Uterine blood flow of cows during the oestrous cycle and early pregnancy: effect of the conceptus on the uterine blood supply.

Blood flow to each uterine horn of cows during the oestrous cycle and early pregnancy was determined daily by use of electromagnetic blood flow probes placed around both middle uterine arteries. The pattern of blood flow to uteri of pregnant and non-pregnant cows was similar until Day 14 after mating or oestrus. Between Days 14 and 18 of pregnancy blood flow to the uterine horn containing the conceptus increased (P less than 0.01) 2- to 3-fold, whereas blood flow to the non-gravid uterine horn in these cows remained constant. No corresponding increase in blood flow to the uterine horn ipsilateral to the ovary bearing the CL was observed in non-pregnant cows during this 4-day period. By Day 19 of pregnancy, blood flow to the gravid uterine horn had returned to a level similar to that observed on Day 13. Blood flow to both uterine horns of pregnant cows remained constant from Days 19 to 25 and then increased to the gravid horn (P less than 0.01) markedly until Day 30 whereas blood flow to the non-gravid horn remained low. Uterine blood flow during the oestrous cycle of non-pregnant cows was positively correlated (P less than 0.01) with systemic concentrations of oestradiol and the ratio of oestradiol (pg/ml) to progesterone (ng/ml). There was no association between oestradiol concentrations and blood flow to the gravid uterine horn. These data indicate local control of uterine blood flow by the bovine conceptus which may function to create optimal conditions for the continuation of pregnancy.     

Ovarian capillary blood flow in seasonally anoestrous ewes induced to ovulate by treatment with GnRH

The microsphere technique was used to obtain estimates of ovarian capillary blood flow near ovulation, in 8 seasonally anoestrous ewes, which were induced to ovulate by GnRH therapy. Plasma progesterone concentrations were monitored in jugular blood sampled between Days 4 and 7 after the onset of the preovulatory LH surge. The ewes were then slaughtered. Three of the ewes were treated with a single injection of 20 mg progesterone before GnRH therapy. In these ewes and 1 other, plasma progesterone values increased after ovulation and reached 1.0 ng/ml on Day 7 following the preovulatory LH surge (normal, functional CL), whilst in the other 4 ewes progesterone concentrations increased initially then declined to 0.5 ng/ml by Day 7 (abnormal CL). In the ewes exhibiting normal luteal function, the mean ovarian capillary blood flow was significantly greater (P less than 0.01) than that for ewes having abnormal luteal function. Irrespective of the type of CL produced, capillary blood flow was significantly greater (P less than 0.05) in ovulatory ovaries than in non-ovulatory ovaries. These findings indicate that the rate of capillary blood flow in ovaries near ovulation may be a critical factor in normal development and maturation of preovulatory follicles and function of subsequently formed CL.     

Termination of pregnancy and induction of premature luteolysis by the antiprogestagen, mifepristone, in dogs

Five pregnant beagle bitches were treated with 2.5 mg mifepristone/kg body weight, twice a day, for 4.5 days starting at Day 32 of gestation. Results of fetal ultrasonography and assay of serum progesterone concentrations every 2-4 days were compared to those in 5 control bitches. Mifepristone resulted in a premature (P less than 0.01) termination of pregnancy (36 +/- 1 vs 65 +/- 1 days), without side effects. The antiprogestagen also caused progesterone to decline to less than 1 ng/ml by Day 40-45 after the preovulatory LH peak (vs 64-67 days in controls) and reduced (P less than 0.05) mean concentrations on Days 34-50 (2.2 +/- 0.5 vs 6.3 +/- 0.3 ng/ml). The results suggest that antiprogestagen therapy is a safe means to terminate unwanted pregnancy in dogs, and that luteal function in pregnant bitches is dependent on luteotrophic support that is blocked by antiprogestagen treatment, directly or indirectly, due to termination of pregnancy.     

