The effect of pre-ovulatory anaesthesia on ovulation in laparoscopically inseminated domestic cats.

Laparoscopic intrauterine artificial insemination (AI) of electroejaculated spermatozoa was used to compare embryo development and conception rates in domestic cats inseminated either before or after ovulation. Females were given a single (100 iu) injection of pregnant mares' serum gonadotrophin (PMSG) followed by either 75 or 100 iu human chorionic gonadotrophin (hCG) 80 h later. Cats were anaesthetized (injectable ketamine HCl/acepromazine plus gaseous halothane) 25-50 h after administration of hCG for laparoscopic assessment of ovarian activity and for transabdominal AI into the proximal aspect of the uterine lumen. At the time of AI, 23 cats were pre-ovulatory (25-33 h after hCG injection) and 30 were post-ovulatory (31-50 h after hCG injection). Pre-ovulatory females produced 10.5 +/- 1.1 follicles and no corpora lutea compared with 1.9 +/- 0.5 follicles and 7.5 +/- 0.9 corpora lutea for the post-ovulatory group (P < 0.05). Six days later, the ovaries of nine pre-ovulatory and 12 post-ovulatory females were re-examined and the reproductive tracts flushed. On this day, pre-ovulatory cats produced fewer corpora lutea (2.8 +/- 1.5; P < 0.05) and embryos (0.4 +/- 0.3; P < 0.05) than post-ovulatory females (18.9 +/- 3.3 corpora lutea; 4.6 +/- 1.2 embryos). Two of the 14 cats (14.3%) inseminated before ovulation and not flushed became pregnant compared with 9 of 18 cats (50.0%) inseminated after ovulation and up to 41 h after hCG injection (P < 0.05). These results indicate that ovulation in cats is compromised by pre-ovulatory ketamine HCl/acepromazine/halothane or laparoscopy or by both and that electroejaculated spermatozoa deposited by laparoscopy in utero, after ovulation, result in a relatively high incidence of pregnancy. Because ovulation usually occurs 25-27 h after injection of hCG, the lifespan for fertilization of the ovulated ovum appears to be at least 14 h in vivo in cats.     

Time of ovulation in goats (Capra hircus) induced to superovulate with PMSG

The timing of ovulation in feral goats treated with 1200 i.u. PMSG +/- 50 micrograms GnRH was studied by repeated laparoscopy. Experiment 1 established that superovulation began as early as 30 h after withdrawal of progestagen-impregnated sponges and was not completed at 54 h if goats received PMSG alone. GnRH synchronized ovulation, leading to 91% of ovulations appearing between 36 and 48 h after sponges were withdrawn. Experiment 2 established that superovulation continued until up to 77 h in goats treated only with PMSG. The stress of repeated laparoscopy appeared to delay or abolish ovulation in some females. The mean (+/- s.e.) ovulation rate was greater in goats treated with GnRH (12.7 +/- 1.3) than in those that received PMSG only (9.7 +/- 1.1; P less than 0.05). Out of 47 of the females in Exp. 1, 43 had one or more corpora lutea at laparoscopy 24 h after withdrawal of progestagen. These early corpora lutea were associated with an increased concentration of plasma progesterone during the periovulatory period. Experiment 3 provided evidence that these corpora lutea arose before the withdrawal of progestagen-impregnated sponges.     

Human chorionic gonadotropin and luteinizing hormone-releasing hormone reverse the blockade of ovulation in pregnant mare's serum gonadotropin-primed immature rats by the anti-androgenic drug, hydroxyflutamide

