oestrus.

Effect of oxytocin on concentrations of prostaglandin H synthase-2 mRNA in ovine endometrial tissue in vivo

Oxytocin is an acute stimulus of prostaglandin (PG) F2alpha secretion from the ovine uterine endometrium. The high level of PGF2alpha secretion induced by oxytocin and the short half-life of the prostaglandin synthase-2 (PGHS-2) enzyme implies that synthesis of PGHS-2 may be essential at this time. The objective of this study was to determine if the increase in PGF2alpha secretion induced by oxytocin is associated with an increase in PGHS-2 mRNA. In experiment 1, oxytocin induced a rapid increase in serum concentration of 13,14-dihydro-15-keto-prostaglandin F2alpha (the stable metabolite of PGF2alpha; PGFM) that was detected within 7.5 min (P < 0.05) and peaked at 25 min post injection. This was associated with an unusually rapid increase in the concentration of PGHS-2 mRNA at 25 min post oxytocin injection (P < 0.05). Endometrial concentrations of PGHS-2 mRNA returned to basal levels at 90 min post injection. Experiment 2 was conducted to further characterize the time course of induction of PGHS-2 mRNA following oxytocin administration. Oxytocin induced a rapid increase in serum concentrations of PGFM. As in experiment 1, an increase in concentrations of PGHS-2 mRNA was detected at 25 min after oxytocin (P = 0.06). Concentrations of PGHS-2 mRNA were intermediate at 40 min and returned to basal levels at 60 min post injection. Thus, there is a rapid increase in endometrial concentrations of PGHS-2 mRNA following oxytocin stimulation of PGF2alpha secretion. This increase in PGHS-2 mRNA may be required to maintain PGHS-2 enzyme levels during pulsatile secretion of PGF2alpha at luteolysis.

Cellular mechanisms by which oxytocin stimulates uterine PGF2 alpha synthesis in bovine endometrium: roles of phospholipases C and A2

The objective of these experiments was to identify the cellular mechanisms by which oxytocin stimulates prostaglandin (PG) F2 alpha synthesis in bovine endometrial tissue. Uteri were collected on the day after spontaneous luteal regression. Caruncular endometrial explants were dissected and incubated in vitro to assess PGF2 alpha release or phospholipase (PL) C activity. Oxytocin (10(-6) M) stimulated PGF2 alpha release and PLC activity within 30 min of incubation (P < 0.01). The highest stimulation was observed at 100 min (P < 0.01). Oxytocin stimulated PLC activity at 10(-9) M and higher doses, whereas an increase in PGF2 alpha release was not detected until 10(-8) M (P < 0.09). Melittin, a stimulator of PLA2 activity, stimulated PGF2 alpha release at 10(-6) M and higher doses (P < 0.01). Aristolochic acid, an inhibitor of PLA2 activity, blocked the ability of oxytocin to stimulate PGF2 alpha release at 10(-5) M and higher doses (P < 0.01). Aristolochic acid (10(-4) M) reduced the stimulation of PGF2 alpha release induced by A1F4-, a nonspecific stimulator of G protein (10(-5) M) and melittin (10(-4) M; P < 0.05). Aristolochic acid had no effect on the ability of oxytocin or A1F4- to stimulate PLC activity (P > 0.10). By comparing the time course of stimulation and dose-response relationships between PGF2 alpha and PLC activity, it appears that oxytocin may stimulate PGF2 alpha secretion by activating PLC. The effects of melittin and aristolochic acid indicate that PLA2 may play a role in mediating the stimulatory effect of oxytocin on PGF2 alpha secretion, as well.

Effects of progesterone withdrawal on uterine secretion of prostaglandin F2 alpha in response to oxytocin in ewes

Two experiments were conducted to determine if withdrawal of progesterone during the luteal phase of the oestrous cycle affected the ability of the ovine uterus to secrete prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin. In Experiment 1, 18 ewes were ovariectomized on Day 9 and Day 12 after oestrus. Ewes were subdivided into three treatment groups (n = 6 per group): Group-1 ewes underwent sham surgery; Group-2 ewes received oestradiol (OVX + O); and Group-3 ewes received oestradiol + progesterone (OVX + O,P). Oxytocin was administered to each ewe on Days 10, 13 and 15 after oestrus. Concentrations of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) were determined in samples of jugular venous blood for 2 h after oxytocin challenge. The magnitude of the PGFM response 24 h after ovariectomy was greater (P < 0.1) in ewes from which progesterone had been withdrawn (OVX + O) than in ewes in which progesterone was maintained (intact controls and OVX + O,P). Therefore, progesterone appears to exert an inhibitory effect on uterine secretory responsiveness to oxytocin which is removed by progesterone withdrawal. In Experiment 2, ewes were ovariectomized on Day 11 and assigned to 1 of 4 treatment groups (n = 6 per group): Group 1, no steroid replacement (OVX); Group 2, oestradiol replacement (OVX + O); Group 3, progesterone replacement (OVX + P); or Group 4, progesterone + oestradiol replacement (OVX + O,P). Ewes received oxytocin on Day 12 and Day 15. On Day 12, uterine secretory responsiveness to oxytocin was greatest in ewes in the OVX + O group (P < 0.1). Responsiveness was low in ewes in the OVX group, as it was in ewes in both groups that received progesterone replacement. Therefore, the increase in uterine secretory responsiveness to oxytocin following progesterone withdrawal is dependent on oestradiol replacement.

