Prolonged Corpus Luteum Research Articles

Effect of a single dose of a proprietary extended-release oxytocin formulation on corpus luteum function in cycling mares

There is increasing clinical use of oxytocin treatment to prolong function of the corpus luteum (CL) to suppress estrus in performance mares. A common oxytocin treatment protocol involves administering 60 units of oxytocin intramuscularly (IM) once daily on days 7 to 14 after ovulation (day 0). In an effort to eliminate the need for daily administration, we have been evaluating the use of a proprietary extended-release formulation of oxytocin (ER-OT). We previously demonstrated that IM administration of 2,400 units ER-OT on day 7 and again on day 10 resulted in prolonged CL function in 75% of the treated mares (Sarnecky, et al., J Equine Vet Sci. 2019;77:28-30). That two-injection protocol reduced the number of treatments by 75% (i.e., two injections vs. eight injections from day 7 to 14). We hypothesized the number of ER-OT treatments can be further reduced to one and still maintain efficacy. In an initial study evaluating a single dose of ER-OT, IM administration of 4,800 units of ER-OT once on Day 8/9 resulted in prolonged CL function in 50% of the treated mares compared to 12.5% in untreated control mares (P>0.1), which although promising, indicated further work was needed (Clement et al., Clinical Theriogenology. 2022;14:280). The objective of this study was to evaluate the effect on CL function of a single dose of 4,800 units ER-OT on day10. Mares were examined via transrectal palpation and ultrasonography to determine the day of ovulation (day 0) and then randomly assigned to a nontreated control group and an ER-OT-treated group (n = 9 mares/group). Mares in the treated group received 2.0 mL of ER-OT containing 4,800 units oxytocin IM once on day 10. Starting 15 minutes before treatment, mares were monitored visually every 15 minutes for three hours and no signs of colic were observed. Jugular blood samples were collected on day 0 and then every Monday, Wednesday and Friday for 50 days for determination of the serum progesterone concentration. Mares were classified as having prolonged CL function if their progesterone concentration remained >1.0 ng/mL continuously for at least 30 days. The proportion of mares in each group with prolonged CL function was compared using Fisher's Exact Test (GraphPad Software, Inc., San Diego, CA). There was a tendency for CL function to be prolonged in more ER-OT-treated mares than control mares (6/9 [67%] vs. 2/9 [22%], respectively; P = 0.08). Although these results did not reach statistical significance, the 67% incidence of prolonged CL function in the ER-OT-treated mares suggests a single dose of ER-OT has the potential to be efficacious though additional work is still needed.

Effect of human chorionic gonadotropin treatment on the duration of oxytocin-induced prolonged corpus luteum function in mares

Oxytocin is used increasingly in mares to prolong corpus luteum (CL) function to suppress estrus. When mares develop prolonged CL function in response to oxytocin treatment, the CL generally remains functional for 60–90 days. However, a longer duration of CL function can make this method of estrus suppression even more clinically useful. We hypothesized that human chorionic gonadotropin (hCG) treatment during the period of oxytocin-induced prolonged CL function would extend the duration of CL function (i.e. beyond 90 days). Prolonged CL function was induced in mares (n = 14) by treating them with 60 units of intramuscular oxytocin once daily on days 7–14 after ovulation. Mares were then randomly assigned equally to a control group that received no additional treatment and an hCG-treated group that received 2,500 units of intramuscular hCG on days 30, 45, 60, 75, and 90 after ovulation. Jugular blood samples were collected for progesterone concentration determination on the day of ovulation and then 3 times (M, W, and F) weekly for 120 days. Duration of CL function was not different (p > 0.05) and it was 78.0 ± 7.5 and 91.4 ± 20.4 days (mean ± standard deviation [SD]) in control and hCG-treated mares, respectively. Therefore, hCG treatment (during the period of oxytocin-induced prolonged CL function) did not extend CL function, hence alternative methods should be explored.