The present study was designed to examine mechanism(s) of the anti-ovulatory action of the anti-androgen, hydroxyflutamide (OH-F). Prepubertal rats were treated with 4 IU pregnant mare's serum gonadotropin (PMSG) (day -2) to induce first estrus and ovulation. They received OH-F in sesame oil or oil alone at 08:00 and 20:00 h on day 0 (the day of proestrus) and ovulations were assessed on the morning of day 1. Eighty-three percent of control animals ovulated with a mean of 7.7 +/- 1.1 corpora lutea per rat. Hydroxyflutamide blocked ovulation in all but 2 of the 12 rats receiving this drug alone. All of OH-F treated rats that received 5 and 25 IU human chorionic gonadotropin (hCG) ovulated with means +/- SEM of 9.1 +/- 0.1 and 7.3 +/- 1.4 corpora lutea per rat, respectively. The dose of 0.2 IU hCG was essentially ineffective, while the effect of 1.0 IU hCG was intermediate. At the dose of 20 ng and above (100 and 500 ng) luteining hormone-releasing hormone (LHRH) completely overcame the ovulation blockade in the OH-F treated animals, while a 4-ng dose was ineffective. At 18:00 h on the day of proestrus, serum LH levels in control animals were 17.56 +/- 2.60 ng/mL, which were 920% above basal levels (1.90 +/- 0.13) indicating a spontaneous LH surge. This surge was suppressed in OH-F treated rats. Injection of LHRH, at the dose of 20 ng and above, reinstated the LH release in OH-F treated animals. Thus, the anti-androgen, OH-F, inhibits ovulation in PMSG-treated immature rats through its interference with the preovulatory LH surge; the inhibition can be reversed by hCG or LHRH. Hydroxyflutamide does not appear to interfere at the level of the pituitary, but may have direct action at the hypothalamic and (or) extrahypothalamic sites involved in the generation of positive feedback signals that control LH release.     

Immunocytochemical localization of aromatase in immature rat ovaries treated with PMSG and hCG,and in pregnant rat ovaries

Summary Immunocytochemical localization of aromatase cytochrome P-450 was examined in immature rat ovaries treated with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG), and in pregnant rat ovaries. It is well known that PMSG and hCG treatments induce ovulation about 12 h after hCG injection.At 24 h after hCG injection, many antral follicles were recognized in immature rat ovaries and only the granulosa cells in the antral follicles were stained weakly with the anti-aromatase antibody. At 0 to 9 h after hCG injection, in addition to the antral follicles, some large Graafian follicles could be observed in the rat ovaries, and the granulosa cells of these follicles were positively stained for aromatase. Each follicle was surrounded by the basal lamina which shows lineally distinct positive reaction against anti-laminin antibody. At 12 h after hCG injection, some large Graafian follicles without oocyte were weakly positive to the anti-aromatase antisera, and the outline of their basal lamina stained with anti-laminin antibody became irregular in shape and fragmentous. At 15 to 18 h after hCG injection, the luteinized cysts could be seen, and the granulosa-lutein cells of these cysts were almost negative for aromatase. Fragmentous reaction to the anti-laminin antibody was observed around the luteinized cysts.In the ovaries of day 4 in pregnancy, only the granulosa cells of the large antral follicles were weakly stained, but corpora lutea negatively reacted to the anti-aromatase antibody. At 7 to 19 days in gestation, both the granulosa cells of antral follicles and pregnant luteal cells were positively stained against aromatase antisera. The luteal cells were increased in size during pregnancy. And weakly positive reaction was detected on day 7 of pregnancy, then the immunoreaction became stronger in the corpora lutea on day 15 and 19 of pregnancy.The localization of aromatase was immunocytochemically examined in immature rat ovaries treated with PMSG and hCG injection, and the reaction of the granulosa cells of the antral follicles against anti-aromatase antibody became strongly positive about 12 h before ovulation and the became very weak suddenly after ovulation. In rat-ovaries, the pregnant corpora lutea was positively stained for aromatase after day 7 of pregnancy.This study was supported by Grants from the Ministry of Education, Science and Culture, Japan, and from USPHS Research Grants HD04945, USA     

Chorionic gonadotropin administration in domestic cats causes an abnormal endocrine environment that disrupts oviductal embryo transport

Fecal steroid analysis was used to investigate relationships between endocrine parameters and embryo characteristics in domestic cats subjected to chorionic gonadotropin stimulation and artificial insemination (AI). In Study 1, normal endocrine patterns were assessed in 12 cycling domestic queens. Fecal estradiol (E) patterns established an anovulatory cycle length of 18.3 +/- 0.4 d with estrus lasting 6.3 +/- 0.3 d. Eight females (67%) exhibited at least one spontaneous ovulation based on sustained increases in fecal progestagens (P). In Study 2, queens were mated during natural estrus (NE, n = 5) or subjected to exogenous i.m. gonadotropin stimulation, 100 IU eCG followed by 75 IU hCG 80 h later, (GS, n = 5). Compared with NE queens, fecal E concentrations were higher (P < 0.05) and remained elevated longer after ovulation induction with hCG. In Study 3, gonadotropin-stimulated queens (n = 7) were artificially inseminated and ovariohysterectomized 160 h after hCG. Ancillary follicles and/or corpora lutea were observed in 5 of 6 (83%) ovulating queens. Both fecal E and number of unovulated follicles observed at ovariohysterectomy were negatively correlated with the percentage of embryos recovered from the uterus (r = -0.91 and r = -0.87, respectively; P < 0.05). In summary, exogenous gonadotropin administration causes an abnormal endocrine environment in domestic cats, likely due to ancillary follicle development. The sustained elevations in estradiol appear to impair oviductal transport of embryos, possibly leading to the reduced fertility typically observed in cats subjected to gonadotropin stimulation and AI.     

