The GnRH precursor is present in the anterior pituitary gland and an important increase of its content precedes serum LH surge induced by estradiol-17 beta in female primates

Estradiol-17 beta (E2 17 beta) is well known to evoke a preovulatory-like LH surge in ovariectomized monkeys even in the absence of the integrity of the hypothalamo-pituitary connections. LH release from the anterior pituitary (AP) is reliant on stimulation by hypothalamic GnRH which is derived from proteolytic cleavage of a precursor (designated Pro-GnRH-GAP) which also results in the production of an associated peptide (GAP). The present study examined the effects of E2 17 beta on the hypothalamic content of Pro-GnRH-GAP, GnRH and GAP while incidental observations revealed the presence of Pro-GnRH-GAP and its products in the AP. Changes in GnRH and GAP were closely related at all times after E2 17 beta treatment. However, the pattern of change in the hypothalamus and AP was inversely related. Pro-GnRH-GAP levels remained unchanged in the hypothalamus whereas in the AP the peptide increased markedly (48 hrs. post E2 17 beta) prior to the LH surge and declined to low levels (72 hrs. post E2 17 beta) at the time of the LH surge. The increase in Pro-GnRH-GAP in the AP that precedes the rise in GnRH and accompanying LH surge by 24 hrs. strongly indicates that AP GnRH is more important than hypothalamic GnRH for the mediation of the E2 17 beta-induced LH surge in female primate.     

Pituitary response to repeated copulation and/or gonadotropin-releasing hormone administration in llamas and alpacas.

The response of the pituitary gland and ovary to repeated copulatory periods and/or gonadotropin-releasing hormone (GnRH, i.v. 1000 micrograms) administration was determined in llamas and alpacas. Eighty adult females (41 llamas and 39 alpacas with ovulatory follicles) were divided into three general groups for each species as follows: copulation (one or two copulations at either 6- or 24-h intervals) GnRH treatment (one or two treatments at either 6- or 24-h intervals), and combined treatment (copulation followed by GnRH treatment, or GnRH followed by copulation at either 6- or 24-h intervals). An additional control (nontreated) group was composed of 4 llamas and 4 alpacas. The first copulation or treatment with GnRH provoked LH release sufficient to cause ovulation in most of the females (alpacas, 89%; llamas, 92%); urinary pregnanediol glucuronide values, used to verify ovulation, were significantly elevated 48 h after copulation and/or GnRH treatment. A second stimulus, copulation or GnRH, provoked no LH response with concentrations similar to those in nontreated controls and in females not ovulating. Llamas and alpacas thus were refractory to a second copulatory or GnRH stimulus with regard to LH release for up to 24 h following an initial ovulatory release of LH.     

LH release in mink (Mustela vison). Pattern of the LH surge and effect of metabolic status

The mink is a seasonal breeder with induced ovulation and delayed implantation. Reproductive processes are strongly influenced by energy supply and body condition. Items for which there is paucity or complete lack of data were the main objectives of this study: the temporal relationship between copulation and the pre-ovulatory LH surge and the influence of energy supply on LH release. A total of 30 yearling female mink with a well defined metabolic status was used. Twelve females kept in the laboratory were measured in six consecutive one-week balance periods each including the measurement of heat production by means of indirect calorimetry, and 18 females were kept under conventional farm conditions. The animals were fed so as to maintain energy balance (CON), flush fed by 2 weeks food restriction followed by 2 weeks refeeding (FLUSH), or kept in a negative energy balance (NEG). Plasma concentrations of the thyroid hormones, IGF-1 and insulin were determined weekly (n = 12), or 1 week after change in energy supply to the FLUSH group (n = 18). On the day of mating, blood samples for LH and oestradiol-17beta (E2) were taken before and immediately after mating and then 4, 8, 12, 24, 30 and 48 h thereafter. Frequent blood samplings, each lasting 60 min, were taken during the LH surge from two other females surgically fitted with venous access ports. Peak concentrations of LH were recorded on the first sampling, an average 16 min after mating. The concentrations remained elevated for 12 h, but almost decreased to basal values 24 h after mating. Plasma E2 was high before mating and peak values were attained 4 h after mating after which it decreased. Energy supply had no significant influence on LH and E2, but there was a tendency for a more sluggish LH release in NEG animals. The lack of response in FLUSH animals was explained by these animals having a lower intake of metabolisable energy than CON animals, the total intake not being significantly different from the NEG group. Plasma concentrations of thyroid hormones, IGF-1 and insulin were not significantly affected by the treatment, but in FLUSH animals the values mirrored energy supply, and in the NEG group, the values tended to decrease during the course of the experiment. It was concluded that the pre-ovulatory LH surge is an immediate response to mating, and that reproductive activity in the mink is maintained over a wide range of energy supply and body condition.     

