Suppression of pulsatile luteinizing hormone secretion by gonadotrophin-releasing hormone antagonist does not affect episodic progesterone secretion or corpus luteum function in ewes.

Progesterone secretion has been observed to be episodic in the late luteal phase of the oestrous cycle of ewes and is apparently independent of luteinizing hormone (LH). This study investigated the effects of suppressing the pulsatile release of LH in the early or late luteal phase on the episodic secretion of progesterone. Six Scottish Blackface ewes were treated i.m. with 1 mg kg-1 body weight of a potent gonadotrophin-releasing hormone (GnRH) antagonist on either day 4 or day 11 of the luteal phase. Six ewes received saline at each time and acted as controls. Serial blood samples were collected at 10 or 15 min intervals between 0 and 8 h, 24 and 32 h, and 48 and 56 h after GnRH antagonist treatment and daily from oestrus (day 0) of the treatment cycle for 22 days. Oestrous behaviour was determined using a vasectomized ram present throughout the experiment. Progesterone secretion was episodic in both the early and late luteal phase with a frequency of between 1.6 and 3.2 pulses in 8 h. The GnRH antagonist abolished the pulsatile secretion and suppressed the basal concentrations of LH for at least 3 days after treatment. This suppression of LH, in either the early or late luteal phase, did not affect the episodic release of progesterone. Daily concentrations of progesterone in plasma showed a minimal reduction on days 11 to 14 after GnRH antagonist treatment on day 4, although this was significant (P < 0.05) only on days 11 and 13. There was no effect of treatment on day 11 on daily progesterone concentration, and the timing of luteolysis and the duration of corpus luteum function was unaffected by GnRH antagonist treatment on either day 4 or day 11. These results indicate that the episodic secretion of progesterone during the luteal phase of the oestrous cycle in ewes is independent of LH pulses and normal progesterone secretion by the corpus luteum can be maintained with minimal basal concentrations of LH.     

Luteinizing hormone secretion in hypophysial stalk-transected pigs given progesterone and pulsatile gonadotropin-releasing hormone

This study was conducted to determine whether progesterone inhibits luteinizing hormone (LH) secretion in female pigs by a direct action on the pituitary gland. Eight ovariectomized, hypophysial stalk-transected gilts were given 1-microgram pulses of gonadotropin-releasing hormone iv every 45 min from Day 0 to 12. On Days 5-12, each of four gilts received either progesterone or oil vehicle im at 12-hr intervals. Serum progesterone concentrations in steroid-treated gilts reached 70 +/- 6.8 ng/ml (mean +/- SE) by Day 8 and remained elevated thereafter, whereas serum progesterone concentrations in oil-treated controls were less than 1 ng/ml for the entire study. Daily serum LH concentrations were not different between gilts treated with progesterone or oil. The 1-microgram pulses of gonadotropin-releasing hormone reliably evoked pulses of LH in both treatment groups. The LH pulse frequency and amplitude, assessed from samples collected every 15 min for 6 hr on Day 12, were similar for progesterone- and oil-treated gilts. These results provide evidence that progesterone does not act at the pituitary gland to alter LH secretion in pigs.     

Prostaglandin F and progesterone secretion by porcine endometrium and corpus luteum in vitro

Slices of porcine endometrium and corpus luteum tissue obtained from mature sows throughout the luteal phase of the oestrous cycle were incubated in culture medium which was analysed at regular intervals over a period of 8 hours for prostaglandin F and progesterone. Prostaglandin F secretion was greatest by endometrium obtained during the mid III to late I luteal stage of the cycle and the increased levels secreted by this tissue were paralleled by high levels of secretion from corpus luteum tissue. The addition of indomethacin (10 μg/ml) to the culture medium completely abolished prostaglandin F secretion by both endometrium and luteal tissue indicating that the high levels of the prostaglandin were due to synthesis. Progesterone secretion by the corpus luteum was maximal from early luteal tissue and had declined to considerably lower levels by late stage tissue when prostaglandin secretion was greatest. The possible physiological significance of luteal prostaglandin F secretion is discussed.     

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

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.     

