Plasma progesterone concentration depends on sampling site in pigs

The objective of this study was to examine a possible difference in progesterone concentrations between the systemic venous blood and the caudal vena cava in early pregnant gilts. Nineteen crossbred pregnant gilts were offered three different regimens of feeding to examine influence of feeding on the secretion pattern of progesterone. The groups were high (H-H), low (L-L) and low-high (L-H) receiving 3.6, 1.8 and 1.8/3.6 kg/day, respectively. Catheters were placed in a jugular vein and the caudal vena cava (to sample ovarian secretion) on day 19 of pregnancy. Two consecutive samples taken at 30-min intervals were collected four times a day for 5 days (days 20-24). In addition, three gilts were simultaneously sampled from both catheters at 30-min intervals for 12 h on day 22. Progesterone concentration was significantly lower in the jugular vein compared with the caudal vena cava in all three feeding groups (P<0.001). An indication of episodic pattern of progesterone production occurred in plasma collected from the caudal vena cava, but not from the jugular vein. Dietary intake did not cause a profound effect on plasma progesterone concentrations during days 20-24 of gestation. It seemed that ovarian progesterone was released into the vena cava in an episodic pattern and there were implications that these episodes were temporally associated with LH pulses.     

Evidence for the secretion of immunoreactive neurophysin I in addition to oxytocin from the ovary in cattle

In Exp. I, blood samples were collected simultaneously from the posterior vena cava and jugular vein or aorta from 7 heifers every 5-20 min for 2-5 h. Concomitant pulsatile secretion of oxytocin and immunoreactive neurophysin I was detected in the vena cava, but not in the jugular vein or aorta. Concentrations of oxytocin and immunoreactive neurophysin increased earlier and were higher in the vena cava than in the jugular vein or aorta after the injection of a luteolytic dose of prostaglandin F-2 alpha analogue during the mid-luteal phase of the oestrous cycle, demonstrating its ovarian but not pituitary origin. In Exp. II, blood samples were collected from the jugular vein every 12 h during 1 week after oestrus. Follicular growth had been stimulated during the preceding oestrous cycle with PMSG (10 heifers and cows) or with FSH (5 animals); 6 heifers served as controls. There was a high correlation between the number of follicles or CL and the increase in oxytocin and immunoreactive neurophysin I. Although PMSG had a greater luteotrophic effect than did FSH on progesterone secretion, a similar stimulation of oxytocin and immunoreactive neurophysin I was not observed. It is concluded that immunoreactive neurophysin I and oxytocin are secreted from the ovary in concentrations dependent upon the number of corpora lutea (and of follicles) present. During the mid-luteal period the secretion occurs in a concomitant pulsatile fashion.     

Mechanism whereby nitric oxide (NO) infused chronically intrauterine in ewes is antiluteolytic rather than being luteolytic