Preliminary study of the contraceptive effect of a self-assembling intrauterine device (iUPODs) in mares maintained in a paddock with a fertile stallion

There is an urgent need for practical methods of population control (i.e., contraception and/or sterilization) for free-roaming (i.e., “wild” or “feral”) horses and burros on Western Public Lands in the United States. The objective of this study was to evaluate the contraceptive efficacy of a novel self-assembling three-part polymer-coated magnetic intrauterine device termed as an intrauterine POD (self-assembling; iUPOD) when there are natural breeding conditions when iUPOD use was managed by veterinary professionals with no prior experience with the device. Six mares were administered an iUPOD and were then housed continuously with a fertile stallion for 91 days. The intrauterine POD retention and contraceptive efficacy were 100%. Two mares had prolonged corpus luteum function (for 37 and 91 days) immediately after iUPOD placement. For the estrous cycles of the other mares, the duration of diestrus was 7.8 ± 2.7 days (mean ± S.D.). Four of the mares (67%) became pregnant when in a paddock with the same stallion the year after iUPOD removal. These results are encouraging for use of the iUPOD as a practical and reversible method of fertility control in free-roaming horses and burros.

The effect of basic fibroblast growth factor 2 on the bovine corpus luteum depends on the stage of the estrous cycle and modulates prostaglandin F2α action

The roles of fibroblast growth factor 2 (FGF2) in the corpus luteum (CL) function and its modulatory effect on prostaglandin (PG) F2α during the bovine estrous cycle were studied using the following design of in vivo and in vitro experiments: (1) effects of FGF2 and FGF receptor 1 inhibitor (PD173074) on bovine CL function in the early (PGF2α-resistant) and mid (PGF2α-responsive) luteal stage in vivo, (2) the modulatory effect of FGF2 on PGF2α action during the luteal phase in vivo and (3) effects of FGF2 and PD173074 on bovine CL secretory function in vitro. Cows were treated by injection into the CL with: (1) saline (control), (2) FGF2, (3) PD173074, (4) FGF2 followed by intramuscular (i.m.) PGF2α, (5) PD173074 followed by i.m. PGF2α and (6) i.m. PGF2α as a positive control. For in vitro experiments, CL explants were treated with the aforementioned factors. Progesterone (P4) concentrations of blood samples or culture media were determined by radioimmunoassay. Relative mRNA expressions of the genes involved in angiogenesis and steroidogenesis were determined by quantitative real-time PCR. Although FGF2 treatment on day 4 of the estrous cycle did not change the cycle length, FGF2 with PGF2α decreased the P4 concentrations observed during the estrous cycle compared to the control group (P < 0.001). Moreover, FGF2 treatment on day 10 prolonged CL function as indicated by a significantly greater concentration of P4 on day 21 compared to the control group. In the in vitro study, FGF2 decreased cytochrome P450 family 11 subfamily A member 1 (CYP11A1) and hydroxy-delta-5-steroid dehydrogenase (HSD3B1) mRNA expression (P < 0.01) and decreased P4 production in the early-stage CL (P < 0.001). However, FGF2 + PGF2α or PGF2α alone resulted in an elevation of steroidogenic acute regulatory protein and CYP11A1 mRNA expression and P4 secretion in the early-stage CL (P < 0.01). In the mid-luteal phase, FGF2 upregulated CYP11A1 and HSD3B1 mRNA expression (P < 0.01), while FGF2 + PGF2α increased only HSD3B1 mRNA expression (P < 0.001). In conclusion, FGF2 seems to play a modulatory role in CL development or luteolysis, differentially regulating steroidogenesis and angiogenic factors as well as PGF2α actions.

