Role of luteinizing hormone-releasing factor (LH-RF) and LH on maintenance of early gestation in rats.

The role of luteinizing hormone (LH) and LH-releasing hormone (LH-RH) in the maintenance of early pregnancy in rats was studied. Serum levels of progesterone (P) and LH were measured daily in untreated pregnant rats from Day 4 through parturition. Serum levels of P and LH were determined on Days 11 and 15 of pregnancy in animals treated with antisera to LH (LH-A/S) and to LH-RH (LH-RH-A/S) on Days 8-10. Serum levels of P peaked on Days 7 and 16 in untreated animals, after which they declined sharply just before delivery. Serum LH fluctuated between 30-160 ng/ml during pregnancy but did not exhibit any distinctive peaks. Treatment with .2 ml LH-A/S on Days 8-10 reduced serum P to virtually undetectable levels on Day 11, and only a slight recovery was evident on Day 15. Lower doses of LH-A/S had no effect. Administration of 1.3 ml LH-RH-A/S had no effect on serum levels of P or LH, and did not impede fetal development. The results indicate that LH is essential to the luteotropic complex of early pregnancy in the rat, and also that LH-RH-A/S can maintain to some extent basal levels of P and LH during early pregnancy.     

Rat placental luteotropin: initial secretion and luteolytic quality

The secretion of placental lactogen begins early in pregnancy. Previous studies indicate that rat placental lactogen (rPL) is secreted from Day 8 of pregnancy and that it is luteolytic as well as luteotrophic. This study establishes the onset of both the luteotrophic and the luteolytic effects of placental lactogen in pregnant rats subject to timed hypophysectomy. Pregnancy was preserved in all groups with the administration of dydrogesterone (9 beta, 10 alpha-pregna4,6-diene-3, 20 dione), a progesterone analog, and diethylstilbestrol, an estrogen analog. Plasma progesterone and 20 alpha-hydroxypregn-4-ene-3-one (20-OHP) were measured in serial serum samples by RIA. The data indicate that rPL is secreted as early in pregnancy as the seventh day. Rats hypophysectomized on Day 6 of pregnancy or later had ovaries that contained corpora lutea that secreted increasing quantities of progesterone during pregnancy. On Day 16 serum progesterone values were lowest in animals operated on Days 4 and 5 compared to animals operated on Days 6 or 8. The 20-OHP serum values from animals operated on Days 4 and 5 declined steadily from Day 8 to Day 16. These findings indicate progestational incompetency, which was confirmed morphologically. Thus, rPL secretion begins by Day 7 and it is both luteotrophic and luteolytic.     

Changes in circulating inhibin levels during pregnancy and early lactation in the Japanese monkey

Changes in immunoreactive (ir-) inhibin concentrations in serum throughout pregnancy and early lactation up to one month after parturition were characterized in 6 Japanese monkeys (Macaca fuscata fuscata) by a heterologous radioimmunoassay (RIA) based on a bovine RIA. Serum levels of FSH, LH/monkey chorionic gonadotropin (mCG), estradiol-17 beta, and progesterone were also monitored for the entire period. Ir-inhibin levels in the serum were low (under 0.5 ng/ml) before conception. Three marked increases in serum ir-inhibin levels were found during pregnancy. The first increase was noted during early pregnancy, with a peak (2.2 +/- 0.2 ng/ml) at Day 22 of pregnancy (Day 0 = day of LH surge). The second increase was noted after Day 38 until Day 72 of pregnancy, when a peak value was noted (19.0 +/- 1.4 pg/ml). Plateau levels were maintained until late pregnancy, and a final rise was evident near the term with a peak (36.7 +/- 3.8 ng/ml) at Day 158 of pregnancy, 5 days before parturition. After parturition, ir-inhibin levels in the serum plummeted to nonpregnant levels within one day, and were maintained during early lactation. The first rise in serum inhibin during pregnancy was parallel to the rise of mCG and estradiol-17 beta, and the second and third rise were well correlated with serum estradiol-17 beta. Serum FSH was maintained at low levels throughout pregnancy, followed by a slight increase after parturition when serum inhibin decreased abruptly. Both bioactivity and immunoreactivity of inhibin were detected in the placental homogenates obtained at 120 days of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of calf removal on serum luteinizing hormone and cortisol concentrations in postpartum beef cows