Nitric oxide (NO) has been reported to be luteolytic in vitro and in vivo in cows. However, an NO donor reversed PGF2alpha-induced inhibition of rat luteal progesterone secretion in vitro and an NO donor or endothelin-1 stimulated bovine luteal tissue secretion of prostaglandins E (PGE; PGE1, PGE2) in vitro without affecting progesterone or PGF2alpha secretion. In addition, chronic infusion of an NO donor into the interstitial tissue of the ovarian vascular pedicle adjacent the luteal-containing ovary prevented the decline in circulating progesterone, while a nitric oxide synthase (NOS) inhibitor did not affect luteolysis. The objective of this experiment was to determine whether an NO donor or NOS inhibitor infused chronically intrauterine adjacent to the luteal-containing ovary during the ovine estrous cycle was luteolytic or antiluteolytic. Ewes were treated either with vehicle (N=5), diethylenetriamine (DETA-control for DETANONOate; N=5), (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETANONOate-long acting NO donor; N=6), l-arginine (N=5), l-nitro-arginine methyl ester (l-NAME-NOS inhibitor; N=6), or NG-monomethyl-l-arginine acetate (l-NMMA; NOS inhibitor; N=5) every 6h from 2400h (0h) on day 8 through 1800h on day 18 of the estrous cycle. Jugular venous blood and inferior vena cava plasma via a saphenous vein cathether 5cm anterior to the juncture of the ovarian vein and inferior vena cava were collected every 6h for analysis for progesterone and PGF2alpha and PGE, respectively, by RIA. Corpora lutea were collected at 1800h on day 18 and weighed. Weights of corpora lutea were heavier (P< or =0.05) in DETANONOate-treated ewes when compared to vehicle, DETA, l-arginine, l-NAME, or l-NMMA-treated ewes, l-arginine luteal weights were heavier than vehicle, DETA, l-arginine, l-NAME, or l-NMMA-treated ewes, and luteal weights of vehicle, DETA, l-NAME, or l-NMMA-treated ewes did not differ amongst each other (P> or =0.05). Profiles of progesterone in jugular venous blood on days 8-18 differed (P< or =0.05) in DETANONOate-treated ewes when compared to vehicle, DETA, l-arginine, l-NMMA or l-NAME-treated ewes, which did not differ (P> or =0.05) amongst each other. The PGE:PGF2alpha ratio profile in inferior vena cava plasma of DETANONOate-treated ewes was increased (P< or =0.05) when compared to all other treatment groups. In a second experiment, conversion of [3H PGE2] to [3H PGF2alpha] by day 15 ovine caruncular endometrium in vitro was determined in vehicle, DETA, or DETANONOate-treatment groups. Conversion of [3H PGE2] to [3H PGF2alpha] was decreased (P< or =0.05) only by DETANONOate. It is concluded that NO is not luteolytic during the ovine estrous cycle, but may instead be antiluteolytic and prevent luteolysis by altering the PGE:PGF2alpha ratio secreted by the uterus.     

Ultrasound-guided cannulation of the caudal vena cava in the bovine for selective sampling of ovarian effluent

The accuracy of real-time, B-mode ultrasonography was assessed in the visualization and placement of the cannula tip, cranial to the entrance of the ovarian veins as they enter the caudal vena cava of the bovine. A cannula containing a wire guide was introduced into the coccygeal vein via a 14-gauge needle, and was then directed cranially into the caudal vena cava. Once the caudal vena cava was successfully cannulated (7 of 14 cows), ultrasonography allowed for the visualization of the cannula in 7 out of 7 cows. The tip of the cannula was successfully placed cranial to the entrance of the ovarian effuent into the vena cava in 6 of these 7 animals using ultrasound guidance. This was confirmed using progesterone or prostaglandin F(2alpha) radioimmunoassay (RIA). The primary limitation to this technique was the initial catherization of the coccygeal vein which was not achieved in 7 of 14 cows attempted in this study. Successful cannulation was limited to large framed Holstein cows that had at least one calf. Results from this study indicate that real-time, B-mode, ultrasonography is an effective tool for the visualization and accurate placement of the cannula tip within the caudal vena cava. This finding could have implications for research in ovarian hormonal physiology in the cyclic, postpartum or anestrous cow.     

Effects of arterial infusions of adrenalin and acetylcholine on luteal secretion of progesterone and oxytocin in goats

The effects of close intra-arterial infusion of acetylcholine and adrenalin on ovarian secretion of progesterone and oxytocin were examined on Day 10 of the estrous cycle in goats (estrus = Day 0). Acetylcholine (15 micrograms/min) was without effect, but adrenalin (10 micrograms/min) significantly (P < 0.001) raised both progesterone and oxytocin concentrations in ovarian vein plasma. These results show that luteal hormone secretion is enhanced in the goat by beta-adrenergic stimulation and suggest that, as in the sheep and cow, there may be neuroendocrine involvement in the regulation of caprine luteal function.     

