Corpus Luteum Weight Research Articles

Evidence that the maternal pituitary suppresses the secretion of relaxin in the pregnant rat.

The role of the pituitary in regulating relaxin synthesis and secretion by the corpus luteum during the second half of pregnancy was investigated by hypophysectomizing rats carrying either one conceptus (1C) or a full complement (FC) of conceptuses (n greater than or equal to 8) on day 13 of pregnancy. Serum and luteal relaxin levels, serum progesterone levels, and luteal weights in 1C rats were markedly lower during the period from days 14 through 20 of pregnancy than those in FC rats, as has been previously reported. After hypophysectomy of 1C rats (H1C), serum relaxin levels, serum progesterone levels, and corpus luteum weights increased to values that were not significantly different from those of FC rats. Additionally, hypophysectomized FC rats (HFC) had higher serum relaxin levels than FC rats. Luteal relaxin content was unaffected by hypophysectomy in spite of increased relaxin secretion. Other workers have suggested that placental testosterone may support luteal function during the second half of pregnancy. Serum testosterone levels in 1C rats were markedly lower than those in FC rats, but did not increase after hypophysectomy in either H1C or HFC rats. It is concluded that the putuitary has a suppressive effect on relaxin secretion (and perhaps synthesis) as well as progesterone secretion and corpus luteum growth, and that increased luteal function after hypophysectomy is not due to increased placental testosterone secretion.

Control of corpus luteum function in the pregnant rabbit: role of the placenta ("placental luteotropin") in regulating responsiveness of corpora lutea to estrogen.

Experiments were performed to examine the interaction between estrogen and "placental luteotropin," the two luteotropins thought to be required for corpus luteum maintenance in the pregnant rabbit. Experiment 1 was designed to determine whether estrogen alone was luteotropic in the absence of "placental luteotropin." Pregnant rabbits were assigned to the following groups: Group A, sham hysterectomy; Group B, hysterectomy; Group C, hysterectomy plus estradiol on Day 20; and Group D, hysterectomy plus estradiol on Day 22. "Placental luteotropin" was removed on Day 21 of pregnancy by hysterectomy and estrogen was administered via an estradiol-filled Silastic implant which was placed s.c. before (Day 20, Group C) or after (Day 22, Group D) hysterectomy. Daily blood samples were taken for radioimmunoassay of serum progesterone and estradiol concentrations. Corpus luteum weights were measured at autopsy on Day 27. Hysterectomy caused serum progesterone concentrations to fall rapidly from 13 +/- 1 ng/ml on Day 21 to 2 +/- 1 ng/ml on Day 23, and to 1 ng/ml or less on Days 24-27. In sham hysterectomized rabbits (Group A), pregnancy was maintained and serum progesterone concentrations remained elevated at 9-15 ng/ml throughout (Days 20-27). Estradiol treatment (Groups C and D) did not prevent or reverse luteal regression induced by hysterectomy and serum progesterone concentrations declined in a similar fashion to Group B. Serum estradiol concentrations were 4-8 pg/ml in all groups and did not vary substantially with stage of pregnancy or treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Transitory Increases of Luteinizing Hormone and Follicle-Stimulating Hormone Following Luteectomy in Hemiovariectomized Primates Significantly Increase Progesterone Secretion In Vitro by the Subsequent Corpus Luteum 1

Ten chronically hemiovariectomized cynomolgus and rhesus monkeys were luteectomized 5.5 +/- 0.3 days after the midcycle luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surge in two consecutive cycles. The corpus luteum (CL) was removed, weighed, dispersed with collagenase and the luteal cells counted. Luteal cells (50,000/ml) were incubated in Ham's F10 medium for 3 h at 37 degrees C either in the presence or absence of 100 ng/ml human chorionic gonadotropin (hCG). Daily blood samples were taken from the monkeys throughout the study for determination of LH, FSH, estradiol (E2) and progesterone levels. Within 5 days following each luteectomy (LX), all monkeys responded with a significant increase in FSH and LH (P less than 0.05). Ovulatory LH/FSH surges occurred 14.4 +/- 0.5 days after the first LX. Hormonal profiles of serum progesterone prior to the first and second LX, CL weight and number of luteal cells/CL were similar (P greater than 0.05). However, luteal cells obtained at the second LX produced more progesterone (P less than 0.05) in vitro under basal and hCG-stimulated conditions than cells from the first LX. The areas under the LH and FSH curves following the first LX were highly correlated (P less than 0.05) with the in vitro progesterone production following the second LX. Thus, the monkeys with the largest areas under the LH and FSH curves subsequently had the highest in vitro progesterone production.

