Progesterone-treated Ewes Research Articles

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.

Progesterone and the surge release of gonadotropins in the ewe

On day 12 of an estrous cycle, 4 groups of ewes were treated with either blank (no steroid) or 3 different sizes of progesterone-containing rubber implants to study the effect of maintained progesterone levels on preovulatory events. Following luteolysis progesterone levels were 0.55 ± 0.13 ng/ml in control ewes and 0.62 ± 0.10 ng/ml, 0.99 ± 0.09 ng/ml and 1.85 ± 0.04 ng/ml in the 3 groups of progesterone-treated ewes. Preovulatory surges of LH and FSH occurred in 5 5 , 5 5 ; 4 5 , 3 5 ; 4 5 , 3 5 and 0 5 , 0 5 ewes in these 4 groups respectively. Eleven days after implant insertion, all ewes responded to a GnRH challenge. The height of all FSH peaks was depressed by progesterone treatment (P<0.05). Three groups of ewes were ovariectomized at day 6 of a cycle and treated with estradiol-17β and progesterone-containing implants. After 8 days of treatment, progesterone implants were removed in sections to give 3 different rates of decline in serum progesterone levels. The gonadotropin surges occurring following progesterone removal were delayed by the slower rates of progesterone decline. Another group of ewes was treated as in experiment 2, but the progesterone implants were all removed together after 8 days. Subsequent replacement of progesterone implants, after 12 or 18 hours, blocked the gonadotropin surges in all, or 2 of 6 ewes respectively. When replaced after 24 hours, implants producing low progesterone (1.38 ± 0.22 ng/ml) did not block gonadotropin surges, but in 2 of 5 ewes high progesterone did (2.87 ± 0.22 ng/ml). Removal of progesterone implants, 12 or 24 hr after replacement, produced secondary gonadotropin surges of smaller magnitude than the initial peaks (P<0.01).

Mechanism by which progesterone shortens the estrous cycle of the ewe.

Progesterone administered early in the estrous cycle of ewes decreases the average life of corpora lutea. The effects of exogenous progesterone during estrus on patterns of concentrations of luteinizing hormone (LH) and progesterone in peripheral plasma and of prostaglandin (PGF2 a) in utero-ovarian venous plasma were studied. In experiment 1, eight ewes received 40mg of progesterone (i.m.) in corn oil and eight were given only corn oil 8 h after the onset of estrus (Day 0). Mean cycle length in progesterone-treated ewes was less than in control ewes (12.5 ± 1.7 vs 16.3 ± 0.2 days: P<0.05). The concentrations of LH during and immediately following the surge were decreased by progesterone and returned to control values by 30 h after treatment. Mean concentration of PGFSa in uterine venous plasma on Day 5 proestrus did not differ significantly between groups. In experiment 2, ewes were injected (i.m.) with corn oil containing 0 (n = 6) or 40 mg (n = 6) of progesterone 8 and 32 h after the onset of estrus. Beginning on Day 5, blood samples were collected via a catheter in one utero-ovarian vein every 8 h until the onset of the next estrus for quantification of PGF2 �. Five of six progesterone-treated ewes had short cycles (11.0 ± 1.0 days), while cycles averaged 17.0 ± 0.3 days for the six control ewes. Concentrations of LH were lower 8 h after the second injection of progesterone but reached control levels by 32 h. Concentrations of progesterone in peripheral plasma of progesterone-treated and control ewes did not differ on Days 4 to 7. The first peak of PGF20 occurred earlier in progesterone-treated (Day 8.0 ± 0.3) than in control ewes (Day 12.3 ± 1.0; P<0.01). Analyses of the regressions of PGF2a on estradiol-17i3 revealed that plasma concentrations of estradiol at the same hour and at 16 and 24 h previous to PGF,0 could account for some of the variation in PGF2a. Decreased concentrations of LH immediately following exogenous progesterone did not interfere with the ability of the young corpus luteum to produce progesterone. Earlier peaks of PGF2 a following exogenous progesterone during estrus may be more important than reduced LH in causing earlier regression of corpora lutea.

Influence of ovarian steroids on the response of ovine uterine arterial smooth muscle to norepinephrine.