Prolongation of the luteal phase by prostaglandin E(2) during the estrous cycle in the cow. A preliminary report

An experiment was conducted to determine the effects of prostaglandin E(2) (PGE(2)) on ovarian progesterone secretion during the estrous cycle in the cow. Intraluminal uterine catheters were implanted in three beef cows (2 treated, 1 control), and 1.3 mg of PGE(2) were infused into the uterus every 4 hours from days 9 through 21 post-estrus. Blood samples were collected from the jugular vein at 2-hour intervals from days 9 to 21 and twice daily from day 22 to 28 post-estrus. Progesterone was measured by applying a specific, direct plasma radioimmunoassay in all samples without extraction. Intrauterine infusion with PGE(2) resulted in maintenance of luteal-phase progesterone secretion until day 21 post-estrus, 4 days after luteal regression occurred in the vehicle-treated cow. In this study, we demonstrated that PGE(2) can prolong the presence of luteal phase plasma progesterone concentrations by possibly stimulating in vivo steroidogenesis by the corpus luteum during the estrous cycle in the cow.     

Effect of the season on some aspects of the estrous cycle in Martina Franca donkey

The Martina Franca (MF) donkey breed, with 48 jackasses and 515 jennies, is considered an endangered breed according to the data from the Monitoring Institute for Rare Breeds and Seeds in Europe. The knowledge of the estrous cycle characteristics has a great impact for assisted reproduction, especially in endangered species. In this study, the estrous cycle characteristics were investigated in 12 MF jennies throughout the year. Estrous cycle, estrous and diestrous lengths, follicular growth and ovulation, and estradiol-17β (E2) and progesterone (P4) plasma concentrations were monitored in MF jennies and compared in different seasons. In all jennies (100%) estrous cycle was detected during the whole year, with no differences in the estrous cycle length among seasons. However, a significant increase of estrous length in spring and summer compared with autumn and winter was found. Diestrus was shorter in summer than in the other seasons. Estrous behavior was always shown and characterized by rhythmic eversion of the vulvar labia (winking) with exhibition of the clitoris, urination, male receptivity and clapping, with sialorrhoea, neck and head extension, and back ears. Estrus was characterized by the ovulation of a larger follicle in spring and summer than in autumn and winter. The pattern of E2 and P4 plasma concentrations during the estrous cycle were similar to that reported for the mare, but without differences among the four seasons, so that a negligible effect of environmental conditions on ovarian E2 and P4 secretion was hypothesized, despite the larger diameter of the ovulating follicle in spring and summer.     

Levels of prostaglandin F (PGF) in bovine endometrium uterine venous, ovarian arterial and jugular plasma during the estrous cycle (38789).

Prostaglandins F (PGF) were measured in uterine vein, ovarian artery, and jugular vein plasma and in the endometrial tissues at various times during the bovine estrous cycle, and were compared to peripheral plasma progesterone levels. Four groups of heifers at days 1-5, 10-14, 15-17 and 20-0 of the estrous cycle were studied. Low levels of PGF (48 plus or minus 12 ng/g dry tissue were measured in the endometrium on days 1-14 of the cycle. Higher values (131 plus or minus 9.0) were found at days 15 until the day of estrus (p less than 0.001). Similarly, very low levels of PGF were observed in the uterine vein plasma at days 1-14 (0.162) plus or minus 0.044) ng/mlM plus or minus S.E.), whereas on days 15 until the day of estrus the levels ranged from 1.5 to 3.0 ng/ml. The increases in uterine vein PGF on day 15 occurred even while peripheral plasma progesterone levels were still high. However, PGF was not elevated in either the ovarian artery or the jugular vein at any time during the cycle, even when uterine vein levels were greatly elevated. No differences in PGF content were detected in endometrial tissue from uterine horns adjacent or opposite to the functional corpus luteum.     

