Functional anatomy of the ovaries of pregnant and lactating Cape porcupines, Hystrix africaeaustralis

The constituent cell types of the ovary of the porcupine were similar to those of New World hystricomorph rodents and accessory corpora lutea and luteal bodies were formed through the luteinization of the membrana granulosa or theca interna of antral follicles. All luteal bodies were histologically similar. The total volume of luteal tissue per female was not affected by fetal age and was unrelated to circulating concentrations of maternal plasma progesterone. Maternal plasma progesterone concentrations were correlated with fetal age. Follicular activity occurred throughout pregnancy but was not affected by fetal age or related to circulating values of oestradiol-17 beta. The formation of accessory corpora lutea during pregnancy is regarded as important in supplementing progesterone during pregnancy.     

Adrenal and ovarian sources of progesterone secretion in young female fallow deer, Dama dama

Six young female fallow deer, including 3 that were ovariectomized at 9 months of age, were blood sampled at frequent intervals after i.v. injections of (1) ACTH analogue (tetracosactrin), (2) GnRH analogue (buserelin) and (3) saline solution on separate occasions at 11, 13, 15 and 18 months of age. Relative to prechallenge plasma values, ACTH administration resulted in a 4-10-fold increase in mean plasma progesterone concentrations, but only a 10-45% increase in mean plasma cortisol concentrations, within 40 min for entire and ovariectomized does during the prepubertal periods (11, 13 and 15 months) and for ovariectomized does during the post-pubertal period (18 months). Post-pubertal entire does exhibited high mean basal plasma progesterone concentrations (3-4 ng/ml) indicating a luteal source of secretion, with the ACTH-induced progesterone response being additive to the luteal progesterone but of similar magnitude to responses in the ovariectomized does. There was no significant ACTH challenge effect on mean plasma LH concentrations for entire or ovariectomized does at all ages. GnRH administration had no significant effects on mean plasma concentrations of progesterone and cortisol of entire and ovariectomized does, although there was a small increase in mean plasma progesterone values in post-pubertal does that may have reflected a luteal response to GnRH (via LH). GnRH challenge resulted in marked increases in mean plasma LH concentrations but the response patterns were different for the 2 types of does, being more rapid and of higher magnitude for ovariectomized does.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of luteinizing hormone (LH), pregnancy-specific protein B (PSPB), or arachidonic acid (AA) on secretion of progesterone and prostaglandins (PG) E (PGE; PGE(1) and PGE(2)) and F(2alpha) (PGF(2alpha)) by ovine corpora lutea of the estrous cycle or pregnancy in vitro