Effect of superovulation induction on embryonic development on day 5 and subsequent development and survival after nonsurgical embryo transfer in pigs

To evaluate the effects of eCG dosage on recovery and quality of Day 5 embryos and on subsequent development and survival after embryo transfer, batches of 5 to 10 donor sows were treated with 1000 or 1500 IU eCG. Recipients from the same batch were synchronously treated with 800 IU eCG. Ovulation was induced with 750 IU hCG (72 h after eCG) in donors and recipients. Donors were inseminated and embryos were collected at 162 h after hCG (120 h after ovulation). Ovulation rate was lower using 1000 IU eCG (28.5+/-11.7; n=48) than 1500 IU eCG (45.7+/-20.3; n=32; P<0.0001). Embryo recovery rate (82.9+/-16.9%) and percentage expanded blastocysts (56.2+/-31.4%) were similar (P>0.05). Expanded blastocysts from each group of sows were pooled into 2 groups within eCG treatment, containing embryos from normally ovulating sows (< or = 25 corpora lutea [CL]) or from superovulated sows (> 25 CL). Average diameter and number of cells of a random sample of the expanded blastocysts per pool were recorded. The average diameter of blastocysts (160.5+/-11.5 microm) was not affected by eCG dosage or ovulation rate (P>0.10). The average number of cells per embryo was higher in the 1000 IU eCG group (84.3+/-15.3) than in the 1500 IU eCG group (70.2+/-1.9; P<0.05) but was similar for normal and superovulated donors within each eCG group (P>0.10). Of the 4 groups, litters of 28 to 30 blastocysts were nonsurgically transferred to 27 synchronous recipients. Pregnant recipients were slaughtered on Day 37 after hCG treatment to evaluate embryonic development and survival. Pregnancy rate for the 1000 and 1500 IU eCG donor groups was 71% (10/14) and 46% (6/13; P>0.10), respectively. The number of implantations and fetuses for the 1000 IU eCG groups was 12.9+/-3.0 and 11.1+/-2.7, and 14.2+/-7.0 and 10.5+/-4.6, respectively, for the 1500 IU eCG groups (P>0.10). After post-priory categorizing the litters of blastocysts to below or above the average diameter (158 microm) of the transferred embryos, irrespective of eCG dosage or ovulation rate, the pregnancy rate was 43% (6/14) and 77% (10/13; P<0.10), respectively. Post-priory categorizing the transferred litters to below or above the average number of cells per embryo litter, irrespective of eCG dosage or ovulation rate, showed no differences in pregnancy rates or number of implantations and fetuses (P>0.10). It was concluded that eCG dosage affects embryonic development at Day 7 after hCG, and this effect was not due to ovulation rate. Embryonic survival after nonsurgical transfer was not related to eCG dosage but tended to be related to the diameter of the blastocysts.     

The duration of ovulation in pigs, studied by transrectal ultrasonography, is not related to early embryonic diversity