Chronic utero-ovarian vein catheterization with subsequent occlusion prolongs the estrous cycle and changes electromyographic activity in the myometrium of ewes

The objective of our study was to determine the effect of chronic utero-ovarian vein catheterization in ewes on estrous cycle length, plasma progesterone (P) concentration, and myometrial electromyographic activity. Cyclic ewes with inferior vena cava catheters were used as controls. Estrus was synchronized in ten ewes and 10 to 12 d following estrus, the ewes were anesthetized, fitted with myometrial electromyograph leads and with utero-ovarian vein (n = 5) or inferior vena cava (n = 5) catheters. After surgery, ewes returned to estrus as expected (16 to 18 d interestrus interval). The second cycle of four of five ewes with utero-ovarian vein catheters were prolonged (40 to 58 d). The inferior vena cava catheterized ewes had normal length second cycles. Plasma P concentrations reflected the estrous cycles: low ( 0.05).     

Steroid feedback inhibition of pulsatile secretion of gonadotropin-releasing hormone in the ewe

The long-term negative feedback effects of sustained elevations in circulating estradiol and progesterone on the pulsatile secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) were evaluated in the ewe following ovariectomy during the mid-late anestrous and early breeding seasons. GnRH secretion was monitored in serial samples of hypophyseal portal blood. Steroids were administered from the time of ovariectomy by s.c. Silastic implants, which maintained plasma concentrations of estradiol and progesterone at levels resembling those that circulate during the mid-luteal phase of the estrous cycle; control ewes did not receive steroidal replacement. Analysis of hormonal pulse patterns in serial samples during 6-h periods on Days 8-10 after ovariectomy disclosed discrete, concurrent pulses of GnRH in hypothalamo-hypophyseal portal blood and LH in peripheral blood of untreated ovariectomized ewes. These pulses occurred every 97 min on the average. Treatment with either estradiol or progesterone greatly diminished or abolished detectable pulsatile secretion of GnRH and LH, infrequent pulses being evident in only 3 of 19 steroid-treated ewes. No major seasonal difference was observed in GnRH or LH pulse patterns in any group of ewes. Our findings in the ovariectomized ewe provide direct support for the conclusion that the negative-feedback effects of estradiol and progesterone on gonadotropin secretion in the ewe include an action on the brain and a consequent inhibition of pulsatile GnRH secretion.     

Secretion of progesterone, estradiol-17beta, PGE, PGF2alpha, and pregnancy-specific protein B by 90-day intact and ovariectomized pregnant ewes

Ninety-day pregnant ewes were either laparotomized, ovaries left in situ or bilaterally ovariectomized, and a jugular venous catheter and an inferior vena cava catheter via the saphenous vein were installed. Seven days later, placenta slices were collected and incubated in vitro for 4 h. Secretions of progesterone, PGE, estradiol-17beta and pregnancy-specific protein B (PSPB) in vitro by placenta from ovariectomized ewes were increased (P < or = 0.05) by 2.7-, 3.6-, 2.2-, and 2.4-fold, respectively, when compared to placenta slices from intact 90-day pregnant ewes. Secretion of PGF2alpha in vitro was unchanged (P > or = 0.05). Ovariectomy decreased (P < or = 0.05) jugular venous progesterone for 78 h followed by a quadratic increase (P < or = 0.05), whereas progesterone remained unchanged (P > or = 0.05) in intact ewes over the 162-h sampling period. Ovariectomy increased (P < or = 0.05) PGE in inferior vena cava plasma over the last half of the 162-h sampling period, whereas concentration of PGF2alpha did not change (P > or = 0.05). Increases in PGE occurred before the increase in progesterone. Concentrations of PSPB in inferior vena cava plasma of ovariectomized pregnant ewes increased (P < or = 0.05) during the last half of the 162-h sampling period, but not in intact ewes (P > or = 0.05). PSPB increased before PGE and progesterone. Concentrations of estradiol-17beta in jugular venous plasma of ovariectomized pregnant ewes increased (P < or = 0.05) during the last half of the sampling period, but not in intact ewes (P > or = 0.05). Increases in estradiol-17beta occurred before increases in PSPB. It is concluded that these data support the hypothesis that estradiol-17beta may control placental secretion of PSPB; PSPB may regulate placental secretion of PGE; and PGE may regulate placental secretion of progesterone.     