Twenty ovariectomized ewes were used in an experiment of 2 × 2 factorial design to examine the effects of estradiol-17β and progesterone on the in vitro constriction of uterine arteries. Animals received the following treatments for 4.5 days: 1) corn oil (controls); 2) estradiol-17β (54 ±3mg in silastic capsule implants); 3) progesterone (15 mg injected twice-daily); and 4) estradiol-17β plus progesterone. Vasoconstriction was monitored during perfusion of uterine arterial segments with Krebs Henseleit solution into which was injected saline, norepinephrine (8μg) and saline, respectively, each at 15-min intervals. Progesterone increased (P<.05) while exogenous estradiol-17β decreased (P<.08) the response to norepinephrine compared to responses of arteries of control ewes. Arteries from control and estradiol-17β plus progesterone-treated ewes did not differ in their response to norepinephrine. No constriction of any artery occurred following exposure to saline. These data suggest that ovarian steroids alter the ability of arterial smooth muscle cells to respond to neurotransmitter.

CHANGES IN SERUM LEVELS OF LH AND FSH IN PROGESTERONE-TREATED OVARIECTOMIZED EWES FOLLOWING A SINGLE INJECTION OF ESTROGEN

The effect of dose and duration of progesterone treatment on estrogen-induced LH and FSH release was studied in ovariectomized ewes. In each of two years, groups of ewes were injected with 5 or 10 mg progesterone daily for 4 or 10 days before an injection of 1 mg estradiol-17β. Experiments were conducted in early July (year 1) or mid-August (year 2). Jugular blood was collected immediately before and hourly from 14 to 30-h after estrogen injection. Serum hormone levels were determined by radioimmunoassay. Combined data from the two years showed that an LH release occurred in four of five ewes treated with 5 mg progesterone for either 4 or 10 days, five of five ewes treated with 10 mg progesterone for 4 days but only one of five ewes treated with 10 mg progesterone for 10 days. The onset of estrus and the rise in LH both tended to occur earlier after estrogen treatment in year 2 than in year 1, suggesting an effect of season. Only one ewe showed a simultaneous release of LH and FSH; in the remainder, the levels of FSH declined after estrogen injection and remained depressed throughout the sampling period. Mean FSH levels tended to be higher in ewes receiving 10 mg progesterone than in ewes receiving 5 mg progesterone in year 2, but the reverse tended to occur in year 1 (progesterone dose × year, P &lt;.05). The results suggest that a 10-day treatment with a moderate dose of progesterone can reduce the incidence of LH release induced by a high dose of estrogen and that the estrogen-induced LH release in progesterone-treated ovariectomized ewes is usually not accompanied by a release of FSH.

Cervical mucus in estrous ewes after treatment with estrogen, progestogens and intrauterine devices.

The influence of estradiol, 6-alpha-methyl-17alpha-acetoxyprogesterone (MAP), and a unilaterally placed IUD on cervical mucus production was studied in estrous ewes. The animals received either 60 mg MAP from Days 9 to 21 of the extended estrous cycle, 25 mcg estradiol from Day 9 until estrus, or an IUD. MAP treatment significantly (p less than .05) increased cervical mucus production at estrus compared with the other treatments. However, the percentage of dry matter, chloride concentration, and spinnbarkeit did not markedly vary between groups. The protein content was markedly increased by estradiol. In a 2nd experiment, ewes received intravaginal sponges containing either 60 mg MAP, 30 mg 9-fluro-11beta-17-dihydroxyprogesterone-17-acetate (Cronolone), or 60 mg Cronolone from Day 9 to 21 of the extended estrous cycle. All 3 treatments significantly (p less than .01) increased cervical mucus production at estrus. There was little difference in the measured chemical and physical properties of cervical mucus between controls and treated animals. The increased production of cervical mucus in progesterone-treated animals may account for the reported reduction in the number of sperm in progesterone-treated ewes.

Blockage of estrogen-induced release of luteinizing hormone by reserpine and potentiation of synthetic gonadotropin-releasing hormone-induced release of luteinizing hormone by estrogen in the ovariectomized ewe.