Age-related changes in the suppression of serum luteinizing hormone by estradiol-17beta in developing steers

Serum luteinizing hormone (LH) concentrations were measured at 4, 6, 8 and 10 mo of age in estradiol-17beta (E(2))-treated (n = 4) and contemporary control steers (n = 4). Serum LH was measured in samples collected at 30-min intervals starting at 0600 h for 12 h and for an additional 6 h following luteinizing hormone-releasing hormone (LHRH) injection. Estradiol-17beta suppressed mean serum LH concentrations at all ages (P<0.01), but it suppressed pulsatile release of LH only at 4 and 6 mo (P<0.01), not 8 and 10 mo of age. Luteinizing hormone release in response to LHRH, expressed as the area under the secretory curve, was larger and LH concentrations returned to pre-LHRH levels later in E(2)-treated steers (P<0.01). Peak LH concentrations after LHRH varied with age (P<0.05) but not E(2) treatment. These results suggest that E(2) suppression of LH in steers occurs at the hypothalamic level and developmental changes take place within the hypothalamicpituitary axis in absence of androgen feedback from the testis.     

Rapid recovery of estrogen-induced pituitary gonadotropin surges after luteectomy in rhesus monkeys

In the presence of a functional corpus luteum, positive estrogen feedback on the surge modes of gonadotropin secretion is blocked in rhesus monkeys. We investigated the effects of luteectomy (Lx) on the time required for recovery of pituitary responsiveness (LH/FSH surges) to positive estrogen feedback. Estradiol-17 beta-3- benzoate (EB, 50 microgram/kg sc) was given: 1) 24th prior to, 2) the day of, or 3) 24 h after luteal ablation. Daily measurements of serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17 beta (e2) and progesterone (P) were made on each monkey for 5 days. Serum P fell to undetectable levels within 24 h after Lx, whereas E2 levels in circulation peaked within 24h after injection of EB. Among early follicular phase monkeys, this EB treatment results in typical midcycle type LH/FSH surges within 48h. Lx alone was not soon followed by significant changes in pituitary gonadotropin secretion. When circulating P levels were undetectable the pituitary responded fully to EB; that is, typical midcycle type FSH/LH surges occurred. When serum P was in the midst of declining after Lx, gonadotropin surges were present, but attenuated. However, when P levels remained elevated for more than 24 h after EB injection, the surge modes of FSH/LH secretion remained fully blocked. These results demonstrate that the suppressive influence of luteal secretions (principally progesterone) on positive estrogen feedback regulation of the surge modes of pituitary gonadotropin secretion is quite transient in these primates.     

Steroid hormone feedback on LH in prepubertal Holstein heifers

A significant dose-response relationship between gonadotropin-releasing hormone (GnRH) and time to luteinizing hormone (LH) peak, peak serum LH and total serum LH was obtained in prepubertal Holstein heifers (28 weeks of age) (Experiment 1). For the second experiment, the effect of steroid feedback on the anterior pituitary was determined. A steady infusion of saline, estradiol-17 beta or progesterone was maintained for 24 h while GnRH, in various schemes, was administered 8 h after the beginning of steroid infusion. Estradiol-17 beta infusion (2.08 micrograms/h), although it did not affect peripheral concentrations of estrogen, caused an LH release 24 to 30 h later in 37.5% of the heifers. This amount of exogenous estrogen did not affect the LH response to a single GnRH (4 micrograms) challenge. When the same GnRH dosage (4 micrograms) was administered 6 times at hourly intervals, the heifers infused with estradiol had a lower response after the first 2 injections of GnRH and a greater response after the last 4 injections than heifers infused with saline. When GnRH was infused (4 micrograms/h) for 6 h, beginning 8 h after steroid infusion, estradiol infusion caused a significantly higher peak LH and total LH release than an infusion of either saline or progesterone (7.3 micrograms/h). The progesterone infusion had no effect on the GnRH-stimulated LH release. We conclude that prepubertal dairy heifers have an anterior pituitary capable of responding to the feedback effect of estrogen in a positive manner.     

