Prostaglandin metabolism in the ovine corpus luteum: catabolism of prostaglandin F(2alpha) (PGF(2alpha)) coincides with resistance of the corpus luteum to PGF(2alpha)

To examine possible mechanisms involved in resistance of the ovine corpus luteum to the luteolytic activity of prostaglandin (PG)F(2alpha), the enzymatic activity of 15-hydroxyprostaglandin dehydrogenase (PGDH) and the quantity of mRNA encoding PGDH and cyclooxygenase (COX-2) were determined in ovine corpora lutea on Days 4 and 13 of the estrous cycle and Day 13 of pregnancy. The corpus luteum is resistant to the action of PGF(2alpha) on Days 4 of the estrous cycle and 13 of pregnancy while on Day 13 of the estrous cycle the corpus luteum is sensitive to the actions PGF(2alpha). Enzymatic activity of PGDH, measured by rate of conversion of PGF(2alpha) to PGFM, was greater in corpora lutea on Day 4 of the estrous cycle (P < 0.05) and Day 13 of pregnancy (P < 0.05) than on Day 13 of the estrous cycle. Levels of mRNA encoding PGDH were also greater in corpora lutea on Day 4 of the estrous cycle (P < 0. 01) and Day 13 of pregnancy (P < 0.01) than on Day 13 of the estrous cycle. Thus, during the early estrous cycle and early pregnancy, the corpus luteum has a greater capacity to catabolize PGF, which may play a role in the resistance of the corpus luteum to the actions of this hormone. Levels of mRNA encoding COX-2 were undetectable in corpora lutea collected on Day 13 of the estrous cycle but were 11 +/- 4 and 44 +/- 28 amol/microgram poly(A)(+) RNA in corpora lutea collected on Day 4 of the estrous cycle and Day 13 of pregnancy, respectively. These data suggest that there is a greater capacity to synthesize PGF(2alpha), early in the estrous cycle and early in pregnancy than on Day 13 of the estrous cycle. In conclusion, enzymatic activity of PGDH may play an important role in the mechanism involved in luteal resistance to the luteolytic effects of PGF(2alpha).     

Influence of luteinizing hormone and prostaglandin F(2alpha) on progesterone secretion in superfused minced bovine luteal tissue in the early stage of the estrous cycle

Minced luteal tissue of bovine corpora lutea from Day 4, 5, and 6 of the estrous cycle (n = 4 corpora lutea each) was superfused for 9 h, and the progesterone secretion under the influence of 100 ng luteinizing hormone (LH)/ml and/or 1,000 ng prostaglandin F(2alpha) (PGF(2alpha))/ml was determined. In vivo, this period of the estrous cycle is characterized by a transition from PGF(2alpha) refractoriness to PGF(2alpha) sensitivity. The investigations were carried out in order to examine whether this transition is reflected by a change in the hormone secretion pattern in vitro. The basal secretion was higher on Day 6 than on Day 4 and 5 (P < 0.01). PGF(2alpha) slightly increased the progesterone secretion, but there was no statistically significant difference (P > 0.05). LH, however, stimulated the progesterone secretion by about 30% in luteal tissue collected from Day 4 and 5 (P < 0.01). In luteal tissue collected from Day 6, the LH-induced increase in hormone secretion was not statistically significant due to two corpora lutea that showed no response at all to LH. The progesterone secretion of the two other corpora lutea, however, was increased by 30% (P < 0.01). When PGF(2alpha) and LH were simultaneously added, the LH-induced progesterone secretion was not inhibited; PGF(2alpha) even seemed to intensify the action of LH. The difference between the hormone secretion under the influence of LH alone and that under the influence of a combination of LH and PGF(2alpha), however, was not statistically significant. It is concluded that in cattle the end of the refractoriness to PGF(2alpha) in vivo is not reflected by a corresponding change of the hormone secretion pattern in vitro.     

