Reduced Progesterone Concentrations Research Articles

Luteal function and conception in lactating cows and some factors influencing luteal function after first insemination

The objective of this study was to investigate the types and incidence of luteal sub-function in lactating cows after artificial insemination (AI) and their relationship with pregnancy, and to clarify the relationship between luteal function and parity, body condition score (BCS), milk yield, and dietary intake. In 19 cows, milk samples were collected daily from AI to confirmation of pregnancy. Milk progesterone concentrations were determined by EIA. Based on peak progesterone concentration and the day of onset of luteal phase, 15 of 30 progesterone profiles (50%) were normal, with progesterone concentration reaching 1.0 ng/ml within 5 days after insemination and ≥2.0 ng/ml thereafter. In addition, 6 (20%) were insufficient, (progesterone concentration remained <2.0 ng/ml), 5 (17%) were delayed (progesterone reached 1.0 ng/ml after 5 days), 2 (7%) were both delayed and insufficient, one (3%) was short (progesterone >1.0 ng/ml for only 7 days), and one (3%) remained basal. Cows with a normal profile had a higher ( P<0.05) pregnancy rate than those with an abnormal profile (87% versus 33%, respectively). The amount of progesterone secreted in milk after first AI, as indicated by progesterone area under curve (AUC), was negatively correlated with milk yield ( r=−0.83, P<0.01), dry matter intake ( r=−0.81, P<0.05), total digestible nutrients ( r=−0.82, P<0.05), and digestible crude protein ( r=−0.79, P<0.05). Cows that produced more milk and consumed more dry matter had less progesterone during the luteal phase. In conclusion, abnormal luteal function was associated with reduced pregnancy rates and high milk production and increased dietary intake during breeding were associated with reduced progesterone concentrations.

Direct enzyme immunoassay of progesterone in bovine plasma

ABSTRACTThe present study was undertaken to develop a novel, practical and simple procedure for enzyme immunoassay (EIA) of plasma progesterone in cows. Diluted plasma was heated for 70°C for 30 min and applied directly to wells of a microtitre plate without extraction. Then plasma was incubated with antiprogesterone antibody and horseradish peroxidase‐labeled progesterone. The sensitivity of the assay was estimated as 4.4 pg/mL (0.11 pg/well). The intra‐assay and interassay coefficients of variation were 5.7–19.1% and 6.6–19.3%, respectively. When 0.3, 1 and 3 ng of progesterone were added to plasma, the recovery rates ranged between 79.9 and 108.4%. Only 4 h were needed to complete an assay to measure progesterone concentration. To apply the present direct EIA, progesterone concentration in plasma was assayed in crossbred cows used for the embryo transfer program. During insertion of controlled‐internal drug release (CIDR), progesterone concentrations were kept at a high level, although the removal of CIDR with treatment of dinoprost trometamine reduced progesterone concentration drastically. These results suggest that the present direct EIA is a practical and suitable method for measuring the plasma concentration of progesterone.

Effects of alpha-MSH on progesterone and nitric oxide release by cultured ovarian granulosa cells in experimental rat autoimmune oophoritis.

The peptide alpha-melanocyte-stimulating hormone (alpha-MSH) occurs within the pituitary, brain, skin, ovary and other tissues, and has potent anti-inflammatory activity. For this reason, we examined its effects on an autoimmune disease: the experimental autoimmune-oophoritis (EAO). We analyzed the effect of the peptide on the release of nitric oxide (NO) and progesterone from cultured ovarian granulosa (GL) cells at 0, 7, 14, 21 and 28 days after sensitization of the rats. On day 0 the progesterone levels were higher in estrous rats than those in proestrus and diestrus. The NO amount did not differ among the diverse days of the cycles. The administration of alpha-MSH induced a decrease of NO in estrus and diestrus, but did not affect progesterone release. The EAO rats showed a period of constant diestrus ranging from about 7 to 14 days after immunization. At the onset (day 7) and the end of this period (day 14), the NO significantly increased in estrous rats which was correlated with a reduction in progesterone concentration. This effect was reverted by alpha-MSH. At 21 and 28 days, progesterone release increased only when the rats were in proestrus, while NO production was similar to that on day 0. Administration of alpha-MSH reduced progesterone release when the rats were in proestrus and these results were correlated with an increase in NO only at day 14. The results obtained suggest that alpha-MSH could act as a modulator of EAO, specially when the rats are in estrus.