Prostaglandin F2 alpha, oxytocin and progesterone secretion by bovine luteal cells at several stages of luteal development: effects of oxytocin, luteinizing hormone, prostaglandin F2 alpha and estradiol-17 beta

Bovine luteal cells from Days 4, 8, 14 and 18 of the estrous cycle were incubated for 2 h (1 x 10(5) cells/ml) in serum-free media with one or a combination of treatments [control (no hormone), prostaglandin F2 alpha (PGF), oxytocin (OT), estradiol-17 beta (E) or luteinizing hormone (LH)]. Luteal cell conditioned media were then assayed by RIA for progesterone (P), PGF, and OT. Basal secretion of PGF on Days 4, 8, 14 and 18 was 173.8 +/- 66.2, 111.1 +/- 37.8, 57.7 +/- 15.4 and 124.3 +/- 29.9 pg/ml, respectively. Basal release of OT and P was greater on Day 4 (P less than 0.01) than on Day 8, 14 and 18 (OT: 17.5 +/- 2.6 versus 5.6 +/- 0.7, 6.0 +/- 1.4 and 3.1 +/- 0.4 pg/ml; P: 138.9 +/- 19.5 versus 23.2 +/- 7.5, 35.4 +/- 6.5 and 43.6 +/- 8.1 ng/ml, respectively). Oxytocin increased (P less than 0.01) PGF release by luteal cells compared with control cultures irrespective of day of estrous cycle. Estradiol-17 beta stimulated (P less than 0.05) PGF secretion on Days 8, 14 and 18, and LH increased (P less than 0.01) PGF production only on Day 14. Prostaglandin F2 alpha, E and LH had no effect on OT release by luteal cells from any day. Luteinizing hormone alone or in combination with PGF, OT or E increased (P less than 0.01) P secretion by cells from Days 8, 14 and 18. However on Day 8, a combination of PGF + OT and PGF + E decreased (P less than 0.05) LH-stimulated P secretion. These data demonstrate that OT stimulates PGF secretion by bovine luteal cells in vitro. In addition, LH and E also stimulate PGF release but effects may vary with stage of estrous cycle.     

Effects of in vivo and in vitro administration of prostaglandin F2 alpha on lipoprotein utilization in cultured bovine luteal cells

Two experiments were conducted to determine if a loss in the ability to utilize lipoprotein-cholesterol is one mechanism whereby prostaglandin F2 alpha (PGF2 alpha) decreases steroidogenesis in bovine luteal cells. In the first experiment, serum-free cultures of bovine luteal cells were treated with PGF2 alpha (100 ng/ml) for 5 days prior to addition of lipoproteins. Exposure to PGF2 alpha completely suppressed low-density lipoprotein (LDL)- and high-density lipoprotein (HDL)-stimulated progesterone production (p less than 0.01) compared to control (no PGF2 alpha) cultures. Luteal cells cultured in the presence of LDL + luteinizing hormone (LH, 10 ng/ml) + PGF2 alpha produced significantly less progesterone than luteal cells cultured with LDL + LH (p less than 0.05). Treatment with PGF2 alpha had no significant effect on HDL + LH-stimulated progesterone synthesis. In the second experiment, cows were injected with a luteolytic dose of PGF2 alpha (25 mg), and the corpora lutea were removed at 0 (no PG), 1, 4, or 12 h post-injection. Dissociated luteal cells were placed in culture for 7 days, either with or without LH (10 ng/ml), and lipoproteins were added on Days 5-7. LH stimulation of progesterone production was apparent in cultures obtained at 0 and 12 (p less than 0.05) but not 1 and 4 h post-PGF2 alpha. Addition of either LDL or HDL increased progesterone synthesis in all cultures, regardless of time following in vivo administration of PGF2 alpha. It is concluded that PGF2 alpha can inhibit bovine luteal cell utilization of either LDL or HDL in vitro. However, luteal cell utilization of lipoproteins in vitro is not adversely affected by in vivo exposure to PGF2 alpha, if collected within 12 h post-PGF2 alpha.     