Changes in lipid contents and fatty acid compositions in ovine corpora lutea during the estrous cycle and early pregnancy

Changes in lipid contents and fatty acid compositions of each lipid fraction were examined in corpora lutea from 34 unmated ewes between Days 8 and 16 of the estrous cycle and from 6 ewes at Day 16 of pregnancy. Four patterns were observed during advancement of the estrous cycle. Luteal concentrations of free cholesterol and triglyceride (neutral lipids) increased between Days 14 and 16, during luteal regression, in a manner approximated by exponential functions of time, whereas luteal concentrations of phospholipid (polar lipids) increased and then decreased between Days 8 and 16 in a manner approximated by a sin function of time. Likewise, within the various lipid class component fatty acids, changes in palmitic acid weight percentages were approximated by sin functions of time, whereas arachidonic acid weight percentages increased between Days 14 and 16 in a manner approximated by exponential functions of time. Pregnancy either inhibited or reversed the changes in luteal lipid profiles, especially arachidonic acid percentages, between Days 14 and 16 of the estrous cycle. Luteal lipid profiles of corpora lutea from Day 16 pregnant sheep approximated lipid profiles of corpora lutea recovered from sheep between Days 12 and 14 of the estrous cycle. Comparison of luteal lipid profiles after tissue incubations at either 0 or 37 degrees C for 2 h revealed an effect of reproductive status on fatty acid metabolisms at Day 16. Changes observed in luteal lipid contents and fatty acid compositions during advancement of the estrous cycle represent aspects of lutein cell maturation and impending senescence that can be inhibited or reversed by pregnancy.     

Lipoprotein lipase activity in the bovine corpus luteum during the estrous cycle and early pregnancy.

Lipolytic activity measured at pH 8.6 in bovine corpora lutea exhibited classical properties of lipoprotein lipase (LPL) in terms of serum and heparin stimulation and NaCl inhibition. LPL activity was measured in 23 corpora lutea collected at different stages of the estrous cycle and early pregnancy. The LPL activity in cyclic corpora lutea (mumole FA released/hr/100 mg acetone powder) was low at Days 4-8 of the estrous cycle (3.1 +/- 1.5: mean +/- SE) and at Days 19-20 (1.6 +/- 0.6). However, high activity of the enzyme was found at Days 12-15 of the cycle (11.8 +/- 1.8); these concentrations were significantly (P less than 0.01) elevated over those found at Days 4-8 and 19-20. The enzyme activity began to decline at Days 16-18 of the estrous cycle (5.1 +/- 1.7). Low enzyme activity was found in the corpora lutea removed from two cows at Day 22 of pregnancy. Progesterone concentrations were measured in 16 of the 23 corpora lutea and a good correlation (r = 0.75, P less than 0.01) was found between lipoprotein lipase and progesterone concentrations of the tissue. The data suggest that LPL may be involved in controlling the transfer of fatty acids, including arachidonic, from plasma lipoproteins to luteal tissue.     

Age at puberty, ovulation rate, uterine length, prenatal survival and litter size in Chinese Meishan and Yorkshire females

Studies on the ovulation rate, prenatal survival and litter size of Chinese Meishan pigs have given widely divergent results depending on the extent of inbreeding of the animals, their original genetic diversity, the age and parity, and the conditions of management. To obtain meaningful results, it is necessary to characterize the population under study. The following report characterizes populations of Meishan and Yorkshire of a widely diverse background. First farrowing data were collected on 21 Meishan and 20 Yorkshire gilts. Meishan gilts had 12.4 fully formed piglets and Yorkshire gilts had 7.4 fully formed piglets (P < 0.01). Meishan gilts averaged 1.86 mummified fetuses per litter vs 0.05 per Yorkshire litter (P < 0.01). Yorkshire piglets averaged 1.3 kg body weight at birth vs 0.9 kg for Meishan piglets (P < 0.01). At 47 days of second gestation, 19 Meishan and 12 Yorkshire sows averaged 22.7 and 16.3 corpora lutea (CL), respectively (P < 0.01). Uterine length and number of fetuses were not different (P > 0.40) in the two breeds. Daily estrous detection of 50 Meishan and 34 Yorkshire gilts began at 60 and 120 days of age, respectively. Meishan gilts reached sexual maturity at 95 days of age, which was 105 days earlier than Yorkshire gilts (P < 0.01). Meishan gilts were in estrus nearly 1 day longer than Yorkshire gilts at first, second and third estrus (P < 0.05). No differences in cycle length between breeds were detected for the first or second estrous cycle (P > 0.60). Nineteen Meishan gilts were slaughtered at 51 days of gestation and their reproductive tracts were recovered. The mean number of dissected CL (17.0), number of fetuses (13.1), total uterine length (396 cm), spacing per fetus (29.9 cm), allantoic (124.9 ml) and amniotic (32.2 ml) volumes, crown-rump length (82.8 mm), weight (35.4 g), sex, and direction of each fetus were determined. Chinese Meishan gilts reached puberty much earlier and were in estrus longer than Yorkshire gilts and Meishan sows had more CL than Yorkshire sows.     