Secretion of LH, FSH and oestradiol-17 beta during the follicular phase of the oestrous cycle in the ewe

Plasma concentrations of LH, FSH and oestradiol-17 beta were measured in blood samples taken at 15 min intervals for 48 h during the follicular phase of four Merino ewes. The amplitude of pulses of LH and the mean concentration of LH were higher at the beginning of the follicular phase, 36-24 h before the preovulatory surge of LH (amplitude 2.4 ng ml-1, mean concentration 3.9 ng ml-1), than at the end, 24-0 h before the preovulatory surge (amplitude 1.2 +/- 0.1 ng ml-1; mean concentration 1.4 +/- 0.1 ng ml-1). There was no change in the inter-pulse interval during this time (mean 74 +/- 5 min). Over the same period, oestradiol levels increased from 7-8 pg ml-1 to a peak of 10-15 pg ml-1. Mean FSH concentrations declined (36-24 h: 3.6 ng ml-1 vs 24-0 h: 1.8 +/- 0.3 ng ml-1) before rising at the time of the preovulatory surge of LH and again 24 h later. It was concluded that the biphasic response of LH to oestrogen that is seen in ovariectomized ewes may also operate during the follicular phase of the oestrous cycle in entire ewes.     

Effects of copulation on timing of the LH surge following synchronization of estrus in the bovine

Forty-four crossbred postpubertal bovine females were used to study how mating with a bull affected estradiol-17beta (E(2)) secretion and timing of the preovulatory LH surge. Estrous cycles were synchronized with two injections of prostaglandin-F(2alpha) (PGF(2alpha)) 11 d apart. Females were either isolated from males (NE) or exposed to epididectomized bulls (BE) after the second PGF(2alpha) injection. Females exposed to bulls were allowed to mate once and then were separated from the bull. Blood samples were collected at 2-h intervals from the second PGF(2alpha) injection until 12-h post injection to monitor progesterone (P(4)) and luteinizing hormone (LH) concentrations and at hourly intervals from 12 h to 60 h post-injection to monitor LH secretion and timing of the preovulatory LH surge. Samples were also collected at 4-h intervals until 60 h post-injection to monitor estrogen (E(2)) secretion. LH surges were detected in 16 and 14 of 22 females from the BE and NE groups, respectively, during the 60-h period after PGF(2alpha) injection Mean P(4) concentrations and time of P(4) decline to <1 ng/ml were not different between the two treatment groups (P>0.30). Mean E(2) concentration during the 60-h sampling period was different (P<0.003) between BE and NE groups, and a significant treatment effect (P<0.002) occurred 48 h, 52 h and 60 h after the second PGF(2alpha) injection. However, mean LH concentration before the LH surge, duration of the LH surge and peak LH concentration during the surge were not different between the BE and NE groups (P>0.40). Mean time for the second PGF(2alpha) injection to the beginning of the LH surge was 51.6 +/- 1.5 h (X +/- S E) for the females not exposed to bulls and 48.5 +/- 1.4 h for females exposed to bulls (P>0.14). In this study, the presence of and/or mating by a bull did not affect LH secretion or timing of the preovulatory LH surge after PGF(2alpha) administration.     