Luteal inadequacy during the early luteal phase of subfertile cows

A study was made of early luteal function (up to Day 6) in cyclic and pregnant heifers and also in older, subfertile cows. There were no differences in vivo or in vitro between cyclic and pregnant heifers, indicating no luteotrophic effect of the embryo at this stage, but the increase in postovulatory peripheral progesterone concentrations was delayed (P less than 0.01) and occurred more slowly (P less than 0.001) in the subfertile cows than in the heifers. The corpora lutea of the subfertile cows were heavier (P less than 0.001) than those of the heifers on Day 6. Basal progesterone production by dispersed luteal cells was similar between heifers and subfertile cows, but there was a difference (P less than 0.001) in the pattern of response to exogenous LH and PGE-2. Cells from subfertile cows were less sensitive to the stimulatory effects of PGE-2 and although LH increased (P less than 0.001) progesterone production by all cells, this stimulation by a low dose of LH was inhibited by PGE-2 in luteal cells from subfertile cows. This effect did not occur in the luteal cells from heifers. These results indicate the possibility that luteal inadequacy, due to a diminished response to circulating luteotrophic hormones, may contribute to embryo mortality in subfertile cows.     

Effect of rate of change of luteinizing hormone concentration on in-vitro progesterone secretion within rat corpora lutea during differentiation.

Immature rats were injected with pregnant mares' serum gonadotrophin followed by human chorionic gonadotrophin (hCG). Ovaries were removed 0, 2, 5 or 8 days after hCG and either prepared for morphometric analysis or perifused with 0, 5 or 30 ng luteinizing hormone (LH)/min. In a second study, ovaries were removed on Day 2 or 8 and perifused with 0.1 mg 8-br-cyclic adenosine 5'-phosphate/ml (8-br-cAMP). On Day 0, the granulosa cells of the preovulatory follicles were small (53 +/- 0.5 microns2) with a cytoplasmic to nuclear (Cy:Nu) ratio less than or equal to 1.5. By Day 2, corpora lutea (CL) were present and composed of 95% small luteal cells (diameter less than 125 microns2, Cy:Nu greater than or equal to 3.0) and 5% large luteal cells (diameter greater than 125 microns2, Cy:Nu ratio greater than or equal to 3.0). The percentage of large luteal cells increased to 36 +/- 7% by Day 5, suggesting that they are derived from a select population of small luteal cells. Basal progesterone secretion increased from 38 +/- 5 on Day 0 to 1010 +/- 48 pg/mg/ml on Day 8. The rate of 5 ng LH/min stimulated progesterone secretion on Days 0, 2 and 8; 30 ng LH/min stimulated progesterone secretion on Days 0, 2 and 8, but not on Day 5; 8-br-cAMP stimulated progesterone secretion on both Days 2 and 8. These data demonstrate that once granulosa cells are induced to luteinize they lose their capacity to secrete progesterone in response to 5 ng LH/min and do not regain their responsiveness to LH rate until they completely differentiate. The loss of this LH responsiveness appears to be due to an inability to stimulate sufficient intracellular cAMP concentrations, since cAMP stimulates progesterone secretion on both Days 2 and 8.     

Progesterone production, LH receptors, and oxytocin secretion by ovine luteal cell types on days 6, 10 and 15 of the oestrous cycle and day 25 of pregnancy

Corpora lutea were collected from sheep on Days 6, 10, and 15 of the oestrous cycle and Day 25 of pregnancy and dissociated into single cell suspensions. Purified preparations of large and small luteal cells were prepared by elutriation on all days except Day 6. Basal progesterone production by large cells was 6-8-fold higher than by small cells (36-65 vs 6-9 fg/cell/min). Oxytocin secretion was maximal on Day 6 (1.0 fg/cell/min) and declined thereafter. The number of receptors for LH increased between Day 6 and Day 10 and the two cell types had an equal number of receptors on Days 10 and 15 (19,000-23,000). Large cells on Day 25 of pregnancy had fewer receptors (12,000) than did small cells (26,000). Progesterone secretion by small luteal cells from all days examined was stimulated by LH (0.01-1000 ng/ml) in a dose-dependent manner; maximum sensitivity to LH occurred on Day 10. Despite the presence of receptors for LH on large cells, LH failed to stimulate progesterone production. Basal production of progesterone by large and small cells, and the response of small cells to LH, was not influenced by day examined. Re-combinations of large and small cells from Day 10 synergized to increase progesterone secretion. Prostaglandin E-2 (0.1-1000 ng/ml) did not stimulate progesterone secretion by large or small cells.     