Physiological role of 20alpha-dihydroprogesterone during the estrous cycle in goats

The relationships between the effects of single or repeated subcutaneous injections of 25 mg progesterone on luteal function during the estrous cycle in goats as well as the secretion of 20alpha-dihydroprogesterone or 15-keto-13, 14-dihydro-prostaglandin F(2alpha) (PGFM), the major metabolite of PGF(2alpha), were investigated. A single dose of progesterone given on Day 4, 10, or 18 of the estrous cycle increased the concentration of 20alpha-dihydroprogesterone and did not affect the length of the cycle. Each dose of progesterone on Days 2 to 5 increased the concentration of 20alpha-dihydroprogesterone (with a later decrease each day to a nadir which then increased daily) and shortened the cycle. The 20alpha-dihydroprogesterone concentration remained high; when it decreased, the concentration of the luteolytic agent PGFM began to increase. Daily doses of 25 mg 20alpha-dihydroprogesterone given on Days 2 to 5 had no effect on the length of the cycle. These results indicate that during the estrous cycle in goats, progesterone is catabolized to the biologically inactive steroid 20alpha-dihydroprogesterone, but much of the progesterone that is given early in the luteal phase of the estrous cycle causes premature luteolysis by stimulating an increase in the release of PGF(2alpha) . The secretion of 20alpha-dihydroprogesterone may help to regulate progesterone production during the estrous cycle in goats.     

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.     

Different effects of subnormal levels of progesterone on the pulsatile and surge mode secretion of luteinizing hormone in ovariectomized goats

This study tested the hypothesis that endocrinological threshold levels of progesterone that induce negative feedback effects on the pulsatile and surge modes of LH secretion are different. Our approach was to examine the effects of subnormal progesterone concentrations on LH secretion. Long-term ovariectomized Shiba goats that had received implants of silastic capsules containing estradiol were divided into three groups. The high progesterone (high P) group received a subcutaneous implant of a silastic packet (50 x 70 mm) containing progesterone, and the low progesterone (low P) group received a similar implant of a small packet (25 x 40 mm) containing progesterone. The control (non-P) group received no treatment with exogenous progesterone. Blood samples were collected daily throughout the experiment for the analysis of gonadal steroid hormone levels and at 10-min intervals for 8 h on Days 0, 3, and 7 (Day 0: just before progesterone treatment) for analysis of the pulsatile frequency of LH secretion. Then estradiol was infused into the jugular vein of all animals at a rate of 3 microg/h for 16 h on Day 8 to determine whether an LH surge was induced. Blood samples were collected every 2 h from 4 h before the start of the estradiol infusion until 48 h after the start of the infusion. In each group, the mean +/- SEM concentration after progesterone implant treatment was 3.3 +/- 0.1 ng/ml for the high P group, 1.1 +/- 0.1 ng/ml for the low P group, and <0.1 ng/ml for the non-P group, concentrations similar to the luteal levels, subluteal levels, and follicular phase levels of the normal estrous cycle, respectively. The estradiol concentration ranged from 4 to 8 pg/ml after estradiol capsule implants in all groups. The LH pulse frequency was significantly (P < 0.05) suppressed on Day 3 (6.2 +/- 0.5 pulses/8 h) and on Day 7 (2.6 +/- 0.9 pulses/8 h) relative to Day 0 (9.0 +/- 0.5 pulses/8 h) in the high P group. In both the low P and non-P groups, however, the changes of pulsatile frequency of LH were not significantly different, and high pulses (7-9 pulses/8 h) were maintained on each of the 3 days they were tested. An LH surge (peak concentration, 100.3 +/- 11.0 ng/ml) occurred in all goats in the non-P group, whereas there was no surge mode secretion of LH in either the high P or the low P group. The results of this study support our hypothesis that the threshold levels of progesterone that regulate negative feedback action on the LH pulse and the LH surge are different. Low levels of progesterone, around 1 ng/ml, completely suppressed the LH surge but did not affect the pulsatile frequency of LH secretion.     