The duration of ovulation in pigs was studied by transrectal ultrasonography. The number of preovulatory follicles was counted on both ovaries at 30-minute intervals from 36 hours after the onset of estrus (Group A: naturally ovulating sows that were group-housed and were inseminated and caged during scanning) or 40 hours after treatment with human chorionic gonadotropin (hCG) (Group B: tethered sows that had been induced to ovulate but were not inseminated). The duration of ovulation was (mean+/-SD) 1.8+/-0.6 hours (range 0.75 to 3.25) in Group A (n=13) and 4.6+/-1.7 hours (range 2.0 to 7.0) in Group B (n=8). The difference was significant (P<0.01). In Group A and B sows, respectively, the course of ovulation, expressed as the relation between the relative follicle count (percentage of the maximum follicle count; Y) and the time (percentage of the duration of ovulation; X) was: Y = 104.3( *)e(-0.023( *)X) (R(2)=0.95) and Y = 98.9( *)e(-0.018( *)X) (R(2)=0.92). The onset of ovulation occurred at approximately two-thirds of the duration of the estrus (Group A: 67+/-6%; Group B: 60+/-10%). Group A sows were artificially inseminated and were slaughtered at 98+/-8 hours (range 77 to 110) after ovulation. The difference between the maximum follicle count and the corpora lutea count was zero or only 1 in 81% (21 26 ) of the ovaries. Embryonic diversity (within-litter SD of the number of nuclei or of the number of cell cycles) was not related to the duration of ovulation, neither at the level of ovary nor of sow (P>0.05). In conclusion, transrectal ultrasonography was found to be an appropriate nonsurgical method of studying the duration of ovulation in pigs. The duration of ovulation varied both between sows and between groups of sows, and was not related to early embryonic diversity.     

Formation of ovarian follicular cysts and corpora lutea after treatment with antihistamine or indomethacin in prepubertal gilts

Roles of histamine and prostaglandins in the induction of ovarian cysts after unilateral ovarian manipulation (MAN) and in the process of ovulation were evaluated in prepubertal gilts treated with pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Administration of pyrilamine maleate, an H1 receptor antagonist, before MAN or hCG injection reduced the number of cysts formed but did not alter ovulation rate. Administration of cimetidine, an H2 receptor antagonist, failed to alter the incidence, number, or diameters of cysts formed in response to MAN or the ovulation rate on non-MAN ovaries. Administration of indomethacin, an inhibitor of prostaglandin synthesis, before MAN or hCG injection did not alter the incidence, number, or diameters of cysts formed on MAN ovaries but reduced the number of corpora lutea on non-MAN ovaries. Excessive accumulation of fluid in ovarian cysts apparently was mediated by histamine interacting with the H1-type receptor. Enhanced secretion of prostaglandins produced by the cyclooxygenase pathway did not contribute to development of ovarian cysts but, unlike histamine, was required for formation of corpora lutea in prepubertal gilts treated with PMSG and hCG.     

The relationship between ovulation rate and embryonic survival in gilts

Norwegian Landrace gilts were inseminated on the second day of their second oestrus and slaughtered 28 to 34 days after insemination. The number of corpora lutea (ovulation rate) and normal embryos was counted and the embryonic survival rate was calculated for the 306 pregnant gilts. Mean (+/-S.D.) ovulation rate, number of normal embryos and embryonic survival rate were 14.17+/-2.48, 10.55+/-3.30 and 74.8%+/-20.7%, respectively. The significant (P<0.001) curvilinear regression of embryonic survival rate on ovulation rate gives a maximum embryonic survival rate at 13.2 ovulations. Increased ovulation rate gives increased number of normal embryos up to 18.1 ovulations. Ovulation rate should be considered when assessing factors affecting embryonic survival in pigs.     

The interaction of testosterone and gonadotropins in stimulating estradiol and progesterone secretion by cultures of corpus luteum cells isolated from pigs in early and midluteal phase.

The first objective of this research was to define the capacity of corpora lutea of pig to secrete estradiol in the presence of an androgen substrate which was testosterone. The second objective was to define the synergism between gonadotropic hormones such as LH, FSH, and PRL and testosterone as measured by estradiol and progesterone secretion by two types of porcine luteal cells. Luteal cells were collected from newly forming corpora lutea (0-3 days after ovulation) and from mature corpora lutea (8-10 days after ovulation). After dispersion, luteal cells were suspended in medium M199 supplemented with 10% of calf serum and grown as monolayers at 37 degrees C. Control cultures were grown in medium alone while other cultures were supplemented with either testosterone alone at a concentration of 1 x 10(-7) M or with 10, 100, 500 ng LH plus testosterone, 10, 100, 500 ng FSH plus testosterone or 10, 100, 500 ng PRL plus testosterone. After 2 days of cultivation all cultures were terminated and media were frozen at 20 degrees C for further steroid analysis. Testosterone added to the culture medium in the absence of gonadotropins was without effect on estradiol and progesterone secretion by luteal cells collected in the corpora lutea of the early luteal phase. On the other hand testosterone added to the medium significantly increased progesterone and estradiol secretion by cultured luteal cells collected in the midluteal phase of the cycle. No additive stimulatory action of gonadotropins and testosterone on progesterone secretion was observed in cultures of luteal cells from the early luteal phase but this was not the case in cultures of luteal cells from the midluteal phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of immunization against progesterone on oestrus, cycle length, ovulation rate, luteal regression and LH secretion in the ewe