Prolactin administration during the luteal and follicular phase of the oestrous cycle of gilts

In Exp. I infusions of prolactin (0.5 mg in 2 ml sterile saline) were repeated every 2 h for 36 h on Days 12-13 of the cycle. In Exp. II infusions of prolactin were administered from Days 17 to 19 (60 h) at 2-h intervals. Control gilts were given 2 ml sterile saline at similar intervals during the same period. Basal prolactin concentrations before initiation of infusions ranged from 1.3 +/- 0.1 to 5.6 +/- 2.2 ng/ml in both experiments. By 5 min after a prolactin infusion, mean plasma prolactin concentration ranged from 74.9 +/- 5.8 to 113.0 +/- 9.5 ng/ml, but then declined to approximately equal to 10 ng/ml just before the next infusion of prolactin. Administration of prolactin during the luteal phase of the oestrous cycle of the gilts had no effect on basal levels of progesterone, oestradiol or LH. During the follicular phase there were no differences (P greater than 0.05) between control and prolactin-treated gilt progesterone and LH concentrations, but oestradiol plasma values were decreased (P less than 0.05) on the 2nd and 3rd day of prolactin treatment. Our results would indicate that prolactin does not play a major role in the regulation of the oestrous cycle of the pig.     

Induction of luteal regression in the marmoset monkey (Callithrix jacchus) by a gonadotrophin-releasing hormone antagonist and the effects on subsequent follicular development

Doses of 100 or 200 micrograms of a novel GnRH antagonist ([N-acetyl-D beta Na11-D-pCl-Phe2-D-Phe3-D-Arg6-Phe7-Arg8-D-Ala10]NH2 GnRH) (4 animals/dose) were administered on Days 10/11 of the luteal phase and induced a marked suppression of circulating bioactive LH and progesterone concentrations within 1 day of treatment (P less than 0.01). Thereafter, progesterone concentrations remained low or undetectable until after the next ovulation. Similar results were obtained when 200 micrograms antagonist were given on Days 5/6 of the luteal phase (N = 4). The interval from injection of antagonist (200 micrograms but not 100 micrograms) to ovulation (based on a rise in progesterone above 10 ng/ml) was significantly longer than that from prostaglandin-induced luteal regression to ovulation in control cycles (N = 4/treatment) (range, 13-15 days after antagonist vs 8-10 days after prostaglandin, P less than 0.01). This delay of 4-5 days was equivalent to the duration for which LH concentrations were significantly suppressed by 200 micrograms antagonist when administered to ovariectomized animals (N = 3). Corpus luteum function during the cycle after GnRH antagonist treatment appeared normal according to the pattern of circulating progesterone. These results show that corpus luteum function and preovulatory follicular development in the marmoset monkey are dependent on pituitary gonadotrophin secretion.     

Function of abnormal corpora lutea in vivo after GnRH-induced ovulation in the anoestrous ewe

Anoestrous Romney Marsh ewes with and without progesterone treatment (+P, -P) were treated with small-dose (250 ng) multiple injections of GnRH at 2-h intervals for 48 h. Animals were slaughtered on Days 4, 5, 7 and 11 after the end of GnRH treatment and luteal function was assessed by the measurement of daily plasma progesterone concentrations. In all animals which ovulated (29/32, 91%) peripheral progesterone concentrations rose to 0.5-1.0 ng/ml within 3 days of the end of GnRH treatment. In 7/7 (100%) +P animals and 5/22 (23%) -P animals, progesterone concentrations continued to rise and were maintained at levels greater than 1.5 ng/ml until slaughter. In the remaining -P animals, plasma progesterone concentrations declined to reach basal levels by Day 5. Corpora lutea recovered from these animals showed signs of premature regression on Day 5 and were fully regressed by Day 7. Progesterone priming delayed the occurrence of the LH surge which occurred 39.1 +/- 3.6 h after the end of GnRH treatment in the +P animals compared to 20.2 +/- 1.74 h (P less than 0.001) in the -P animals in which luteal function was abnormal and 22.4 +/- 4.35 h in the -P animals in which luteal function was normal. These results show that abnormal luteal function occurs in the majority of GnRH-treated ewes in the absence of progesterone pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fetal growth and reproductive performance in ewes administered GnRH agonist on day 12 post-mating

