Differential regulation of the secretion of luteinizing hormone and follicle-stimulating hormone around the time of ovulation in the bitch

Plasma concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were determined 3-6 times daily in six Beagle bitches from the start of the follicular phase until 5 d after the estimated day of ovulation. The aim of the study was to gain more detailed information regarding the changes in and the temporal relation between these hormones around the time of ovulation. In all bitches, the pre-ovulatory LH surge was accompanied by a pre-ovulatory FSH surge. The mean duration of the pre-ovulatory FSH surge (110 +/- 8 h) was significantly longer than that of the pre-ovulatory LH surge (36 +/- 5 h). The FSH surge started concomitantly with the pre-ovulatory LH surge in four bitches, and 12 h before the start of the LH surge in the other two bitches. The pre-ovulatory LH surge had a bifurcated pattern in four bitches. The mean plasma LH concentration before (1.9 +/- 0.4 microg/L) and after (1.9 +/- 0.3 microg/L) the pre-ovulatory LH surge were similar. The mean plasma FSH concentration during the period 72-28 h before the pre-ovulatory LH surge (1.6 +/- 0.3 U/L) was lower (P < 0.001) than that during the period 100-144 h after the pre-ovulatory LH surge (3.1 +/- 0.2U/L). In conclusion, this study demonstrated concurrent pre-ovulatory surges of FSH and LH and provided more evidence for differential regulation of the secretion of FSH and LH.     

The influence of estradiol-17beta and progesterone on peripheral serum concentrations of luteinizing hormone and follicle stimulating hormone in the ovariectomized ewe

Serum gonadotropin concentrations were high and variable and fluctuated episodically in short and long term ovariectomized ewes. Treatment with solid silastic implants releasing progesterone (serum levels 1.81 +/- 0.16 ng/ml) had no consistent effect. Treatment with implants releasing estradiol-17beta significantly depressed mean serum gonadotropin concentrations and peak height to values usually seen in intact ewes. This occurred regardless of implant size and serum estradiol-17beta concentrations (range 11 +/- 0.3 pg/ml to 98 +/- 12.8 pg/ml). Progesterone and estradiol-17beta together significantly depressed the frequency of peaks in LH concentration. Following progesterone removal, 95% of the ewes treated with progesterone and estradiol-17beta implants experienced a transient increase in serum LH concentrations similar to the preovulatory surge in intact ewes. Eighty-four percent of the LH surges were accompanied by a surge in serum FSH concentrations. However, following progesterone removal, 5.1 +/- 2.1 FSH surges were observed over six days. Gonadotropin surges occurred regardless of estradiol-17beta implant size and with or without the influence of supplemental estradiol-17beta.     

Bromocriptine-induced premature oestrus is associated with changes in the pulsatile secretion pattern of follicle-stimulating hormone in beagle bitches

The secretory profiles of LH and FSH were investigated before and during the administration of bromocriptine in six beagle bitches. Plasma samples were obtained via jugular venepuncture at 10 min intervals for 6 h every 2 weeks until the next ovulation. Bromocriptine treatment was started 100 days after ovulation. Both before and after bromocriptine treatment, LH and FSH pulses occurred together. The mean duration of the FSH pulse (120 min) was significantly longer than that of the LH pulse (80 min). The interoestrous interval in the bitches treated with bromocriptine was significantly shorter than that of the preceding cycle (160 +/- 3 versus 206 +/- 24 days). The mean basal plasma FSH concentration (7.4 +/- 0.6 versus 6.1 +/- 0.7 iu l-1) and the mean area under the curve for FSH (46.6 +/- 4.7 versus 40.4 +/- 4.4 iu l-1 in 6 h) increased significantly after the start of the bromocriptine treatment. In contrast, the differences in mean basal plasma LH concentration (2.1 +/- 0.2 versus 2.0 +/- 0.2 micrograms l-1) and the mean area under the curve for LH (19.0 +/- 3.1 versus 19.5 +/- 2.5 micrograms l-1 in 6 h) between the day before and 14 days after the start of the bromocriptine treatment were not significant. Bromocriptine administration also lowered the mean amplitude of the FSH pulse and shortened the mean duration of the FSH pulse, without influencing the LH pulse. In addition to demonstrating the concurrent pulsatile secretion of LH and FSH, the results of the present study demonstrate that the bromocriptine-induced shortening of the interoestrous interval in the bitch is associated with an increase in plasma FSH concentration without a concomitant increase in plasma LH concentration. This finding indicates that treatment with the dopamine agonist bromocriptine increase plasma FSH to a concentration that results in the enhancement of follicle development.     