Pathology of the corpus luteum of cows

The corpus luteum (CL) is a transient endocrine organ which can manifest a number of pathologic conditions such as cysts, inflammation, adhesions, dysfunction and neoplasia. Luteal and follicular cysts are the most commonly encountered abnormalities and need to be distinguished from cysts within a normal CL. Inflammatory lesions are also frequently encountered and can be caused by viral, bacterial, or iatrogenic causes. If inflammation is severe, adhesions and subfertility/infertility can result. Luteal dysfunction is a broad classification of another pathologic condition encountered in the cow. Generally this results in abnormal production of progesterone or abnormal luteal lifespan resulting in infertility. Neoplasms are relatively rare in the CL but include both primary and metastatic tumors. Understanding the pathologic conditions that occur within the CL will allow a more accurate clinical assessment of these very dynamic endocrine structures.     

Effect of several biogenic amines on in vitro progesterone secretion by the bovine corpus luteum

1. The effect of several biogenic amines on secretion of progesterone (P4) was examined using bovine corpora lutea (n = 6), removed on day 13 of the oestrus cycle, enzymatically dispersed and cultured in vitro. 2. Luteal cell cultures were co-incubated with 0, 10, 50 or 100 ng of luteinizing hormone (LH) and 50 ng of epinephrine (EPI), norepinephrine (NOR), dopamine (DOPA), melatonin (MEL), N-acetyl-50H-serotonin (N-acetyl-50H-tryptamine; NacS), serotonin (50H-tryptamine; 5HT) or saline control. 3. EPI, NOR and DOPA decreased baseline release of P4. 4. The magnitude of the response of P4 to LH was depressed when cells were co-incubated with DOPA, EPI and 5HT and stimulated when cells were co-incubated with MEL and NacS. 5. These data indicate that the biogenic amines might modulate ovarian steroidogenesis supplementary to hypothalamic-hypophyseal hormonal mechanisms.     

Role of prostaglandin E2 in basal and noradrenaline-induced progesterone secretion by the bovine corpus luteum

The role of prostaglandin E2 (PGE2) in basal and noradrenaline (NA)-stimulated utilization of high density lipoprotein (HDL) as a source of cholesterol for progesterone synthesis was examined. In Experiment 1, a cannula was inserted into the aorta abdominalis through the coccygeal artery (cranial to the origin of the ovarian artery) in mature heifers, to facilitate infusion of NA (4 mg/30 min; n = 3) on day 10 of the estrous cycle. Three other heifers were similarly cannulated to serve as control. Before, during, and after NA or saline infusion, blood samples from the vena cava were collected every 5-15 min for analysis of PGE2, progesterone, and cholesterol. Each NA infusion stimulated (P < 0.01) secretion of both hormones in heifers. Short-duration increases (P < 0.05) in progesterone were observed due to the infusion of NA while cholesterol was not altered significantly. In addition, increases in PGE2 concentrations (P < 0.05) compared to controls were seen after NA infusion. Therefore, we used an in vitro model to verify the effect of PGE2 on HDL utilization by luteal cells from day 5 to 10 of the estrous cycle. In the preliminary experiment, 10(-6) M of PGE2 out of four different doses examined was selected for further studies, since it evoked the highest release of progesterone. In the next experiment, it was found that HDL increases progesterone secretion by luteal cells and both PGE2 and LH increased (P < 0.05) the response to HDL while NA did not. In the last in vitro experiment, progesterone stimulated PGE2 secretion by luteal cells. In conclusion, PGE2 may be directly involved in the utilization of cholesterol from HDL for progesterone synthesis. Furthermore, PGE2 may influence NA-stimulated progesterone secretion by the corpus luteum (CL). It is concluded that there is a positive feedback loop between progesterone and luteal PGE2 during days 5-10 of the estrous cycle.     

Changes in rabbit corpus luteum progesterone secretion and cellular morphology following unilateral luteectomy or ovariectomy.