Serum luteinizing hormone (LH) and cortisol concentrations were measured in ten fall calving, Angus cows averaging 38 +/- 8 days postpartum. Calves from five cows were weaned at the beginning of the study. Blood samples were collected at 20 min. intervals for 48 h after weaning and for 8 h on day 4 and day 6 postweaning. Mean serum LH concentrations increased (P<0.01) in weaned cows (W) from 0.55 +/- 0.01 ng/ml at time of calf removal to 1.3 +/- 0.04 ng/ml 48 h afterwards. Comparable LH concentrations for suckled cows (S) were 0.65 +/- 0.08 ng/ml and 0.62 +/- 0.03 ng/ml respectively. Average serum LH concentrations at 48 h after weaning were greater (P<0.01) for W cows than S cows and a treatment by time interaction occurred (P<0.01) with serum LH concentrations increasing (P<0.01) from time of calf removal to 48 h after calf removal in W cows. Frequency of LH peaks increased (P<0.01) in W cows and by 48 h after weaning was greater (P<0.01) in W cows than in S cows. Magnitude of LH peaks did not differ between the two groups. Serum cortisol concentrations were not different between W and S cows except for a transient elevation (P<0.01) in W cows from 7.6 +/- 0.9 ng/ml to 11.9 +/- 1.0 ng/ml 9 to 12 h after calf removal. Since serum LH concentrations were increased in W cows but not in S cows at 48 h and serum cortisol concentrations increased transiently in W cows we suggest that circulating cortisol levels may not be a physiological inhibitor of LH secretion in the suckled postpartum beef cow.     

The Sulawesi Crested Black Macaque (Macaca nigra) menstrual cycle: changes in perineal tumescence and serum estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone levels.

Events in the normal menstrual cycle of the endangered Sulawesi Crested Black Macaque (Macaca nigra) were characterized. Daily blood samples were obtained during 10 menstrual cycles from five M. nigra demonstrating regular cycles. The amount of perineal tumescence was scored daily. Serum levels of estradiol and progesterone were determined by RIA, serum LH levels were determined by the mouse Leydig cell bioassay, and serum FSH levels were determined by the rat granulosa cell aromatase bioassay. Cycle length was 39.8 +/- 1.0 days (mean +/- SEM) with an LH surge occurring 25 +/- 1.5 days from the onset of menses. After menses, both LH and estradiol were initially depressed, with estradiol first exceeding 50 pg/ml 8 days before the LH surge. In five cycles, peak estradiol levels (340 +/- 44 pg/ml) occurred on the day of the LH surge (637 +/- 58 ng/ml) and in the other five cycles, on the day before the LH surge. There was a broad increase of FSH in midcycle without a well-defined surge corresponding to the LH surge. Progesterone began increasing on the day of the LH surge and reached peak levels (6.8 +/- 0.96 ng/ml) 8 days later. Maximal perineal tumescence was generally associated with the time of the LH surge, but variation between animals made it impossible to predict accurately the day of the LH surge by perineal tumescence scores alone.     

Serum luteinizing hormone levels in cattle under various reproductive states

Serum lutinizing hormone (LH) levels in cattle during various reproductive states were measured by radioimmunoassay. A sharp LH peak observed at estrus (22.72 ± 5.68 ng/ml) was about 26 times higher than at other stages of the cycle (0.87 ± 0.06 ng/ml). LH levels during the first 90 days of pregnancy (0.75 ± 0.15 ng/ml) were similar to those of the estrous cycle, except during estrus, while those during the second (0.22 ± 0.07 ng/ml) and third trimesters of pregnancy (0.22 ± 0.08 ng/ml) were significantly lower. Higher levels than those of the cycling cows, except during estrus, were seen in ovariectomized cows (2.21 ± 0.56 ng/ml). Levels of LH in cows with cystic follicles (2.00 ± 0.49 ng/ml) were higher than the levels in the cycle. LH levels in bulls (1.29 ± 0.39 ng/ml) were comparable to that of estrous cows. Serum LH of calves increased with age from 1.00 ± 0.32 ng/ml (less than 30 days of age), to 2.30 ± 0.83 ng/ml (181 to 210 days of age), and the level after 151 days was significantly higher than that of the cyclic cows, except during estrus.     

Changes in serum LH concentrations during normal and abnormal sexual development in the pig.