Changes in uterine secretion of prostaglandin F2 alpha in response to oxytocin during the estrous cycle, early pregnancy, and estrogen-induced pseudopregnancy in swine

Thirty-one sows were used in an experiment designed to determine whether the ability of the porcine uterus to release prostaglandin (PG) F2 alpha in response to oxytocin was suppressed in pregnancy and pseudopregnancy. Sows were assigned to one of three treatment groups: nonbred (nonpregnant) controls (n = 8), pseudopregnant (5 mg estradiol benzoate, i.m., daily on Days 11-15 postestrus; n = 8), or bred (bred once daily throughout the estrous period; n = 15). Jugular venous blood samples were collected daily for quantification of progesterone. Pregnancy was determined by uterine examination at slaughter 51-72 days postmating. On the basis of progesterone and embryo recovery, bred sows were classified into three subgroups: confirmed pregnant (n = 4), suspected pregnant based on delayed luteal regression (n = 5), or bred/not pregnant (n = 6). All sows received an injection of oxytocin (30 IU, i.v.) on Days 12, 15, and 18 postestrus. Jugular venous blood samples were collected from 60 min prior to through 120 min after injection of oxytocin for quantification of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM). Magnitude of response above baseline and area under the PGFM response curve (AUC) were calculated for each sow on each day and compared among treatment groups by analysis of variance. Responses in pregnant and suspected-pregnant sows were not different on any day examined; therefore the two groups were combined (n = 9) and considered pregnant for all subsequent analyses. Responses in the nonpregnant and bred/not pregnant sows were pooled and compared to the responses in the pregnant and pseudopregnant sows. Magnitudes of response were similar between these pooled groups on Day 12 (p > 0.5), but were less in pregnant and pseudopregnant sows on Days 15 and 18 (p < 0.01). When nonpregnant and bred/not pregnant sows were compared to each other, the magnitudes of the response were similar on Days 12, 15, and 18 (p > 0.3 on each day). In contrast, when pregnant and pseudopregnant sows were compared, pseudopregnant sows had a lower magnitude of response that was consistent across all 3 days (p < 0.02). Similar relationships were apparent for the AUC. These results demonstrate that uterine secretory responsiveness to oxytocin is suppressed during early pregnancy and that this effect may be mediated through estrogen secreted by conceptuses.

Luteolytic effect of prostaglandin F2 alpha and two metabolites in ewes

Twenty-three ewes were used in an experiment to determine the point in metabolism at which prostaglandin (PG) F2 alpha loses its luteolytic activity. Ewes exhibited at least one normal estrous cycle (15 to 19 d) and then were randomly assigned to one of four treatment groups: 1) control, 2) PGF2 alpha, 3) 15-keto-PGF2 alpha, or 4) 13,14-dihydro-15-keto-PGF2 alpha (PGFM). Each ewe received an i.m. injection of the designated treatment (5 mg in 1 mL of sterile saline) during the midluteal phase of the estrous cycle (d 8, 9, 10, or 11 after estrus). An identical second injection was given to each ewe 3 h after the first injection. Beginning at 9 h after injection, concentrations of progesterone were lower (P < .01) in the PGF2 alpha-treated ewes than in ewes in the other three groups. These differences were maintained throughout the duration of the 48-h sampling period in five of the six ewes that received PGF2 alpha. None of the ewes in the other three treatment groups exhibited any change in concentrations of progesterone. Ewes were classified as completing luteolysis if concentrations of progesterone decreased to less than 1 ng/mL within 48 h after the first injection. Five of the six ewes receiving PGF2 alpha completed luteolysis (P < .05), whereas none of the ewes in the other three groups completed luteolysis. The interestrous interval was reduced by approximately 5 d in the PGF2 alpha-treated group compared with the other three treatment groups (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular mechanisms mediating the stimulation of ovine endometrial secretion of prostaglandin F2 alpha in response to oxytocin: role of phospholipase A2

Four experiments were conducted to determine whether phospholipase (PL) A2 mediates the stimulatory effect of oxytocin on the release of prostaglandin (PG) F2 alpha from ovine endometrial tissue. Caruncular endometrial tissue was collected from ovariectomized ewes on the day after a steroid replacement protocol had been completed. The replacement protocol consisted of progesterone for 10 days (12 mg/day) followed by oestradiol on days 10 and 11 (100 micrograms/day) and had been shown previously to provide endometrial tissue that would release PGF2 alpha in response to oxytocin in vitro. In experiment 1, oxytocin (10(-7) M) and melittin (1.76 x 10(-6) M; a stimulator of PLA2) stimulated release of PGF2 alpha from tissue explants (P < 0.05). Aristolochic acid (10(-4) M; an inhibitor of PLA2) decreased oxytocin- and melittin-induced release of PGF2 alpha by 77% and 71% respectively (P < 0.05). Experiment 2 was conducted to establish the minimum inhibitory dose of aristolochic acid. Basal release of PGF2 alpha was inhibited at 10(-5) M aristolochic acid, but 10(-4) M was required to block the stimulatory effect of oxytocin. Experiment 3 was carried out to identify the precise intracellular locus at which aristolochic acid was exerting its effect. Oxytocin (10(-7) M), AlF4- (5 x 10(-2) M NaF, 10(-5) M AlCl3), melittin (1.76 x 10(-6) M) and arachidonic acid (AA; 20 micrograms/ml) stimulated release of PGF2 alpha (P < 0.05). Aristolochic acid (10(-4) M) blocked the release of PGF2 alpha stimulated by oxytocin, AlF4- or melittin by > 80% (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular mechanisms mediating the stimulation of ovine endometrial secretion of prostaglandin F2 alpha in response to oxytocin: role of phospholipase C and diacylglycerol