LH regulates luteal progesterone secretion during the estrous cycle in ewes and cows. However, PGE, not LH, stimulated ovine luteal progesterone secretion in vitro at day 90 of pregnancy and at day 200 in cows. The hypophysis is not obligatory after day 50 nor the ovaries after day 55 to maintain pregnancy in ewes. LH has been reported to regulate ovine placental PGE secretion up to day 50 of pregnancy and by pregnancy-specific protein B (PSPB) after day 50 of pregnancy. The objective of this experiment was to determine if and when a switch from LH to PGE occurred as the luteotropin regulating luteal progesterone secretion during pregnancy in ewes. Ovine luteal tissue slices of the estrous cycle (days 8, 11, 13, and 15) or pregnancy (days 8, 11, 13, 15, 20, 30, 40, 50, 60, and 90) were incubated in vitro with vehicle, LH, AA (precursor to PGE(2) and PGF(2alpha) synthesis), or PSPB in M199 for 4 h and 8 h. Concentrations of progesterone in jugular venous plasma of bred ewes increased (P< or =0.05) after day 50 and continued to increase through day 90. Secretion of progesterone by luteal tissue of non-bred ewes on days 8, 11, 13 and 15 and by bred ewes on days 8, 11, 13, 15, 20, 30, 40, and 50 was increased (P< or =0.05) by LH, but not by luteal tissue from pregnant ewes after day 50 (P> or =0.05). LH-stimulated progesterone secretion by luteal tissue from day 15 bred ewes was greater (P< or =0.05) than day 15 luteal tissue from non-bred ewes. Concentrations of progesterone in media were increased (P< or =0.05) when luteal tissue from pregnant ewes on day 50, 60, or 90 were incubated with AA or PSPB. Concentrations of PGE in media of non-bred ewes on days 8, 11, 13, or 15 and bred ewes on days 8 and 11 did not differ (P> or =0.05). Concentrations of PGE were increased (P< or =0.05) in media by luteal slices from bred ewes on days 13, 15, 20, 30, 40, 50, 60, and 90 of vehicle, LH, AA or PSPB-treated ewes. In addition, PSPB increased (P< or =0.05) PGE in media by luteal slices from pregnant ewes only on days 40, 50, 60, and 90. Concentrations of PGF(2alpha) were increased in media (P<0.05) of vehicle, AA, LH, or PSPB-treated luteal tissue from non-bred ewes and bred ewes on day 15 and by luteal tissue from bred ewes on days 20 and 30 after which concentrations of PGF(2alpha) in media declined (P< or =0.05) and did not differ (P> or =0.05) from non-bred or bred ewes on days 8, 11, or 13. It is concluded that LH regulates luteal progesterone secretion during the estrous cycle of non-bred ewes and up to day 50 of pregnancy, while only PGE regulates luteal progresterone secretion by ovine corpora lutea from days 50 to 90 of pregnancy. In addition, PSPB appears to regulate luteal secretion of progesterone from days 50 to 90 of pregnancy through stimulation of PGE secretion by ovine luteal tissue.     

Temporal relationships between peripheral plasma concentrations of oxytocin, progesterone and 13, 14-dihydro-15-keto-prostaglandin F2α during the oestrous cycle and early pregnancy in the ewe

Peripheral plasma concentrations of oxytocin, 13,14-dihydro-15-keto-prostaglandin F_2α(PGFM), progesterone and LH were determined at 3 hourly intervals during the oesterous cycle (n = 3) and in early pregnancy (n = 4) in sheep. The progesterone and LH concentrations showed that the cycling ewes were samples during the periods of luteal regression (decreasing progesterone concentrations), the preovulatory gonadotrophin surge and the beginning of the next luteal phase (increasing progesterone concentrations). The pregnant ewes had basal LH concentrations and luteal phase concentrations of progesterone (>lng/ml afte day 5 following mating) throughout the whole of the sampling period. Oxytocin concentrations in the non-pregnant ewes decreased around the time of luteal regression to reach low concentrations (mean concentrations of approximately 18pg/ml) during the preovulatory period and then increased after the preovulatory surge. PGFM concentrations exhibited a pulsatile pattern with increasing concentrations as progesterone levels fell. In the pregnant ewes oxytocin concentrations gradually fell until approximately 16 days post-mating (approximately 7–8pg/ml). The magnitude of the pulses in PGFM concentrations were also lower than in the cycling ewes. These results demonstrate that the increased concentrations of PGFM which are found during the period of luteal regression are not caused by increased peripheral concentrations of oxytocin.     

Plasma concentrations of 13,14-dihydro-15-keto prostaglandin F2-alpha (PGFM), progesterone and estradiol in pregnant and nonpregnant diestrus cross-bred bitches