Presence and Localization of Tumor Necrosis Factor α in the Corpus Luteum of Nonpregnant and Pregnant Pigs1

The objectives of this study were to determine whether tumor necrosis factor alpha (TNF alpha) is present in porcine corpus luteum (CL) and, if so, to ascertain which cells of the CL were associated with TNF alpha. The influence of the reproductive state of the animals on the amount or cellular localization of TNF alpha in the CL was also investigated. Western blot analysis demonstrated the presence of a 34-kDa immunoreactive TNF alpha-like protein in CL from nonpregnant and pregnant pigs. The intensity of TNF alpha immunostaining in bands observed in Western blots did not differ when luteal protein from nonpregnant pigs or from pregnant pigs was analyzed. Positive immunostaining for TNF alpha, determined by immunocytochemistry, was localized within endothelial cells of luteal sections. Positive immunocytochemical staining was recorded in all reproductive states examined except in CL that had undergone functional luteolysis (reduced progesterone concentration). A single-cell assay for TNF alpha secretion (a reverse hemolytic plaque assay) confirmed in vitro secretion of TNF alpha by a cell type in luteal tissue with a size and nuclear morphology similar to an endothelial cell. The presence of TNF alpha in the endothelial cells in functional CL is consistent with a role for TNF alpha in the regulation of vascular development of the CL in swine.

The effects of altered suckling intensity, boar exposure in lactation and gonadotropins on endocrine changes, fertility and the incidence of lactational oestrus in multiparous sows

AbstractOne of the more promising techniques for the improvement of sow productivity has been the use of partial weaning or the separation of the sow and litter for periods of between 3 to 12 h/day towards the end of lactation. The purpose of the present study was to examine changes in steroid hormone concentrations, oestrus and fertility responses in lactating sows subjected to altered sucking, boar exposure and gonadotropins in mid lactation and at weaning. Thirty-two crossbred sows were allocated at random to one of four experimental treatments. Treatment 1 sows (no. = 8) were separated from their respective litters for 3 h/day from 12 days post partum through until weaning which was carried out at 21 days post partum. Treatment 1 sows were also given in-pen boar exposure for 1 h/day between day 12 post partum and weaning. Treatment 2 sows (no. = 8) were given the same protocol of litter separation (LS) and boar exposure (BE) as in treatment 1 and they were also given a combination of gonadotropins (Gn) on day 17 of lactation. Treatment 3 sows (no. = 8) were given LS + BE as above and the sows were injected with Gn on the day of weaning. Treatment 4 sows were controls given no LS, BE or Gn (no. = 8). During lactation, treatment 1 sows exhibited significantly (P &lt; 0·05) reduced progesterone concentrations compared with treatment 2 sows. There were no other significant effects of treatment for any of the periods considered. The separation of sows from their piglets with or without gonadotropic treatment did not result in lactational oestrus in any treated sows. No significant treatment differences were found in the subsequent litter size (piglets born alive or total number of piglets). In conclusion, the present results have demonstrated no significant effects of LS, BE and Gn treatment during lactation on sow and litter performance. This was associated with low levels of peripheral plasma progesterone in all lactating sows.