The first objective was to describe and evaluate the relationship between the ability of oxytocin to stimulate the activity of phospholipase (PL) C and its ability to stimulate the release of prostaglandin (PG) F2 alpha in ovine endometrial tissue. Caruncular endometrial tissue was collected from ovariectomized ewes after completion of an 11-day steroid replacement protocol. In experiment 1, explants were incubated either in the presence (10(-6) M) or absence of oxytocin for 0, 1, 3, 10, 30 or 100 min to examine the time-course for activation of PLC and release of PGF2 alpha in response to oxytocin. An increase in the activity of PLC was detected at 3 min while an increase in the release of PGF2 alpha was not detected until 10 min (P < 0.05). In experiment 2, explants were incubated in the presence of various oxytocin analogues (10(-6) M) to compare their abilities to activate PLC and release PGF2 alpha. Oxytocin and three receptor agonists stimulated the activity of PLC and the release of PGF2 alpha (P < 0.05) while two oxytocin receptor antagonists had no effect on either response. In experiment 3, explants were incubated in the presence of oxytocin or arginine vasopressin at 10(-9) to 10(-6) M to establish dose-response curves for the activation of PLC and release of PGF2 alpha. For both hormones, significant increases (P < 0.05) in the release of PGF2 alpha were observed at 10(-8) M while increases in PLC activity were not detected until 10(-7) M was used. In experiment 4, explants were pretreated with either U-73122 (an inhibitor of PLC activity) or U-73343 (an inactive analogue of U-73122). Explants were then treated with control medium, oxytocin or AlF4-. Both oxytocin and AlF4-stimulated the activity of PLC and the release of PGF2 alpha (P < 0.05). U-73122 blocked the ability of oxytocin to stimulate the release of PGF2 alpha (P < 0.05) but had no effect on its ability to stimulate the activity of PLC (P > 0.1). Based on the results from these experiments, the role of PLC in mediating the stimulatory effect of oxytocin on the release of PGF2 alpha remains unclear. The second objective was to evaluate the role of diacylglycerol (DAG) in mediating the stimulatory effect of oxytocin on endometrial secretion of PGF2 alpha. In experiment 5, explants were incubated in vitro with varying doses of two DAG analogues.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in peripheral concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha induced by progesterone in swine

This experiment was designed to examine the effects of progesterone on endogenous and oxytocin-induced secretion of prostaglandin F2 alpha (PGF2 alpha) in sows. Peripheral concentrations of 13,14-dihydro-15-keto-PGF2 alpha (PGFM) were used as an indirect measure of uterine PGF2 alpha secretion. Eight sows received twice daily injections of progesterone (160 mg/injection) on d 1 to 5 after estrus. Another eight sows received comparable injections of a corn oil injection vehicle. Each sow then received i.v. injections of oxytocin (30 IU) on d 10, 12, and 15 after estrus. Concentrations of PGFM were determined in jugular venous blood samples collected at -60, -45, -30, -15, 0, 2, 5, 10, 15, 30, 45, 60, 90, and 120 min after each oxytocin injection. The mean concentrations of PGFM in samples collected before injection of oxytocin (baseline), the magnitude of the PGFM response to oxytocin, and the area under the PGFM response curve (AUC) were calculated for the three oxytocin challenges administered to each sow. Baseline, magnitude, and AUC were low on d 10 after estrus and similar for the two treatment groups. On d 12 baseline, magnitude, and AUC remained low in the control sows; however, all three response variables increased in sows that received progesterone. By d 15, all three variables were high and similar in both treatment groups. In conclusion, progesterone, administered early in the estrous cycle, seems to promote premature secretion of PGF2 alpha as indicated by the high basal concentrations of PGFM observed before injection of oxytocin on d 12.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of bovine somatotropin on reproductive function in lactating dairy cows

Several recent experiments have reported that chronic treatment with bovine somatotropin (bST) increased the number of days open without affecting the services per conception. The physiological basis for these effects was examined. Eleven lactating Holstein cows received daily injections of bST (40 mg) and 10 received daily injections of vehicle. Treatment was initiated between 32 and 85 d post partum and continued for up to 180 d. Eight of 11 bST-treated cows experienced at least one period of extended ovarian acyclicity during treatment. Only 3 of 10 control cows did so (P = 0.05). Concentrations of progesterone during luteal phases were lower in bST-treated cows than in controls (P = 0.06). Baseline concentrations of LH were suppressed in bST-treated cows compared with those of controls (P < 0.04). Neither the pulse frequency of LH nor the expression of estrous behavior was affected by bST (P > 0.30). These results indicate that chronic administration of a high dose of bST can reduce reproduction performance by promoting ovarian acyclicity.

Regulation of pulsatile secretion of prostaglandin F2 alpha from the ovine uterus by ovarian steroids

Two experiments were conducted to determine how progesterone and oestradiol regulate pulsatile secretion of PGF2 alpha from the ovine uterus. In Expt 1, ovariectomized ewes received: (1) no treatment, (2) oestradiol, (3) progesterone, or (4) oestradiol and progesterone (n = 5 ewes per treatment group) to approximate the changes in steroids that occur during the oestrous cycle. Jugular venous blood samples were collected at 30 min intervals for 48 h beginning at 08:00 on day 14 of steroid replacement. Blood samples were collected from five intact ewes at a comparable time of the oestrous cycle for comparison. The number and magnitude of pulses in 13,14-dihydro-15-keto-PGF2 alpha (PGFM) in jugular venous blood samples were used to assess uterine secretion of PGF2 alpha. Experiment 2 was conducted as Expt 1, except that the progesterone replacement protocol was modified to duplicate more closely the temporal pattern of progesterone observed in intact ewes. Results were similar in both experiments. Intact ewes averaged 4.4 +/- 0.6 pulses per 48 h blood sampling period. The frequency of pulses was less in ovariectomized ewes (P < 0.05). The number of pulses was increased by progesterone treatment (P < 0.01); the number of pulses in ovariectomized ewes receiving progesterone replacement was similar to that observed in intact ewes. There was a tendency for oestradiol to have a positive effect on the number of pulses (P = 0.12). The magnitude of pulses in intact ewes averaged 419 +/- 38 pg ml-1 and was much less in ovariectomized ewes (P < 0.05) than in intact ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Activity of phospholipase C and release of prostaglandin F2 alpha by endometrial tissue from ewes during the oestrous cycle and early pregnancy