These experiments tested the effects of reserpine on estrogen-induced LH release and the effects of estrogen on gonadotropin-releasing hormone-induced LH release in ovariectomized ewes. Injection of 50, 200, or 500 mug of estradiol benzoate (EB) into progesterone-treated ewes, or of 50 mug of EB into non-treated ewes induced a large surge in serum LH levels approximately 15 h later. Injection of 5 mg/ewe of reserpine 6 h prior to the EB, blocked the LH surge. Reserpine reduced, but did not block the release of LH induced by injection of 20 mug or 40 mug of synthetic gonadotropin-releasing hormone (GnRH). Injection of graded doses (5, 10, or 20 mug) of GnRH into progesterone-treated ewes that had been treated with reserpine, induced increases in serum LH levels that were proportional to the logarithm of the dose. In the final series of experiments both progesterone-treated and non-treated ewes were injected with reserpine and then with either EB or oil. Fifteen hours after receiving EB or oil they were injected with either GnRH or the diluent. GnRH elevated serum LH levels significantly higher in ewes given EB than in those given oil. LH levels in ewes given oil and diluent were not elevated. These data suggest that reserpine blocked EB-induced LH release by an action on the central nervous system and that EB acted directly on the anterior pituitary to increase the response to GnRH.

Ultrastructure of Sheep Endometrial Stromal Cells After Ovariectomy and Hormone Treatment

Mitochondria, dense bodies, lysosomes, lipid, and rough endoplasmic reticulum (RER) were quantitated in the endometrial stromal cells of ewes after either ovariectomy alone or ovariectomy and treatment with estradiol or progesterone. The most striking change in the endometrial stromal cell was seen in the RER. After ovariectomy, the RER was scant and poorly developed. In ewes treated with estradiol, the RER was abundant and extensively dilated. In progesterone-treated ewes, the RER was less well-developed than in estradiol-treated ewes but somewhat more abundant than in ovariectomized control ewes. The increased RER in estradiol-treated ewes probably reflects increased protein synthesis by the endometrial stromal cells.

Effects of progesterone on endometrial prostaglandins in sheep

The effects of progesterone on endometrial levels of prostaglandins were investigated in intact and ovariectomized ewes. In the first experiment 17 ewes were ovariectomized bilaterally on day 4 of the estrous cycle. Eight ewes served as controls and 9 ewes received 10 mg progesterone on days 4 through 8. All ewes were killed on day 9. The concentration (ng/g) and content (ng/uterus) of PGF 2α were lower (P<.05) in the progesterone-treated ewes (18 and 204, respectively) compared to the controls (64 and 575, respectively). In the second experiment, 20 intact ewes received 40 mg progesterone in corn oil and 20 intact ewes received corn oil only on days 0 and 1 of the estrous cycle. Ten ewes in each group were killed on day 5 and ten on day 9. A significant increase (P<.05) in PGF 2α content, but not concentration, was detected due to progesterone treatment. PGF 2α did not vary with day or the interaction of day with progesterone treatment. No differences in PGF 1α content or concentration were detected in either experiment. The results suggest that progesterone, by itself, is not responsible for the previously reported increase in levels of prostaglandin in the endometrium of ewes at day 14 of the estrous cycle. The luteolytic effect of progesterone given early in the estrous cycle could result in part from increased levels of PGF 2α.

Influence of ovarian hormones on sperm "breakage" and disappearance in sheep uteri.