Influence of prolactin on foetal survival in rabbit does

Experiments were conducted to assess the influence of prolactin levels on foetal survival in pregnant does. All the females were mated within 12 h following parturition (Day 0), and slaughtered on Day 28 to study reproductive performance. In Experiment 1, lactation was terminated at birth and females in the treated group (Group P, n = 34) were injected with 1 mg of ovine prolactin daily from Day 7 to Day 21. Females in the control group (Group CP, n=31) received no prolactin. On Day 16, the ovine prolactin concentration in Group P was 32.5 ng ml −1. The concentration of rabbit prolactin was higher and the serum level of progesterone was lower in Group P than in Group CP on Day 16 ( P < 0.01). The ovulation rate was similar in both groups but late foetal mortality (> Day 15) was significantly higher in Group P (24.5% vs. 10.6%; P < 0.01). In Experiment 2, females were allowed to suckle seven young and received 1 mg of bromocriptine daily from Day 14 to Day 18 (Group B, n = 34). Females in the control group (Group CB, n=31) received no bromocriptine. The concentration of prolactin was lower in Group B than in Group CB on Days 14 and 18 ( P < 0.01), and the concentration of progesterone was higher in Group B on Day 18 ( P < 0.01). The ovulation rate and early and late foetal mortality were similar in both groups but the number of resorbed foetuses was higher in Group B than in Group CB (1 vs. 0.5; P < 0.05). These results suggest that hyperprolactinaemia during lactation is responsible for the reduced progesterone concentration and the increased late foetal mortality observed in pregnant lactating does. However, short-term suppression of prolactin release after suckling does not improve foetal survival.

Genital lesions following long-term administration of clenbuterol in female pigs.

Pathologic findings, lectin histochemistry, and nuclear estrogen receptors were studied in the reproductive organs of gilts treated with clenbuterol. A ration containing 1 ppm of clenbuterol was fed for 40 days to four Landrace x Large white, 9-month-old gilts, weighing 134 to 172 kg at slaughter (gilt Nos. 5-8). Four gilts (Nos. 1-4) served as controls. Treated animals had macroscopic lesions characterized by microcystic ovaries and uterine atrophy. Histopathologic lesions included atretic degeneration of many ovarian follicles, complete absence of functional corpora lutea, a reduction in the number of endometrial glands, and a decrease in cytoplasmic volume of endometrial and glandular epithelial cells. In ovaries, uterus, and vagina lectin histochemistry, performed with thirteen different biotinylated lectins, revealed a different staining distribution between control and treated gilts. The binding pattern of Ricinus communis agglutinin-I (RCA-I) and -II (RCA-II) in the ovaries of control gilts, displayed labeling of cytoplasm in theca interna cells of Graafian follicles. There was no labeling of the same cells in treated gilts. Labeling patterns with Griffonia simplicifolia agglutinin-I (GS-I), Phaseolus vulgaris agglutinin (PHA), RCA-I and RCA-II documented a difference in the vascularity of the theca interna between Graafian follicles of control and treated gilts. The GS-I and Ulex europaeus agglutinin-I (UEA-I) binding patterns in uterus and vagina of treated gilts when compared to control gilts suggested that there was a block of the cycling activity in the proliferative stage. Immunohistochemical staining for estrogen receptors in the endometrium was positive in all but one treated gilts, and negative to weakly positive in control gilts. Serum progesterone concentrations were decreased in treated animals when compared to control; estradiol concentrations were similar in both group of gilts. Cystic ovaries, uterine atrophy, and reduction in progesterone concentrations suggested that clenbuterol changed ovarian hormonal activity in treated animals.

The effect of RU486 administered during the proliferative and secretory phase of the cycle on the bleeding pattern, hormonal parameters and the endometrium.

Seventeen healthy women aged 24-45 years with regular menstrual periods, proven fertility and not using steroidal contraceptives or IUD were recruited for the study. The volunteers were followed during one control, one treatment and one follow-up cycle. Daily morning urine samples were obtained during the control and the treatment cycle. The samples were analysed with regard to pregnanediol glucuronide (P2-G), oestrone glucuronide (E1-G), oestradiol (E2), progesterone (P4), LH and creatinine. During the entire 3-month study the subjects kept a record of uterine bleeding and side effects. The subjects received 50 mg RU486 daily either on cycle days 7-10 (n = 7) or on cycle days 20-23 (n = 10). An endometrial biopsy was taken on cycle day 10 in the first group and on cycle days 21-28 in the second group of patients. Treatment during the proliferative phase caused significant prolongation of the cycle length due to a delay of the oestrogen and LH surge. However, once the oestrogen concentration started to increase, the remaining part of the cycle was normal. The length of the follow-up cycle was similar to that of the control cycle. The morphology of the endometrium did not differ from control samples taken from untreated women at the same time of the cycle. All ovulating women (n = 9) treated in the mid-luteal phase started to bleed on the 3rd to 4th day of the treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryonic Loss in Mares: Incidence, Possible Causes, and Diagnostic Considerations