Oxytocin appears to play an important role in regulating uterine secretion of prostaglandin F2 alpha (PGF2 alpha) in sheep. Changes in uterine secretion of PGF2 alpha throughout the oestrous cycle and early pregnancy may be due to changes in the intracellular regulatory pathways that control synthesis of PGF2 alpha in response to oxytocin. In this experiment, caruncular endometrial tissue was collected from ewes throughout the oestrous cycle and early pregnancy. Endometrial tissue was incubated in vitro to assess release of PGF2 alpha and activity of phospholipase C (PLC) in response to oxytocin. Release of PGF2 alpha in the presence of arachidonic acid was used to assess the activity of prostaglandin H2 endoperoxide synthase (PGS). In non-pregnant ewes, oxytocin stimulated release of PGF2 alpha from endometrial tissue collected on days 14 and 16, but not on days 4-7, 10 or 12 after oestrus. This coincided with times when oxytocin stimulated the activity of PLC. Release of PGF2 alpha was enhanced by the addition of arachidonic acid to tissues collected on days 12, 14 and 16 after oestrus. As with tissue from nonpregnant ewes, oxytocin could stimulate release of PGF2 alpha on days 14 and 16 of early pregnancy. Yet, oxytocin had no effect on activity of PLC in tissue from pregnant ewes. Release of PGF2 alpha in the presence of arachidonic acid by tissue from pregnant ewes was similar to that in nonpregnant ewes at comparable times after oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of copper status on luteinizing hormone secretion in dairy steers

Two experiments were conducted to examine the effects of Cu status on neuroendocrine regulation of LH secretion in dairy steers. In Experiment 1, 18 Holstein steers were assigned randomly to treatment groups in a completely randomized design. Treatments consisted of basal diet alone (control) or supplemented with 5 ppm of Mo or with 20 ppm of Cu. At 8 and 16 wk, Cu concentrations in liver were higher in the group receiving Cu and lower in the group receiving Mo than in the control. Pulse frequencies of LH were not affected by any treatment. Serum LH concentration at 16 wk tended to be lower in the group receiving Mo than in either the control or the group receiving Cu. The ability of the pituitary gland to release LH in response to GnRH was not affected at 17 wk. Concentrations of LH in the pituitary glands were lower in the group receiving Mo than in that receiving Cu or in the controls. No differences in Cu or Mo concentrations were observed in pituitary, median eminence, or hypothalamic tissues. In Experiment 2, 12 Holstein steers were assigned to treatment groups receiving the basal diet supplemented with either 20 ppm or Cu or with 10 ppm of Mo. Spontaneous and GnRH-induced secretion of LH were not influenced by treatments after 8 mo of experiment. Reduction in Cu status has little effect on the endogenous secretion of LH in dairy steers.

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.

Uterine secretion of prostaglandin F2 alpha in the ewe: regulation at the cellular level by ovarian hormones and the conceptus

Changes in the ability of the uterus to secrete prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin may play a critical role in determining when endogenous secretion of PGF2 alpha begins. The cellular mechanisms that regulate uterine secretion of PGF2 alpha in response to oxytocin have not been completely defined. Several intracellular components that may contribute to this regulation have been studied, including phospholipase C (PLC), prostaglandin H endoperoxide synthase (PGS) and receptors for oxytocin. All of these components change during the oestrous cycle and are associated with the development of uterine secretory responsiveness to oxytocin. Progesterone appears to play the principal role in regulating oxytocin receptors, PLC and PGS. The conceptus appears to suppress the increase in receptors for oxytocin and PLC activity that typically occurs around the time of luteal regression.

Changes in uterine secretion of prostaglandin F2 alpha and luteal secretion of progesterone in response to oxytocin during the porcine estrous cycle

The purpose of this experiment was to determine whether the ability of oxytocin to stimulate uterine secretion of prostaglandin F2 alpha (PGF2 alpha) and luteal secretion of progesterone changes during the porcine estrous cycle. Nineteen multiparous sows were observed for estrus. After one estrous cycle of normal length, sows were assigned randomly to receive an injection of oxytocin (30 IU, i.v.) in the EARLY (Days 4-6; n = 6), MID (Days 9-11; n = 7), or LATE (Day 15; n = 6) stage of the estrous cycle. Concentrations of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) and progesterone were determined in jugular venous serum samples collected at -60, -45, -30, -15, 0, 2, 5, 10, 15, 30, 45, 60, 90, and 120 min after injection of oxytocin. The magnitudes of the PGFM and progesterone responses and the area under the respective response curves (AUC) were calculated for each sow. Concentrations of PGFM did not change in response to oxytocin administered during the EARLY or MID portions of the estrous cycle. Concentrations increased rapidly in 4 of 6 sows that received oxytocin LATE in the estrous cycle. Both magnitude and AUC were greater LATE in the estrous cycle than at either EARLY or MID cycle (p less than 0.05). Thus, uterine secretory responsiveness to oxytocin develops between Days 11 and 15 postestrus in the sow. For progesterone, a transient increase was observed immediately following injection of oxytocin at MID cycle (p less than 0.05), but not at the other times examined. Therefore, oxytocin appears to be capable of stimulating secretion of progesterone from the functionally mature corpus luteum.