A quantitative relationship between conceptus number and ovarian steroid dehydrogenase activity in pregnant rats.

The effects of a conceptus-derived substance on the activity of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 20 alpha-HSD in the ovary were studied in the rat. On day 7 of pregnancy (day 1 = insemination), rats were laparotomized and the desired number of conceptuses was aspirated from the uterus; thus, rats carrying one, two, three, four, five to seven or eight to ten conceptuses were prepared. They were autopsied on day 15 and 3 beta-HSD and 20 alpha-HSD activity in the corpus luteum (CL) or non-luteal ovarian tissue ( NLO ) was determined. Conceptus number was directly related to 3 beta-HSD and inversely related to 20 alpha-HSD activity in the CL. The serum progesterone level and CL weight were also directly related to conceptus number. Neither 3 beta-HSD nor 20 alpha-HSD activity in the NLO was affected by conceptus number. These results indicated that 3 beta-HSD and 20 alpha-HSD in the CL are probably regulated by placental hormone secreted in proportion to the number of conceptuses; in the NLO these enzymes may be controlled by a different mechanism.

Dissimilarity of corpora lutea within the same ovaries or those from right and left ovaries of pigs during the oestrous cycle.

A total of 48 corpora lutea from the right and left ovaries of 2 gilts on Day 9 and 2 gilts on Day 13 of the oestrous cycle were analysed for gonadotrophin binding, progesterone concentration and 3 enzyme activities. The weights of corpora lutea from the right and left ovaries on Days 9 and 13 did not differ, but the values on Day 13 were lower than those on Day 9. The specific binding of 125I-labelled hCG, progesterone concentration, and activities of cytochrome c oxidase (a mitochondrial enzyme), beta-N-acetyl-D-glucosaminidase (a lysosomal enzyme) and glucose 6-phosphate dehydrogenase (a cytosol enzyme) differed, with some exceptions, among the corpora lutea within the same ovaries and those from the right and left ovaries on Days 9 and 13 of the cycle. The gonadotrophin binding differences amongst the corpora lutea appeared to be due to the differences in the total number of available receptors rather than in the receptor affinities. There was no strict correspondence between the magnitude of gonadotrophin binding and luteal progesterone concentration. These data show that porcine corpora lutea within the same ovaries, and those from the right and the left ovary, are quite dissimilar.

The importance of a luteolytic effect of the pituitary in understanding the placental control of the rat corpus luteum.

In rats bearing a full complement of conceptuses (FC-bearing rats) progesterone secretion increases about 1.5 times and the corpora lutea double in weight between days 12 and 16. Reducing the number of conceptuses to one (by aspirating all but the single conceptus) at any time between days 7 and 12 of pregnancy (day 1 = insemination) caused progesterone secretion and corpus luteum weight to remain at or below the day 12 level until term. When rats bearing one conceptus were hypophysectomized on day 12, however, serum progesterone increased and fell after day 12 in a pattern almost identical to that in FC-bearing rats, except that the peak and trough occurred about 2 days later; hypophysectomy on day 15 or 18 also increased serum progesterone to values approaching those in intact FC-bearing rats. In a series of rats bearing experimentally determined conceptus numbers between 0 and 5 or naturally occurring ones of 6-16, the serum level of placental lactogen on day 12 (the day of the first peak of secretion of this hormone) was directly proportional to conceptus number over the entire range. The pattern of rat placental lactogen secretion between days 7 and 23 in FC-bearing rats included two peaks, on day 12 and on days 18-21, but in one-conceptus-bearing rats, the level was only slightly higher than the PRL level, and it remained unchanged, even by hypophysectomy, until term. Serum PRL levels bore no relation to conceptus number, were very low, and were unaffected by hypophysectomy except in the FC-bearing rats, in which lypophysectomy prevented the rise that normally occurs after day 21. These results, especially in relation to others previously reported, show that by day 12 of pregnancy, the rat pituitary, instead of merely becoming luteotropically inactive, produces a substance that inhibits further development of the corpora lutea. The results also imply that the placentas maintain luteal growth and progesterone secretion as much by suppressing this luteolytic activity as by stimulating the corpus luteum directly.