Fertilization rates were similar for normal and subfertile mares, and much of the difference in fertility between normal and subfertile mares was due to embryonic loss. Fertilization rate estimates for mares ranged from 71 to 96 per cent. The incidence of embryonic loss detected by ultrasonography between Days 11 and 50 was approximately 9 per cent for normal mares, and the estimated incidence of embryonic loss before Day 14 was also 9 per cent. Therefore, the estimated incidence of embryonic loss in normal mares between fertilization and Day 50 is approximately 18 per cent (Fig. 1). In subfertile mares, the corresponding estimate for embryonic loss between fertilization and Day 50 is 80 per cent, with most embryonic losses occurring before Day 14 in subfertile mares (Fig. 1). The high rate of early embryonic loss in subfertile mares could be related to embryonic defects, oviductal environment, or uterine environment. Oviductal embryos from subfertile mares were less viable than embryos from normal mares; therefore, embryonic defects were important in early embryonic losses in subfertile mares. These defects might be inherent within the embryo or might arise from the early oviductal environment. The uterine environment of subfertile mares was adequate to support normal embryos in early gestation; however, the relationship between the uterine environment and the increased metabolic demands of the conceptus in the late embryonic or early fetal periods requires further study. The uterine environment is also altered in mares with endometritis; therefore, endometritis may also be an important factor in embryonic loss in some mares. Uterine-induced luteolysis, as well as the effect of the pathogen or the resulting inflammation, may lead to embryonic loss. An increased susceptibility of some subfertile mares to endometritis could result in embryonic loss secondary to a postcoital endometritis that persists until the embryo reaches the uterus at Days 5 or 6 postovulation. Although progesterone is critical to embryonic survival, the cause-and-effect relationship between progesterone and spontaneous embryonic loss remains unclear. Reduced progesterone concentrations could be related to endometritis, failure of maternal pregnancy recognition, or luteal insufficiency. Progesterone supplementation may be indicated for some mares, but the value of exogenous progesterone for prevention of spontaneous embryonic loss has not been critically tested. A number of other factors have been associated with embryonic loss in mares.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of Trypanosoma congolense infection on the oestrous cycle of the goat

The oestrous cycle of four goats was monitored during the course of an infection with T. congolense maintained with sub-curative doses of diminazene aceturate. Four uninfected control goats also given diminazene aceturate acted as controls. Cyclical ovarian function was monitored by daily determination of plasma progesterone concentrations. According to plasma progesterone profiles, control goats continued to cycle throughout the experiment, completing 24 cycles in total. Mean (± SEM) cycle length in the control of goats was 21·1 ± 0·8 days, with mean plateau progesterone concentrations during the luteal phase averaging 8·95 ± 0·28 ng/ml. Three goats developed persistent corpora lutea following T. congolense infection. In two of these goats the luteal phase was extended for 48 and 94 days respectively, and the presence of corpora lutea on the ovaries confirmed at autopsy. In the third goat, the persistent corpus luteum regressed spontaneously after an extended cycle of 53 days. After a short 6 day cycle this goat completed 2 oestrous cycles of normal length. Progresterone concentrations were reduced by approximately half during the period of extended luteal function in the 3 infected goats with persistent corpora lutea. The fourth infected goat continued to cycle throughout the experiment, but also exhibited reduced progesterone concentrations in the cycle following infection.

Effect of an inhibitor of 3 beta-hydroxysteroid dehydrogenase on progesterone concentrations and embryo survival in sheep.