Reproductive hormone concentrations during estrus,pregnancy, and pseudopregnancy in the Labrador bitch

Serum luteinizing hormone (LH), estrone, estradiol-17β, and progesterone were measured during the estrous cycle, pregnancy and parturition in seven adult pregnant Labrador bitches and during the estrous cycle and one gestation length equivalent in six adult pseudopregnant bitches. Although the duration of proestrus was similar in both groups, the duration of estrus was longer in the bitches that subsequently became pregnant. Mean serum LH concentrations were similar in both groups during most of the study. However, during Weeks 6 to 9 after the preovulatory LH peak, serum LH concentration was higher in both pseudopregnant and pregnant groups of animals and declined to basal levels thereafter. Mean serum estrone concentrations in the pregnant animals were higher than those of pseudopregnant animals and remained elevated throughout gestation, followed by a decline at whelping. Serum estradiol-17β levels were higher during the 4 wkimmediately following ovulation in the pseudopregnant group compared with those observed in pregnant animals. Serum progesterone concentrations generally remained higher during pseudopregnancy compared with those of the pregnant animals during gestation.In conclusion, a major difference between pregnant and pseudopregnant bitches is a pregnancy-specific elevation in estrone levels. The placenta may be a likely source of estrone during pregnancy.     

Pulsatile plasma profiles of FSH and LH before and during medroxyprogesterone acetate treatment in the bitch

The aim of this study was to investigate the effect of medroxyprogesterone acetate (MPA) on pulsatile secretion of gonadotropins in the bitch. Five intact Beagle bitches were treated with MPA in a dose of 10mg/kg body weight subcutaneously at intervals of 4 weeks for a total of 13 injections, starting during anestrus. The 6-h plasma profiles of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were determined before, and 3, 6, 9, and 12 months after the start of MPA treatment. After 6 months of MPA treatment basal plasma LH concentration was transiently increased significantly. Basal plasma FSH concentration and the area under the curve above the zero level (AUC0) for FSH were significantly higher after 3 months of MPA treatment than before or after 9 and 12 months of treatment. MPA treatment did not significantly affect pulse frequency, pulse amplitude, or AUC above the baseline for either LH or FSH. During treatment 58 significant LH pulses were identified, and although each LH pulse coincided with an increase in plasma FSH concentration, in 17 cases the amplitude of the increase was too small to be recognized as a significant FSH pulse. In conclusion, MPA treatment did not suppress basal plasma gonadotropin levels in the bitches. On the contrary, it caused a temporary rise in the basal concentration of both FSH and LH, which may have been due to a direct effect of MPA on the ovary. In addition, several LH pulses were not accompanied by a significant FSH pulse, suggesting that MPA treatment attenuated the pulsatile pituitary release of FSH.     

Endocrine, luteal and follicular responses after the use of the short-term protocol to synchronize ovulation in goats