The effects of active immunization against progesterone on reproductive activity were studied in Merino ewes. Immunization against progesterone caused a shortening (P less than 0.01) of the interval between ovulations from 17-18 days (controls) to between 6 and 10 days (immunized group); this was associated with a corresponding reduction in the interval between LH surges. The immunized ewes also had higher (P less than 0.05) ovulation rates (1.72) than controls (1.25) and exhibited a reduced (P less than 0.01) incidence of oestrus (26% v. 95%). Many immunized ewes continued to ovulate despite the persistence of corpora lutea from earlier ovulations which led to an accumulation on the ovaries of many corpora lutea of different ages. The frequency of LH pulses in ewes immunized against progesterone (1.8 +/- 0.2 pulses/4 h) was significantly (P less than 0.001) higher than that of control ewes (0.3 +/- 0.1 pulses/4 h). This study highlights the importance of progesterone in the control of oestrus, ovulation, ovulation rate, luteal regression and the secretion of LH in the ewe.     

Gonadotropin induction of ovulation and corpus luteum formation in young estrogen receptor-alpha knockout mice

Estrogen receptor-alpha (ERalpha) knockout (ERalphaKO) female mice are infertile. Initially, they exhibit normal follicular development, but by 4-5 wk of age, they begin to develop hemorrhagic ovarian cysts. Follicles in adult ERalphaKO female mice progress to the graafian stage, but there are no corpora lutea (CL). To test whether ERalpha is required for ovarian folliculogenesis, ovulation, and CL formation, eCG and hCG were used to ovulate 3- to 5-wk-old ERalphaKO and wild-type (WT) sibling mice. Gonadotropin administration resulted in ovulation in both ERalphaKO and WT mice. Gonadotropin-treated ERalphaKO females that ovulated produced 7.09 +/- 0.77 oocytes per mouse, whereas gonadotropin-treated WT female mice had 16.17 +/- 0.84 oocytes. Surprisingly, ruptured ERalphaKO ovarian follicles developed into CL that had normal morphology. Gonadotropin-treated ERalphaKO mice had 3-fold higher concentrations of serum progesterone than did control ERalphaKO mice that had been administered saline rather than gonadotropins. Thus, the CL in gonadotropin-treated ERalphaKO mice appeared to be steroidogenically functional. On the basis of these findings, ovarian folliculogenesis, ovulation, and CL formation can occur in the absence of ERalpha, although to a lesser extent than in WT mice.     

Effects of a GnRH agonist on oocyte number and maturation in mice superovulated with eCG and hCG

The objective was to investigate the effects of a gonadotropin-releasing hormone agonist (GnRH) on ovulation rate and the number and maturation of oocytes in mice superovulated with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). Thirty 3-month-old BALB/C female mice (weight: 25-30 g) were assigned to three experimental groups: control, superovulated, and superovulated with GnRH pretreatment (n=10 per group). Control mice received an i.p. injection of 0.1 ml physiological saline solution. Superovulation was induced with 5 IU eCG (i.p.) and 5 IU hCG 48 h later. Mice in the superovulated with GnRH pretreatment group were given GnRH (20 mg/kg Fertirelin, i.m.), 24 h before superovulation. Thirteen hours after hCG administration, mice were sacrificed by cervical dislocation and blood samples were collected to determine serum progesterone concentration (by radioimmunoassay). Ovaries and oviducts were also harvested to enumerate corpora lutea and cumulus-enclosed oocytes. Progesterone concentrations were not significantly different among groups. The oocyte number and the maturation, ovulation rate, and the number of corpora lutea were higher in GnRH-treated mice than both controls and superovulated mice. In conclusion, GnRH given 24 h before superovulation with eCG-hCG increased the number and maturation of oocytes and the rate of ovulation in mice.     