Oestradiol-17beta responsiveness, plasma LH profiles, pituitary LH and FSH concentrations in long-term ovariectomised Holstein cows at 24 h, 48 h and 21 days following treatment with an absorbable GnRH agonist implant

Non-lactating OVX Holstein cows (N = 34) were used to investigate the effect of s.c. placement of an absorbable GnRH agonist implant (Ovuplant; deslorelin 2.1mg, Peptech Animal Health, Australia) on the relationship of plasma LH, oestradiol responsiveness and pituitary LH content. On the day of implant insertion (Day 0), one group (OVU-48h; N = 5) received Ovuplant and had blood samples collected at hourly intervals to characterize the LH response, while a second group (CON-48 h; N = 5) remained untreated and acted as controls. Blood samples were collected every 10 min over 6 h from CON-48 h and OVU-48 h, at 24 h post-implant insertion. These cows were then slaughtered at 48 h post-implant insertion and their pituitaries recovered. Another group received Ovuplant (OVU-21d+E2; N = 10) or were left untreated (CON-21d+E2) and 21 days later were injected i.m. with 0.5 mg 17beta-E2. Blood samples were collected every 10 min for 4 h on the day before E2 injection to characterize LH pulse frequency and amplitude. Beginning 14 h later, blood samples were collected hourly for 12 h to characterize the expected LH surge. These cows were slaughtered and their pituitary glands recovered and assayed for LH and FSH content. Peak plasma LH concentrations (59 +/- 19 ng/ml) were measured after 30 min of Ovuplant insertion. They had returned to pre-treatment levels by 7 h. By 24 h post-implant insertion, OVU-48 h plasma LH profiles were characterized by reduced LH pulse frequency (0.23 +/- 0.09 pulses/h versus 0.75 +/- 0.26 pulses/h; OVU-48 h versus CON-48 h; P < 0.05). The cows that received Ovuplant had lower LH pulse amplitude, LH pulse frequency and mean LH concentrations after 20 days. Injection of 0.5 mg 17beta-E2 induced an LH surge in every one of the control cows with their peak concentrations measured 18 h post injection. No increase in LH was detected in any Ovuplant treated cows. Pituitary FSH content was reduced in Ovuplant treated cows after 48 h, but not that of LH. In conclusion, absorbable deslorelin implants induced a substantial but temporary release of LH, but even 21 days later their LH profiles were characterized by marked suppression of pulsatile LH and an absence of response to E2. These results suggest the implant has prolonged biological activity.     

Gonadotropin-releasing hormone at estrus: luteinizing hormone, estradiol, and progesterone during the periestrual and postinsemination periods in dairy cattle

Administering gonadotropin-releasing hormone (GnRH) improved conception rates in our previous studies. Our objective was to determine if the effect of GnRH was mediated through serum luteinizing hormone (LH) and/or by altered secretion of serum progesterone (P) and estradiol-17 beta (E) during the periestrual and post-insemination periods. Cattle were given either GnRH (n = 54) or saline (n = 55) at 72 h and inseminated artificially (AI) 80 h after the second of two injections of either prostaglandin F2 alpha or its analog, cloprostenol. Progesterone and E were measured in blood serum collected during 3 wk after AI (estrus) from 60 females. Blood was collected for LH determinations via indwelling jugular cannulae from 14 cows and 11 heifers. Collections were taken every 4 h from 32 to 108 h after the second PGF injection (PGF-2) (periestrual period) and at more frequent intervals during 240 min after administration of GnRH (n = 18) or saline (n = 7). Ten females had a spontaneous preovulatory LH surge before GnRH treatment (GnRH-spontaneous), whereas GnRH induced the preovulatory LH surge in six females. A spontaneous LH surge appeared to be initiated in two heifers at or near the time of GnRH treatment (spontaneous and/or induced). The remaining seven cows had spontaneous LH surges with no subsequent change in LH after saline treatment. Serum P during the 21 days after estrus was lower (p less than 0.05) in both pregnant and nonpregnant (open) cattle treated previously with GnRH compared with saline. Serum P during the first week after estrus was greater (p less than 0.01) and increased (p less than 0.05) more rapidly in saline controls and in GnRH-spontaneous cattle than in those exhibiting GnRH-induced or GnRH-spontaneous and/or-induced surges of LH. Conception rate of cattle receiving GnRH was higher (p = 0.06) than that of saline-treated controls. These data suggest that GnRH treatment at insemination initiated the preovulatory LH surge in some cattle, but serum P in both pregnant and open cows was compromised during the luteal phase after GnRH treatment. Improved fertility may be associated with delayed or slowly rising concentrations of serum progesterone after ovulation.     