Seasonal variation of the ovarian follicular dynamics and luteal functions of sheep in the subtropics

This study was undertaken to describe the development of individual follicles and corpora lutea (CL) in Ossimi ewe lambs at different seasons of the year in the subtropics. Seven ewe lambs underwent daily ultrasonographic examination for 20 interovulatory periods (IOP) during spring, winter and autumn. Ovarian follicles >or=2 mm and corpora lutea were counted and measured. Blood samples were taken for progesterone (P(4)) analysis. All ewe lambs included, but one, were cyclic in all seasons studied. Three (65%) and two (35%) follicular waves were detected per estrous cycle. None of the characteristics of the large follicles was affected by season. Follicles >or=2 mm in diameter were significantly higher in winter. The CL developed slowly in autumn. Serum P(4) level was higher in autumn. Double ovulation was observed only in autumn. The data demonstrated that Ossimi sheep in the subtropics were cyclic in most seasons of the year. Season affected mainly the luteal functions with little influences on the follicular characteristics.     

The proestrous prolactin surge is not the sole initiator of regressive changes in corpora lutea of normally cycling rats.

During the estrous cycle, secretion of prolactin is largely restricted to a surge on proestrus. We investigated whether this proestrous prolactin surge initiates regression of the corpora lutea of the preceding cycle. Adult rats were killed prior to the prolactin surge (Proestrus group), following the prolactin surge (Estrus group), after chemical blockade of the prolactin surge with bromocryptine (Estrus+BRC group), and after blockade of the prolactin surge and administration of prolactin (Estrus+BRC+PRL group). Corpora lutea of the current (proestrus) or preceding (estrus) cycle were dissected out, weighed, and sectioned for immunohistochemistry or cultured for examination of in vitro progestin production. Numbers of luteal monocytes/macrophages, differentiated macrophages, and apoptotic nuclei per high-power field were greater for Estrus and Estrus+BRC+PRL than for Estrus+BRC, which in turn had greater numbers than Proestrus (P< 0.05). In contrast, BRC completely reversed the decline in luteal weight observed between Proestrus and Estrus (P<0.05). Number of major histocompatibility complex II-positive cells was not different between groups (P>0.05). Finally, progestin production by corpora lutea in vitro was lower for Proestrus than for the other groups (P<0.05). The results indicate that the prolactin surge alone is not responsible for initiation of apoptosis or immune cell infiltration in regressing corpora lutea of the estrous cycle, although prolactin increases these markers of regression. Prolactin does cause a decline in luteal weight; however, the corpora lutea retain the capacity for steroidogenesis. We conclude that although prolactin has a role in luteal regression, it is not solely responsible for the initiation of this process.     

Effect of prostaglandin F2 alpha on release of progesterone and leukotriene B-4 by cells from corpora lutea of mares.

Corpora lutea were recovered from mares either 4 to 5 days or 12 to 13 days after ovulation. Mixed populations of luteal cells were prepared by collagenase digestion and were incubated for 24 h in the presence or absence of prostaglandin (PG) F-2 alpha (250 ng/ml). PGF-2 alpha significantly (P = 0.03) reduced progesterone secretion by cells from late diestrous corpora lutea and tended (P = 0.06) to reduce secretion by early diestrous cells. PGF-2 alpha had no significant effect on leukotriene B-4 (LTB-4) production by cells from early diestrous corpora lutea, but significantly (P = 0.03) increased LTB-4 production by late diestrous luteal cells. It seems possible that LTB-4 could play a role as an intermediary in the action of PGF-2 alpha in luteolysis in the mare.     