Serum levels of luteinizing hormone (LH) were determined in fetal and prepubertal pigs from Day 49 postcoitum to 25 weeks of age, and also in unilaterally cryptorchid, freemartin and castrated pigs of similar ages. Serum LH was undetectable in the second trimester of pregnancy, but then gradually increased up to 2 weeks after birth in both sexes. 2-week-old pigs showed irregular LH peaks exceeding 2 ng/ml. Serum LH concentrations decreased during the 3rd and 4th weeks of life. Mean LH concentrations were approximately 2 ng/ml in castrated pigs and 1.3 + or -.7 ng/ml in freemartins. The differentiation and functional activity of the testis appeared to be well correlated with the changes in serum LH concentrations. Changes in serum LH could not be correlated with normal and abnormal gubernacular development.     

Inhibition of luteinizing hormone secretion during quiescent interval of testicular androgen production in immature mice

We reported [1] that the proliferation of seminal vesicle cells in mice takes place largely in the neonatal (days 0-15) and pubertal (days 25-35) periods and that between neonatal and pubertal proliferations, a quiescent interval of cell proliferation due to markedly diminished secretion of androgens occurs. The present study was carried out to investigate the mechanism for this quiescent interval of Leydig cell activity. Serum LH concentrations were moderate (0.29 ng NIH-LH-S1/ml) at 8 days of age, low (0.13 ng/ml) at 18 days, and high (0.78-0.60 ng/ml) at 30, 40 and 60 days. The LH level on day 18 was almost the same as that found in hypophysectomized adult mice (0.12 ng/ml). These changes with age in serum LH concentrations paralleled those for serum total androgen (testosterone plus 5 alpha-androgens) concentrations. The injection of HCG (1 IU/day) or LH releasing hormone (0.1 or 0.4 microgram/6h) for 1 or 2 days resulted in significant and marked increases on day 18 in testicular and serum androgen levels and/or the proliferation of seminal vesicle cells measured with 5-[125I]iodo-2'-deoxyuridine uptake by the whole seminal vesicles. These findings lead to the hypothesis that the quiescent interval of testicular androgen production due to inhibition of pituitary LH secretion occurs around day 20 in mice.     

Failure of naloxone to stimulate luteinizing hormone secretion during pregnancy and steroid treatment of ovariectomized beef cows

The response of serum luteinizing hormone (LH) to naloxone, an opiate antagonist, and gonadotropin-releasing hormone (GnRH) was measured in cows in late pregnancy to assess opioid inhibition of LH. Blood samples were collected at 15-min intervals for 7 h. In a Latin Square arrangement, each cow (n = 6) received naloxone (0, 0.5, and 1.0 mg/kg BW, i.v.; 2 cows each) at Hour 2 on 3 consecutive days (9 +/- 2 days prepartum). GnRH (7 ng/kg body weight, i.v.) was administered at Hour 5 to all cows on each day. Mean serum LH concentrations (x +/- SE) before naloxone injection were similar (0.4 +/- 0.1 ng/ml), with no serum LH pulses observed during the experiment. Mean serum LH concentrations post-naloxone were similar (0.4 +/- 0.1 ng/ml) to concentrations pre-naloxone. Mean serum LH concentrations increased (p less than 0.05) following GnRH administration (7 ng/kg) and did not differ among cows receiving different dosages of naloxone (0 mg/kg, 1.44 +/- 0.20; 0.5 mg/kg, 1.0 +/- 0.1; 1.0 mg/kg, 0.9 +/- 0.1 ng/ml). In Experiment 2, LH response to naloxone and GnRH was measured in 12 ovariectomized cows on Day 19 of estrogen and progesterone treatment (5 micrograms/kg BW estrogen: 0.2 mg/kg BW progesterone) and on Days 7 and 14 after steroid treatment. On Day 19, naloxone failed to increase serum LH concentrations (Pre: 0.4 +/- 0.1; Post: 0.4 +/- 0.1 ng/ml) after 0, 0.5, or 1.0 mg/kg BW.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of zearalenone and estradiol benzoate on serum concentrations of LH, FSH and prolactin in ovariectomized gilts