The effect of an inhibitor of 3 beta-hydroxysteroid dehydrogenase on peripheral progesterone concentration during the luteal phase of the oestrous cycle and on embryo survival was determined in sheep. Following administration of 10, 50, 100 or 250 mg epostane (4,5-epoxy-17-hydroxy-4,17,dimethyl-3-oxo-androstane-2-carbonitrile) progesterone concentrations were significantly lower than control levels 4 h after injection, from 2.5 to 22 h, 1.5 to 24 h and 1 to 24 h after injection respectively. There appeared to be no effect on peripheral oestradiol concentrations. Adrenal progesterone production was small and not influenced by epostane treatment. Epostane was administered on day 9 of the oestrous cycle to cause a reduction in progesterone concentrations for approximately 12-18 h on day 9 only (group 1, 250 mg epostane on day 9), or a series of such reductions on 3 consecutive days (group 2, 50 mg epostane on days 9, 10 and 11) or a continuous reduction for 3 days (group 3, 250 mg epostane on days 9, 10 and 11). The proportion of ewes that were pregnant was significantly (P less than 0.05) lower in ewes treated to give a continuously low progesterone concentration for 3 days than in either controls or ewes in which progesterone concentration was reduced for less than 24 h (in controls and groups 1, 2 and 3 the proportion was 85, 92, 54 and 18% of ewes treated respectively). Embryo survival was not affected by administration of 250 mg epostane on days 9, 10 and 11 if luteal phase levels of progesterone were maintained by insertion of a silicone elastomer implant of the steroid.(ABSTRACT TRUNCATED AT 250 WORDS)

Mastopathie und Mammakarzinom: Besteht ein typisches Hormonprofil?

Carcinoma of the breast and mastopathy are statistically correlated with the functioning of the gonads. The authors studied whether in 58 women with carcinoma of the breast and in 36 patients with mastopathy any change was seen in the secretory pattern of gonadal steroids and whether there were any latent changes in the secretion of prolactin and TSH. A group of 43 women with benign gynaecological diseases served as controls. Before making the diagnosis via immediate section for microscopic examination we determined the basal values of prolactin, LH, FSH, TSH and the oestrogen fractions E1, E2, E3, total oestrogens and progesterone. In addition, we measured the increase in prolactin and TSH after stimulation with metoclopramide. Postoperatively this was followed by measuring the basal values of prolactin and TSH and their secretory performance in respect of TRH. All histological diagnoses were made by an experienced pathologist. Examinations were performed under strictly standardised conditions, taking into account stress, circadian variation and the nutritional status. The following group-specific significant results were obtained (p less than 0.05-0.01): Mastopathy: high serum values of all oestrogen fractions and of total oestrogens, high PRL release through MTC stimulation, prolactin secretory effect after MTC in accordance with the degree of severity of epithelial proliferation, early onset of menopause. Carcinoma of the breast: Low PRL and TSH release on MTC stimulation, low progesterone concentrations during the second cycle phase, relatively high serum concentrations of oestradiol during the first cycle phase, PRL basal values increased postoperatively, compared with preoperative values. The results led to the following conclusions: In mastopathy patients there is a connection between high oestrogen concentrations and consecutively high prolactin release. The morphological substrate is represented by an enhanced proliferation of epithelium. In patients with cancer of the breast reduced progesterone concentrations during the second half of the cycle lead us to suspect an increased incidence of luteal insufficiency; in addition, it appears that the daily prolactin secretion rate in this group is on a reduced level.

Effects of chronic treatment with a GnRH agonist on oestrous behaviour and on the secretion of LH and progesterone in the ewe

A study was carried out to investigate a novel approach to oestrus synchronization in the ewe by treatment with a gonadotrophin releasing hormone (GnRH) agonist. Groups of ewes were initially treated on Day 2, 10 or 14 of the oestrous cycle with 10 μg GnRH analogue (D-Ser(Bu t) 6 des Gly GnRH ethylamide) per ewe per day for 14 days. Behavioural oestrus was inhibited during GnRH agonist treatment and recurred from 8 to 38 days after the treatment in an unsynchronized manner. Luteal activity during treatment was not impaired but reduced progesterone concentrations occurred in cycles after the treatment. The rhythm of ovarian function, generally characterized by prolonged follicular development, was impaired. During the treatment and subsequent recovery period, integrity of pituitary function was examined by measuring luteinizing hormone (LH) after GnRH agonist was injected, and after stimulation test doses of 150 ng natural GnRH were administered. During treatment there was, with time, a decline in pituitary response to the agonist which suggested that pituitary release of LH was exhausted. After the 14-day treatment the stimulation test with GnRH revealed a gradual return to normal responsiveness although this was not complete three weeks after the treatment when compared to control ewes. This lowered pituitary activity could cause the impaired ovarian function.