Expression of monocyte chemoattractant protein-1 and distribution of immune cell populations in the bovine corpus luteum throughout the estrous cycle.

This study characterizes the expression of monocyte chemoattractant protein-1 (MCP-1) and the relative distribution of immune cell populations in the bovine corpus luteum throughout the estrous cycle. Immunodetectable MCP-1 was evident in corpora lutea of cows at Days 6, 12, and 18 postovulation (Day 0 = ovulation, n = 4 cows/stage). Day 6 corpora lutea contained minimal MCP-1 that was confined primarily to blood vessels. In contrast, relatively intense staining for MCP-1 was observed in corpora lutea from Days 12 and 18 postovulation. MCP-1 was again most evident in the cells of the vasculature, but it was also observed surrounding individual luteal cells, particularly by Day 18. An increase in immunohistochemical expression of MCP-1 on Days 12 and 18 postovulation corresponded with increases in MCP-1 mRNA and protein in corpora lutea as determined by Northern blot analysis and ELISA. Monocytes and macrophages were the most abundant immune cells detected in the bovine corpus luteum, followed by CD8+ and CD4+ T lymphocytes. In all instances, Day 6 corpora lutea contained fewer immune cells than corpora lutea from Days 12 and 18. In conclusion, increased expression of MCP-1 was accompanied by the accumulation of immune cells in the corpora lutea of cows during the latter half of the estrous cycle (Days 12-18 postovulation). These results support the hypothesis that MCP-1 promotes immune cell recruitment into the corpus luteum to facilitate luteal regression. These results also raise a provocative issue, however, concerning the recruitment of immune cells several days in advance of the onset of luteal regression.     

An ultrasonographic study of luteal function in breeds of sheep with different ovulation rates

Development and demise of luteal structures were monitored using daily transrectal ultrasonography in 2 breeds of sheep differing in ovulation rates (nonprolific Western white-faced cross-bred, n = 12 and prolific pure-bred Finn sheep, n = 7), during 1 estrous cycle in the mid-breeding season. Jugular blood samples were collected once a day for radioimmunoassay (RIA) of progesterone. The mean diameter of ovulatory follicles was higher in Western white-faced than in Finn ewes (6.4 +/- 0.2 and 5.3 +/- 0.2 mm, respectively; P < 0.001). The mean volume of luteal structures was higher (P < 0.05) in Western white-faced compared with Finn sheep from Days 5 to 15 of the cycle (Day 0 = day of ovulation). This accounted for the higher (P < 0.05) total luteal volumes recorded in Western white-faced ewes on Day 7 and from Days 11 to 15, despite the higher ovulation rate in Finn ewes (2.7 +/- 0.3 and 1.7 +/- 0.2, respectively; P < 0.05). Mean serum progesterone concentrations were higher (P < 0.05) in Western white-faced than in Finn ewes from Days 4 to 14. Daily total luteal volumes were positively correlated with daily serum progesterone concentrations throughout the cycle in Finn sheep (r > or = 0.40, P < 0.02), and during luteal growth and regression (r > 0.60, P < or = 0.00001) but not during mid-cycle in white-faced ewes (r = 0.16; P = 0.22). During the growth of the corpora lutea (CL), luteal tissue volume increased faster (P < 0.05) than serum progesterone concentrations in both breeds of sheep. During luteolysis, the decrease in luteal volumes parallelled that in serum progesterone concentrations in Finn (P = 0.11) but not in Western white-faced ewes, where luteal volumes decreased more slowly (P = 0.02) in relation to progesterone secretion. Increased ovulation rate in prolific Finn ewes resulted in more but smaller CL, and lower serum progesterone levels compared with nonprolific Western white-faced ewes. We conclude that breed-specific mechanisms exist to control the formation of luteal tissue and progesterone secretion in cyclic ewes differing in prolificacy. The mechanisms may involve ovulation of Graafian follicles at different sizes and inhibitory paracrine effects of CL on co-existing CL.     