Six ovariectomized gilts were given zearalenone (Z), estradiol benzoate (EB) or vehicle in a replicated 3 x 3 Latin square design. Zearalenone was added to 2.3 kg of a corn-soybean ration at a dose of 1 mg Z/kg body weight; EB was given intramuscularly at 0.1 mg EB/kg body weight. Control gilts received vehicle solvent for both Z and EB. Blood samples were collected from indwelling jugular cannulas at 6-h intervals for 48 h before Z, EB or vehicle was given. After treatment, blood samples were drawn at 6-h intervals for an additional 84 h. Serum concentrations of luteinizing hormone (LH) decreased (P<0.001) from 4.67 ng/ml to 0.29 ng/ml within 6 h of EB. From 54 to 84 h after EB, serum concentrations of LH rose to 15.60 ng/ml (P<0.001). Serum concentrations of LH were reduced (P<0.001) in a similar pattern after Z (3.70 ng/ml to 0.49 ng/ml), but a rise in serum LH was not observed 54 to 84 h after Z (1.30 ng/ml). Serum concentrations of LH remained unchanged (P=0.55) in gilts given vehicle. Serum concentrations of follicle stimulating hormone (FSH) were suppressed (P<0.03) at 6 h in EB (19.10 vs 11.35 ng/ml) and Z gilts (16.16 vs 11.41 ng/ml) but remained unchanged in vehicle gilts. Serum concentrations of FSH did not change in EB or Z gilts during the next 36 h. These data indicate that the suppressive action of Z on serum concentrations of LH and FSH was similar to that of EB, while the biphasic stimulatory effect of EB for LH was not manifested by Z.     

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.     

Circulating immunoreactive inhibin, gonadotropin, and prolactin levels during pregnancy, lactation, and postweaning estrous cycle in the rat

Serum inhibin levels were measured by heterologous RIA during pregnancy, lactation, and the post-weaning estrous cycle in the rat and correlated with changes in serum FSH and LH and prolactin. Blood was serially collected by cardiac puncture under light ether anesthesia from adult Sprague-Dawley rats on alternate days throughout the experimental period. For the first 8 days of pregnancy, immunoreactive inhibin levels remained high, then gradually decreased to reach a nadir at Day 16, and subsequently rose steeply until parturition. The pattern of serum immunoreactive inhibin levels during early pregnancy does not support a corpus luteum source and the dramatic rise from Day 16 to Day 22 correlates with the recommencement of follicular development in the ovary. Inhibin levels decreased rapidly on the day after birth and were suppressed until Day 8 of lactation, slowly increasing thereafter to reach a plateau from Day 14 until weaning (Day 22.5 of lactation). These changes in inhibin levels positively correlated with LH and FSH and negatively with prolactin, and are consistent with an ovarian source for inhibin associated with the recommencement of follicular development resulting from the diminution of the suckling stimulus. Immediately after weaning, serum immunoreactive inhibin levels showed a 4-day cyclic pattern corresponding to the estrous cycle identified by vaginal smear. Inhibin levels peaked on the day of proestrus, reached a nadir on the day of estrus, and rose slowly during metestrus and diestrus to a new peak at proestrus. Serum FSH levels showed an inverse correlation to inhibin levels consistent with a feedback relationship with inhibin.     

Levels of lutenizing hormone, estradiol and progesterone in serum during the estrous cycle and pregnancy in the beagle bitch (38491).

Levels of luteinizing hormone (LH), estradiol-17 beta and progesterone were determined by specific radioimmunoassays in sera obtained from Beagle bitches during proestrus, estrus and diestrus. Concentrations of LH (expressed as NIH-LH-SI equivalents) were 2.8 plus or minus 0.1 ng/ml in proestrus, 35.5 plus or minus 10.0 ng/ml during early estrus and 2.2 plus or minus 0.1 ng/ml in early diestrus. Peak levels of estradiol-17beta (68.9 plus or minus 11.0 ng/ml) were detected 24 hr prior to the LH peak, declined rapidly and reached basal levels (17.8 plus or minus 6.3 ng/ml) by five days following the LH peak. Levels of progesterone were 1.7 plus or minus 0.3 ng/ml during proestrus, 3.5 plus or minus 0.3 ng/ml during early estrus and 23.3 plus or minus 2.8 ng/ml on day 5 after the LH peak . Progesterone levels remained elevated through day 28 of diestrus and pregnancy. A significant decrease (p smaller than 0.05) in levels of prosgesterone occurred between day 28 of pregnancy and one day prior to shelping (3.3 plus or minus 1.2 ng/ml, with a further decrease on the day of whelping (1.1 plus or minus 0.2 ng/ml). Levels of estradiol-17beta and LH did not change significantly (p smaller than 0.0k) during diestrus or pregnancy.     