Oestradiol-17 beta in the blood during seasonal reactivation of the diapausing blastocyst in a wild population of tammar wallabies.

Oestradiol-17 beta was measured by radioimmunoassay in cardiac blood from 143 pregnant and post-partum tammar wallabies shot in the wild during reactivation of the diapausing blastocyst, embryonic development, birth and post-partum oestrus. A transient rise in circulating oestradiol on 3 January coincided with or shortly preceded corpus luteum growth and blastocyst expansion; before 5 January mean corpus luteum weight was 14.3 +/- 0.44 mg (n = 65), while thereafter it exceeded 20 mg in two-thirds of the animals. Expanded blastocysts were first noted on 5 January. A second rise in the concentration of oestradiol in plasma, which occurred in late January, preceded parturition and coincided with follicular maturation; the mean (+/- S.E.M.) oestradiol concentration before 17 January was 27.9 +/- 1.10 pmol/1 (n = 110), whereas on or after this date it was 57.3 +/- 4.15 pmol/1 (n = 33). Thus oestradiol levels in peripheral plasma increased at parturition and postpartum oestrus, and showed a rise early in gestation which may be related to the termination of diapause.

The removal of fallopian tubes has no adverse effect on subsequent ovarian function in rabbits

The effect of bilateral salpingectomy on ovarian function was studied in the rabbit. Nine rabbits underwent a microsurgical removal of both fallopian tubes, and nine other rabbits underwent sham operations. Four weeks after surgery the rabbits were mated, and the number of ovulation sites were recorded 18 hours after mating. Serum progesterone (P) levels were also determined prior to the operation and at 6 days and 8 days after mating. Eight days after mating the ovaries were recovered, and the corpora lutea were removed and weighed. The mean number and weights of corpora lutea as well as serum P levels did not differ significantly between the groups. These findings suggest that the absence of fallopian tubes has no effect on subsequent ovulatory function in this animal model.

Control of corpus luteum function during the second half of pregnancy in the rat: a direct relationship between conceptus number and both serum and ovarian relaxin levels.

The effects of conceptus or fetus removal on several parameters of luteal activity (serum and ovarian relaxin immunoactivity levels, serum progesterone immunoactivity levels, and corpus luteum weights) were investigated during the second half of pregnancy in the rat. Conceptuses were aspirated from the uteri of pregnant rats on day 8 (d8) of pregnancy so that they carried 0, 1, 2, 5, or 10 or more conceptuses until they were autopsied on d10, d12, d14, d16, d18, or d20 of pregnancy. A direct relationship existed between the number of conceptuses and the rate and/or degree of increase in all of the parameters of corpus luteum activity. The conceptuses had no local effect on ovarian relaxin levels or on luteal weights when the conceptus side ovary was compared with the nonconceptus side ovary. In pregnant rats in which all but two fetuses were removed (all placentas were left undisturbed), there were no significant differences on d18 or d20 in any parameter of corpus luteum activity between fetectomized and sham-operated rats. It appears, therefore, that the placenta plays the dominant role in the regulation of all of the above parameters of corpus luteum activity during the second half of pregnancy in the rat. The specific factor(s) or mechanism(s) by which the placenta promotes relaxin synthesis, progesterone secretion, and corpus luteum growth have yet to be clearly and unequivocally characterized in the rat. The fact that conceptus number and the rate and/or degree of increase of all of the parameters of luteal activity measured from d12 through d18 are directly related is consistent with the possibility that the placental support of these activities is mediated through a common mechanism during this period in the rat.

Oestradiol administration raises luteal LH receptor levels in intact and hysterectomized pigs.