Effect of dietary energy and previous bovine somatotropin on milk yield, mastitis, and reproduction in dairy cows

Thirty multiparous lactating Holstein cows were blocked according to time of calving and assigned to a 2 x 3 factorial arrangement of treatments in a randomized complete block design to evaluate the effects of two dietary energy concentrations either without or with bST (20.6 mg/d per cow) administered to cows that had not or had received bST during the preceding lactation. Subcutaneous injection of bST began 28 to 35 d postpartum and continued for 39 wk. The dietary energy concentration x bST interaction was not significant for any response variable. Compared with DMI of control cows, DMI was higher for cows receiving bST, being 1.6 and 2.4 kg/d higher for cows receiving bST for one and two lactations, respectively. Milk, fat, and protein yields were higher for cows receiving bST than for controls. Those receiving bST for a second lactation also produced more milk than controls until wk 20; thereafter, milk yields were similar to those of controls. Somatotropin administration had no adverse effect on udder health. Cows receiving bST tended to ovulate less regularly than controls, which may be attributed to their higher milk yield. However, BW gains during lactation were similar for all treatments, indicating that bST-treated cows built energy reserves for the subsequent lactation. Although energy concentrations of the diets had no significant impact on yield, the higher energy diet tended to depress milk fat concentration. Administration of bST to dairy cows for a second, consecutive lactation yielded responses similar for the first 20 wk of the study to those receiving bST for the first time. However, after wk 20, milk yield was less than that by cows receiving bST for the first lactation but similar to that of control cows.

Hormonal regulation of uterine secretion of prostaglandin F2 alpha during luteolysis in ruminants

In recent years, considerable progress has been made in our understanding of the endocrine mechanisms that control the pattern and timing of uterine secretion of prostaglandin F2 alpha (PGF2 alpha) during luteolysis in ruminants. Oxytocin may be important in establishing a pulsatile pattern of secretion. Neurohypophyseal oxytocin appears to be released in a pulsatile fashion and may initiate each episode of PGF2 alpha secretion from the uterus. Uterine PGF2 alpha stimulates release of oxytocin from the corpus luteum. Luteal oxytocin further stimulates secretion of PGF2 alpha from the uterus and may induce a transient refractoriness of the uterus to subsequent stimulation with oxytocin. Uterine refractoriness subsides after approximately 6 h. A similar desensitization phenomenon occurs in response to PGF2 alpha at the level of the corpus luteum. Together, uterine and luteal refractoriness may account for the interval between pulses of PGF2 alpha observed during luteolysis. Uterine secretory responsiveness to oxytocin increases at luteolysis, when endogenous, pulsatile secretion of PGF2 alpha normally begins. Thus, the acquisition by the uterus of responsiveness to oxytocin may determine when endogenous secretion of PGF2 alpha occurs during the estrous cycle. Uterine secretory responsiveness to oxytocin develops slowly, in the presence of progesterone. Progesterone exerts two types of effects that contribute to the regulation of PGF2 alpha secretion. First, prolonged exposure to progesterone appears to promote uterine accumulation of arachidonic acid, prostaglandin endoperoxide synthase, and other substances needed for synthesis of PGF2 alpha. Second, progesterone exerts a suppressive effect on secretion, which wanes after prolonged exposure. Together, these effects of progesterone ensure that PGF2 alpha is secreted only at the appropriate time to induce luteolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of progestagen treatment on concentrations of prostaglandins and oxytocin in plasma from the posterior vena cava of post-partum beef cows

The role of PGF-2 alpha in determining the lifespan of corpora lutea in the post-partum beef cow was investigated. In control cows (N = 5) induced to ovulate at Day 28 to 36 post partum by injection of 1000 i.u. hCG, corpora lutea had an average lifespan of only 8 days. In cows pretreated with 6 mg implants of a progestagen (norgestomet, N = 4) for 9 days, with implant removal 2 days before injection of hCG, luteal lifespan averaged 17.5 days. Concentrations of PGF-2 alpha in 9 hourly samples of plasma collected from the posterior vena cava via indwelling catheters were higher on Days 4 through 9 after injection of hCG (P less than 0.05) in the cows with short-lived corpora lutea. Greater release of PGF-2 alpha could therefore be a major factor in premature luteal regression. Concentrations of PGFM and oxytocin did not differ between cows with corpora lutea of short or normal lifespan. In a second experiment, concentrations of PGF-2 alpha in plasma from the posterior vena cava were examined during treatment with norgestomet (N = 8) or in contemporary controls (N = 7). In progestagen-treated cows, PGF-2 alpha was higher than in control cows (P less than 0.05), beginning on Day 3 of treatment and peaking on Day 5. It is concluded that the post-partum uterus increases secretion of PGF-2 alpha very early after first exposure to endogenous or exogenous progestagen.