Influence of prostaglandin F autoantibodies on the estrous cycle of the guinea pig.

Adult female guinea pigs were actively immunized with prostaglandin F-2alpha conjugated to bovine serum albumin (BSA). Control animals, immunized against BSA continued to cycle normally, while the animals immunized against prostaglandin F-2alpha stopped cycling after one to three normal cycles. Laparotomy at 30 days after the last estrus revealed no recently formed corpora lutea. During the remaining 70 days of observation the antibody titer increased to 1:700, accompanied by increasing total serum estrogens (136 pg/ml at day 100) and a slow decline in circulating progesterone levels (0.6 ng/ml at day 100). The ovaries at day 100 contained degenerated corpora lutea and luteinized follicles. The suppression of the estrous cycle in the present experiments was interpreted as resulting from prolongation of luteal function as well as from inhibition of ovulation.     

Luteal regression in the normally cycling rat: apoptosis, monocyte chemoattractant protein-1, and inflammatory cell involvement

In hypophysectomized rats, prolactin induces regression of the corpora lutea. Luteal regression is accompanied by infiltration of monocytes/macrophages, declines in luteal mass and plasma progestins, and increased staining for monocyte chemoattractant protein-1 (MCP-1). We investigated whether similar events are induced during the estrous cycle, after the proestrous prolactin surge. Rats were killed on proestrus or on estrus, and one ovary was frozen for immunohistochemical detection of MCP-1, monocytes/macrophages (ED1-positive), and differentiated macrophages (ED2-positive) and for in situ detection of apoptotic nuclei. Corpora lutea of the current (proestrus) or preceding (estrus) cycle were dissected from the ovaries of additional rats and frozen for the same analyses and for determination of total protein content. In sections of whole ovaries, intensity and distribution of MCP-1 staining were increased in corpora lutea of multiple ages on estrus as compared to proestrus, as were numbers of differentiated macrophages and apoptotic nuclei per high-power field. Sections of isolated corpora lutea showed these increases on estrus, and the number of monocytes/macrophages per high-power field was also significantly increased. Accompanying these inflammatory/immune events, the corpora lutea on estrus showed decreased weight and total protein per corpus luteum, as compared to corpora lutea on proestrus. These changes are consistent with a proposed role for prolactin in the initiation of luteal apoptosis and of a sequence of inflammatory/immune events that accompany regression of the rat corpus luteum during the normal estrous cycle.     

The relationship between vaginal mucous impedance and serum concentrations of estradiol and progesterone throughout the sheep estrous cycle

The objective of this experiment was to assess the relationship between electrical resistance of the vaginal mucosa and serum concentrations of estradiol (E2) and progesterone (P4) during the estrous cycle in ewes. Vaginal impedance was recorded daily using a 2-electrode impedometer in 10 nonprolific Western white-faced and 7 prolific Finn ewes, during the mid-breeding season (October to December). Transrectal ultrasonography of ovaries was performed once a day to confirm ovulation and monitor follicle growth (follicles > or =3 mm in diameter) and development of corpora lutea (CL). Jugular blood samples were collected daily for radioimmunoassay (RIA) of estradiol and progesterone. In all ewes, a decline in vaginal impedance (to <40 ohms) was closely associated with the onset of behavioral estrus. In both breeds of sheep, there was no significant correlation between daily serum concentrations of estradiol and vaginal impedance throughout the estrous cycle. Daily serum concentrations of progesterone and the E2:P4 ratio were correlated with vaginal impedance during the period of luteolysis and follicular phase in both breeds (Western white-faced ewes: r = 0.62, P = 0.0002 and r = -0.56, P = 0.0002; Finn ewes: r = 0.61, P = 0.001 and r = -0.45, P = 0.03, respectively) and early in the cycle (Days 0 to 2, Day 0 = day of ovulation) in white-faced ewes (r = 0.61, P = 0.0003 and r = -0.36, P = 0.052, respectively) but not during the remaining portion of the luteal phase in either breed. In conclusion, vaginal mucous impedance appears to be primarily controlled by progesterone, but it also changes in response to shifts in the E2:P4 ratio when progesterone concentrations are low. Impedometric characteristics of the vaginal mucosa in cyclic ewes are an indicator of serum concentrations of progesterone and E2:P4 ratios during the terminal stage of the estrous cycle.     