Occupied and unoccupied LH receptors in corpora lutea, and LH and progesterone concentrations in circulating plasma, were measured in non-pregnant gilts that had been treated with oestradiol-17 beta benzoate to prolong luteal function. Oestradiol benzoate (5 mg, administered on Day 12 after oestrus) delayed luteal regression and the decline in LH receptor levels at luteolysis and raised unoccupied receptor levels from 11.8 +/- 1.14 fmol/mg protein on Days 10--15 after oestrus to 31.8 +/- 3.26 fmol/mg protein on Days 15--21. There was no simultaneous rise in occupied receptor levels and occupancy decreased from 29.8 +/- 3.01 to 11.5 +/- 1.26%. Basal plasma LH concentrations were unchanged by oestradiol, but mean corpus luteum weight and plasma progesterone concentrations were slightly reduced. Oestradiol benzoate on Day 12 caused a similar increase in unoccupied receptor levels in gilts hysterectomized on Days 6--9 after oestrus, from 17.0 +/- 5.83 to 34.5 +/- 6.00 fmol/mg protein, determined on Days 15--18. Plasma concentrations of LH and progesterone were unchanged by oestradiol. Unoccupied receptor levels in corpora lutea and plasma LH and progesterone were unaltered by hysterectomy in untreated gilts. Occupied receptor levels were not influenced by hysterectomy or oestradiol. It is concluded that oestradiol-17 beta raises luteal LH receptor levels by a mechanism independent of the uterus.

Unilateral uteroovarian relationship in pregnant cattle and role of uterine vein

The hypothesis of a unilateral uteroovarian relationship between location of embryos and maintenance of corpora lutea (CL) was tested in superovulated cattle. Ovulations were induced in both ovaries and a uterine horn was isolated subsequent to insemination to produce unilateral pregnancy. The mean weight of CL on day 24 was greater (P<.05) on the gravid side (2580 mg) than on the nongravid side (1200 mg; n=5), supporting the hypothesis. Involvement of the main uterine vein in the unilateral pathway between a gravid horn and the adjacent ovary was demonstrated in an experiment which utilized separation of uterine horns, anastomosis of uterine veins between sides, and insertion of embryos into one side by embryo transfer. Mean weight of CL on day 24 was less (P<.05) when the gravid horn was contralateral to the CL (950 mg; n=3), than when the gravid horn was ipsilateral to the CL (4760 mg) or when the gravid horn was contralateral to the CL and the uterine vein from the contralateral side was anastomosed to the vein on the ipsilateral side (3580 mg; n=3).

Accuracy of Predicting Stages of Bovine Estrous Cycle by Gross Appearance of the Corpus Luteum

Four readily identifiable changes in appearance of corpora lutea (Stages I to IV) occur during a bovine estrous cycle. Accuracy of estimating the stage of an estrous cycle by appearance of corpora lutea was determined in a double-blind study. One investigator observed estrus in a group of heifers while another with no prior knowledge of reproductive histories of the heifers estimated stage of the estrous cycle by visual inspection of their corpora lutea. Stage of the estrous cycle (Stage I, days 1 to 4; Stage II, days 5 to 10; Stage III, days 11 to 17; Stage IV, days 18 to 20) was estimated correctly in 41 of 48 heifers. The correlation between estimated and actual days of the estrous cycle was .81. In addition, concentrations of progestins and weights of corpora lutea during estimated stages of the estrous cycle were similar to many other investigations. Stages of the estrous cycle in heifers can be estimated from appearance of corpora lutea.

The effect of estradiol on hormonally stimulable adenylyl cyclase activity and on progesterone production in normal and regressing corpora lutea from control and human chorionic gonadotropin-treated pseudopregnant rabbits.

The effect of administering a luteolytic dose of hCG (100 IU, iv) to 9-day pseudopregnant rabbits that received either no other treatment (controls) or one of two estradiol (E-1.5 or E-15) treatments was studied. E-1.5 and E-15 consisted of 1.5 μg estradiol (E) every 12 h and 15 μg E every 12 h, respectively; these treatments were administered sc in sesame seed oil starting at 2200 h on day 8 and continued through 2200 h on day 11. Animals were bled daily from days 9–12 and sacrificed between 1000–1100 h on day 12, at which time serum and corpora lutea (CL) progesterone content, weight, and adenylyl cyclase activities stimulated by LH (10 μg/ml) and isoproterenol (Iso; 10−4m) were determined. We found that 1) neither low (E-1.5) nor high (E-15) E treatment prevented functional luteolysis (drop in serum progesterone) induced by hCG; 2) E-15 but not E-1.5 prevented structural luteolysis (CL weight loss) induced by hCG; 3) E-15 but not E-1.5 resulted in CL progesterone levels that, after hCG, were indistingu...