Pituitary luteinizing hormone-releasing hormone receptors in ovariectomized cows after challenge with ovarian steroids

Acute changes of bovine pituitary luteinizing hormone-releasing hormone (LHRH) receptors in response to steroid challenges have not been documented. To investigate these changes 96 ovariectomized (OVX) cows were randomly allotted to one of the following treatments: 1) 1 mg estriol (E3); 2) 1 mg 17 beta-estradiol (E2); or 3) 25 mg progesterone (P) twice daily for 7 days before 1 mg E2 and continuing to the end of the experiment. Serum was collected at hourly intervals from 4 animals in each group for 28 h following estrogen treatment. Four animals from each treatment were killed at 4-h intervals from 0 to 28 h after estrogen injection to recover pituitaries and hypothalami. Treatment with E3 or E2 decreased serum luteinizing hormone (LH) within 3 h and was followed by surges of LH that were temporally and quantitatively similar (P greater than 0.05). Progesterone did not block the decline in serum LH, but did prevent (P less than 0.05) the E2-induced surge of LH. Serum follicle-stimulating hormone (FSH) was unaffected (P less than 0.05) by treatment. Pituitary concentrations of LH and FSH were maximal (P less than 0.001) at 16 h for E3 and 20 h for E2, whereas P prevented (P greater than 0.05) the pituitary gonadotropin increase. Concentrations of LHRH in the hypothalamus were similar (P greater than 0.05) among treatments. Pituitary concentrations of receptors for LHRH were maximal (P less than 0.005) 12 h after estrogen injection (approximately 8 h before the LH surge), even in the presence of P. This study demonstrated that in the OVX cow: 1) E2 and E3 increased the concentration of receptors for LHRH and this increase occurred before the surge of LH; and 2) P did not block the E2-induced increase in pituitary receptors for LHRH but did prevent the surge of LH.     

LH secretion around the time of the preovulatory gonadotrophin surge in the ewe

Blood samples were taken once an hour from 17 ewes starting on Day 15 of a natural oestrous cycle and continuing for 4 days or until 36 h after the onset of oestrus. On Days 12, 16, 17 and 18 of the cycle, blood samples were also taken every 5 min for 6 h, between 09:00 and 15:00 h. LH pulse frequency rose and amplitude fell between the luteal and follicular phase of the oestrous cycle ( ). In the period from 48 h before to 40 h past the peak of the preovulatory LH surge, LH pulse frequency did not change. LH pulse amplitude was similar prior to and following the LH surge. During the preovulatory LH surge, LH pulse amplitude rose markedly ( ), with the visible, discrete components of pulses ranging from twice to 20 times those seen prior to or following the surge. The amplitude of LH pulses on the downslope of the LH surge was greater than that on the upslope of the surge (P < 0.05). We conclude that the preovulatory LH surge may consist of an amalgamation of high frequency, high amplitude pulses of LH secretion.     

Observations on variability in LH release and fertility during oestrus in the domestic cat (Felis catus)

Hormonal changes, behaviour, ovulation and fertility were examined in response to coitus at two different times during oestrus in the female domestic cat housed in conditions of natural light (N = 13). On Day 2 or Day 4/5 of oestrus females were allowed 1 copulation in 15 min (single matings) or 2-3 copulations in 30 min (multiple matings). Plasma LH, oestradiol-17 beta and progesterone concentrations during the 24-h period after coitus were measured by radioimmunoassay; ovulation was assumed to have occurred if progesterone values were elevated 7-30 days after coitus. With the exception of 2 out of 3 animals receiving single matings on Day 2 of oestrus, all animals showed subsequent elevated progesterone values. Females receiving multiple matings had significantly greater releases of LH as measured by the area under the curve than those receiving single matings. There was significantly greater variability in the LH response of queens on Day 2 of oestrus compared to those on Day 4/5 for peak values and area under the curve; the only failure in release of LH was in queens on Day 2. Oestradiol levels did not differ significantly between Day 2 and Day 4/5 of oestrus. Progesterone values remained less than 1 ng/ml for 24 h after coitus. Both LH peak values and area under the curve were significantly greater for animals that became pregnant. There were also significant differences in coital behaviour between queens on Day 2 and those on Day 4/5 of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of 6- and 7-hydroxy metabolites of 3 beta,17 beta-dihydroxy-5 alpha-androstane on gonadotrophin and prolactin secretion and on sex accessories weight of male rats