The objective of this study was to determine whether removal of corpora lutea (CL) from one ovary (unilateral luteectomy; ULL) or removal of the entire ovary (unilateral ovariectomy; ULO) of pseudopregnant rabbits would cause compensatory growth and progesterone production by the contralateral ovary. Pseudopregnancy was induced in rabbits with hCG (Day 0). On the first day of pseudopregnancy, one group of rabbits received a sham operation (controls), another group underwent ULL, and a third group underwent ULO. On Day 11 of pseudopregnancy, each rabbit underwent laparotomy, the ovarian artery and vein were cannulated, and the ovary(ies) was removed and perfused in vitro for 6 h. The mean CL weight increased by 33% in the ULL group and by 28% in the ULO group as compared to sham-operated controls. Peripheral estradiol and progesterone levels in sham-operated control, ULL, and ULO groups were similar. Ovarian venous estradiol levels were similar in the control and ULL groups, but were significantly increased in the remaining ovary of the ULO group. Both ovarian venous progesterone in vivo and progesterone secretion in vitro increased significantly in contralateral ovaries from ULL and ULO rabbits as compared to sham-operated controls. Progesterone secretion by ovaries perfused in vitro increased significantly in the contralateral ovary of the ULL and ULO groups. Mean number of luteal cells per CL increased significantly in the ULL group, but not in the ULO group. In contrast, luteal cell volume increased significantly in the ULO, but not in the ULL group. The stimuli responsible for increased progesterone production following ULL and ULO result in morphological changes in the remaining CL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteinizing hormone,total estrogens and progesterone secretion during lactation and after weaning in sows

Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low (< 1 ng/ml) during lactation and averaged 1.9 ± .3, .6 ± .3 and 1.2 ± .3 on days 1, 3 and 5 after weaning. Estrogens were variable during lactation, averaged 121 ± 36 pg/ml on day 1 after weaning and decreased thereafter. Estrus began on day 3 after weaning in 1 sow and on day 5 in the remaining 10 sows.In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low (< 1 ng/ml) until after ovulation when progesterone increased. Estrus began on day 4 after weaning in all seven sows.Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.     

Corpus luteum size and plasma progesterone concentration in cows

It is often assumed that a larger corpus luteum will produce more progesterone and generate higher circulating plasma concentrations. The aim of the study was to determine whether the size of the corpus luteum does actually determine circulating plasma progesterone concentrations. Data were collated from a number of studies on various aspects of luteal function in non-lactating dairy cows to allow comparisons to be made between corpus luteum weight and plasma progesterone concentration across the luteal phase. In these studies oestrous cycles had been synchronised and animals slaughtered on day 5, day 8 or day 16 following oestrus. Both corpus luteum weight and plasma progesterone concentration increased between day 5 and day 8. Plasma progesterone concentration but not luteal weight also increased between day 8 and day 16. On day 5 there was a strong relationship between corpus luteum weight and plasma progesterone (R² = 0.64; P < 0.001). However, no such relationship was present on day 8 or day 16. These results indicate that while during the early stage of corpus luteum development a relationship between size and progesterone is present, by day 8 of the cycle, the size of the corpus luteum is no longer of importance in determining circulating progesterone concentrations.     

Effects of prostaglandins on the bovine corpus luteum: granules, lipid inclusions and progesterone secretion

Corpora lutea collected at 15, 30 and 60 min after prostaglandin F2 alpha (PGF2 alpha) treatment were compared to control corpora lutea at 60 min after saline treatment. There were decreases (P less than 0.05) in the relative percentages of cytoplasm occupied by granules in large luteal cells (LLC) by 30 min and in small luteal cells (SLC) by 60 min. Differences were not observed among the groups for lipid inclusions. Luteal progesterone was decreased at all post-PGF2 alpha treatment times when compared to 60-min controls (P less than 0.05). PGF2 alpha was then compared with prostaglandin F1 alpha (PGF1 alpha), prostaglandin E1 (PGE1), and 17-phenyl-18,19,20-trinor-prostaglandin F2 alpha (17-phenyl-PGF2 alpha) in 60-min trials with plasma progesterone and luteinizing hormone (LH) determined every 5 min. LH was not affected by these treatments. Like PGF2 alpha, 17-phenyl-PGF2 alpha induced a greater loss of granules from LLC then SLC. 17-phenyl-PGF2 alpha also induced an increase in the lipid content of LLC. Treatments with PGF2 alpha and 17-phenyl-PGF2 alpha were associated with decreased concentrations of luteal progesterone but PGF1 alpha and PGE1 were without effect on this variable. In contrast to PGF1 alpha, PGE1 increased both luteal progesterone and the area occupied by cytoplasmic granules. The latter effect was greater in LLC than SLC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Allopregnanolone alters the luteinizing hormone, prolactin, and progesterone serum levels interfering with the regression and apoptosis in rat corpus luteum