The canine corpus luteum (CL) typically sustains elevated plasma progesterone concentrations for 2 months or more, with a peak approximately 15-25 days after ovulation, followed by a slow decline. The processes involved in the slow, protracted regression of the CL over the remaining 1.5-2-month period in nonpregnant bitches and until shortly prepartum in pregnant bitches are not well characterized. The rapid luteolysis that occurs immediately prepartum appears to be a result of a prepartum rise in peripheral PGF. The potential role of PGF in the slow regression process in the several weeks preceding parturition and in nonpregnant bitches after 15-25 days after ovulation is not known. Therefore, plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2-alpha (PGFM), progesterone (P4) and estradiol (E2) were determined and compared in bitches during nonpregnant diestrus (n = 9) or pregnancy (n = 8). During the gradual decrease in plasma concentrations of progesterone in both groups, the P4 pattern appeared unrelated to changes in either E2 or PGFM concentrations. The PGFM pattern was different between diestrus and pregnant bitches (P > 0.01); there was an apparent progressive but slow increase in PGFM in pregnant bitches from Days 30 to 60, followed by a large increase prior to parturition; concentrations declined immediately postpartum. However, there were no increases in PGFM during the same interval in nonpregnant bitches. Mean estradiol concentrations were sporadically elevated during the last third of pregnancy and less so in nonpregnant diestrus; there was no acute prepartum increase in estradiol associated with the PGFM increase. In summary, although there were no apparent changes in peripheral PGF2alpha concentration involved in regulating the slow protracted phase of luteal regression in nonpregnant bitches, modest increases in PGFM may play a role in ovarian function after mid-gestation in pregnant bitches. Furthermore, the acute prepartum rise in PGFM was not dependent on any concomitant increase in estradiol concentrations.     

Endocrine profiles during the estrous cycle and pregnancy in the Baird's tapir (Tapirus bairdii)

Serum samples were collected 1–3 times weekly from two Baird's tapirs (Tapirus bairdii) for 6 months in 1987–1988, and for more than 3 consecutive years beginning in 1989 to characterize hormone patterns during the estrous cycle and pregnancy. Based on serum progesterone concentrations, mean (±SEM) duration of the estrous cycle (n = 20) was 30.8 ± 2.6 days (range, 25–38 days) with a luteal phase length of 18.1 ± 0.4 days (range, 15–20 days). Mean peak serum progesterone concentrations during the luteal phase were 1.35 ± 0.16 ng/ml, and nadir concentrations were 0.19 ± 0.03 ng/ml during the interluteal period. Distinct surges of estradiol preceded luteal phase progesterone increases in most (14/20) cycles. Gestation length was 392 ± 4 days for three complete pregnancies. Mean serum progesterone concentrations increased throughout gestation and were 1.83 ± 0.13, 2.73 ± 0.13, and 4.30 ± 0.16 ng/ml during early, mid- and late gestation, respectively. Serum estradiol concentrations began to rise during mid-gestation, increasing dramatically during the last week of pregnancy. Patterns of serum estriol and estrone secretion during pregnancy were similar to that observed for estradiol. In contrast to progesterone and estrogens, serum cortisol concentrations were unchanged during pregnancy or parturition. Females resumed cycling 16.2 ± 2.0 days after parturition (n = 4) and, on two occasions, females became pregnant during the first postpartum estrus. These data suggest that the tapir cycles at approximately monthly intervals and that increases in serum progesterone are indicative of luteal activity. The interluteal period is relatively long, comprising approximately 40% of the estrous cycle. During gestation, progesterone concentrations are increased above luteal phase levels, and there is evidence of increased estrogen production during late gestation. The absence of increased cortisol secretion at the end of gestation suggests that this steroid does not play a major role in initiating parturition in this species. © 1994 Wiley-Liss, Inc.     

Relationship of pre-ovulatory follicle size, estradiol concentrations and season to pregnancy outcome in dairy cows

This study was carried out to evaluate effects of pre-ovulatory follicle size, plasma concentrations of estradiol and progesterone, and season on pregnancy outcomes in dairy cows. Holstein cows (n = 144) were synchronized and inseminated (Ovsynch/TAI protocol) in two distinct periods (cold versus warm season). Blood samples were collected daily from AI (day 0) to day 8 and on days 15, 22, 29, 36 and 64 to measure progesterone and estradiol. Pregnancy diagnosis was performed at days 29, 43 and 64. The pre-ovulatory follicle size was larger and the plasma estradiol concentrations on the day of AI were greater in animals that became pregnant. Plasma progesterone concentrations diverged and became greater after day 5 post-AI, in cows diagnosed pregnant, as compared to non-pregnant cows. The overall pregnancy rate (33%) or late embryonic/early fetal losses (23%) did not differ between seasons, but plasma estradiol concentrations on the day of AI and plasma concentrations of progesterone in pregnant cows were lower in the warm season. Reduced CL function, measured as plasma progesterone concentrations, from days 22 or 29 post-AI onward for cold and warm season, respectively, was associated with subsequent late embryonic/early fetal mortality. Overall, pregnancy was related to diameter of the pre-ovulatory follicle and plasma E2 on the day of AI, but embryonic/fetal losses were not. Season did not affect these outcomes, even though it influenced luteal function after AI.     