The effect of the so-called Short-Term Protocol (5-day progesterone treatment+PGF(2)alpha) on ovarian activity and LH surge was studied in goats. The goats received 250IU eCG at the time of device withdrawal (eCG group; n=7), or 200microg of EB (estradiol benzoate) 24h after device withdrawal (EB group; n=8), or received neither eCG nor EB (control group; n=8). The Short-Term Protocol induced greater (4.1+/-1.1ng/ml) progesterone serum concentrations at 24h after start of the treatment, that declined to 0.2+/-0.1ng/ml at 12h after device withdrawal. In all of the groups, the maximum concentration of estradiol-17beta was reached at about 36h after device withdrawal. Maximum concentration was greater in the EB group (76.9+/-24.6pmol/l) than in the control group (41.8+/-9.0pmol/l; P<0.01), with the eCG group showing intermediate concentration (70.3+/-32.5pmol/l; P=NS). The LH peak occurred earlier in the eCG group (38.4+/-2.0h after device withdrawal) and in the EB group (41.0+/-4.1h), than in the control group (46.3+/-5.1h; P<0.05). Ovulation occurred earlier in the eCG group (5/7) and in the EB group (8/8) (58.8+/-2.7h and 63.0+/-5.6h, respectively), than in the control group (7/8) (70.2+/-8.3h; P<0.05). In summary, the Short-Term Protocol induced similar concentrations of progesterone among treated goats. In addition, eCG or EB resulted in a similar increase in estradiol-17beta and a similar LH surge, which induced ovulation in most females (86.7%) in a consistent interval (about 60h) after the end of progesterone exposure.     

Induced ovulation and changes in pituitary responsiveness to continuous infusion of gonadotropin-releasing hormone during the ovarian cycle in the bullfrog, Rana catesbeiana

Chronic (2-4 days) constant-rate infusions of mammalian gonadotropin releasing hormone (GnRH) were performed in female bullfrogs, Rana catesbeiana. The magnitude and temporal relationship of profiles of plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH) and sex steroids [testosterone (T), estradiol-17 beta (E2) and progesterone (P)] during GnRH infusion were dependent on ovarian stage. However, in all females, the same biphasic increase in plasma gonadotropins was apparent and initial elevations in gonadotropins were accompanied by correlated increments in plasma T and E2. Complete pituitary "desensitization" to chronic GnRH infusion was not observed. Females in early follicular stages were relatively unresponsive to infusions of 1.0-10.0 micrograms/h GnRH; elevations in plasma LH were marginal and FSH was unchanged. Females with fully developed (preovulatory) ovaries were more responsive: infusion of 1.0 micrograms/h GnRH produced significant elevations in plasma LH by 2 h followed by even larger increases ("surges") after 12 h. This LH "surge" was preceded by a decline in plasma T and E2 and was accompanied by abrupt elevations in plasma P and by ovulation. Postovulatory females showed a more gradual and smaller increase in plasma LH. Infusion of GnRH in the female bullfrog establishes a clear relationship between pituitary responsiveness and the ovarian cycle not evident from acute GnRH injection; GnRH was most effective immediately before ovulation. These data are also the first to detail periovulatory changes in plasma gonadotropins and ovarian steroids in an amphibian.     

Effect of induced suprabasal progesterone levels around estrus on plasma concentrations of progesterone, estradiol-17beta and LH in heifers

A controlled study was carried out to investigate the effects of suprabasal plasma progesterone concentrations on blood plasma patterns of progesterone, LH and estradiol-17beta around estrus. Heifers were assigned to receive subcutaneous silicone implants containing 2.5 g (n=4), 5 g (n=4), 6 g (n=3), 7.5 g (n=3) or 10 g (n=4) of progesterone, or implants without hormone (controls, n=5). The implants were inserted on Day 8 of the cycle (Day 0=ovulation) and left in place for 17 d. The time of ovulation was determined by ultrasound scanning. Blood was collected daily from Days 0 to 14 and at 2 to 4-h intervals from Days 15 to 27. Control heifers had the lowest progesterone concentrations on Days 20.5 to 21 (0.5 +/- 0.1 nmol L(-1)); a similar pattern was observed in heifers treated with 2.5 and 5 g of progesterone. In the same period, mean progesterone concentrations in the heifers treated with 6, 7.5 and 10 g were larger (P < 0.05) than in the controls, remaining between 1 and 2.4 nmol L(-1) until implant removal. A preovulatory estradiol increase started on Days 16.4 to 18.4 in all the animals. In the controls and in heifers treated with 2.5 and 5 g of progesterone, estradiol peaked and was followed by the onset of an LH surge. In the remaining treatments, estradiol release was prolonged and increased (P < 0.05), while the LH peak was delayed (P < 0.05) until the end of the increase in estradiol concentration. The estrous cycle was consequently extended (P < 0.05). In all heifers, onset of the LH surge occurred when progesterone reached 0.4 to 1.2 nmol L(-1). The induction of suprabasal levels of progesterone after spontaneous luteolysis caused endocrine asynchronies similar to those observed in cases of repeat breeding. It is suggested that suprabasal concentrations of progesterone around estrus may be a cause of disturbances oestrus/ovulation.     