Effect of Chronic Administration of Oxytocin on Corpus Luteum Function in Cycling Mares

The objective of this study was to determine if intramuscular administration of 60 units of oxytocin once daily for 29 days, regardless of when treatment was initiated during the estrous cycle (i.e., without monitoring estrous behavior and/or detecting ovulation), would induce prolonged corpus luteum (CL) function in cycling mares. Mares were randomly assigned to two groups: (1) saline-treated control (n = 7) and (2) oxytocin-treated (n = 9) subjects. Control mares received 3 cc of saline, and oxytocin-treated mares received 60 units (3 cc) of oxytocin intramuscularly for 29 consecutive days. Treatment was initiated in all mares on the same day (day 1), independent of the day of the cycle. Jugular blood samples for determination of progesterone concentration were collected three times weekly (M, W, and F) for 21 days before treatment was initiated to confirm that all mares had a luteal phase of normal duration immediately before treatment. Beginning on the first day of treatment, blood samples were collected daily for eight days and then three times weekly through day 80. Mares were considered to have prolonged CL function if serum progesterone remained >1.0 ng/mL continuously for at least 25 days after the end of the treatment period. The proportion of mares with prolonged CL function was higher in the oxytocin-treated group than in the saline-treated group (7/9 vs. 1/7, respectively; P < .05). Three of the seven oxytocin-treated mares that developed prolonged CL function initially underwent luteolysis within 4–7 days of the start of oxytocin treatment and then developed prolonged CL function after the subsequent ovulation during the treatment period. In the other four oxytocin-treated mares that developed prolonged CL function, progesterone remained >1.0 ng/mL throughout the treatment period and into the post-treatment period. All mares with prolonged CL function maintained elevated progesterone concentrations through at least day 55 of the study. In conclusion, intramuscular administration of 60 units of oxytocin for 29 consecutive days effectively prolonged CL function in mares, regardless of when treatment was initiated during the estrous cycle. Importantly, this represents a protocol for using oxytocin treatment to prolong CL function that does not require detection of estrous behavior or day of ovulation.

Estradiol-17β-Induced Changes in the Porcine Endometrial Transcriptome In Vivo.

Estradiol-17β (E2) is a key hormone regulating reproductive functions in females. In pigs, E2, as the main conceptus signal, initiates processes resulting in prolonged corpus luteum function, embryo development, and implantation. During early pregnancy the endometrium undergoes morphological and physiological transitions that are tightly related to transcriptome changes. Recently, however, the importance of E2 as a primary conceptus signal in the pig has been questionable. Thus, the aim of the present study was to determine the effects of E2 on the porcine endometrial transcriptome in vivo and to compare these effects with transcriptome profiles on day 12 of pregnancy. Microarray analysis revealed differentially expressed genes (DEGs) in response to E2 with overrepresented functional terms related to secretive functions, extracellular vesicles, cell adhesion, proliferation and differentiation, tissue rearrangements, immune response, lipid metabolism, and many others. Numerous common DEGs and processes for the endometrium on day 12 of pregnancy and E2-treated endometrium were identified. In summary, the present study is the first evidence for the effect of E2 on transcriptome profiles in porcine endometrium in vivo in the period corresponding to the maternal recognition of pregnancy. The presented results provide a valuable resource for further targeted studies considering genes and pathways regulated by conceptus-derived estrogens and their role in pregnancy establishment.

Evaluation of a Proprietary Slow-Release Oxytocin Formulation on Corpus Luteum Function in Mares

Prolonging function of the corpus luteum (CL) is a method of suppressing estrus that relies on continued secretion of endogenous progesterone to keep mares out of heat naturally. The use of oxytocin treatment to prolong CL function is gaining increasing use, and the most common treatment protocol involves administration of 60 units of oxytocin intramuscularly (IM) once daily on days 7–14 after ovulation (eight daily treatments). Although that protocol induces prolonged CL function in ≥70% of treated mares, the need for daily administration is a drawback to its use. Therefore, the objective of this study was to evaluate the efficacy of a proprietary slow-release oxytocin formulation (SR-OT) for prolonging CL function that requires only two treatments. Mares were examined via transrectal palpation and ultrasonography to determine the day of ovulation (day 0) and then randomly assigned to a nontreated control group and an SR-OT treatment group (n = 8 mares/group). Mares in the treated group received 1.0 mL of SR-OT containing 2,400 IU oxytocin IM once on day 7 and again on day 10 after ovulation. Jugular blood samples were collected on day 0 and then every Monday, Wednesday, and Friday for 50 days for determination of the serum progesterone concentration. Mares were classified as having prolonged CL function if their progesterone concentration remained >1.0 ng/mL continuously for at least 30 days. Corpus luteum function was prolonged in 0/8 (0%) control mares and 6/8 (75%) of the SR-OT–treated mares (P < .01). The demonstrated efficacy of this two-injection, SR-OT protocol represents a 75% reduction in the number of oxytocin treatments compared with daily administration of oxytocin from day 7–14, making it a more practical treatment protocol.