It has recently been shown that 3 beta,17 beta-dihydroxy-5 alpha-androstane (3 beta-diol), a known testosterone metabolite, may be further hydroxylated in position 6 and 7. Because of the possible involvement of 3 beta-diol in the control of gonadotrophin secretion, this work was aimed at investigating the effects of 3 beta,6 alpha,17 beta-trihydroxy-5 alpha-androstane (6 alpha-triol), 3 beta,7 alpha,17 beta-trihydroxy-5 alpha-androstane (7 alpha-triol), 3 beta,6 beta,17 beta-trihydroxy-5 alpha-androstane (6 beta-triol) and 3 beta,7 beta,17 beta-trihydroxy-5 alpha-androstane (7 beta-triol) on the secretion of LH, FSH and prolactin in long term castrated male rats. The four triols, 3 beta-diol and 3 alpha,17 beta-dihydroxy-5 alpha-androstane (3 alpha-diol), used for comparison, were given in a single subcutaneous dose of 2 mg/rat. Animals were killed 2, 5, 8 and 24 h after injection. None of the six steroids produces any significant effect on serum levels of FSH and prolactin at the 4 time intervals considered. On the contrary, LH levels are significantly reduced 2, 5 and 8 h after the injection of 7 beta-triol. This effect appears rapidly but is short lasting, since it disappears in the 24 h blood sample, 3 alpha-Diol also inhibits LH secretion but at later time intervals (8 and 24 h). None of the other steroids has any significant effect on serum LH levels. The four triols administered at the daily dose of 2 and 4 mg/rat for 6 days are totally ineffective in increasing the weight of the ventral prostate and of the seminal vesicles of prepuberal castrated male rats.     

Pre- and Postpubertal LH and Estradiol Pattern in Gilts Subjected to Intermittent Inescapable Electroshock

The effect of intermittent electroshock on LH and es-tradiol secretory pattern and on reaching puberty was studied in 24 prepubertal gilts. Twelve gilts 115-168 days of age received unpredictable and inescapable electroshocks 0-5 times daily between 8 am and 4 pm and 12 gilts served as controls. At an age of 168 ± 0.7 days all gilts were moved, regrouped and exposed to a boar for 30 min. Observa-tions for signs of oestrus were carried out twice daily. Indwelling jugular catheters were inserted into 8 gilts on each treatment after the initial boar contact. Blood samples were collected to determine LH profiles for 4 h every 15 min on day 2 and day 4 after the in-itial boar contact. The remaining 4 gilts on each treatment were catheterized one day prior to the initial boar contact and blood was collected to determine LH profiles the day before initial boar contact and day 1 and day 2 after initial boar contact for 6 h every 15 min. In addition, blood samples were collected and analyzed for LH and estradiol from all gilts daily at 8 am, 12 am and 4 pm for the first 3 days following the initial boar con-tact and thereafter every 4 h until the end of oestrus (diurnal samples). Samples taken daily at noon the first 5 days following initial boar contact were analyzed for Cortisol. The electroshock treatment significantly increased the age at puberty (p=0.04) and tended to decrease the mean LH concentration prior to the preovulatory LH surge (p=0.08) and the maximal concentration of LH during the preovulatory LH surge (p=0.07). The apparent down regulation of the plasma concentration of LH was not as-sociated with increased activity in the hypothalamus-pituitary-adrenal axis in that the basal concentration of Cortisol was not affected by treatment. This indicates that other physiological mechanisms are involved in stress-induced suppression of LH.     

Influence of gonadotropin-releasing hormone pulse amplitude, frequency, and treatment duration on the regulation of luteinizing hormone (LH) subunit messenger ribonucleic acids and LH secretion