Changes in rat luteal ultrastructure and P450scc mRNA and protein content after in vivo treatment with a gonadotropin-releasing hormone agonist

Previous studies have demonstrated that plasma progesterone levels decrease in pregnant rats treated in vivo with a gonadotropin-releasing hormone agonist (GnRH-Ag), without changes in testosterone or estradiol levels in ovarian vein plasma. The objective of this study was to determine the loci of GnRH-Ag disruption of progesterone synthesis by examining luteal mitochondria, lipid droplets, cellular composition, and P450 side-chain cleavage (P450scc) enzyme and mRNA content in the pregnant rat. On Day 7 or 11 of pregnancy, osmotic minipumps containing GnRH-Ag were implanted into 5-7 rats. Sham operations were performed on 5-6 controls at each time period. Five micrograms per day of GnRH-Ag were released for about 24 h, after which corpora lutea and jugular vein plasma were collected. The corpora lutea were prepared for microscopy or analyzed for P450scc enzyme and mRNA content. Plasma progesterone levels were measured by RIA. In those rats treated with GnRH-Ag, progesterone levels had decreased, and within the luteal cells, there was an increase in the number of lipid droplets and a decrease in the number of tubular cristae within the mitochondria. Concomitantly, P450scc enzyme and mRNA content decreased on both Day 8 and Day 12 of pregnancy. Also, GnRH-Ag treatment decreased the ratio of large to small steroidogenic luteal cells on Day 8 of pregnancy, but did not alter cellular ratios on Day 12 of pregnancy. These observations suggest that treatment with GnRH-Ag inhibits progesterone synthesis by decreasing the amount of P450scc mRNA and enzyme content, which may alter the mitochondrial cristae structure on Day 8 and Day 12 of pregnancy. The reduction in tubular cristae and P450scc enzyme in the mitochondria may account for the increase in lipid droplets, as less cholesterol is converted to pregnenolone. An additional mechanism of inhibition may be the reduction in the number of large steroidogenic luteal cells, which appear to be the major source of progesterone in the rat corpus luteum on Day 8 of pregnancy.     

Evidence of an association between the survival of embryos and the periovulatory plasma progesterone concentration in the ewe

Plasma progesterone concentration and embryo survival were determined during successive pregnancies in ewes throughout one breeding season. The probability of an embryo surviving was associated with the progesterone concentration on the days around ovulation, with the timing of the increase from periovulatory to luteal values, and with the rate at which progesterone concentrations increased. Individual embryo survival decreased both as the number of corpora lutea increased, and towards the end of the breeding season; the latter effect could be explained entirely by differences in progesterone concentration. Considerable variation in progesterone secretion and in embryo survival was observed within the same ewes during successive pregnancies. Such variability in progesterone concentrations during early pregnancy may be a cause of some embryo mortality.     

Lipoprotein-stimulated and estradiol-maintained progesterone secretion by dissociated rabbit luteal cells in vitro