Activity of phospholipase C and release of prostaglandin F2 alpha by endometrial tissue from ovariectomized ewes receiving progesterone and estradiol

Progesterone and estradiol interact to regulate secretion of prostaglandin (PG) F2 alpha from the ovine endometrium in response to oxytocin. Two experiments were conducted to determine if these effects were due to changes in activity of phospholipase C or in the second messenger responsive pathways that regulate production of PGF2 alpha. In both experiments, ovariectomized ewes were assigned to one of four treatment groups (control, estradiol, progesterone, progesterone and estradiol). Steroids were administered, in vivo, to mimic the changes that occur during the estrous cycle. On Day 16 of steroid treatment, endometrial tissue was collected and incubated, in vitro, to measure activity of phospholipase C and release of PGF2 alpha. Treatment with progesterone, in vivo, enhanced basal and oxytocin-induced activity of phospholipase C and release of PGF2 alpha, in vitro. Estradiol suppressed oxytocin-induced activity of phospholipase C, both in the presence and absence of progesterone. In contrast to its effects on phospholipase C, estradiol inhibited basal and oxytocin-induced release of PGF2 alpha when administered alone, but not when administered with progesterone. Steroids had similar effects on the release of PGF2 alpha induced by phorbol 12-myristate 13-acetate and A23187. It was concluded that progesterone and estradiol regulate endometrial release of PGF2 alpha by affecting both the activity of phospholipase C and its associated second messenger responsive pathways that may regulate production of PGF2 alpha.

Physiological responses to intramammary or intravenous treatment with endotoxin in lactating dairy cows

Twenty-one, middle to late lactation Holstein cows were assigned to one of three treatments in a completely randomized design to examine physiological changes associated with intramammary or intravenous administration of Escherichia coli endotoxin. Treatments were 1) Hank's balanced salt solution infusion in two contralateral quarters (control), 2) E. coli endotoxin infusion in two contralateral quarters, and 3) intravenous infusion of E. coli endotoxin. Blood was sampled and rectal temperature was measured at 30-min intervals. Endotoxin treatment was at 0900 h and sampling continued until 1700 h. Serum prolactin, cortisol, and 13,14-dihydro-15-keto-prostaglandin F2 alpha were measured. A pyretic response was observed in intravenous and intramammary treatment groups after endotoxin treatment. Response peak was higher (41.1 vs. 40.3 degrees C) and occurred later (6 vs. 4.5 h posttreatment) in the intramammary than the intravenous treatment group. Significant prolactin peaks were observed also in intravenous and intramammary endotoxin treatment groups. Prolactin peaked higher (288 vs. 112 ng/ml) and occurred sooner (1 vs. 4 h posttreatment) in the intravenous than in the intramammary treatment group. Cortisol followed a trend similar to prolactin. Cortisol peaked higher (100 vs. 82 ng/ml) and sooner (2.5 vs. 4.5 h posttreatment) in the intravenous than in the intramammary treatment group. Concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha increased rapidly posttreatment in the intravenous group only.

Effects of testosterone and 5alpha-dihydrotestosterone on luteal lifespan in dairy heifers

Endogenous concentrations of testosterone increase approximately 7 d prior to estrus in cattle and goats. Inhibition of testosterone synthesis results in a delay of luteal regression in both species. The purpose of this experiment was to determine if treatment with testosterone or 5alpha-dihydrotestosterone (DHT), 2 to 6 d prior to the endogenous rise in testosterone, would result in premature luteal regression. Sixteen heifers were randomly assigned to one of three treatment groups: 1) Control (n = 6); 2) testosterone (100 mug, n = 5); or 3) DHT (100 mug, n = 5). Each heifer received a single injection of the appropriate steriod on Day 8, 9, 10, 11 or 12 post estrus. Jugular venous blood samples were collected at frequent intervals for 24 h to quantify testosterone, and then daily for 14 d to quantify progesterone. Concentrations of testosterone increased within 15 min of injection of testosterone, and reached a maximum at 30 min. Concentrations were maintained at > 2 ng/ml throughout the first 24 h after injection. Based on concentrations of progesterone, neither androgen had any effect on the lifespan of the corpus luteum or the level of luteal function.

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

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

Effects of adrenalectomy on serum concentrations of progesterone during the luteal phase of sheep

An experiment was conducted to test the hypothesis that the adrenal gland influences luteal activity in sheep. Twelve Finnish Landrace x Southdown ewes were either bilaterally adrenalectomized (n = 6) or sham adrenalectomized (n = 6) during the breeding season. At approximately 37 and 47 d after surgery, all ewes received intramuscular injections of cloprostenol to synchronize estrus. Blood samples were taken via jugular venipuncture at 48-h intervals between 1 and 19 d after the last cloprostenol treatment. Serum concentrations of progesterone were determined in each of these samples. Analysis of variance showed that concentrations of progesterone during the luteal phase were lower (P<0.05) in adrenalectomized ewes than in sham-operated controls, but that patterns of progesterone were similar for both groups of sheep. Based on these results, we conclude that the adrenal gland does not appear to be necessary for initiation of luteal regression in ewes.

Effects of progesterone and estradiol-17 beta on uterine secretion of prostaglandin F2 alpha in response to oxytocin in ovariectomized ewes

Twenty ovariectomized ewes were used in an experiment designed to examine the interaction of progesterone, estradiol, and oxytocin in the regulation of uterine secretion of prostaglandin F2 alpha (PGF2 alpha). All ewes underwent a steroid pretreatment that mimicked the changes in progesterone and estradiol which occur during the six days immediately prior to estrus. After pretreatment, ewes were randomly assigned to 1 of 4 treatment groups: 1) control (n = 4); 2) estradiol-17 beta (n = 6); 3) progesterone (n = 4); and 4) progesterone and estradiol-17 beta (n = 6). Progesterone was injected twice daily for 15 days. The dose of progesterone varied with day postestrus in a manner designed to simulate endogenous luteal secretion of progesterone. Estradiol-17 beta was administered in s.c. Silastic implants. The implants maintained circulating concentrations of estradiol at 3 pg/ml. On Days 5, 10, and 15 of treatment, ewes were injected with oxytocin (10 IU in 1.0 ml saline, i.v.). Jugular venous blood samples were collected beginning one-half hour prior to and continuing for 2 hours post-oxytocin injection for quantification of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). No changes in concentration of PGFM following injection of oxytocin were observed on Day 5 or 10 in any treatment group. Concentrations of PGFM increased following injection of oxytocin on Day 15 only in groups receiving progesterone. Both the area under the PGFM response curve (p = 0.08) and peak response (p = 0.06) were greater in ewes treated with progesterone and estradiol-17 beta than in those receiving progesterone alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of phospholipase C in mediating oxytocin-induced release of prostaglandin F2 alpha from ovine endometrial tissue