Reinitiation of ovulatory cycles in incubating female turkeys by an inhibitor of serotonin synthesis, P-chlorophenylalanine

Nest deprivation of incubating turkeys caused a decrease in serum prolactin (Prl) levels from 1184.5 +/- 116.4 ng/ml to 896.8 +/- 83.0 ng/ml 1 day after initiation of deprivation, with a further decline to 156.5 +/- 111.7 ng/ml at the end of the 22-day experimental period. Serum luteinizing hormone (LH), progesterone and estradiol levels following nest deprivation were similar to those in birds allowed to incubate (controls). Oral administration of p-chlorophenylalanine (PCPA, 50 mg/kg) to incubating turkeys for 3 consecutive days reduced nesting frequency (P less than 0.05) on the 4th day after initiation of treatment and the nesting virtually ceased by the 9th day. Pretreatment Prl was 1655 +/- 210 ng/ml and declined (P less than 0.05) after PCPA administration to a low of 28.6 +/- 2.8 ng/ml. In addition, PCPA caused a sustained rise in serum LH peaking (5.59 +/- 1.09 ng/ml) 3 days after treatment initiation. Contrary to nest deprivation, serum levels of progesterone and estradiol increased (P less than 0.05) as a consequence of PCPA treatment. Seven of 8 PCPA-treated birds later came into lay when their Prl levels and nesting frequency increased again. The results suggest a role for serotonin (5-HT) in incubation behavior, and Prl and LH secretion in turkeys.     

Periovulatory changes in serum concentration and ovarian content of 5 alpha-androstane-3 alpha, 17 beta-diol in the adult rat

The high amounts of 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) present in immature female rats decline towards first ovulation, but on the day of first proestrus a peak is seen. This raises the possibility that during adulthood similar proestrous peaks may occur. Therefore, serum concentrations and ovarian content of 3 alpha-diol were estimated every two hours between 0900 and 2100 h in adult cyclic rats on the day of proestrus. In the same rats, serum concentrations of estradiol (E2), progesterone (P) and luteinizing hormone (LH) were measured, as were ovarian contents of E2 and P. A significant elevation in ovarian 3 alpha-diol was found between 0900 and 1700 h proestrus, whereas serum concentrations of 3 alpha-diol were elevated from 1300 to 2100 h. The high morning values of ovarian 3 alpha-diol correlated with those for ovarian E2 (p less than 0.005); the elevated serum concentrations of 3 alpha-diol during the afternoon correlated with serum P (p less than 0.005) and with serum LH concentrations (p less than 0.005). Serum and ovarian values were positively correlated for P and E2, but not for 3 alpha-diol. The rise in serum 3 alpha-diol could be prevented by blocking the LH surge with sodium pentobarbitone (Nembutal; 35 mg/kg b.w.) administered at 1300 h. In Nembutal-treated rats, the concentration of 3 alpha-diol at 1700 h (886 pg/ml) was significantly lower than in saline-treated control rats (1135 pg/ml; p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Continuous subcutaneous infusion of human menopausal gonadotropin in anovulatory women with decreased FSH/LH ratio and androgen excess

Ten women of polycystic ovarian-type (PCO-type) anovulation, having a decreased ratio of FSH to LH and androgen excess, resistant to the previous clomiphene, bromocriptine and/or daily im injections of human menopausal gonadotropine (hMG), were treated with continuous sc infusion of 150 IU/day hMG. The treatment was initiated on cycle day 2-5 and continued until the dominant follicle reached 20 mm or more in diameter, when an im bolus of 10,000 IU human chorionic gonadotropin was given. The treatment elevated the geometric mean of pretreatment serum FSH (8.6 mIU/ml) to 15.9 mIU/ml (p less than 0.001), while serum LH decreased from 29.4 mIU/ml to 20.7 mIU/ml (p less than 0.01). This resulted in a highly significant increase in the FSH/LH ratio from 0.29 to 0.77 (p less than 0.0001). Follicle enlargement was demonstrated in 13 of the 14 treatment cycles, 12 of which were ovulatory. Pregnancy ensued in 4 cases, 1 of which was a quadruplet pregnancy. Continuous infusion of hMG was indicated as an effective way of inducing ovulation in PCO-type anovulation resistant to conventional methods of ovulation induction.     

Secretory dynamics of bioactive and immunoactive LH during the oestrous cycle of the sheep