Hormonal changes in spontaneous and aglépristone-induced parturition in dogs

To increase our understanding of the endocrine changes associated with parturition in dogs, plasma concentrations of progesterone (P4), 15-ketodihydroprostaglandin F(2alpha) (PGFM), estradiol-17-beta (E2beta), cortisol, ACTH, prolactin (PRL), LH, and FSH were measured in six spontaneously whelping bitches and in six bitches in which parturition was induced with the progesterone-receptor blocker aglépristone on day 58 of pregnancy. Expulsion of pups in the induced group took place in the presence of P4 concentrations that were still elevated. PGFM concentrations increased before parturition in both groups, but levels were lower in the induced bitches. PGFM levels reached a maximum in both groups during parturition and quickly decreased in the spontaneously whelping group after parturition, but remained elevated in the induced group. In both groups, cortisol concentrations reached similar maximum levels during the last 30 h before the onset of expulsion. During the 3 days postpartum, cortisol concentrations were higher in the induced group. The highly variable ACTH concentrations did not differ significantly throughout the study within or between groups. In both groups, E2beta concentrations decreased and PRL concentrations increased between the late gestational period and the 30-h period before parturition. Concentrations of both LH (spontaneously whelping group) and FSH (both groups) decreased between late gestation and the postpartum period. The results of this study illustrate the hormonal changes around parturition in the bitch, and reveal that aglépristone-induced parturition is associated with still incomplete luteolysis, an altered PGFM profile, and elevated postpartum cortisol concentrations as compared with spontaneously whelping dogs.     

Effect of variable suckling intensity and estrogen administration upon serum luteinizing hormone in Brahman cows

Ten mature Brahman cows were randomly allotted within calving intervals to either a suckled (S) or nonsuckled (NS) treatment group. All cows received a 20 mg intramuscular injection of estradiol-17beta (E2), suspended in 2 ml of corn oil, to determine the effect of suckling on the estrogen induced LH surge. Starting on day 21 postpartum the S cows were suckled at six hour intervals for 24 hours, at which time they were challenged with a 20 mg E2 injection. The suckling regimen was continued for 48 hours postinjection. The NS cows were separated from their calves on day 21 postpartum and received no suckling stimulus for 72 hours. At 24 hours after calf separation, the NS cows were challenged with a 20 mg E2 injection. Blood samples were removed at two hour intervals beginning 10 hours post E2 injection until 36 hours postinjection, at which time blood samples were removed at four hour intervals until 48 hours postinjection. Blood samples were processed to yield serum and assayed for luteinizing hormone (LH) via radioimmunoassay. The injection of a 20 mg dose of E2 induced an LH surge in all cows. The NS cows were found to exhibit a longer (P<.05) duration of the estrogen induced LH surge than the S cows, 15.6 +/- .98 and 12.4 +/- .75 hours, respectively. The timing parameters (time to start of LH surge, time to peak LH value and time to end of surge) and LH concentration parameters (LH concentration at start of LH surge, peak value of LH surge and LH concentration at end of LH surge) were not different between suckling regimens. No blockage of the LH response to estrogen challenge was found on day 22 postpartum. Suckling did depress the duration of the LH surge indicating some blockage due to suckling stimuli.     

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.     

Sex hormones correlated with sex skin swelling and rectal temperature during the menstrual cycle of the pigtail macaque (Macaca nemestrina).