How to Use Oxytocin Treatment to Prolong Corpus Luteum Function for Suppressing Estrus in Mares

Prolonging function of the corpus luteum (CL) is a method of suppressing estrus that uses continued secretion of endogenous progesterone to keep mares out of heat naturally. The most common method of prolonging CL function has been intrauterine insertion of a glass ball (i.e., marble). However, several recent reports have described deleterious complications associated with their use, including the presence of multiple glass balls, fragmentation of the glass ball(s), and/or pyometra. Therefore, the use of other methods for prolonging CL function is warranted. Alternatives to using an intrauterine glass ball for prolonging CL function include (1) oxytocin treatment, (2) inducing a late-diestrus ovulation, (3) intrauterine infusion of plant oils, and (4) manual reduction of the conceptus after day 16 of gestation. Of these, oxytocin treatment is the most practical and efficacious method of prolonging CL function. As described here, one oxytocin protocol involves administering 60 units of oxytocin intramuscularly (IM) once daily on days 7 to 14 after ovulation, which induces prolonged CL function in 60% to 70% of treated mares. Alternatively, by extending the duration of oxytocin treatment to 29 days, administration of 60 units of oxytocin IM can be initiated randomly at any point in the estrous cycle with no loss in efficacy (i.e., over 70% response).

Effect of Administration of Oxytocin During Diestrus on Corpus Luteum Function and Endometrial Oxytocin Receptor Concentration in Cycling Mares

The objectives of this study were to (1) compare the effect of twice versus once daily administration of oxytocin on days 7-14 after ovulation on the duration of corpus luteum (CL) function and (2) determine the effect of oxytocin treatment on endometrial oxytocin receptor concentration in mares. In experiment 1, mares were randomly assigned to three groups on day 7: (1) untreated control group (n = 7), (2) twice daily oxytocin treatment group (n = 7), and (3) once daily oxytocin treatment group (n = 8). Oxytocin-treated mares received 60 U of oxytocin intramuscularly (IM) the respective number of times each day on days 7 through 14. One of seven control mares (14%), five of seven (71%) twice daily oxytocin-treated mares, and five of eight (63%) once daily oxytocin-treated mares had prolonged CL function. There was no significant difference in the proportion of mares with prolonged CL function between the two oxytocin-treated groups, and collectively, oxytocin treatment increased (P < .05) the proportion of mares with prolonged CL function compared with no treatment. In experiment 2, mares were randomly assigned to two groups (n = 5/group): (1) saline-treated control mares, and (2) oxytocin-treated mares. Beginning on day 7, control mares received 3 mL of sterile saline IM twice daily, and oxytocin-treated mares received 60 U of oxytocin IM twice daily through day 14. On day 15, endometrial oxytocin-binding capacity was determined (as a measure of oxytocin receptor concentration), and there was no difference (P > .1) between control and oxytocin-treated mares (1,465.7 ± 108 and 1,382.8 ± 108 fmol/mg protein [mean ± standard error of mean], respectively).

Differential luteolytic function between the physiological breeding season, autumn transition and persistent winter cyclicity in the mare