Two experiments were conducted to determine if the ability of oxytocin to stimulate release of prostaglandin (PG)F2 alpha from ovine uterine tissue involved activation of phospholipase C (PLC). In the first experiment, 9 ewes were injected with progesterone for 11 d (12 mg/d, im). On days 11 and 12, ewes received an injection of estradiol (100 micrograms, im). Caruncular endometrial tissue was collected on d 13 and incubated in the presence or absence of oxytocin (10(-6) M). Concentrations of PGF2 alpha and its metabolite, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), in culture media were determined by radioimmunoassay. PLC activity was determined by measuring the intracellular accumulation of 3H-inositol phosphates after preincubation with 3H-inositol. Concentrations of PGF2 alpha and total PGF (PGF2 alpha + PGFM) in culture media were greater for explants treated with oxytocin than for controls (p. less than .02, p less than .06, respectively). A similar effect of oxytocin on intracellular concentrations of 3H-inositol phosphates was observed (p less than .01). A second experiment was conducted to determine if agonists of second messengers, produced by activation of PLC, could stimulate release of PGF2 alpha from ovine endometrial tissue. Seven ewes were treated with progesterone and estradiol as in experiment 1. Explants of caruncular tissue from each ewe were incubated with 1) control medium, 2) A23187 (10(-5) M), 3) oxytocin (10(-6) M), 4) phorbol 12-myristate 13-acetate (PMA, 10(-7) M), 5) PMA + A23187 and 6) PMA + oxytocin. Significant stimulatory effects of oxytocin, PMA and A23187 on concentrations of PGF2 alpha and total PGF in culture media were observed (p. less than .05, p less than .1, p less than .1, respectively). In conclusion, oxytocin stimulated release of PGF2 alpha and activity of PLC in explants of ovine endometrial tissue in vitro. Second messengers associated with activation of PLC enhanced release of PGF2 alpha from ovine endometrial tissue.

Effect of an estrogen antagonist (tamoxifen) on cloprostenol-induced luteolysis in heifers

Experiments were conducted to determine the role of estrogens on endogenous PGF2 alpha secretion and luteolysis following injection of cloprostenol in heifers. In Exp. 1, eight luteal-phase heifers were used to evaluate tamoxifen (T) as an estrogen antagonist. Heifers received T (35 mg i.v.) or ethanol:saline vehicle (ES) every 4 h for 44 h. All received cloprostenol (500 micrograms i.m.) immediately after the start of T or ES, and received estradiol-17 beta (500 micrograms i.m.) 12 h later. Each ES heifer had a surge of luteinizing hormone (LH) within 48 h of estradiol injection, whereas T-treated heifers did not. Estrus was observed in three ES-treated heifers, but not in T-treated heifers. In Exp. 2, 10 heifers received T (35 mg i.v.) or ES every 4 h for 64 h beginning on d 15 postestrus. Cloprostenol (500 micrograms i.m.) was injected 16 h after the start of treatment. Concentrations of LH were similar (P greater than .05) in both groups. In ES heifers, concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) increased; in T-treated heifers, PGFM remained at pre-cloprostenol levels. Luteolysis was induced in all heifers. Progesterone (P4) decreased to less than or equal to 1 ng/ml at similar (P greater than .05) rates in ES-treated and T-treated heifers. Mean concentration of P4 288 h post-cloprostenol was greater (P less than .05) in ES-treated than in T-treated heifers. Three ES-treated heifers, but no T-treated heifers, were in standing estrus. We conclude that T effectively antagonizes estrogen in cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

Maintenance of the corpus luteum of early pregnancy in the ewe. IV. Changes in luteal sensitivity to prostaglandin F2 alpha throughout early pregnancy

Two experiments were conducted to examine the temporal aspects of luteal resistance to the luteolytic effect of prostaglandin (PG) F2 alpha during early pregnancy. In Exp. 1, 14 pregnant and 12 nonpregnant ewes were treated with PGF2 alpha either on d 10 or 13 post-estrus. Jugular venous blood samples were collected at -30 min, 0, 6, 12, 18, 24, 30 and 36 h post-injection for quantification of progesterone. The difference (delta P) between pre-treatment and post-treatment concentrations of progesterone was calculated for each ewe. There was a significant interaction between pregnancy status and day of treatment on delta P (P less than .05). Pregnant and nonpregnant ewes treated on d 10 showed a large delta P. A large delta P also was observed in nonpregnant ewes treated on d 13 post-estrus. However, delta P in pregnant ewes treated on d 13 was smaller than in the other three groups (P less than .05). The temporal patterns of concentrations of progesterone in serum were different among treatment groups (P less than .05). A suppression in the concentration of progesterone was observed by 24 h post-injection in all four treatment groups. Progesterone returned to pre-treatment levels only in pregnant ewes treated on d 13. In Exp. 2, 47 pregnant ewes were treated with PGF2 alpha on d 10, 13, 16, 19, 22, 26 or 30 postestrus. Blood samples were collected and data were analyzed as described for Exp. 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in the lateral mobility of receptors for luteinizing hormone (LH) in the luteal cell plasma membrane when occupied by ovine LH versus human chorionic gonadotropin