After intrauterine insemination of large animals the endocrine state PR of the female has been shown to influence the fate of the sperm cells. Since factors that influence the fate of sperm cells in the female reproductive tract can affect fertility this study was undertaken to acquire more information concerning hormonal effects on sperm breakage and disappearance in the sheep uterus. Mature parous Rambouillet ewes were used 9 ewes in each of 7 experimental groups. In 45 of the ewes (both ovaries were removed about 2 months before experimental treatment. The other 18 ewes were checked for estrus twice daily by use of vasectomized rams. The ejaculation of seminal fluid into estrous ewes was prevented. Experimental groups were: Group 1 estrous ewes used on the day that heat was detected Group 2 ovariectomized ewes injected with 300 mcg of estradiol-17beta per day for 5 days Group 3 ovariectomized ewes injected with 300 mcg of estradiol-17beta and 5 mg of progesterone per day for 5 days Group 4 ovariectomized ewes injected with 20 mg of progesterone and 5 mcg of estradiol-17beta per day for 5 days and then 20 mg of progesterone and 300 mcg of estradiol-17beta for 1 day followed by 300 mcg of estradil-17beta per day for 20 days Group 5 ovariectomized ewes with no hormonal treatment Group 6 luteal phase ewes used 9 days after estrus and Group 7 ovariectomized ewes injected with 20 mg of progesterone and 5 mcg of estradiol-17beta for 2 days followed by 20 mcg of progesterone per day for 3 days. Semen was deposited in both uterine horms of each ewe after both ends of the horn had been ligated. Less than 2% of the sperm cells used had tailless heads. Ewes were killed 5 hours after insemination. Uterine horns were removed and sperm cells flushed out with saline solution. The numbers of intact tailless and total spermatozoa recovered from the uterus were analyzed statisticaly. From ovariectomized untreated ewes (Group 5) sperm cells deposited in the uterus were recovered intact. Significantly fewer sperm cells were recovered intact from estrous ewes (Group 1) or from any of the ewes treated primarily with estradiol (Groups 2 3 and 4). Greater numbers of intact spermatozoa were recovered from luteal phase or ovariectomized progesterone-treated ewes (Groups 6 and 7) than from any of the other treated groups. Greater numbers of tailless sperm heads were recovered from estrous or ovariectomized estradiol-treated ewes (Groups 1 and 2) than from luteal phase ovariectomized progesterone-treated ewes (Groups 6 and 7). The fewest total sperm were recovered from ovariectomized ewes primarily treated with estriol (Groups 2 3 and 4). The greatest total sperm were recovered from the luteal phase ewes. The disappearance of sperm cells was greatest in ewes treated primarily with estradiol (Groups 2 3 and 4) and least in luteal phase or progesterone-injected ewes (Groups 6 and 7). It is thought that most sperm cells that disappeared from the uterus were phagocytosed. Results indicate that ovarian hormones influenced both the breakage and the disappearance of sperm cells in the sheep uterus.

Ability of Corpora Lutea Induced Experimentally in Progesterone-Treated Ewes to Prevent Subsequent Ovulation

Ability of Corpora Lutea Induced Experimentally in Progesterone-Treated Ewes to Prevent Subsequent Ovulation

SEASONAL CHANGES IN THE OCCURRENCE OF OESTRUS FOLLOWING PROGESTERONE SUPPRESSION OF OVARIAN FUNCTION IN THE MERINO EWE.

Summary. Three groups of Merino ewes (a total of 150) kept in yards were studied for a period of 1 year. Vasectomized rams were with one group and occurrence of oestrus was noted. The presence and number of corpora lutea were observed by laparotomy at 6-week intervals. The annual rhythms in these characteristics were determined. A second group of ewes received progesterone treatments at intervals of 6 weeks. Half the ewes were with vasectomized rams continuously but rams were with the others for only 1 week after the final progesterone injection. The period from the final injection to the onset of oestrus was determined. Introduction of rams increased the number of ewes showing oestrus at the beginning (late summer) and end (late winter) of the breeding season. The period to onset of oestrus was related to dose and frequency of progesterone injections, the time of the year, and introduction of rams. Periods to onset of oestrus became progressively longer after mid-winter (June) and a proportion of progesterone-treated ewes did not show oestrus in the 1 week period after cessation of progesterone injections in July, at a time when all untreated ewes were experiencing oestrous cycles. The implications of the seasonal change in the effects of progesterone on the ewes are discussed in relation to the sexual season. A third group of ovariectomized ewes received progesterone followed by oestrogen, also at intervals of 6 weeks. The number of ewes showing oestrus during the period January to June was dependent on the dose of progesterone independently of the effect of dose of oestrogen. The relationship did not hold at other times. In general, there was considerable heterogeneity in mean responses and slopes of the dose-response lines.

Transfer of sheep ova.

Summary. The results are described of transfers of ova between sheep. Where necessary, treatment with progesterone was used to synchronize the heats of donor and recipient ewes. pms was used to increase the number of ova shed by donor ewes. Data are given on the onset of heat after treatment in donor and recipient ewes and on the numbers of ova shed, recovered and fertilized among donor ewes. Of a total of fifty transfers, twenty-six were successful; most of the successful transfers were made to untreated recipients and to treated recipients in which transfer was delayed until the second heat after treatment with progesterone. Factors that may have affected the success of transfers were: failure to synchronize heats of donors and recipients; the transfer, in progesterone-treated ewes, of ova at the first cycle after treatment; omission of antibiotics from the serum used for recovery, storage in vitro and transfer of ova; the clinical (scrapie) history of the experimental ewes. There was no evidence of any effect of the time of storage in vitro (up to 5½ hr) on the success of transfers among ova transferred on the day of recovery.