8-hour rhythm of ovarian progesterone secretion in ewe

Pulse character of hormones secretion in the hypothalamus-pituitary-gonads system is a necessary condition of physiological regulation of reproduction. At the same time, the rhythms of ovarian hormones secretion have not been adequately explored. The researches study mainly three sexually mature ewes. The stages of oestrus cycle were determined on behavioral reactions of females in the presence of ram. Blood samples from jugular vein were collected hourly over 24-hour period during follicular (15-16 days), early (3-4 days) and middle (7-9 days) luteal phase of oestrus cycle, pregnancy (40-105 days) and lactation (30-45 days). 27 experiments were performed. Plasma progesterone was determined by enzyme-immunoassay method. There was no diurnal rhythm of ovarian progesterone secretion in ewes. During early and middle luteal phase of oestrus cycle and lactation, an 8-hour rhythm of progesterone secretion was detected. Follicular phase of oestrus cycle and pregnancy were characterized by irregular rises of fluctuations of progesterone level. It seems that the 8-hour rhythm of progesterone secretion during luteal phase and lactation is controlled by action of intraovarian generator of ultradian rhythms.     

Changes in the ovarian dynamics and endocrine profiles in goats treated with a progesterone antagonist during the early luteal phase of the estrous cycle

The aim of the present study was to determine the physiological role of endogenous progesterone in the regulation of ovarian dynamics, gonadotropin and progesterone secretion during the early luteal phase in the goat. Cycling Shiba goats received subcutaneously a vehicle (control group, n=5) or 50 mg of RU486 (RU486 group, n=4) daily from 1 to 7 days after ovulation (day 0) determined by transrectal ultrasonography. Ovarian dynamics were monitored by the ultrasonography and blood samples were collected daily until the subsequent ovulation for analysis of progesterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion. Blood samples were also collected at 10 min intervals for 6 h on day 3 and day 7 for the analysis of pulsatile patterns of LH and FSH. The LH pulse frequency was significantly (P<0.05) higher in the RU486 group than in the control group on day 7 (4.8+/-1.1 pulses/6 h versus 1.2+/-0.4 pulses/6 h). The shape of the FSH pulses was unclear on day 3 and day 7 in both groups and the overall means of FSH concentration for 6 h on day 3 and day 7 were not significantly different between the RU486 and the control groups. The pattern of daily FSH concentrations showed a wave-like fluctuation in both groups. There was no significant difference in the inter-peak intervals of the wave-like pattern of daily FSH secretion between the RU486 and the control groups (4.1+/-0.6 days versus 4.5+/-0.6 days). The maximum diameter of the largest follicle that grew from day 1 to day 7 in the RU486 group tended to be greater than that in control goats (6.4+/-0.8 mm versus 5.0+/-0.8 mm, P=0.050), whereas no significant difference was detected in the size of the corpus luteum and progesterone concentrations between the control and RU486 groups on almost all days during the treatment period. These results indicate that the rise of the progesterone concentration suppresses the pulsatile LH secretion and follicular growth, whereas progesterone has no physiological role in the regulation of FSH secretion and luteal function during the early luteal phase of the estrous cycle in goats.     

Seasonal and hormonal control of pulsatile LH secretion in the dairy goat (Capra hircus)

In Exp. 1, the changes in pulsatile LH secretion at the onset of the breeding season were observed in 20 intact, mature Saanen does. Blood was sampled every 20 min for 6 h each week from the beginning of August until the onset of ovulatory activity, as evidenced by cycles in plasma progesterone. The first doe ovulated at the end of August and all were cycling by the end of September. As the first ovulation approached, LH pulse frequency increased by 67% and mean levels of LH increased by 47%. These changes were progressive rather than abrupt. In Exp. 2, seasonal changes in the inhibition of pulsatile LH secretion by ovarian steroids were studied in ovariectomized Saanen does. The animals were untreated (N = 4) or given subcutaneous oestradiol implants (N = 4) and blood was sampled every 10 min for 6 h, twice during the breeding season and twice during the anoestrous season. In each season, the second series of samples was taken after the animals had been treated with progesterone, administered by intravaginal implants. Season did not significantly affect LH secretion in goats not treated with oestradiol, but LH pulse frequency was 54% lower during the anoestrous season than during the breeding season in oestradiol-treated goats. Mean LH concentrations were affected in the same manner as pulse frequency, but pulse amplitude was increased by oestradiol treatment in both seasons. Progesterone had no detectable effect on LH secretion in either season. In Exp. 3, the response to repeated melatonin injections at a set time after dawn was investigated in 11 oestradiol-treated, ovariectomized goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative analysis of functions of cow and reindeer female reproductive organs: Progesterone content in vessels of reproductive organs