Reproductive performance and fetal growth was determined in GnRH (4 microg synthetic GnRH agonist, Receptal) administered (i.m.) to ewes on day 12 post-mating (n = 103) compared to control ewes (n = 97) during the breeding season. Plasma progesterone and LH concentrations were analyzed. A total of 13 ewes was slaughtered on day 45 of pregnancy (six from control, seven from GnRH treated groups). GnRH administration on day 12 post-mating increased plasma progesterone concentration (4.39+/-0.25 ng/ml) compared to control group (3.43+/-0.15 ng/ml) on days 13-15 post-mating (P < 0.01). GnRH administration also increased plasma LH concentration between 1 and 4 h after GnRH administration (P < 0.01). Pregnancy rate was higher in GnRH treated group (84%) than control (66%) group (P < 0.05). The ewes in GnRH administered group had more twins (P < 0.05) than those in control group. The ovarian weights (P < 0.05) and the number of corpora lutea (CL) (P < 0.01) were greater in ewes slaughtered on day 45 of pregnancy in GnRH treated group than those in control group. GnRH administration on day 12 post-mating did not have any effect on products of conception at day 45 of pregnancy except on crown-rump length (CRL) of fetuses and cotyledon weight. CRL of fetuses and cotyledon weight in GnRH treated group was higher than those in control group (P < 0.05). In conclusion GnRH administration improved reproductive performance of ewes when administered on day 12 post-mating probably through its beneficial effect on embryo survival by enhancing luteal function, but not through stimulating fetal growth.     

Effects of endothelin and relaxin on rat uterine segment contractility.

In order to determine the effects of endothelin (ET) and relaxin on uterine contractility, immature female rats were treated with estrogen (E, 1 microgram s.c., Days 1-3) or estrogen and progesterone (2 mg s.c. [E + P], Days 2 and 3), and killed; the uterine horns were removed and suspended in muscle baths. Initially, we determined the contractile response to varying doses of ET and how this response was altered by pretreatment with progesterone. Uterine strips from animals treated with E + P (n = 10) were less sensitive to the stimulatory effects of ET than were strips from E-treated animals (n = 10). This difference was significant at ET doses above 2.5 nM. After completion of the dose-response studies, contractile patterns in response to ET and relaxin were then studied in animals treated with E (n = 10) or E + P (n = 9). ET (5 nM) significantly increased uterine contractility, mostly through an effect on the frequency of contractions (p less than 0.01). Relaxin (25 ng/ml) decreased contractility, affecting all contractile parameters measured (p less than 0.01). ET stimulated contractility in uterine horn segments previously inhibited by relaxin (p less than 0.01), and relaxin reduced the increased contractility produced by earlier exposure to ET (p less than 0.01). These data indicate that ET and relaxin can interact reversibly to control contractility in uterine horn segments in vitro, and that progesterone pretreatment can diminish the contractile response to the stimulatory effects of ET.     

Comparison of in-vitro production of progestagens by the corpora lutea of early pregnancy of the rat and hamster

Immature rats and adult hamsters were killed on Days 2, 4 or 8 of pregnancy (Day 1 = sperm positive vaginal smear). Dispersed luteal cells (5 X 10(4) cells) were incubated for 2 h in the absence or presence of graded doses of ovine LH. In the absence of LH, incubation of rat luteal cells compared to hamster cells produced about 3-6-fold as much progesterone, 26-66 times as much 20 alpha-dihydroprogesterone and about the same amounts of 17 alpha-hydroxyprogesterone. For the rat, 1 ng LH was the minimal dose which stimulated synthesis of progesterone and 17 alpha-hydroxyprogesterone by luteal cells on Days 2 and 4 whereas 10 ng LH stimulated maximal production of progesterone by Day-8 luteal cells. As pregnancy progressed from Day 2 to Day 8, there was an inverse relationship between the levels of progesterone and 20 alpha-dihydroprogesterone accumulated by rat luteal cells. For the hamster, 1 ng LH significantly stimulated accumulation of progesterone and 17 alpha-hydroxyprogesterone by Day-2 luteal cells but not by Day-4 or Day-8 cells. Hamster luteal cells on Day 4 produced the highest levels of progesterone in response to 10 or 100 ng LH, with a maximal rate of accumulation by Day-8 cells with 10 ng LH.     