Steroids synthesized in the central nervous system are termed "neurosteroids". They are synthesized and metabolized in several brain areas. The objective of this work was to determine if 1 intracerebroventricular allopregnanolone injection in rats can interfere in luteal regression in a close relationship with modifications in LH, progesterone, and prolactin serum concentrations. Allopregnanolone was injected during proestrus morning and the animals were sacrificed on oestrous morning. Ovulation test and histological analysis were performed in the oestrus morning with light and electron microscopy. Serum prolactin, LH, and progesterone levels were measured by radioimmunoassay. The allopregnanolone injection significantly decreased luteinizing hormone serum level and the number of oocytes on oestrus. Progesterone and prolactin serum levels were increased after this injection. The inhibition of apoptotic figures due to allopregnanolone administration was detected in the already formed corpora lutea belonging to the previous ovary cycle and it was significantly lower than in vehicle group (control). When the GABA(A) antagonist (bicuculline) was administered alone or previously to allopregnanolone, no effect on the ovulation rate was observed. No changes in the apoptotic cell numbers were observed with respect to those of vehicle group. These results show that the effect of centrally injected allopreganolone over reproductive function could be due to a centrally originated LH mediated effect over ovarian function that affects luteal regression, through the inhibition of apoptosis and stimulation of progesterone and prolactin release.     

Plasma levels of LH and prolactin in cows following enucleation of the persistent corpus luteum.

LH and prolactin were measured in plasma of 5 cows before and after enucleation of the persistent corpus luteum. Two cows returned to normal oestrous cycles following enucleation and did not differ from normal, cycling cows, with respect to hormone levels. Three other ones developed follicular cysts following enucleation and had decreased levels of LH and prolaction as compared with cycling cows. On the day of enucleation the fluctuations in LH-levels were higher than either before or after enucleation.     

Placental lactogen not growth hormone and prolactin regulates secretion of progesterone in vitro by the 40-45 day ovine corpus luteum of pregnancy

The study was designed to compare the direct effect of three prolactin-like hormones on steroidogenesis of ovine luteal cells collected at day 40-45 of pregnancy. 100 ng/ml of ovine placental lactogen or 100 ng/ml of ovine growth hormone or 100 ng/ml of ovine prolactin were added to the media of luteal cell cultures. After 48 h incubation, all cultures were terminated and the media were frozen until further steroid analysis. To determine to what extent growth hormone (GH), prolactin (PRL) and lactogen (PL) regulate the activity of 3 beta-HSD, an enzyme involved in progesterone synthesis, the classical steroidal competitive inhibitor of 3 beta-HSD trilostane, was investigated for its effects on basal and GH-, PRL-, and PL-stimulated progesterone biosynthesis since there is a possibility that the luteotropic effect of these hormones are mediated via 3 beta-HSD. oPL resulted in an increase of progesterone secretion in a statistically significant manner, while GH or PRL had no effect on progesterone secretion. A decrease in progesterone secretion as an effect of 100 mM trilostane was observed in all culture types. An explanation for the luteotropic effect of PL and the lack of this effect for GH is that the GH receptor associates with a different molecule within the ovarian tissue and forms a heterodimeric receptor for PL, and the possibility that physiological effects of native oPL may be mediated through its binding to specific PL receptors, which have low affinities for oGH and oPRL.     

Effects of colchicine on the ovine corpus luteum: role of microtubules in the secretion of progesterone

By 4 h after i.v. injection of ewes at the mid-luteal phase of the oestrous cycle with colchicine (1 mg/kg), the concentration of progesterone in peripheral plasma was halved while the content of progesterone in luteal tissue was doubled. The ultrastructure of the luteal tissue showed some specific drug-induced changes: microtubules were no longer present and the intracellular transport and secretion of granules associated with progesterone secretion appeared to be inhibited.