Progesterone content in blood from paired ovarian and uterine veins as well as from jugular veins of cows and reindeers was studied in the estrous cycle lutein phase and at the earlier stages of pregancy. In the both species, maximal progesterone concentration was detected in blood from vein of the ovary carrying corpus luteum (p < 0.001). In cows, a higher hormone concentration, as compared with jugular vein, has also been determined in vein of the uterus horn closest to ovary with corpus luteum (p < 0.01). In reindeers, blood from all studied vessels of reproductive organs had the progesterone concentration that was statistically significantly higher (p < 0.001) than that from jugular vein. In cows, progesterone concentration in blood from the ovarian vein was found to be higher when corpus luteum was located on the right ovary (p < 0.05) as compared with left-side corpus luteum location. No functional asymmetry of ovaries was revealed in reindeers. A possible role of mechanisms of the hormone local transport between ovary and uterus in adaptation of ruminants to reproduction under Nordic conditions is discussed.     

The preovulatory rise of ovarian ornithine decarboxylase is required for progesterone secretion by the corpus luteum

Ovarian progesterone secretion during the diestrus stage of the estrous cycle is produced by luteal cells derived from granulosa and thecal cells after the differentiation process that follows ovulation. Our results show that blockade of the preovulatory rise of ovarian ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, by treatment with the specific inhibitor alpha-difluoromethylornithine (DFMO) leads to a significant decrease in the ovarian progesterone content and a dramatic fall in the plasma levels of this hormone during the following diestrus. The same inhibition was produced in spite of the fact that both luteinizing and follicle stimulating hormones were given concomitantly with DFMO. On the other hand, the acute rise in the plasma progesterone levels observed after administration of human chorionic gonadotropin to mice at different periods of the estrous cycle was not affected by DFMO administration. Our results indicate that although elevated levels of ODC are not required for acute ovarian steroidogenesis, the preovulatory peak of ovarian ODC activity observed in the evening of proestrus may be critical for the establishment of a constitutive steroidogenic pathway and progesterone secretion by the corpus luteum during the diestrus stage of the murine estrous cycle.     

Control of luteal relaxin release by prostaglandin F2 alpha: differences in the sow cycle and pregnancy

The effect of an in vivo prostaglandin F2 alpha (PGF2 alpha) challenge in pregnant and cyclic sows was compared to determine whether PGF2 alpha-induced release of relaxin (RLX) from the corpus luteum (CL) in late pregnancy is also effective during the cycle. Ovarian venous RLX and progesterone were monitored by radioimmunoassay and RLX localized in the CL by immunohistochemistry. In Day 108 pregnant sows, infusion of PGF2 alpha (100 micrograms) into the ovarian artery resulted in an immediate and sustained rise in ovarian venous RLX with an initial decline in progesterone levels by 30 min which then returned to pretreatment levels. In Day 13 or 15 cyclic sows with functional corpora lutea (i.e., elevated progesterone), RLX was undetectable in ovarian venous blood after 100 micrograms of PGF2 alpha. Administration of PGF2 alpha via either the jugular vein or intramuscular route was also ineffective in releasing RLX from the CL of the cycle. The intensity of RLX immunostaining of the CL was similar in saline and PGF2 alpha-treated sows. These studies indicate that the control of RLX release from the sow CL differs in the estrous cycle and pregnancy.