Relationships between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers

The effects of fasting between Days 8 and 16 of the estrous cycle on plasma concentrations of luteinizing hormone (LH), progesterone, cortisol, glucose and insulin were determined in 4 fasted and 4 control heifers during an estrous cycle of fasting and in the subsequent cycle after fasting. Cortisol levels were unaffected by fasting. Concentrations of insulin and glucose, however, were decreased (p less than 0.05) by 12 and 36 h, respectively, after fasting was begun and did not return to control values until 12 h (insulin) and 4 to 7 days (glucose) after fasting ended. Concentrations of progesterone were greater (p less than 0.05) in fasted than in control heifers from Day 10 to 15 of the estrous cycle during fasting, while LH levels were lower (p less than 0.01) in fasted than in control heifers during the last 24 h of fasting. Concentrations of LH increased (p less than 0.01) abruptly in fasted heifers in the first 4 h after they were refed on Day 16 of the fasted cycle. Concentrations (means +/- SEM) of LH also were greater (p less than 0.05) in fasted (11.2 +/- 2.6 ng/ml) than in control (4.7 +/- 1.2 ng/ml) heifers during estrus of the cycle after fasting; this elevated LH was preceded by a rebound response in insulin levels in the fasted-refed heifers, with insulin increasing from 176 +/- 35 pg/ml to 1302 +/- 280 pg/ml between refeeding and estrus of the cycle after fasting. Concentrations of LH, glucose and insulin were similar in both groups after Day 2 of the postfasting cycle. Concentrations of progesterone in two fasted heifers and controls were similar during the cycle after fasting, whereas concentrations in the other fasted heifers were less than 1 ng/ml until Day 10, indicating delayed ovulation and (or) reduced luteal function. Thus, aberrant pituitary and luteal functions in fasted heifers were associated with concurrent fasting-induced changes in insulin and glucose metabolism.     

Luteal luteinizing hormone receptors during the postovulatory period in the mare

Changes in serum luteinizing hormone (LH) and progesterone concentrations, number of luteal unoccupied LH receptors, receptor affinity constants, luteal weights and luteal progesterone concentrations were determined during the postovulatory period in the mare. The number of unoccupied LH receptors and receptor affinity was less during the early (Days 1-4) and late [Day 15 through 3rd day after start of corpus luteum (CL) regression] luteal phases than during the mid-luteal (Days 9-14) phase of the postovulatory period (P less than 0.01). The number of LH receptors per CL increased 21-fold (P less than 0.001) from Day 1 to Day 14. Receptor affinity increased 5-fold (P less than 0.001) from Day 1 to Day 13. Receptor number was highly correlated with receptor affinity (P less than 0.01) and both were highly correlated with serum and luteal progesterone (P less than 0.01). During regression of the CL, the number of LH receptors and receptor affinity decreased concomitantly with serum and luteal progesterone. Morphologically, luteal cell development and degeneration correlated with the change in receptor numbers, affinity constants and luteal and serum progesterone concentrations. Receptor number and affinity, luteal weight and serum and luteal progesterone concentrations did not differ between the CL from multiple ovulations. Random variations in the data observed between CL from multiple and single ovulations suggested that CL from the two groups were not different in structure and function. In summary, the above results suggest that major factors in regulation of progesterone secretion and maintenance of the equine CL are changes in the number of LH receptors and the affinity constants throughout the postovulatory period.     