Interleukin-1 alpha increases thecal progesterone production of preovulatory follicles in cyclic hamsters

Adult cyclic hamsters were used to study the effects of interleukin-1 alpha (IL-1 alpha) on in vitro steroidogenesis in preovulatory follicles. IL-1 alpha increased progesterone secretion by preovulatory follicles during a 24-h incubation in RPMI-1640 medium containing hCG (100 mIU/ml) (progesterone levels: 17.5 +/- 2.2 vs. 10.6 +/- 1.9 ng/follicle/ml, p less than 0.05). IL-1 alpha alone had no effect on follicular steroidogenesis. The source of increased progesterone secretion was the thecae (9.8 +/- 1.0 vs. 5.8 +/- 0.4 ng/2 thecae/ml, p less than 0.01) and not the granulosa cells (6.6 +/- 0.2 vs. 6.8 +/- 0.5 ng/20,000 viable granulosa cells/ml). IL-1 alpha also stimulated production of testosterone in thecae of preovulatory follicles. The follicular progesterone increase was dependent on the time of incubation and dose of IL-1 alpha. IL-1 alpha at 5-50 U/ml maximally stimulated progesterone production in the preovulatory follicles, and no significant effect of IL-1 alpha was observed until the 12th hour of incubation. The effects of IL-1 alpha on in vitro steroidogenesis in preantral follicles, experimentally induced atretic preovulatory follicles, and newly formed corpora lutea were examined. IL-1 alpha in the presence of hCG also significantly increased progesterone secretion by atretic preovulatory follicles. In the incubation of preantral follicles or newly formed corpora lutea, however, IL-1 alpha did not alter steroidogenesis. These results indicate that IL-1 alpha stimulates progesterone secretion by preovulatory follicles and that the target tissue for this effect is the thecal layer.(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteal function after intrauterine infusion of recombinant bovine interferon-alpha I1 into postpartum beef cows expected to have short or normal luteal phases.

This study was conducted to determine whether intrauterine infusion of recombinant bovine interferon-alpha I1 (rboIFN-alpha I1), which has 70% sequence identity to bovine trophoblast protein-1, will prevent regression of corpora lutea anticipated to have a short lifespan. Twenty-six beef cows in good body condition were allotted to four treatment groups at parturition in a 2 x 2 factorial design. Treatments were: group 1, saline; group 2, rboIFN-alpha I1; group 3, norgestomet-saline; and group 4, norgestomet-rboIFN-alpha I1. Norgestomet implants were inserted on days 21-24 postpartum and removed 9 days later (before injection of human chorionic gonadotrophin (hCG)). Ovulation was induced 30 to 33 days postpartum with 5000 or 10,000 iu hCG. Groups 1 (n = 7) and 3 (n = 5) were given intrauterine infusions (rectocervical approach) twice daily with saline on days 1-12 or 13-24 after hCG injection, respectively. Cows allotted to groups 2 (n = 8) and 4 (n = 6) were given intrauterine infusions (rectocervical approach) of 2 mg rboIFN-alpha I1 twice daily on days 1-12 or 13-24 after hCG injection, respectively. Treatment with both norgestomet and rboIFN-alpha I1 delayed (P less than 0.01) luteolysis. Lengths of luteal phases (days; mean +/- SEM) were 8.4 +/- 0.7 (group 1, saline), 14.1 +/- 1.0 (group 2, rboIFN-alpha I1), 18.6 +/- 1.3 (group 3, norgestomet-saline) and 20.8 +/- 1.2 (group 4, norgestomet-rboIFN-alpha I1). Concentration of progesterone in serum was similar among all groups the first 6 days following hCG-induced ovulation, but differed (P less than 0.01) thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of cellular and vascular changes in equine follicles during hCG-induced ovulation

In contrast to other species, the histology of the equine follicle during ovulation has not been described. Preovulatory follicles were isolated during oestrus at 0, 12, 24, 30, 33, 36 and 39 h (n = 5-6 follicles per time point) after an ovulatory dose of hCG to characterize the cellular and vascular changes associated with ovulation in mares. Pieces of follicle wall were formalin-fixed and processed for light microscopy to evaluate the general follicular morphology and quantify selected parameters. Marked changes were observed in the histology of equine follicles in the hours before ovulation. The thickness of the granulosa cell layer doubled between 0 and 39 h after hCG (77.8 +/- 4.8 versus 158.8 +/- 4.8 microns, respectively; P < 0.01). This expansion was caused primarily by a pronounced accumulation of acid mucosubstances between granulosa cells, which was first detected at 12 h after hCG and peaked at 36-39 h. In contrast, a significant thinning of the theca interna was observed after hCG treatment. Fewer cell layers were present; theca interna cells appeared smaller than before hCG; and the presence of occasional pyknotic cells was noted at 36 and 39 h after hCG. In addition, the theca layers were invaded by numerous eosinophils. No eosinophils were observed in preovulatory follicles isolated between 0 and 24 h after hCG, but the number increased to 14.0 +/- 0.8 and 5.6 +/- 0.3 eosinophils per field (x 400) in theca interna and theca externa, respectively, 39 h after hCG treatment (P < 0.01). Severe oedema, hyperaemia and haemorrhages, and significant increases in the number of blood vessels in theca interna and externa were observed at 33, 36 and 39 h after hCG. This study provides the first in-depth characterization of the sequential cellular and vascular changes that occur in equine follicles before ovulation.     