There is a well-documented increase in luteolytic failure, resulting in spontaneously prolonged corpus luteum (SPCL) function, during estrous cycles of horses in autumn. The cause of this phenomenon may be due to seasonal alterations in PGF 2α and/or in prolactin (PRL) secretion around luteolysis. To investigate this, progesterone (P4), 13, 14-dihydro, 15-keto PGF 2α (PGFM) and PRL concentrations were compared between summer and autumn estrous cycles during natural luteolysis and luteolysis induced by benign uterine stimulation. A single estrous cycle from mares in June–July ( n = 12) was compared to multiple estrous cycles from these 12 mares plus 8 additional mares in September through December. Reproductive behavior was monitored by bringing a stallion in close proximity to the mare and ovarian events by ultrasonography. Blood was collected via jugular cannula every 6 h from d 13 to 17 post-ovulation in untreated control mares ( n = 8 summer, n = 9 autumn). In treated mares, blood collection occurred at 0, 15, 30, 45, 60, 90, 120, 180 and 240 min followed by 6 h intervals for a total of 5 d following intrauterine saline infusion on d 7 ( n = 4 summer, n = 11 autumn). Mares failing to return to estrus for 30 d received intrauterine saline and the described intensive blood sampling protocol on d 30. Progesterone and PRL were determined on daily samples and PGFM on frequent plasma collections by RIA. Duration of ovarian luteal and follicular phases, P4 and PRL concentrations and PGFM secretion around luteolysis were compared between treatments and seasons by ANOVA. Mean P4 declined from June to December in all groups. Pulses of PGFM were detected on d 13–17 in controls and d 7–11 in saline-infused mares. Pulse patterns were not different between groups. The incidence of SPCL increased during autumn in the control group. PGFM pulses were absent on d 13–17 in mares with SPCL, but PGFM pulses could be induced in these mares by saline infusion at d 30. Autumn PGFM profiles were unchanged during spontaneous or saline-induced luteolysis compared with summer. Circulating PRL increased around natural or induced luteolysis. These results provide evidence that changes in luteal function during the autumn transition are not the result of alterations in the ability of the uterus to produce PGF 2α nor due to changed CL sensitivity to PGF 2α. We conclude that seasonal changes in luteolytic function are caused by an alteration in the signal for PGF 2α release.

Dopamine Antagonist Affects Luteal Function But Not Cyclicity During the Autumn Transition

The autumn transition is characterized by a number of anomalies affecting the luteal phase of the estrous cycle, such as declining progesterone secretion from the corpus luteum and increased rate of failure of luteolysis. Prolactin also decreases. We theorized that these events may be linked, possibly through dopamine. We administered domperidone, a specific dopamine D2 receptor antagonist from September 12 to anestrus or January 15, either daily (n = 8), or once per day for the first 7 days of each month (n = 7). Controls (n = 7) received no treatment. Mean progesterone and prolactin concentrations were compared with summer cycles. Time to entry into anestrus and incidence of spontaneously prolonged luteal activity was compared between groups during the autumn transition. Prolactin declined from June through October equally in all groups. There was no difference between groups in time to anestrus. Progesterone decline was prevented (daily treatment) or delayed for a prolonged period (weekly group) in autumn. The incidence of spontaneously prolonged corpus luteum activity was reduced to summer levels in both domperidone groups compared with the control. We concluded that autumn prolactin decline was not driven through dopaminergic D2 receptor inhibition of pituitary lactotrophs. Sustained progesterone synthesis through the autumn may be the result of action of the D2 receptor antagonist with dopamine receptors on the corpus luteum. Autumnal luteolytic function appears to have a dopamine-influenced component. There does not appear to be a causative relationship between autumnal progesterone and prolactin secretion.

Immunolocalization of beclin 1, a bcl-2-binding, autophagy-related protein, in the human ovary: possible relation to life span of corpus luteum

Ovarian tissue homeostasis is maintained by highly regulated cyclic phases of cell proliferation/differentiation and programmed cell death. Compelling evidence indicates that both apoptotic and autophagic types of programmed cell death are involved in the regression of the corpus luteum (CL) in primate species. Beclin 1 is an autophagy-related protein that is involved in the inter-relationships between apoptosis and autophagy, through interaction with the anti-apoptotic protein bcl-2. We studied the presence and expression pattern of beclin 1 in the adult human ovary. In ovarian follicles, beclin 1 immunostaining was found in the theca layer, whereas granulosa cells were negative. After ovulation, beclin 1 immunostaining was present in both theca-lutein and granulosa-lutein areas. The expression of beclin 1 in granulosa-lutein cells was related to the functional and structural status of the CL, being strong at the early and mid luteal phases, barely detectable at the late luteal phase, and absent in granulosa-lutein cells in subsequent cycles. Our results indicated that beclin 1 expression was related to luteal cell survival rather than to cell death. Accordingly, persistent beclin 1 expression was found in granulosa-lutein cells under either physiological (i.e., CL of pregnancy) or pathological (irregularly regressing CL in climacteric women) conditions involving prolonged CL life span. Strong beclin 1 immunostaining was also found in ovarian androgen-producing cells (i.e., secondary interstitial and hilus cells). Our data thus suggest that beclin 1 plays important roles in the regulation of the life span of human CL and ovarian androgen-secreting cells, by maintaining autophagy at levels promoting cell survival rather than cell death.