Elevated activity of 3-hydroxy-3-methyglutaryl coenzyme A reductase (HMG-CoA reductase) was observed in the rabbit ovary and corpus luteum during pregnancy. Based on this study, it was proposed that de novo cholesterol synthesis rather than the uptake of exogenous plasma cholesterol (lipoproteins) was of primary importance in providing steroid substrate for progesterone synthesis by the rabbit luteal cell. Using a perifusion system, the present study challenges this hypothesis by demonstrating that both low- and high-density lipoproteins (at protein concentrations of 100 micrograms/ml and 50 micrograms/ml, respectively) were able to acutely stimulate progesterone production by dissociated rabbit luteal cells. The increase in progesterone synthesis was due to increased cholesterol substrate and not to protein-enhanced progesterone release. The ability of luteal cells to respond to lipoproteins was dependent on both dose- and sequence of treatment, with high-density lipoprotein (HDL) being unable to stimulate progesterone production if preceded by perifusion with low-density lipoprotein (LDL) or HDL. In addition, 17 beta-estradiol appeared to regulate lipoprotein utilization by attenuating the LDL response after 1 h of perifusion. We conclude that lipoproteins may provide cholesterol substrate for progesterone biosynthesis in vitro and that 17 beta-estradiol, in addition to maintaining progesterone production by luteal cells, may also regulate lipoprotein utilization. Thus, maintenance of steady progesterone secretion in response to estradiol supercedes that of LDL-stimulated progesterone secretion by rabbit luteal cells in vitro. This study suggests an interaction between estrogen and lipoproteins that may prove physiologically important in regulating progesterone production by rabbit luteal cells in vivo.     

The secretion of prolactin in intact and lutectomized pregnant ewes. Effect of the anti-progesterone steroid RU 486.

To study the role, if any, of luteal factors in the control of prolactin secretion during the last two thirds of pregnancy in the ewe, we examined: a) the effect of RU 486 administration on prolactin secretion on days 97, 112 and 131 of pregnancy in five intact ewes and in five ewes from which the corpus luteum (CL) was removed on day 78 of pregnancy; and b) the secretory patterns of prolactin on days 60, 80, 100 and 120 of pregnancy in five intact ewes and in five ewes from which the CL was removed on day 70 of pregnancy. In a pilot experiment, we showed that daily i.v. injections (from day 91 to day 105 of pregnancy) of RU 486 at a dose of 50 mg caused a marked release of prolactin, without any effect on the secretion of progesterone and progression of pregnancy. In experiment 1, a single i.v. injection of 50 mg of RU 486 resulted in a significant (P < 0.01) increase in plasma prolactin concentrations on any day of pregnancy examined in the intact and lutectomized ewes. The prolactin responses (the maximum concentrations, the time to maximum concentrations and the area under the response curves) were not different between the two groups in any stage of pregnancy examined. In the two groups, spontaneous parturition occurred at term with alive lambs. There was no difference between the two groups in gestation length and lamb birth weight. In experiment 2, we showed that plasma concentrations of prolactin fluctuated in a pulsatile manner during the last two-thirds of pregnancy. The mean prolactin concentrations, the frequency and the amplitude of prolactin pulses were not significantly different between the intact and the lutectomized ewes in any stage of pregnancy examined. In conclusion, these experiments demonstrated that the ovine CL of pregnancy is not involved in the control of prolactin secretion in the ewe. The stimulation of prolactin secretion by the RU 486 is probably due to its anti-progesterone action exerted at the level of the receptor. The placental progesterone plays a central role in the control of prolactin secretion during the last two-thirds of pregnancy.     

Uterine oxytocin receptors in cyclic and pregnant cows.

Binding of [3H]oxytocin to uterine subcellular preparations ('oxytocin receptor concentrations') was measured in uterine tissue of heifers and multiparous dairy cows at various stages of the oestrous cycle and during early pregnancy. A method for the assay of ovine uterine oxytocin receptors was optimized for use on bovine tissue. Oxytocin receptor concentrations were increased in cyclic animals around the period of luteolysis and oestrus, rising on Day 15 in endometrium and on Day 17 in myometrium while pregnant animals showed no comparable rise. Receptor concentrations then declined on Day 3 after oestrus in myometrium and on Day 5 in endometrium. Some cyclic animals did not show the expected rise in receptors in the late luteal phase; these animals had abnormally high progesterone concentrations for this stage of the cycle. In animals slaughtered on Day 18 after oestrus and/or insemination which had low oxytocin receptor levels, plasma progesterone concentrations were consistently high; while all animals showing the late luteal phase elevation in receptor values had low progesterone concentrations. Oxytocin receptor and progesterone concentrations were negatively correlated (P less than 0.05). These data support the hypothesis that oxytocin receptor level is a key factor in the process of luteolysis in cattle and that in pregnancy there is suppression of uterine oxytocin receptor at the expected time of luteolysis. We suggest that uterine oxytocin receptor levels are partly controlled by circulating steroid hormones and are suppressed during early pregnancy.     