Daily measurement of serum luteinizing hormone, estradiol-17beta, and progesterone were made during the menstrual cycle in nine pigtail macaques (Macaca nemestrina). All data were normalized to the day of the luteinizing hormone peak. Serum estradiol-17beta increased from approximately 100 pg/ml during the early follicular phase to 442 +/- 156 pg/ml during the maximum midcycle concomitant with the luteinizing hormone peak, and a small increase in serum estradiol-17beta was observed during the luteal phase coincident with the progesterone peak. Serum progesterone values increased slightly at the time of the luteinizing hormone peak and increased from 0.2-0.3 ng/ml during the midfollicular phase to peak levels of 8.3 +/- 1.75 ng/ml 9 days after the luteinizing hormone surge. Serum luteinizing hormone remained low and relatively constant throughout the early and midcycle, then sharply increased approximately four-fold to peak values of 6.25 +/- 0.9 ng/ml. Sex skin swelling increased slowly during the follicular phase and declined slowly throughout the early luteal phase. Rectal temperature did not change significantly throughout the menstrual cycle. The similarity of plasma sex hormone changes during the menstrual cycle between women and the pigtail macaque suggested that this nonhuman primate should be a useful animal model for studying human reproduction.     

Effect of exogenous FSH on estrus, ovulation and endogenous hormone release in dairy cows

Fifteen lactating Holstein cows were randomly allotted to receive either 0 mg (group 0), 32 mg (group 1) or 50 mg (group 2) porcine follicle stimulating hormone (FSH-P) injected in 10 fractions at 12 hr intervals beginning on day 9 of the estrous cycle. All cows received 25 mg prostaglandin (PG) on day 11. Jugular blood samples were collected from cows in all groups at 6 hr intervals beginning on day 7 and continuing through expression of estrus. Mean duration to occurrence of estrus and preovulatory LH surge after PG injection was reduced (P<.05) by injection of FSH-P. Mean number of ovulations increased (P<.05) progressively with increased dose of FSH-P. Mean peripheral progesterone declined more uniformly in FSH-P treated cows after PG and increased earlier (P<.05) after estrus in group 2 cows compared to group 0 and 1 cows. Mean plasma estradiol-17beta elevated (P<.05) after PG injection in both FSH-P-treated groups compared to group 0 cows. Both LH and FSH increased (P<.05) for 36 hr after initiation of FSH-P injection in groups 1 and 2, then declined until after PG injection. Peak LH and FSH occurred more uniformly following PG in treated cows. Results indicate that FSH-P increased endogenous gonadotropin release, estradiol-17beta, ovulation rate and reduced duration to estrus and preovulatory gonadotropin release after PG. Injection of 50 mg FSH-P increased plasma estradiol-17beta and ovulation rate compared to injection of 32 mg FSH-P.     

Basal and GnRH-induced secretion of FSH and LH in anestrous versus ovariectomized bitches

The basal and gonadotropin releasing hormone (GnRH)-induced plasma concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were studied in four anestrous and four ovariectomized (OVX) bitches. Blood samples were obtained via jugular venipuncture 40min before and 0, 10, 20, 30, 60, 90, and 120min after the i.v. administration of synthetic GnRH in a dose of 10microg/kg body weight. The basal plasma FSH and LH concentrations were significantly higher in the OVX bitches than in the anestrous bitches. In the anestrous bitches, the plasma FSH concentration was significantly higher than the pretreatment level at 10, 20, and 30min, whereas the plasma LH concentration was significantly elevated at 10 and 20min. The maximal GnRH-induced plasma FSH concentration in the anestrous bitches did not surpass the lowest plasma FSH concentration in the OVX bitches, whereas the GnRH-induced plasma LH concentrations in the anestrous bitches overlapped with the basal plasma LH concentrations in the OVX bitches. In the OVX bitches, GnRH administration did not induce a significant change in the plasma FSH concentration, whereas the plasma LH concentration increased significantly at 10 and 20min. In conclusion, the results of the present study indicate that in anestrous bitches GnRH challenge results in increased plasma levels of both FSH and LH, whereas in the OVX bitches, in which the basal plasma FSH and LH concentrations are higher, only a rise in the plasma LH concentration is present after GnRH stimulation. The results also suggest that a test to measure plasma concentration of FSH in single samples appears to have potential in verification of neuter status in bitches.     