Time of onset and ovarian state prior to entry into winter anestrus

The reproductive activity of 18 light horse mares was followed from September to May, 1989 and 1991. Five mares were evaluated from July to August, 1991. All mares were teased three times per week. Ovarian size, follicular growth, ovulation and corpus luteum development was followed by ultrasonography daily during estrus and once weekly during diestrus/anestrus. Progesterone (P4) was measured by RIA on plasma drawn daily or weekly. Entry into anestrus was considered complete if a mare did not exhibit cyclic estrous behavior, had no follicles > 25 mm, and maintained P4 < 1 ng/ml for at least 30 days. Two mares continued cycling while 16 mares ceased ovarian activity at diverse times during the study period. Winter cycles were the same as summer cycles in length, but not inP4 secretion. Entry into anestrus did not occur until November and peak numbers occurred in January. The time to first ovulation in the spring (March-April) was not affected by the time of entry into anestrus. Spontaneously prolonged corpus luteum (SPCL) function (P4 < 1 ng/ml < 30 days) reached a peak level by December (28% of mares) and rapidly declined in January. Mares entered anestrus from three different ovarian states: after resolution of a SPCL (n = 3), or following luteolysis of a normal CL (n-4), or following follicular atresia (n = 9). These three methods of entry into anestrus were not equally distributed throughout the autumnal transitional period (p<0.001). Half of all anestrous mares entered this state prior to the winter solstice, and did so following follicular atresia. Those who entered anestrus later in the winter did so following lysis of a CL or SPCL. Only one mare who attained anestrus late in the transition period managed follicular growth (ending in atresia and anestrus) followingluteolysis. These data indicate that true anestrus is achieved later than previously reported and that luteal function is altered during winter.

Effects of an antiprogesterone (RU486) on the hypothalamic-hypophyseal-ovarian-endometrial axis during the luteal phase of the menstrual cycle.

The impact of the antiprogesterone RU486 [17 beta-hydroxy-11 beta-(4-dimethylaminophenyl) 17 alpha-(1-propynyl)estra- 4,9-dien-3-one] on the hypothalamic-pituitary-ovarian-endometrial axis was examined in normal cycling women during the mid (MLP)- and late (LLP) luteal phases. During the MLP, 10 women received 3 mg/kg RU486 for 3 days. During the LLP, a single dose of 600 mg RU486 was administered to 4 women, and in another 4 women a single dose of 3 mg/kg was given during corpus luteum rescue by hCG. Longitudinal studies with daily and frequent blood samples (every 10 min for 10 h) were conducted during 3 consecutive cycles (control-treatment-recovery). During the MLP, RU486-induced uterine bleeding occurred in all 10 women 36-72 h after the first dose. No histological evidence of endometrial breakdown was found in endometrial biopsies taken 12-24 h before the onset of bleeding. Significant decreases in LH secretion (P less than 0.001) and LH pulse amplitude (P less than 0.006) and blunted pituitary responses to GnRH (P less than 0.01) were evident by the last treatment day, but LH pulse frequency did not change. Complete luteolysis occurred in 2 of the 10 women. Incomplete luteolysis occurred in 8 women and was associated with an initial decline of serum estradiol (P less than 0.001), but not progesterone levels, followed by rebound increases (P less than 0.001) in LH, estradiol, and progesterone levels 3 days later, which may have reversed the luteolytic processes and prolonged corpus luteum function. Spontaneous luteolysis ensued 3-5 days later with the onset of second episodes of uterine bleeding. For serum FSH, an early rise occurred during the luteal phase in advance of the onset of the second episodes of uterine bleeding. This rise may have resulted in early follicle recruitment and accounted for the shorter duration of the follicular phase during recovery cycles. During the LLP, the single RU486 dose resulted in significant decreases in LH pulse amplitude (P less than 0.03), frequency (P less than 0.05), and secretion (not significant) within 12 h. The recovery cycle was entirely normal. Corpus luteum rescue with incremental doses of hCG did not prevent uterine bleeding after RU486 treatment. These findings indicate that RU486 operates at multiple sites and implies that progesterone is important in the control of luteal function. Further, our data provide a basis for exploring the potential use of RU486 as a once a month birth control agent.