Interrelationships between progesterone, 13,14-dihydro-15-keto PGF-2 alpha (PGFM) and LH in cyclic and early pregnant cows

Plasma progesterone and LH secretion patterns were examined in 18 mature dairy cows during the oestrous cycle and after insemination. Blood samples were collected every 15 min for 8 h per day on Days 3, 5, 6, 7, 8, 9, 10, 12, 14, 16, 17, 18, 19, 20 and 21 of the oestrous cycle, then, in the same cows, at the same times during early pregnancy. PGF-2 alpha secretion rates (as determined by plasma PGFM concentrations) were also monitored on Days 14, 16 and the day of, or equivalent to, luteal regression. Mean daily plasma progesterone concentrations were similar until Day 16 in cyclic and pregnant cows, after which values in non-pregnant animals declined. Regression analysis indicated that progesterone concentrations were best described by a quadratic expression with fitted maximum values on Day 13 in non-pregnant animals but values increased linearly over the whole period to Day 21 in pregnant cows. The frequency, amplitude and area under the curve of LH episodes showed no significant differences between cyclic and pregnant animals. In pregnant cows, the amplitude and area under the curve of progesterone episodes increased linearly between Days 8 and 21, although no such increase occurred in cyclic cows. Low-level PGFM episodes were present in cyclic and pregnant cows on Days 14 and 16 after oestrus, and high amplitude episodes occurred in non-pregnant cows during luteal regression. Pregnant cows showed a significant depression of the amplitude, but not the frequency of episodes at the expected time of luteal regression. These results confirm that the corpus luteum of pregnancy secretes an increasing amount of progesterone per se and per unit of LH until at least Day 21 after mating. They further suggest that the corpus luteum of the cyclic cow may experience small episodes of PGF-2 alpha and be subjected to initial degenerative changes by Day 14 after oestrus, some time before the onset of definitive luteolysis.     

Effects of PGF2alpha and PGF2alpha, 1-15 lactone on the corpus luteum and on early pregnancy in the rhesus monkey.

The effects of prostaglandin (PG)F2alpha and PGF2alpha, 1-15 lactone were compared in luteal phase, non-pregnant and in early pregnant rhesus monkeys. Animals treated with either PG after pretreatment with human chorionic gonadotropin (hCG) had peripheral plasma progesterone concentrations that were not statistically different from those in animals treated with hCG and vehicle. However, menstrual cycle lengths in monkeys treated with PGF2alpha, 1-15 lactone were significantly (P less than 0.02) shorter than those in vehicle treated animals. In the absence of hCG pretreatment, plasma progesterone concentrations were significantly (P less than 0.008) lower by the second day after the initial treatment with either PGF2alpha or PGF2alpha, 1-15 lactone than in vehicle treated monkeys. Menstrual cycle lengths in monkeys treated with either PG were significantly (P less than 0.04) shorter than those in animals treated with vehicle. There were no changes in plasma progesterone concentrations in early pregnant monkeys treated with PGF2alpha, and pregnancy was not interrupted. In contrast, plasma progesterone declined and pregnancy was terminated in 5 of 6 early pregnant monkeys treated with PGF2alpha, 1-15 lactone. These data indicate that PGF2alpha, 1-15 lactone decreases menstrual cycle lengths in non-pregnant rhesus monkeys. More importantly, PGF2alpha, 1-15 lactone terminates early pregnancy in the monkey at a dose which is less than an ineffective dose of PGF2alpha.     

Evidence for a gonadal nonsteroidal factor that specifically inhibits release of luteinizing hormone in ewes.