Immature rats show ovulatory defects similar to those in adult rats lacking prostaglandin and progesterone actions

Gonadotropin-primed immature rats (GPIR) constitute a widely used model for the study of ovulation. Although the equivalence between the ovulatory process in immature and adult rats is generally assumed, the morphological and functional characteristics of ovulation in immature rats have been scarcely considered. We describe herein the morphological aspects of the ovulatory process in GPIR and their response to classical ovulation inhibitors, such as the inhibitor of prostaglandin (PG) synthesis indomethacin (INDO) and a progesterone (P) receptor (PR) antagonist (RU486). Immature Wistar rats were primed with equine chorionic gonadotropin (eCG) at 21, 23 or 25 days of age, injected with human chorionic gonadotropin (hCG) 48 h later, and sacrificed 16 h after hCG treatment, to assess follicle rupture and ovulation. Surprisingly, GPIR showed age-related ovulatory defects close similar to those in adult rats lacking P and PG actions. Rats primed with eCG at 21 or 23 days of age showed abnormally ruptured corpora lutea in which the cumulus-oocyte complex (COC) was trapped or had been released to the ovarian interstitum, invading the ovarian stroma and blood and lymphatic vessels. Supplementation of immature rats with exogenous P and/or PG of the E series did not significantly inhibit abnormal follicle rupture. Otherwise, ovulatory defects were practically absent in rats primed with eCG at 25 days of age. GPIR treated with INDO showed the same ovulatory alterations than vehicle-treated ones, although affecting to a higher proportion of follicles. Blocking P actions with RU486 increased the number of COC trapped inside corpora lutea and decreased ovulation. The presence of ovulatory defects in GPIR, suggests that the capacity of the immature ovary to undergo the coordinate changes leading to effective ovulation is not fully established in Wistar rats primed with eCG before 25 days of age.     

Plasma concentrations of progesterone and 13,14-dihydro-15-keto-prostaglandin F-2 alpha during regression of the corpora lutea of lactation in the bandicoot (Isoodon macrourus)

Plasma progesterone concentrations (mean +/- s.e.m.) declined from 7.5 +/- 1.2 ng/ml and 7.5 +/- 1.0 ng/ml to less than 1 ng/ml after removal of pouch young (RPY) from bandicoots at Days 24 and 30 of lactation respectively. In all 7 bandicoots, the corpora lutea of lactation showed signs of regression and, in 5 of these bandicoots, a premature ovulation had occurred 6-9 days after RPY. There was no change in the concentration of PGFM after RPY, and uterine prostaglandin F-2 alpha may not be involved in luteal regression in the bandicoot.     

Glucocorticoids stimulate the accumulation of lipids in the rat corpus luteum.

We investigated the physiological basis for the trophic effect of glucocorticoids in rat corpora lutea in the absence of pituitary gonadotropins. Immature (Day 29) Sprague-Dawley rats were given eCG and hCG to induce the development of corpora lutea and were hypophysectomized on Day 32. Beginning on Day 40, rats received twice-daily s.c. injections of either dexamethasone (dex; 200 microg/rat/day) or vehicle (controls) and then were killed on Day 44. Plasma 20alpha-dihydroprogesterone, a major steroid produced by the corpora lutea, was higher (p 2-fold of plasma 20alpha-dihydroprogesterone concentration compared to controls. Glucocorticoid receptor protein (about 92 kDa) was detected in both luteal and nonluteal ovarian tissues in this animal model. These effects of glucocorticoids and the presence of the glucocorticoid receptor raise the possibility of a physiological role for glucocorticoids in the rat corpus luteum.