Effects of arachidonic acid and oxytocin on equine endometrial PGF 2α during normal cycles and pseudopregnancy

The effect of excess arachidonic acid or oxytocin on equine endometrial prostaglandin F 2α (PGF 2α ) synthesis was measured in vitro under physiologic and pathophysiologic conditions. Endometrial tissues obtained by uterine biopsy at 5, 10, 12, 14, 16 and 20 days post-ovulation from cycling mares, after 0, 2, 4, 6, 8, 10, 12, 14 or 16 days of progesterone (P 4 ) in ovariectomized mares and at 30 days postovulation in mares undergoing spontaneously prolonged corpus luteum (SPCL) activity were incubated in vitro with and without added arachidonic acid or oxytocin. Endometrial PGF 2α content and synthetic capacities were determined by radioimmunoassay. PGF 2α production increased significantly at Days 12–16. Arachidonic acid did not alter this effect. Oxytocin stimulated additional PGF 2α production on Days 5, 16, and 20. SPCL tissues had minimal PGF 2α production which was increased significantly by arachidonic acid but not oxytocin. PGF 2α synthesis in ovariectomized P 4 treated mares was minimal and did not vary with length of progesterone exposure or addition of arachidonic acid. These results suggest that a) oxytocin may play a role in luteolysis in the equine, b) although arachidonic acid appears not to be limiting to PGF 2 α production under normal physiological conditions, its absence may play a role in pathophysiological conditions, c) factors in addition to progesterone and arachidonic acid are required to initiate PGF 2α synthesis in the mare.

An intravulvosubmucous injection of prostaglandin F 2α in anoestrous cows

Anoestrous cows with a prolonged corpus luteum were subjected to an intravulvosubmucous injection of prostaglandin F 2α (PGF 2α) (2, 4 or 6 mg). Oestrous responses and the subsequent fertility to different doses of PGF 2α were compared. The plasma progesterone of 10 cows treated with 2 mg of PGF 2α was measured by the radioimmunoassay (RIA) method and the peripheral levels immediately before and 4 days after treatment were compared. A total of 79 anoestrous cows was randomly injected with one of the three doses of PGF 2α. The proportions of cows showing oestrus within 7 days of treatment were 37.9% (11/29), 58.3% (21/36) and 78.6% (11/14) for 2, 4 and 6 mg, respectively. There was a significant difference between the groups which received 2 and 6 mg ( P < 0.05). No significant difference was found in the proportions of cows showing oestrus within 3 days of each treatment. The pregnancy rates 60–90 days after artificial insemination (A.I.) with frozen-thawed semen did not show significant differences among the doses of PGF 2α (72.7%, 57.1% and 81.8% for 2, 4 and 6 mg, respectively). In 6 of 10 cows treated with 2 mg PGF 2α, the plasma progesterone clearly declined on the 4th day after treatment, but the oestrous response was observed only in 4 of those 6 cows. The present study indicates that an intravulvosubmucous injection with less than 6 mg PGF 2α is an effective method of inducing oestrus and subsequently satisfactory fertility in anoestrous cows with a prolonged corpus luteum.

Corpus luteum function after indomethacin treatment during the estrous cycle and following hysterectomy in the gilt.