Reduction by human chorionic gonadotropin of the luteolytic effect of prostaglandin F 2 α in ewes

The ability of human chorionic gonadotropin (HCG) to reduce the luteolytic effect of prostaglandin (PGF 2 α ) was demonstrated in cycling ewes. As expected, treatment with 10 mg of PGF 2 α alone on Day 10 of the estrous cycle exerted a potent negative effect on the function and structure of corpus luteum (CL) as indicated by reduced plasma progesterone, CL progesterone, and CL weight. However, the identical PGF 2 α treatment failed to significantly reduce either luteal function or luteal weight when administered to ewes that were also treated with HCG on Days 9 and 10 of the estrous cycle. Treatment with HCG alone had a positive effect on CL as indicated by increased plasma progesterone, CL progesterone, and CL weight. Treatment with HCG did not render the CL totally insensitive to the negative effects of PGF 2 α because plasma progesterone was reduced when the dose of PGF 2 α was doubled. Whether CL regressed or continued to function after treatment with both HCG and PGF 2 α appeared to depend upon a balance between the positive and negative effects of the two hormones.

Growth of the corpus luteum and its progesterone content during pregnancy in the tammar wallaby, Macropus eugenii.

Corpora lutea were obtained from wallabies at different stages of pregnancy, following removal of pouch young to initiate embryonic development. Progesterone was present at a concentration of 11.3 ng/mg in quiescent corpora lutea from lactating animals. Progesterone values rose with increasing corpus luteum weight to reach a maximum of 40--50 ng/mg in corpora lutea weighing 50--60 mg. Total progesterone reached a maximum of 1500 +/- 300 (s.e.m.) ng at Days 21--23 after removal of pouch young, but fell markedly at Days 24 and 25 (900 +/- 150 ng) immediately before parturition.

Effect of oestrogen on fetal survival in the rabbit.

Pregnant rabbits (Day 18) were treated i.m. for 3 days with 10 microgram oestradiol 17beta/kg. The number of dead fetuses was significantly greater than in the control animals but corpus luteum weight and peripheral progesterone concentrations were not affected. Fetal death was therefore not due to luteolysis.

Production of chorionic somatomammotropin (oCS), fetal growth and growth of the placenta and the corpus luteum in ewes treated with 2-bromo-alpha-ergocryptine.

Forty ewes treated with bromocryptine (2-bromo-α-ergocryptine) from midgestation onward were compared with 52 control ewes. RIA for PRL revealed that the treated ewes were severely hypoprolactinemic. No modification of the concentrations of ovine chorionic somatomammotropin (oCS) in blood (as determined by radioreceptor assay) occurred with this treatment at any gestational stage; however, between 80 and 100 days of pregnancy, placental oCS concentrations increased four to six times [136 ± 6 μg/g fresh tissue wt (n = 6), as compared with 22 ± 5 μgg/g fresh wt (n = 12), P < 0.001]. Maximal placental oCS levels occurred 1 month earlier (80–85 days) in the treated animals and were twice those of untreated animals (70 ± 5 μgg/g fresh wt, n = 13 at 110–120 days, P < 0.001). From 110–120 days of pregnancy onwards, placental oCS concentrations in treated animals dropped to control levels. Placental and fetal growth as well as oCS and PRL levels in fetal blood were not modified by maternal hypoprolactinemia. Up to 140 days of pregnancy, the weight of the gestational corpus luteum decreased by 14%, but this decrease was highly significant (703 ± 24 mg, n = 32 in the controls; 607 ± 18 mg, n = 38 in the treated ewes; P < 0.01), although it is known that both PRL and LH are necessary to maintain the cyclic corpus luteum in the ewe. It is suggested, first that oCS biosynthesis may depend on some kind of endocrine control and second, that gestational corpora lutea may be maintained, at least in part, by a placental luteotrophic complex.