Regulation of the synthesis of 3-hydroxy-3-methylglutaryl coenzyme A reductase in the bovine ovary in vivo and in vitro

In order to investigate the pattern of ovarian cholesterol biosynthesis during the bovine estrous cycle, tissue concentrations of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme in the synthesis of cholesterol, were determined by immunoblot techniques. Medium-sized (9-11 mm) and large (14-18 mm) follicles, after removal of follicular fluid by centrifugation, and corpora lutea from the early, early-mid, late-mid, and late stages of the luteal phase were used (n = 5 per group). The specific content (per microgram of tissue homogenate protein) and total content of HMG-CoA reductase in medium-sized and large follicles were substantially lower than those of corpora lutea of the early-mid and late-mid luteal phase. The specific content was elevated in a number of the corpora lutea from the early luteal phase and was low in regressing corpora lutea. Thus during the midluteal phase, when steroid hormone production is elevated, the total and specific contents of HMG-CoA reductase are also elevated. To investigate the mechanisms whereby the levels of HMG-CoA reductase are regulated, primary monolayer cultures of bovine luteal cells (early-mid and late-mid luteal phase) were used. Cells were cultured for 24 h in Dulbecco's modified Eagle's medium containing lipoprotein-poor fetal calf serum (2% vol/vol). At this concentration there was no stimulation of the production of progesterone above that seen with no addition of serum. Under these conditions the total and specific contents, and the synthesis, of HMG-CoA reductase were stimulated by treatment with (Bu)2cAMP (1 mM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of luteinizing hormone on luteal cell populations in hypophysectomized ewes

To examine the effect of purified LH on development and function of luteal cells, 27 ewes were assigned to: (1) hypophysectomy plus 2 micrograms ovine LH given i.v. at 4-h intervals from Days 5 to 12 of the oestrous cycle (oestrus = Day 0; Group H + LH; N = 7); (2) hypophysectomy with no LH replacement (Group N-LH; N = 6); (3) control (no hypophysectomy) plus LH replacement as in Group H + LH (Group S + LH; N = 7); (4) control with no LH treatment (Group S-LH; N = 7). Blood samples were collected at 4-h intervals throughout the experiment to monitor circulating concentrations of LH, cortisol and progesterone. On Day 12 of the oestrous cycle corpora lutea were collected and luteal progesterone concentrations, unoccupied receptors for LH and number and sizes of steroidogenic and non-steroidogenic luteal cell types were determined. Corpora lutea from ewes in Group H-LH were significantly smaller (P less than 0.05), had lower concentrations of progesterone, fewer LH receptors, fewer small luteal cells and fewer non-steroidogenic cells than did corpora lutea from ewes in Group S-LH. The number of large luteal cells was unaffected by hypophysectomy, but the sizes of large luteal cells, small luteal cells and fibroblasts were reduced. LH replacement in hypophysectomized ewes maintained luteal weight and the numbers of small steroidogenic and non-steroidogenic luteal cells at levels intermediate between those observed in ewes in Groups L-LH and S-LH. In Group H + LH ewes, luteal and serum concentrations of progesterone, numbers of luteal receptors for LH, and the sizes of all types of luteal cells were maintained. Numbers of small steroidogenic and non-steroidogenic cells were also increased by LH in hypophysectomized ewes. In Exp. II, 14 ewes were assigned to: (1) sham hypophysectomy with no LH replacement therapy (Group S-LH; N = 5); (2) sham hypophysectomy with 40 micrograms ovine LH given i.v. at 4-h intervals from Day 5 to Day 12 of the oestrous cycle (Group S + LH; N = 5); and (3) hypophysectomy plus LH replacement therapy (Group H + LH; N = 4). Experimental procedures were similar to those described for Exp. I. Treatment of hypophysectomized ewes with a larger dose of LH maintained luteal weight, serum and luteal progesterone concentrations and the numbers of steroidogenic and non-steroidogenic luteal cells at control levels.(ABSTRACT TRUNCATED AT 400 WORDS)     