In vitro steroidogenesis by primary to antral follicles in the hamster during the periovulatory period: effects of follicle-stimulating hormone, luteinizing hormone, and prolactin

Hamster ovarian follicles at Stages 1 to 10 (Stages 1-4: follicles with 1-4 layers of granulosa cells (GC); Stages 5-7: 5-10 layers GC plus theca; Stages 8-10: antral follicles) were isolated on the morning of proestrus or estrus and incubated for 2 h in the absence or presence of follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (Prl), progesterone (P4), 17 alpha-hydroxyprogesterone (17OHP), or androstenedione (A). Steroid accumulations in the media were measured by radioimmunoassay (RIA). On proestrus, without any hormonal stimulus, consistent accumulation of P4 through estradiol-17 beta (E2) occurred in low amounts only from Stage 6 and on; both FSH (5-25 ng) and LH (1-25 ng) significantly stimulated steroidogenesis by Stage 6-10 follicles, and the effects of FSH, except for Stage 10, were largely attributable to LH contamination. However, 25 ng FSH significantly stimulated A production by Stages 1-4, whereas 1-25 ng LH was ineffective. On estrus, follicles at all stages, especially 1-6, showed significant and dose-dependent increases in P4 production in response to FSH; both FSH and LH significantly stimulated P4 and 17OHP accumulation from Stage 5 onwards; however, there was no increase in A and E2 compared to controls. Even the smallest estrous follicles showed a shift to predominance of P4 accumulation. On proestrus, Prl had a negative influence on LH-induced accumulation of P4 and 17OHP by Stages 7-9 and 6-8, respectively, without affecting A or E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of luteinizing hormone and follicle-stimulating hormone and insulin-like growth factor-I on aromatase activity and P450 aromatase gene expression in the ovarian follicles of red seabream,Pagrus major

To clarify the mechanism of estradiol-17beta production in the ovarian follicle of red seabream, in vitro effects of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and insulin-like growth factor (IGF-I) on aromatase activity (conversion of testosterone to estradiol-17beta) and cytochrome P450 aromatase (P450arom) mRNA expression in ovarian fragments of red seabream were investigated. Of the growth factors used in the present study, only IGF-I stimulated both aromatase activity and P450arom gene expression in the ovarian fragments of red seabream. LH from red seabream pituitary, but not FSH, stimulated both aromatase activity and P450arom gene expression. IGF-I slightly enhanced the LH-induced aromatase activity and P450arom gene expression. These data and our previous results indicate that LH, but not FSH, stimulates estradiol-17beta production in the ovarian follicle of red seabream through stimulation of aromatase activity and P450arom gene expression and IGF-I enhances the LH-stimulated P450arom gene expression.     

Effect of estrogen administration on endogenous and luteinizing hormone-releasing-hormone-induced luteinizing hormone secretion and follicular development in the lactating sow

The objectives of this study were to investigate whether estradiol treatment during lactation modifies 1) the patterns of endogenous LH, FSH, and prolactin (PRL) release; 2) the sensitivity of the pituitary to exogenous injections of LHRH; and 3) the responsiveness of the ovarian follicles to gonadotropin. Plasma LH, FSH, and PRL were determined in samples taken repeatedly from 18 sows on Days 24-27 of lactation. Ovaries were then recovered, and follicular development was assessed by measuring the follicular diameter (FFD) and follicular fluid estradiol-17 beta concentration (FFE) of the ten largest follicles dissected from each ovary. Sows were randomly allocated to one of four treatments: 1) Group C (4 sows) received no treatment; 2) Group LHRH (5 sows) received 800 ng of LHRH every 2 h throughout the sampling period; 3) Group E2 (4 sows) received subcutaneous implants containing estradiol-17 beta 24 h after start of sampling; 4) Group LHRH + E2 (5 sows) were administered a combination of LHRH and estradiol-17 beta implants. Between-animal variability for plasma LH, FSH, and PRL was considerable. LH concentration and LH pulse frequency increased (p less than 0.05) after LHRH treatment in the LHRH and LHRH + E2 groups; however, an acute inhibition of LH secretion was observed in the latter group immediately after estradiol implant application. In the absence of LHRH treatment, estradiol caused chronic inhibition of LH secretion. Follicular development was greater in the LHRH and LHRH + E2 groups compared to the C and E2 groups (p less than 0.05 for both FFD and FFE).(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteinizing hormone concentrations in anestrous ewes administered various estrogens