Receptors for LH are internalized by ovine luteal cells 50 times slower when occupied by hCG than when occupied by ovine LH (oLH). To determine if differences in the rate of internalization were due to differences in the lateral mobility of the hormone-receptor complexes in the cell membrane, the diffusion coefficients of oLH- and hCG-LH receptor complexes were measured using fluorescence photobleaching recovery methods. Tetramethylrhodamine isothiocyanate (TRITC)-labeled oLH and hCG, which retained full ability to bind to receptor, were bound to LH receptors on enzymatically dispersed ovine luteal cells. Molecules labeled with TRITC within a 3-micron 2 region of the cell surface were bleached by a 500-msec pulse of 3 mW laser light at a wavelength of 514.5 nm. The laser beam intensity was then attenuated 20,000-fold, and fluorescence from the bleached area was measured by single photon counting as unbleached fluorescent hormone-receptor complexes diffused into the region. Data were analyzed on-line by a NOVA 3/12 computer. The oLH-LH receptor complex had a diffusion coefficient of 1.9 +/- 1.0 X 10(-10) cm2/sec-1, a value comparable to that of cell surface proteins nonspecifically labeled with succinylated Concanavalin A. Fluorescence recovery after photobleaching was 35%. In contrast, hCG-LH receptor complexes were immobile on the time scale of the experiment, implying that the diffusion coefficient was substantially less than 1 X 10(-11) cm2/sec-1. Deglycosylated hCG-TRITC bound to LH receptor had a diffusion coefficient (1.1 +/- 0.1 X 10(-10) cm2/sec-1) similar to that of receptors occupied by oLH. Thus, it appears that the carbohydrate portion of the hCG molecule plays a role in decreasing the mobility of the receptor for LH. These data demonstrate that the rate of lateral movement of the LH receptor in the plasma membrane of luteal cells appears to be modulated by the nature of the bound hormone.

Maintenance of the corpus luteum of early pregnancy in the ewe. III. Differences between pregnant and nonpregnant ewes in luteal responsiveness to prostaglandin F2 alpha

The effects of pregnancy and number of corpora lutea on luteal regression induced with prostaglandin F2 alpha (PGF2 alpha) were examined in 93 ewes. Bred and nonpregnant ewes were assigned randomly to receive a single im injection of PGF2 alpha: 0, 2, 4, 6, 8 or 10 mg/58 kg body weight. Injections were given on d 13 postestrus. The concentration of progesterone in serum 24 h after PGF2 alpha injection was affected by dose (P less than .001). The effect of pregnancy and the interaction of pregnancy with number of corpora lutea on levels of progesterone in serum were significant (P less than .05); therefore, data were partitioned according to pregnancy status and analyzed separately. There was an effect of number of corpora lutea on serum concentration of progesterone in pregnant (P less than .01) but not nonpregnant ewes (P greater than .10). Similar relationships among groups were observed for the concentration of progesterone in luteal tissue. In nonpregnant ewes the minimum dose of PGF2 alpha to produce a significant suppression of progesterone in serum (P less than .05) was 4 mg/58 kg body weight. In pregnant ewes with one or two corpora lutea, the minimum effective doses were 6 and 10 mg/58 kg body weight, respectively. The concentration of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum was related to the dose of PGF2 alpha injected. There were no differences in the concentration of PGFM in serum between pregnant and nonpregnant ewes either before or after injection. Corpora lutea of early pregnancy appear to be resistant to the luteolytic effect of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations of prostaglandins E2, F2 alpha and 6-keto-prostaglandin F1 alpha in the utero-ovarian venous plasma of nonpregnant and early pregnant ewes

The effect of pregnancy on concentrations of prostaglandins E2, F2 alpha and 6-keto-prostaglandin F1 alpha (PGE2, PGF2 alpha and 6-keto-PGF1 alpha) in utero-ovarian venous plasma was examined in ewes on Days 10 through 14 after estrus, an interval which includes the critical period for maternal recognition of pregnancy. The utero-ovarian vein ipsilateral to a corpus luteum was catheterized on Day 9 or 10 in 6 pregnant and 8 nonpregnant ewes. Five blood samples were collected at 30-min intervals for 2 h beginning at 0500 and 1700 h daily. Sampling began at 0500 h on the day after catheterization. The mean and variance within each 2-h collection period were calculated for each ewe. The natural logarithm of the variance in each collection period (ln variance) was used as an estimate of the fluctuations in secretory activity by the endometrial-conceptus complex. Patterns of the mean concentrations of PGE2 were different between pregnant and nonpregnant ewes (P less than 0.01); PGE2 being higher in the pregnant ewes beginning on Day 13. There was a trend for the patterns of ln variance in PGE2 to differ (P less than 0.1) with pregnancy status over the entire period; ln variance was greater in pregnant ewes beginning on Day 13. The patterns of the mean concentrations and ln variances for PGF2 alpha and 6-keto-PGF1 alpha did not differ between pregnant and nonpregnant ewes. There were significant increases in both of these prostaglandins over time, independent of pregnancy status (P less than 0.01). The association of higher concentrations of PGE2 in utero-ovarian venous plasma with early pregnancy is consistent with the hypothesis that PGE2, originating from the uterus and/or conceptus, is one factor involved in maintenance of the corpus luteum of pregnancy.