First postpartum ovulations and corpora lutea in ewes which lamb in the breeding season

Two experiments involving crossbred ewes which lambed during the breeding season were performed to determine whether: (a) the interval to first postpartum ovulation could be reduced by weaning or mastectomy; (b) there are differences in luteal structure and luteinizing hormone (LH) receptor concentration between first postpartum corpora lutea induced with GnRH and normal cycling corpora lutea and (c) pretreatment of postpartum ewes with progesterone would affect luteal LH receptor concentration and luteal phase serum progesterone concentration.In experiment I, the mean interval (±SEM) to the first postpartum ovulation was 22.3 ± 1.1 days and was not significantly altered by weaning or mastectomy. More than half of the ewes had small, short-lived peaks of serum progesterone associated with short-lived corpora lutea prior to the normal luteal phase rise of serum progesterone. In experiment II, 2 h after GnRH injection on day 18 postpartum, serum LH concentrations were higher in ewes which received progesterone treatment on days 13 and 14 than in control ewes. Progesterone treatment did not affect mean corpus luteum weight (157 mg) or concentration of LH receptors (0.95 fmol/mg) in first postpartum corpora lutea, but progesterone-treated ewes had significantly higher endogenous serum progesterone concentrations on days 21–24. GnRH-induced corpora lutea from postpartum ewes were lighter in weight, paler in color, had lower LH receptor concentrations and had a more regressed histological appearance than corpora lutea of a similar age from normal, cycling ewes.     

Ovarian response to gonadotropin treatment initiated relative to wave emergence in ultrasonographically monitored ewes

Follicular recruitment and luteal response to superovulatory treatment initiated relative to the status of the first wave of the ovine estrous cycle (Wave 1) were studied. All ewes (n = 25) received an intravaginal progestagen sponge to synchronize estrous cycles, and ewes were monitored daily by transrectal ultrasonography. Multiple-dose FSH treatment (total dose = 100 mg NIH-FSH-P1) was initiated on the day of ovulation (Day 0 group) in 16 ewes. In the remaining 9 ewes, FSH treatment was started 3 d after emergence of the largest follicle of Wave 1 (Day 3 group). Ewes received PGF(2alpha) with the last 2 FSH treatments to induce luteolysis. Daily blood samples were taken to determine progesterone profiles and to evaluate the luteal response subsequent to superovulation. The ovulation rate was determined by ultrasonography and correlated with direct observation of the ovaries during laparotomy 5 to 6 d after superovulatory estrus when the uterus was flushed to collect embryos. Results confirmed that follicular recruitment was suppressed by the presence of a large, growing follicle. In the Day 0 and Day 3 groups, respectively, mean numbers (+/- SEM) of large follicles (>/= 4 mm) recruited were 6.4 +/- 0.6 and 2.7 +/- 0.7 (P < 0.01) at 48 h after the onset of treatment, and 6.7 +/- 0.5 and 5.1 +/- 0.6 (P = 0.08) at 72 h after the onset of treatment. Ovulation rates were 5.6 +/- 0.8 and 3.3 +/- 0.8 in the respective groups (P < 0.05). The number of transferable embryos was 1.8 +/- 0.5 and 0.3 +/- 0.2 in the respective groups (P < 0.05). Short luteal phases (相似文献   

Ovarian morphology,plasma progesterone concentrations and early embryo survival in the sow

Sixty-five Large White sows were used to examine relationships between ovarian morphology and embryo survival at 30 days gestation and plasma progesterone concentration before and after service.The total mass of luteal tissue was positively correlated with the number of corpora lutea on the ovaries (r = 0.68), and formed a fairly constant proportion of ovarian mass at 30 days gestation. The mean number of embryos per sow was 11.2 ± 0.76, and embryo survival rate was estimated to be 76.5%. There was a positive correlation between ovulation rate and number of embryos at 30 days of pregnancy (r = 0.39). The survival rate of embryos was inversely related (r = ?0.66) to the mean distance between embryos in the uterus. The means of plasma progesterone levels on days 11, 12 and 13 after service were positively correlated with the means of progesterone levels on days 9, 10, 11 and 12 of the cycle before service, the number of corpora lutea, the total mass of luteal tissue and the total mass of the ovaries, but not to numbers of embryos.     