Bilaterally ovariectomized ewes were used to investigate the effect of systemic administration (i.v.) of charcoal-treated aqueous luteal extracts from ovine corpora lutea on plasma concentrations of pituitary gonadotrophins. Jugular blood samples were taken every 15 min at least 5 h before (control period) and 5 h after (treatment period) injection. In Expt 1, the administration of luteal extract from corpora lutea of days 70-76 of pregnancy, but not of the extract prepared from muscular tissue, resulted in a significant decrease of mean concentrations of luteinizing hormone (LH) (P < 0.02) and frequency of LH pulses (P < 0.01). Plasma follicle-stimulating hormone (FSH) concentrations were not affected by injections of either extract. These findings provide the first demonstration of the presence of a nonsteroidal factor in the corpus luteum of midpregnancy that selectively suppresses the secretion of LH. In Expt 2, mean concentrations of LH and FSH and frequency of LH pulses were unaffected by injections of luteal extracts from ovine corpora lutea of days 10-12 of the oestrous cycle or day 15 of pregnancy. These data suggest that some factor(s), probably from the fetoplacental endocrine unit, is required to ensure the production of a significant quantity of the luteal LH-inhibiting factor after day 15 of pregnancy. In Expt 3, treatment of luteal extract from corpora lutea of day 70 of pregnancy with proteolytic enzymes destroyed the LH-inhibiting activity, suggesting the proteic nature of the luteal LH-inhibiting factor. In Expt 4, plasma concentrations of LH were not affected by injection of charcoal-treated extract prepared from fetal cotyledonary tissue of days 110-120 of pregnancy suggesting that the LH-inhibiting factor exclusively originates from the corpus luteum during pregnancy. These experiments provide the first direct evidence for the existence of a potent nonsteroidal factor of luteal origin that specifically inhibits pulsatile secretion of LH, without influencing FSH release in female animals. We propose the term LH-release-inhibiting factor (LH-RIF) to describe this activity.     

Pregnancy, lactation and the oestrous cycle of the pouched mouse, Saccostomus campestris

The anatomy and histology of pouched mouse ovaries were studied during the oestrous cycle, pregnancy and lactation along with the relationship between the ovarian structures and circulating concentrations of progesterone. The structure of the ovaries resembled that of most rodents. Follicular development indicated that ovulation takes place on the night between pro-oestrus and oestrus, i.e. at the time when mating normally occurs. Corpora lutea were accumulating in cyclic females, while successively disappearing during pregnancy, leaving only the set formed after conception. After parturition luteal regression was rapid. Theca interna, included in the corpora lutea, formed glandular stromal tissue after regression of the luteal tissue formed from granulosa cells. The progesterone profile of non-pregnant females indicated a short but functional luteal phase (peak at metoestrus) during the cycle. During pregnancy three peaks of progesterone stood out: (1) when implantation starts, (2) when older sets of corpora lutea showed rejuvenation and placental signs were found in the vaginal smears, and (3) 3 days before expected parturition when luteal development (as judged by histology) reached a peak. The placenta may participate in but not 'take over' the progesterone production during later stages of pregnancy. Very low concentrations of peripheral progesterone during lactation and a very low level of follicular development at that time support an earlier suggestion of a lactational anoestrus in pouched mice.     

Serum oestradiol, progesterone, chorionic gonadotrophin and prolactin concentrations during pregnancy in the Bolivian squirrel monkey (Saimiri sciureus)

Concentrations of chorionic gonadotrophin gradually increased during early pregnancy, reached maximum values at mid-gestation, then declined to low levels. Oestradiol-17 beta concentrations were relatively low (300-600 pg/ml) during early pregnancy, increased thereafter to high levels (10-35 ng/ml), and then appeared to decline towards term. Concentrations of progesterone were constant (100-200 ng/ml) for the first 15 weeks of gestation, suggesting that sequential measurements of progesterone could be used to diagnose early pregnancy. Prolactin concentrations rose during pregnancy, reaching maximum values at term.     