Twenty four anestrous ewes were evenly assigned to one of six groups and administered either sesame oil, estradiol-17β, estradiol-17α, estrone, estradiol benzoate or estradiol valerate. All estrogen treated ewes received 50 μg of the respective estrogen. Blood plasma was collected for 28 hours post-treatment and quantified for luteinizing hormone (LH) by radioimmunoassay. An estrogen induced LH surge was detected in at least three of the four ewes administered either estradiol-17β, estrone, estradiol benzoate or estradiol valerate whereas only one of the four estradiol-17α treated ewes and none of the ewes administered sesame oil had an LH surge. The interval from treatment to peak LH was similar for estradiol-17β (17.3±2.7 hours), estrone (18.5±1.0 hours) and estradiol benzoate (19.0±0.6 hours) treated ewes but delayed 7 to 9 hours for ewes administered estradiol valerate (26.0±1.2 hours).     

Comparable testosterone responses are produced by constant infusion of LH or GnRH in normal men

Luteinizing hormone (LH) was infused continuously at a rate of 1.3 IU/min to 4 normal adult men. A 4 to 5-fold increase in serum LH was noted by 8 hours. Serum FSH declined steadily throughout the infusion period in the face of rising concentrations of gonadal steroids. Basal plasma testosterone of 4.7 +/- 0.4 ng/ml rose progressively to a peak of 11.1 +/- 0.9 ng/ml at hour 56 (p less than 0.005). A similar pattern was demonstrated by plasma androstenedione. Plasma 17 alpha-hydroxyprogesterone rose from a basal concentration of 0.81 +/- 0.14 ng/ml to a peak concentration of 2.6 +/- 0.3 ng/ml at hour 36 of the infusion and subsequently declined. A similar course was followed by serum estradiol-17 beta, which achieved a maximal concentration of 70.0 +/- 10.4 pg/ml at hour 36. Results are compared to those obtained with continuous infusion of GnRH in normal adult men. Testosterone responses were similar, whereas elevations in 17 alpha-hydroxyprogesterone and estradiol were higher following GnRH infusion. This difference may be consequent upon a direct gonadal effect of GnRH, or may be secondary to local regulation of testicular steroidogenesis by estradiol-17 beta.     

The effect of photoperiod on serum concentrations of luteinizing and follicle stimulating hormones in prepubertal heifers following ovariectomy and estradiol injection

Eleven heifers, between 63 and 197 days of age, were exposed to 18 hr light/day (L) or natural photoperiods (N), beginning October 19, 1979. They were ovariectomized 8 weeks later. LH concentrations after ovariectomy were not affected by photoperiod, but the rate of increase of FSH after ovariectomy was greater (P<0.10) for group L than for group N. Three weeks after ovariectomy, heiters were injected, IV, with 0.1 mug/kg estradiol-17beta. LH concentrations initially decreased after injection. This was followed by a series of pulses larger than those prior to injection. FSH concentrations declined after injection and remained low throughout the sampling period. The net response of LH concentrations to estradiol (mean post-injection concentration minus mean pre-injection concentration) was greater (P=0.05) for group L (4.7 +/- 0.49 ng/ml) than for group N (2.9 +/- 0.37 ng/ml). Photoperiod did not affect the net response of FSH concentrations to estradiol. We concluded that exposing prepubertal heifers to 18 hr light/day during the winter resulted in a greater rate of increase of FSH after ovariectomy and greater estrogen-induced LH release. Because the response of LH to estradiol-17beta differed from the response of FSH, these hormones may be regulated differently.