Luteotropic and luteolytic responsiveness of ovine luteal cells in long-term culture

Ovine luteal cells were collected and plated 36 h (Day 2) after injection of human chorionic gonadotropin (Day 0) to induce ovulation. Cells were maintained (Days 2-12) in Medium 199 containing 5% calf serum, which was replaced daily. Progesterone secretion was not stimulated (p greater than 0.05) by luteinizing hormone (LH, 10 ng/ml or 100 ng/ml) at any time during culture. However, it was enhanced (p less than 0.05) with a 24-h pulse of dibutyryl adenosine 3', 5'-monophosphate (dbcAMP) during early (2.2-fold stimulation over basal; Days 5,6) or mid- (1.7-fold stimulation over basal: Days 8,9) culture if the pulsing medium contained serum, but not if serum had been withdrawn for 24 h. Continuous exposure of cultures to dbcAMP (2 mM, Days 3-12) resulted in continuously stimulated (p less than 0.05) progesterone secretion (range 1.8- to 4.1-fold stimulation). An increased (p less than 0.05) percentage of cells staining positive for 3 beta-hydroxy-delta 5-steroid dehydrogenase-delta 5, delta 4-isomerase (3 beta HSD) activity were recovered on Day 12 in cultures incubated (Days 3-12) with dbcAMP. Incubation of cultures continuously with prostaglandin F2 alpha (PGF2 alpha) produced dose-dependent inhibition (p less than 0.05) of progesterone secretion. Reduced numbers of 3 beta HSD-positive cells were recovered from these incubations. These experiments demonstrate luteotropic (dbcAMP) as well as luteolytic (PGF2 alpha) effects on ovine luteal cells in long-term culture. This study provides evidence that these cultures will be useful for investigating the development of hormonal regulation of luteal function.     

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 > or =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.     

Suppression of luteal function in dogs by luteinizing hormone antiserum and by bromocriptine

Beagle bitches were treated with equine anti-LH serum (ALHS) or the dopamine agonist bromocriptine at selected times during the 2-month luteal phase of the ovarian cycle or pregnancy. After a single injection of ALHS (10 ml, i.m.) at Day 42 of pregnancy (N = 2) or the ovarian cycle (N = 3), progesterone was reduced (P less than 0.05) to 7-24% of preinjection values within 1-2 days, and by 4-8 days returned to levels not different from those in control bitches treated with normal horse serum. Injections of bromocriptine (0.1 mg/kg, i.m.) daily for 6 days caused abrupt declines in progesterone which lasted 6-8 days in bitches treated at Day 8 or 22 of pregnancy (N = 5). In bitches treated at Day 42 of pregnancy (N = 3) or in non-pregnant cycles (N = 4) the bromocriptine treatment caused declines (P less than 0.05) in progesterone which were permanent, extensive (less than 2 ng/ml), and therefore abortive. The declines in progesterone in response to immunoneutralization of LH and to prolactin-lowering doses of a dopamine agonist demonstrate that normal luteal function in dogs requires both LH and prolactin.     

Oxytocin stimulates progesterone release from microdialyzed bovine corpus luteum in vitro

A microdialysis system (MDS) was implanted in corpora lutea (CL) from cows (Days 5-7, 8-12, and 15-18 of the estrous cycle); the CL were maintained in organ culture chambers. With this system, active substances can be applied, and a collection of steroids released from luteal cells surrounding the microcapillary (cut-off point = 100 kDa) is possible, while luteal cells maintain cell-to-cell contact. Spontaneous pulses of progesterone release were observed in 90% of control (perfused with Ringer's solution only) at 60-80 min intervals. The infusion of bovine LH (bLH) for 20 min (0.1-10 micrograms/ml) stimulated dose-dependent release of progesterone. Both results indicate that the CL maintains the activity of progesterone release and the ability to respond to LH stimulation in this system. Oxytocin (1-100 microM) also stimulated progesterone release in a dose-dependent manner. Preexposure with oxytocin antagonist blocked the stimulatory effect of oxytocin (p less than 0.01) but not of LH (p less than 0.05), confirming the specificity of the effect. When CL were prestimulated with a low dose of oxytocin (1 microM, 20 min) twice before bLH application, the release of progesterone by bLH (1 micrograms/ml, 20 min) was more pronounced (p less than 0.05). A long-term infusion (3 h) with oxytocin and/or bLH stimulated the release of progesterone for the whole period of time. Oxytocin was most stimulative during the early luteal phase (Days 5-7) and decreased continuously from Days 8-12 to Days 15-18.(ABSTRACT TRUNCATED AT 250 WORDS)