Effects of progesterone administered to dairy heifers on sensitivity of corpora lutea to PGF 2α and on plasma LH concentration

To determine whether progesterone facilitates PGF 2α-induced luteolysis prior to day 5 of the estrous cycle, 48 Holstein-Friestian heifers were assigned at random to four treatments: 1) 4 ml corn oil/day + 5 ml Tris-HCl buffer (control); 2) 25 mg prostaglandin F 2α (PGF 2α); 3) 100 mg progesterone/day (progesterone); 4) 100 mg progesterone/day + 25 mg PGF 2α (combined treatment). Progesterone was injected subcutaneously daily from estrus (day 0) through day 3. The PGF 2α was injected intramuscularly on day 3. Estrous cycle lengths were decreased by progesterone: 20.2 ± 0.56, 19.2 ± 0.31 (control and PGF 2α); 13.2 ± 1.40, and 11.7 ± 1.27 (progesterone and combined). The combination of progesterone and PGF 2α did not shorten the cycle any more than did progesterone alone (interaction, P>0.05). PGF 2α treatment reduced progesterone concentrations on day 6 (P<0.05) and both progesterone and PGF 2α reduced plasma progesterone on day 8 (P<0.01 and P<0.05, respectively). LH was measured in blood samples collected at 10- min intervals for 4 hr on day 4 from three heifers selected at random from each of the four treatment groups. Mean LH concentration for control heifers ranged from 0.35 to 0.63 ng/ml (overall mean, 0.49 ng/ml) and for progesterone-treated heifers ranged from 0.12 to 0.30 ng/ml (overall mean, 0.23 ng/ml). LH concentrations were greater in control heifers (P<0.01). The mean LH pulse rate for control heifers was 2.7 pulses/heifers/4 hr, while that for the progesterone-treated heifers was 1.7 pulses/heifer/4 hr. The mean pulse amplitude for control and progesterone treatments was 0.47 ng/ml and 0.36 ng/ml, respectively. Neither pulse amplitude nor frequency were different between treatment groups.

Effect of aminoglutethimide phosphate on in vitro oestradiol stimulated progesterone synthesis by rabbit corpora lutea.

Slices of rabbit corpora lutea were incubated for 3 and 8 h with oestradiol-17beta in the presence or absence of aminoglutethimide phosphate (AGP) in order to identify a possible site(s) of action of oestrogen on progesterone synthesis. Oestradiol was unable to increase progesterone biosynthesis above controls in luteal tissue exposed to AGP during either incubation period. AGP alone significantly reduced progesterone concentrations and synthesis from [14C]acetate at both time periods while oestradiol alone increased progesterone mass at 8 h. Changes in 20alpha-OH progesterone typically paralleled those of progesterone at 3 h but no effect of the inhibitor was seen at 8 h. Except for an increase in 14C-incorporation into cholesterol esters in the AGP-treated groups at 3 h the concentration or synthesis of sterols from labelled acetate did not respond to treatment. These results suggested that cholesterol side chain cleavage and cholesterol synthesis are not major in vitro sites of action of oestradiol in the rabbit corpus luteum.

Luteolysis Following Carotid or Ovarian Arterial Injection of Prostaglandin F2α in Mares