Sensitivity of bovine corpora lutea to prostaglandin F2alpha is dependent on progesterone, oxytocin, and prostaglandins.

Prostaglandin (PG) F2alpha that is released from the uterus is essential for spontaneous luteolysis in cattle. Although PGF2alpha and its analogues are extensively used to synchronize the estrous cycle by inducing luteolysis, corpora lutea (CL) at the early stage of the estrous cycle are resistant to the luteolytic effect of PGF2alpha. We examined the sensitivity of bovine CL to PGF2alpha treatment in vitro and determined whether the changes in the response of CL to PGF2alpha are dependent on progesterone (P4), oxytocin (OT), and PGs produced locally. Bovine luteal cells from early (Days 4-5 of the estrous cycle) and mid-cycle CL (Days 8-12 of the estrous cycle) were preexposed for 12 h to a P4 antagonist (onapristone: OP; 10(-4) M), an OT antagonist (atosiban: AT; 10(-6) M), or indomethacin (INDO; 10(-4) M) before stimulation with PGF2alpha. Although OP reduced P4 secretion (p < 0.001) only in early CL, it reduced OT secretion in the cells of both phases examined (p < 0.001). OP also reduced PGF2alpha and PGE2 secretion (p < 0.01) from early CL. However, it stimulated PGF2alpha secretion in mid-cycle luteal cells (p < 0.001). AT reduced P4 secretion in early and mid-cycle CL (p < 0.05). Moreover, PGF2alpha secretion was inhibited (p < 0.05) by AT in early CL. The OT secretion and the intracellular level of free Ca2+ ([Ca2+]i) were measured as indicators of CL sensitivity to PGF2alpha. PGF2alpha had no influence on OT secretion, although [Ca2+]i increased (p < 0.05) in the early CL. However, the effect of PGF2alpha was augmented (p < 0.01) in cells after pretreatment with OP, AT, and INDO in comparison with the controls. In mid-cycle luteal cells, PGF2alpha induced 2-fold increases in OT secretion and [Ca2+]i. However, in contrast to results in early CL, these increases were magnified only by preexposure of the cells to AT (p < 0.05). These results indicate that luteal P4, OT, and PGs are components of an autocrine/paracrine positive feedback cascade in bovine early to mid-cycle CL and may be responsible for the resistance of the early bovine CL to the exogenous PGF2alpha action.     

Immune regulation of ovarian function in buffaloes (Bubalus bubalus)

We studied the infiltration of different subsets of immune system cells in the ovarian parenchyma of Egyptian buffaloes during follicular and luteal phases of the estrous cycle. All subsets of leukocytes infiltrated significantly more into corpora lutea (CL) than into Graafian follicles (GF) (P < 0.01) except for plasma cells that were abundant in the GF but not observed in the CL. The number of macrophages, lymphocytes, neutrophils and eosinophils were significantly greater in mature CL than in corpora hemorrhagica (CH) or regressing CL. Moreover, the regressing CL showed significantly more macrophages, lymphocytes and neutrophils than the CH. Large antral follicles were infiltrated with larger number of leukocytes than growing preantral atretic follicles. Macrophages and neutrophils observed in large antral follicles were significantly more abundant in the theca externa than the theca interna (P < 0.01). Only plasma cells were significantly greater in number in the theca intema (P < 0.01). Leukocytes infiltrated significantly more into large mature follicles than large, growing, preantral atretic follicles (P < 0.01). Results of this study reveal the calling of leukocytes in a significant numbers inside the ovarian tissue of buffaloes around the time of ovulation and at luteolysis. It is possible that leukocytes with their powerful bioactive cytokines (IL-1, TNFalpha, GM-CSF, and INF-gamma) may assist in ovarian functions such as ovulation and luteolysis.