The effects of GnRH pulse amplitude, frequency, and treatment duration on pituitary alpha and LH beta subunit mRNA concentrations were examined in castrate-testosterone replaced male rats. Experimental groups received iv GnRH pulses (5, 25, or 125 ng) at 7.5-, 30-, or 120-min intervals for 8, 24, or 48 h. Saline pulses were given to control rats. Acute LH secretion was measured in blood drawn before and 20 min after the last GnRH pulse. In saline controls, alpha and LH beta mRNAs (150 +/- 14, 23 +/- 2 pg cDNA bound/100 micrograms pituitary DNA) fell to 129 +/- 14 and 18 +/- 2, respectively, after 48 h. In animals receiving GnRH pulses (7.5-min intervals), the 125-ng dose stimulated a slight increase (P less than 0.01) in alpha mRNA levels after 8 and 24 h and both LH subunit mRNAs were increased by the 25- and 125-ng doses after 48 h. The 30-min pulse interval injections (25- and 125-ng doses) increased LH beta mRNA levels after 8 h, but alpha mRNAs were not elevated until after 24 h. Maximum (3-fold) increases in alpha and LH beta mRNAs were seen in rats receiving 25-ng pulses every 30 min for 48 h. Using 120-min pulses, LH subunit mRNAs were not increased by any GnRH dose through 48 h. Acute LH release was not seen in rats receiving 5 ng GnRH pulses at any pulse interval.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of luteinizing hormone, progesterone, testosterone, estradiol and corticosterone on ovulation and luteinizing hormone release in hens treated with aminoglutethimide

Aminoglutethimide (AG), an inhibitor of steroidogenesis, was administered s.c. to 5 groups of laying hens at a dose of 200 mg AG/kg body weight 9 h before expected midsequence ovulation. This dose has previously been demonstrated to consistently block ovulation. The injection of AG was followed by s.c. injections of: Group 1, 1.0 mg progesterone; Group 2, 0.1 mg estradiol-17 beta; Group 3, 1.5 mg corticosterone, all at 6 h prior to expected ovulation; Group 4, 1.0 mg testosterone at both 8 h and 5 h before expected ovulation; and Group 5, 25 micrograms of ovine luteinizing hormone (LH) at 8 and 50 micrograms ovine LH at 6 h before expected ovulation. For each group, 4 control hens were injected with AG and the appropriate vehicle. Blood samples were taken at 1- or 2-h intervals from the time of AG injection to the expected time of ovulation. The hens were killed 4 h after expected ovulation and examined for the occurrence of ovulation. In all hens injected with vehicle, ovulation and the preovulatory surges of progesterone, testosterone, estradiol-17 beta and LH were inhibited. The plasma concentration of corticosterone was not reduced following an injection of AG. Four of 6 hens ovulated in response to injection of ovine LH, although neither endogenous LH nor progesterone were released. Thus, LH appears to play a direct role in follicular rupture and extrusion of the ovum. The administration of progesterone induced a significant and prolonged rise in LH, restoring AG-blocked ovulation in all hens treated (n = 6). Injections of testosterone restored LH release in all hens and ovulation in 2 of 7 hens treated. Three of 7 hens ovulated in response to the corticosterone injection. A preovulatory rise in LH was not observed, indicating that corticosterone may exert its ovulation-inducing effect directly on the mature follicle. Estradiol-17 beta did not restore LH release or ovulation in any of the hens treated with AG.     

Temporal relations between plasma concentrations of luteinizing hormone, follicle-stimulating hormone, estradiol-17beta, progesterone, prolactin, and alpha-melanocyte-stimulating hormone during the follicular, ovulatory, and early luteal phase in the bitch

Compared with other domestic animals, relatively little is known about the changes in, and temporal relations between, reproductive hormones around the time of ovulation in the domestic bitch. Therefore, plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol-17beta, progesterone, prolactin (PRL), and alpha-melanocyte-stimulating hormone (alpha-MSH) were determined one to six times daily from the start of the follicular phase until 5 days after the estimated day of ovulation in six Beagle bitches. In all bitches, the pre-ovulatory LH surge was accompanied by a pre-ovulatory FSH surge. A pre-ovulatory PRL or alpha-MSH surge was not observed. The pre-ovulatory FSH and LH surges started concomitantly in four bitches, but in two bitches the FSH surge started 12 h earlier than the LH surge. The FSH surge (110+/-8 h) lasted significantly longer than the LH surge (36+/-5 h). In contrast with the pre-ovulatory FSH surge, the pre-ovulatory LH surge was bifurcated in four of six bitches. The mean plasma LH concentrations before (1.9+/-0.4 microg/L) and after (1.9+/-0.3 microg/L) the LH surge were similar, but the mean plasma FSH concentration before the FSH surge (1.6+/-0.3 U/L) was significantly lower than that after the FSH surge (3.1+/-0.2 U/L). In most bitches the highest plasma estradiol-17beta concentration coincided with or followed the start of the pre-ovulatory LH surge. In five of the six bitches the plasma progesterone concentration started to rise just before or concurrently with the start of the LH surge. In conclusion, the results of this study provide evidence for the differential regulation of the secretion of LH and FSH in the bitch. In addition, the interrelationship of the plasma profiles of estradiol-17beta and LH suggests a positive feedback effect of estradiol-17beta on LH surge release. The start of the pre-ovulatory LH surge is associated with an increase in the plasma progesterone concentration in this species.     