Effects of aglépristone, a progesterone receptor antagonist, administered during the early luteal phase in non-pregnant bitches

Aglépristone, a progesterone receptor antagonist, was administered to six non-pregnant bitches in the early luteal phase in order to determine its effects on the duration of the luteal phase, the interestrous interval, and plasma concentrations of progesterone and prolactin. Aglépristone was administered subcutaneously once daily on two consecutive days in a dose of 10 mg/kg body weight, beginning 12 +/- 1 days after ovulation. Blood samples were collected before, during, and after administration of aglépristone for determination of plasma progesterone and prolactin concentrations. The differences in mean plasma concentration of progesterone and of prolactin before, during, and after treatment were not significant. Also, the duration of the luteal phase in the six treated bitches (72 +/- 6 days) did not differ significantly from that in untreated control dogs (74 +/- 4 days ). However, the intervals during which plasma progesterone concentration exceeded 64 and 32 nmol/l were significantly shorter in the six treated bitches than in untreated control dogs. The interestrous interval was significantly shorter in beagle bitches treated with aglépristone (158 +/- 16 days) than in the same group prior to treatment (200 +/- 5 days ). It is concluded that administration of aglépristone during the early luteal phase in the non-pregnant bitch affects progesterone secretion, but not sufficiently to shorten the luteal phase. The shortening of the interestrous interval suggests that aglépristone administered in the early luteal phase influences the hypothalamic-pituitary-ovarian axis.     

The effect of cloprostenol in non-pregnant and pregnant Norwegian semi-domestic reindeer (Rangifer tarandus tarandus L)

Two non-pregnant and five pregnant 1.5-year-old semi-domestic reindeer were used to study the effect of cloprostenol given during the luteal phase of the oestrous cycle, or at two stages of pregnancy (early December, n = 3, and mid-January, n = 2). Blood samples were collected at 3-hourly intervals from immediately prior to treatment until 6–8 days after treatment, after which blood samples were collected every second day. Prior to each blood collection, the animals were observed for signs of oestrus. Plasma progesterone, oestradiol-17β, luteinizing hormone (LH) and 15-ketodihydro-PGF_2α were analyzed to characterize variations in ovarian function.Treatment with cloprostenol resulted in an immediate and rapid decrease in plasma progesterone concentrations in all treated animals. The fall in plasma progesterone was associated with increase in 15-ketodihydro-PGF_2α. Oestrus, indicated by standing behaviour, was observed on three out of four occasions in the two non-pregnant animals. The average duration of standing behaviour (oestrus) was 27 h (range: 24–30 h).Of the pregnant females that were treated with cloprostenol in the beginning of December (n = 3), two aborted between 72 and 96 h after treatment. One of these developed pyometra after abortion. In one female the foetus died 2 days after treatment, but was retained within the uterus until slaughter 2.5 months later. One of the two females that were treated in mid-January aborted between 62–65 h after injection. The other female retained a live foetus until slaughter in February. There were few endocrinological differences between animals that aborted and those that did not, though aborting animals had lower progesterone concentrations for a longer period of time after treatment.It was concluded that cloprostenol can be used during the luteal phase of the oestrous cycle to induce luteolysis and oestrus. When given during pregnancy, cloprostenol can induce abortion, though undesired side effects make it inappropriate for practical use.     

Progesterone profiles around the time of insemination do not show clear differences between of pregnant and not pregnant dairy cows

In this study, features of progesterone profiles were examined in relation to the outcome of insemination. Three groups of estrous cycles were analyzed: resulting in pregnancy, not resulting in pregnancy and resulting in lost pregnancy. The aim of the study was to identify a complex of progesterone profile features associated with successful insemination. The features used were (1) from the estrous cycle preceding the artificial insemination: estrus progesterone concentration, post-estrus maximum rate of increase in progesterone, luteal phase peak, pre-estrus maximum rate of decline in progesterone and the length of follicular and luteal phase and (2) from the estrous cycle following insemination: estrus progesterone concentration, post-estrus maximum rate of increase in progesterone and days from estrus to post-estrus maximum rate of increase in progesterone. A discriminant analysis did not reveal clear differences between the groups. However, the analysis correctly classified 75% of true pregnant cows. Conversely, only 60% of not pregnant animals were classified as such by the discriminate analysis. Individual analysis of progesterone profile features in pregnant and not pregnant groups of estrous cycles showed that a shorter follicular phase preceding insemination is associated with proper timing of post-ovulatory luteinisation and therefore is more likely to result in pregnancy.