On the day of ovulation (Day 0), 20 pony mares were randomly assigned to one of five groups (4 mares/group) which were given intracarotid arterial (ICA) and intraovarian arterial (IOA) injections on Day 7 as follows: 1) vehicle ICA, vehicle lOA (control); 2) .125 mg PGF20 ICA, vehicle IOA; 3) vehicle ICA, .125 mg PGF20 lOA; 4) .250 mg PGF20 ICA, vehicle lOA; or 5) vehicle ICA, .250 mg PGF20 lOA. Peripheral plasma progesterone and LH concentrations were determined for 0 (pretreatment) and .1, .25, .50, .75, 1, 6, 12, 24, 48, 72 and 96 h posttreatment. The intervals (days) from treatment to cstlus and ovulation, respectively, were shorter (P<0.05) for mares given IOA injection of .125 mg PGF20 (4.7, 12.8), ICA injection of .250 mg PGF20 (6.5, 14.8), or IOA injection of .250 mg PGF20 (2.8, 11.2), than for controls (11.8, 19.5). The intervals for mares given ICA injection of .125 mg PGF20 (9.2, 18.5) did not differ from controls. Compared to pretreatment samples (0 h), progesterone concentration did not change significantly throughout the blood sampling period in mares given ICA injection of .125 mg PGF20; however, a significant reduction in progesterone concentration occurred by 24 h after treatment in mares given IOA injection of .125 mg PGF20. Plasma LH concentration (ng/ml) was higher (P<0.05) at 12 h (3.4) than at 0 h for the .250 mg IOA group (0.8), but did not change significantly in the other groups. The correlation between progesterone and LH was significant for mares which were given .125 mg IOA (r=-.65) and .250 mg IOA (r=-.82). The IOA injection of PGF20 was more effective in causing luteolysis than ICA injection of PGF2 �. These data indicate that the principal site of luteolytic action of exogenous PGF20 in the mare is at the ovarian rather than at the hypothalamic-pituitary level.

Interaction between prolactin, LH, neurohypophysial hormones and hysterectomy on luteal function in rats.

Functional corpora lutea (CL), which were capable of sustaining high levels of plasma progesterone, were maintained in hypophysectomized rats by transplantation of the pituitary or by daily treatment with exogenous prolactin. Treatment of autografted rats with exogenous LH (20 μg/day) for 6 days greatly reduced the plasma concentration of progesterone. Injections of LH to autografted rats for only 2 days markedly reduced progesterone in one half of the experimental animals. Even though exogenous LH was clearly luteolytic in autografted rats, the response in prolactin-treated, hypophysectomized rats depended upon the exact timing of each LH injection relative to each prolactin injection. Exogenous LH for 6 days greatly decreased plasma progesterone when each LH injection (1100 and 2000 hr) occurred 3 hr after a prolactin injection (0800 and 1700 hr). Injection of LH 3 hr before each prolactin injection had no effect on the concentration of plasma progesterone which was the same as in controls treated only with prolactin. Simultaneous injection (0800 and 1700 hr) of LH and prolactin produced an intermediate effect characterized by a slight reduction in progesterone concentration in some rats. The permissive effects of endogenous prolactin and of exogenous prolactin injected 3 hr before LH were manifested in the ability of exogenous LH, given for several days, to induce functional luteolysis and decrease plasma progesterone. Treatment of autografted rats with large dosages of neurohypophyseal hormones did not affect the plasma concentration of progesterone. Hysterectomy of pituitary intact, pseudopregnant rats had no effect on plasma progesterone on days 8 and 10. Plasma progesterone in hysterectomized animals remained elevated on days 12 and 14 whereas the levels in sham-operated controls declined.

Correlation of the secretion of ovarian steroids with function of a single generation of corpora lutea in the immature rat.

Ovulation and luteinization have been artificially induced in prepuberal rats by the administration of 4 IU PMS. Evidence for luteal function was provided by the establishment of pseudopregnancy and the induction of deciduomata. The animal preparation has been successfully used to determine the secretory pattern of ovarian steroids during the first ovulation cycle and pseudopregnancy, to obtain quantitative data on the “functional” capacity of the first generation corpora lutea, and to relate ovarian 20α-OH-steroid dehydrogenase activityactivity to luteal function. Preovulatory secretion of progesterone has been related to the discharge of the ovulating hormone. Post-ovulatory secretion of progesterone has been correlated with luteal function. Ovarian 20α-OH-steroid dehydrogenase activity, localized biochemically in the corpora lutea, provided an index of luteolysis. Increasing enzyme activity resulted in increased 20α-OH-pregn-4-en-3-one and reduced progesterone concentrations in ovarian effluent blood a...