Blood samples were collected every 15 min for 6 h during the follicular (1 day before oestrus), and early (Days +1 to +3), mid- (Days +4 to +8), and full (Days +9 to +14) luteal phases of the oestrous cycle. Serum concentrations of immunoactive LH were measured by radioimmunoassay. The biological activity of serum LH was determined by an in-vitro bioassay that uses LH-induced testosterone production from mouse interstitial cells as an endpoint. Only ovine and bovine LH and hCG had appreciable activity in this bioassay. The temporal pattern of secretion of bioactive LH paralleled the secretory pattern of immunoactive LH at all stages of the ovine oestrous cycle. However, the secretory pattern itself varied regularly through the oestrous cycle. The frequency of secretory excursions of LH was highest during the follicular phase (6.2 +/- 0.9 pulses/6 h) and was progressively reduced through the luteal phase (1.1 +/- 0.1 pulses/6 h during full luteal phase). Conversely, amplitude of secretory excursions of immunoactive LH was low during the follicular phase (0.79 +/- 0.08 ng/ml) and significantly (P less than 0.05) increased during the mid- and full luteal phases (1.49 +/- 0.10 and 2.37 +/- 0.20 ng/ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of GnRH infusion on endocrine parameters and duration of postpartum anestrus in beef cows

The effect of an intravenous infusion of gonadotrophin releasing hormone (GnRH) on the duration of postpartum anestrus in suckled beef cows was studied. Twenty-eight, mature, suckled beef cows were assigned in equal numbers to one of four treatment groups which were based on infusion with saline or GnRH (15ug/hour for 12 hours) and stage postpartum (pp) (20 or 35 days). Serum LH and progesterone were determined by radioimmunoassay for the period which began 5 days pre-infusion and ended at 55 days postpartum (ie: 35 or 20 days post-infusion). Serum LH remained below 5ng/ml during infusion in all control cows. Peak serum LH values, times of LH peaks, and duration of LH responses (means +/- SE) during infusion were 49 +/- 12 ng/ml, 162 +/- 42 minutes and 7.8 +/- 1.3 hours for the 20 day group and 44 +/- ng/ml, 144 +/- 6 minutes, and 8.2 +/- 1.1 hours for the 35 day group respectively. Serum progesterone levels indicated that the proportion of cows showing the onset of estrous cycles within 10 days of infusion was greater in the 20 day pp GnRH group (4/7) than the 20 day pp saline group (0/7) (p < .05) but was not significantly different between the 35 day pp GnRH (4/7) and 35 day pp saline (2/6) groups. The incidence of estrus was not affected by GnRH treatment and was 37% in all cows prior to 55 days pp. It was concluded that infusions of GnRH for 12 hours at a rate of 15 ug/hour could induce estrous cycles in suckled beef cows treated at 20 days postpartum.     

Acute stimulatory effects of prostaglandin F2 alpha on serum progesterone concentrations in pregnant and pseudopregnant pigs.

The objective of this study was to investigate whether PGF2 alpha, administered to pregnant and pseudopregnant gilts in vivo, would cause an acute increase in serum progesterone concentrations prior to luteolysis. Pregnant (n = 9) and pseudopregnant (n = 4) gilts were fitted with a jugular vein cannula on day 40, were treated with 3 ml vehicle (control) i.m. on day 42 and with 15 mg PGF2 alpha on day 45. Blood samples were collected at frequent (5 and 15 min) intervals from 1 h before until 1 h after control and PGF2 alpha injections, at 15 min intervals for 4 h, and then at 5, 6, 9, 21, 33, 45 and 57 h post injection. Progesterone was measured by radioimmunoassay (RIA) in all samples. Porcine LH was measured by RIA in samples collected frequently in the 1 h pre- and 1 h post-injection periods. Serum progesterone concentrations were unchanged in both pregnant and pseudopregnant animals in response to control injection on day 42. However, in both pregnant and pseudopregnant gilts, PGF2 alpha injection on day 45 resulted in an acute increase (approximately 75-80% above pre-treatment levels; p less than 0.05) in serum progesterone lasting approximately 1 h, followed by a return to pre-treatment levels by 2 h, and then a decline to 1 ng/ml or less by 45-57 h (pregnant) or 21-57 h (pseudopregnant), associated with luteolysis. Serum LH concentrations were unchanged between 1 h pre- and post-treatment periods in response to either control or PGF2 alpha-treatment, in both pregnant and pseuodpregnant gilts. These results indicate that PGF2 alpha-injection produces a rapid and transient increase in serum progesterone concentrations which may result from a rapid and direct stimulatory action of PGF2 alpha on porcine luteal cell progesterone synthesis/secretion in vivo.     

Conditions and limits of serum LH radioimmunoassay in normal, hypophysectomized or castred rats]

Serum LH was measured by radioimmunoassay (NIAMD Kits) free and linked hormones were separated by double antibodies method. Influence of concentration on antibody-hormone complex is studied. Hypophysectomised rats serum does not modify results. The standard (rat LH-RP1) has the same action as serum LH. Rat serum LH contents are measured in normal or castred rats.