The influence of dose and duration of estrogen treatment on corpus luteum regression in ewes

Estrogen-induced regression of corpora lutea (CL) was studied in two experiments using 190 cycling ewes. In an experiment with a 3 × 5 factorial design, the minimum amounts of estradiol-17β (E 2), estrone (E 1) and diethylstilbestrol (DES) required to induce CL regression by intramuscular injection were determined. Injections of either 0, 100, 250, 500 or 1,000 μg of each estrogen were administered on days 10 and 11 of the estrous cycle. Each dose level of estrogen significantly reduced CL weight by day 14, and the 250 μg and higher dosages significantly reduced CL progesterone content. The luteolytic potencies of the three estrogens did not differ significantly. In the second experiment, E 2 was infused into the jugular vein of ewes on day 10 of the estrous cycle at a rate of 1.3 to 41.6 μg/hr for either 12, 24, or 48 hours. Infusion of E 2 for 12 hr did not significantly reduce either the weight or progesterone content of CL, even when as much as 500 μg of E 2 (41.6 μg/hr) was administered. In contrast, a total of 62 μg of E 2 infused over a 24-hr period (2.6 μg/hr) significantly reduced CL weight and CL progesterone. Therefore, CL regression induced by infusion of E 2 on day 10 of the cycle was dependent on the duration of the E 2 treatment as well as on the amount of E 2 infused.

Role of rabbit fetuses and placentas in the maintenance of gestation and parturition.

Fifteen pregnant rabbits were used to study the effect of fetectomy on length of gestation, maternal nest building, milk ejection, mortality of pups and placental weight. Fetectomy on day 25 post coitum led to normal delivery of the placentas at term, nest building and milk ejection, indicating that the fetuses were not required for maintenance of gestation and initiation of parturition. In a second experiment involving forty pregnant does, the effects of fetectomy (on days 21 and 25) and dexamethasone administration (on days 25 and 26) on length of gestation and on parturition-related variables were investigated. Fetectomy on day 21, despite dexamethasone administration, did not lead to placental delivery at any time. Dexamethasone treatment on days 25 and 26 induced parturition earlier in the presence of the fetuses than in their absence and the induction of parturition increased the number of stillborn pups. Maternal nest building and milk ejection were normal except does fetectomized on day 21 failed to build nests or eject milk. Corpora lutea from does fetectomized on day 21 or 25 weighed less than those from nonoperated does. Within each stage of gestation and each type of surgery, dexamethasone appeared not to have altered ovarian and corpora lutea weights. (Key Words: Rabbit, Fetectomy, Placentas.

A luteolytic interaction between estradiol and prostaglandin F2alpha in hysterectomized ewes.

The hypothesis that the luteolytic interaction between prostaglandin F/sub 2/..cap alpha..(PGF/sub 2/..cap alpha..) and estradiol is independent of the uterus was evaluated in hysterectomized and hysterectomized, ovarian x-irradiated ewes. Hysterectomies and either sham or x irradiations were performed 7 or 8 days after observation of estrus. After a 72 h recovery period the effects of injections on two consecutive days of: (1) the vehicles for PGF/sub 2/..cap alpha.. and estradiol benzoate (E/sub 2/B), (2) 3.5 mg PGF/sub 2/..cap alpha.., (3) 750 ..mu..g E/sub 2/B, and (4) 3.5 mg PGF/sub 2/..cap alpha.. + 750 ..mu..g E/sub 2/B were compared in sham and ovarian x-irradiated ewes. Results of plasma progesterone determinations and mean corpus luteum weights showed that treatment with PGF/sub 2/..cap alpha.. alone was not luteolytic. Treatment with E/sub 2/B alone had marginal effects on corpus luteum function. For example, plasma progesterone concentrations were depressed (P < 0.05) when compared to vehicle treated controls at isolated times between 60 and 96 h after the first injection in both sham and x-irradiated ewes, and the mean corpus luteum weight for the x-irradiated group was less than that found for the control groups (P < 0.05). However, following treatment with both PGF/sub 2/..capmore » alpha.. and E/sub 2/B, complete luteolysis was observed in three of four sham and three of four x-irradiated ewes. These data suggest a luteolytic interaction between estradiol and PGF/sub 2/..cap alpha.. that is independent of the uterus. In a second experiment, hysterectomized sham and x-irradiated ewes were treated with 7.0 mg PGF/sub 2/..cap alpha... Plasma progesterone determinations and corpus luteum weights suggested that complete luteolysis was observed in all sham-irradiated ewes and in two of four x-irradiated ewes. This dose of PGF/sub 2/..cap alpha.. also proved to be effective in three of four x-irradiated, uterine intact ewes. These results suggest that ovarian follicles are not an absolute requirement for PGF/sub 2/..cap alpha..-induced luteolysis.« less