Indomethacin (IND), a prostaglandin synthetase inhibitor, was used to determine the relationship between prostaglandin (PG) secretion and corpus luteum (CL) function during the luteal phase of the estrous cycle and after hysterectomy in the gilt. In Experiment 1, gilts that had displayed estrous cycles of 18 to 22 days (onset of estrus = Day 0) were randomly assigned to four treatments (n = 7/group): 1) ethanol vehicle (EtOH) daily from Day 10 through Day 17; 2) IND daily from Day 10 through Day 17;3) IND daily from Day 10 through Day 13 and EtOH daily from Day 14 through Day 17; and 4) EtOH daily from Day 10 through Day 13 and IND daily from Day 14 through Day 17. In Experiment 2, 15 gifts were hysterectomized on Days 6 to l0 of the estrous cycle and were randomly assigned to a control (n = 7) or IND-treated (n = 8) group. Treatment, daily for 4 days, began when all gilts had reached Day 18 or later. The daily dose of 10 mg IND/kg BW was calculated on the average body weight of each treatment group. In Experiment 1, ovarian morphology at necropsy on Day 25, serum progesterone and 13,14-dihydro-15-keto prostaglandin F2α (PGFM) concentrations throughout the experimental period, and failure to display estrus by Day 25 suggest that IND treatment during the luteal phase of the estrous cycle prolonged CL maintenance in the pig. The progesterone and PGFM assays were validated in our laboratory. In experiment 2, CL morphology and serum progesterone and luteinizing hormone (LH) concentrations indicate that IND treatment failed to affect luteal function by a direct action on the luteal cell or by suppressing pituitary LH secretion.

Gynecologic Endocrine Emergencies

THE physician dealing with gynecologic and obstetric patients frequently must manage emergencies resulting from faulty endocrine homeostasis (eg, dysfunctional uterine bleeding). In earlier portions of this series, reference had been made to particular problems in the diagnosis and treatment of certain endocrine emergencies as they occur in pregnancy. In this section, we review disruptions of normal gynecologic endocrine function encountered during the reproductive years and early pregnancy: treatment of dysfunctional uterine bleeding, undesirable sequelae of ovulation induction, and finally, a few comments about the use of hormonal agents during gestation. Dysfunctional Uterine Bleeding Etiology.— Dysfunctional uterine bleeding (abnormal uterine bleeding caused by endocrine factors, often defined as such because of its irregular timing and the absence of nonendocrine lesions) is generally synonymous with anovulation. Occasionally, dysfunctional bleeding associated with ovulation does occur, viz, ovulation bleeding, inadequate corpus luteum, prolonged corpus luteum (Halban disease), and irregular shedding. 1 Diagnosis.— Differentiating dysfunctional

ASPECTS OF THE REGULATION OF CORPUS LUTEUM FUNCTION IN ANDROGEN-STERILIZED FEMALE RATS.

ABSTRACT Some aspects of the regulation of function of artificially induced corpora lutea in androgen-sterilized female rats have been studied. The morphology of the vaginal epithelium and the distribution of sudanophilic materials in the luteal cells served as criteria for possible corpus luteum function. Pseudopregnancy, i. e. corpus luteum function during a defined period, as can be observed in female rats after sterile copulation, could not be induced in androgen-sterilized rats by daily cervical stimulation, by three daily injections of reserpine or by the presence of an isotransplanted pituitary gland during the first four days after the induction of corpus luteum formation. Prolonged corpus luteum function during at least 45 days was observed in animals bearing an isotransplanted pituitary gland under the kidney capsule. It is suggested that the evenly distributed sudanophilia in these corpora lutea is a result of the »tonic LH secretion« of the pituitary gland in situ. Comparison with similar studies in male rats led to the conclusion that an ovulation-inducing release of gonadotrophins plays a major role in the termination of the luteal phase in normal female rats. In ovariectomized androgen-sterilized rats treated with progesterone and oestrone a decreased response of the uterus to a traumatic stimulus was noticed as compared with the response in similarly treated normal rats.