Effects of removal in late pregnancy of the corpus luteum, graafian follicle or ovaries on plasma progesterone, oestradiol, LH, parturition and post-partum oestrus in the tammar wallaby, Macropus eugenii

Concentrations of oestradiol-17 beta, progesterone, and luteinizing hormone (LH) were measured in plasma collected at 6- to 12-h intervals from tammars around the time of parturition and post-partum oestrus. Parturition occurred on Day 26 or 27 after reactivation of lactation-delayed pregnancy and coincided with a precipitous decline in progesterone levels. A sharp rise in oestradiol, from basal concentrations of less than 10 pg/ml to a peak of 13 to 32 pg/ml, as well as oestrus, followed the drop in progesterone by 8.3 and 9.8 h, respectively. The LH surge was dependent on the oestradiol rise and followed it by 7 h. Ovulation followed mating by about 30 h and the LH surge by 24 h. Removal of the ovary with the large Graafian follicle prevented the oestradiol rise, oestrus and the LH surge, but not parturition. Peripartum changes in peripheral oestradiol do not appear to be involved in initiation of parturition but the oestradiol rise and associated change in the oestradiol:progesterone ratio are important signals for post-partum oestrus and the LH surge.     

Estrus synchronization and artificial insemination of hair sheep ewes in the tropics

Hair sheep ewes (St. Croix White and Barbados Blackbelly) were used to evaluate 3 methods of estrus synchronization for use with transcervical artificial insemination (TAI). To synchronize estrus, ewes (n = 18) were treated with PGF2alpha (15 mg, im) 10 d apart, with controlled internal drug release (CIDR) devices containing 300 mg progesterone for 12 d (n = 18), or with intravaginal sponges containing 500 mg progesterone for 12 d (n = 18). On the day of the second PGF2alpha injection or at CIDR or sponge removal, sterile rams were placed with the ewes. Jugular blood samples were collected from the ewes at 6-h intervals until the time of ovulation, and daily for 16 d after estrus (Day 0). Plasma was harvested and stored at -20 degrees C until LH, and progesterone concentrations were determined by RIA. There was no difference (P>0.10) in time to estrus among the CIDR-, PGF2alpha- or sponge-treated ewes. All of the ewes in the CIDR group and 94.4% of the sponge treated ewes exhibited estrus by 36 h after ram introduction, while only 72.2% of PGF2alpha-treated ewes showed signs of estrus by this time (P<0.06). The time from ram introduction to ovulation was not different (P>0.10) among the CIDR-, PGF2alpha- or sponge-treated ewes. The time to the preovulatory LH surge was similar (P>0.10) among CIDR, PGF2alpha and sponge treated ewes. Progesterone levels through Day 16 after the synchronized estrus were not different (P>0.10) among treatment groups. Hair sheep ewes (n = 23) were synchronized using PGF2alpha and bred by TAI using frozen-thawed semen 48 h after the second injection. The conception rate to TAI was 2/23 (8.7%) and produced 3 ram lambs. In a subsequent trial, 17 ewes were synchronized with CIDR devices and bred by TAI using frozen-thawed semen 48 h after CIDR removal, resulting in a conception rate of 52.9% (9/17). It is possible to synchronize estrus in hair sheep using either CIDRs, sponges or PGF2alpha. Even though there were no significant differences in the timing of ovulation or the LH surge among the treatment groups, a higher conception rate was achieved in ewes synchronized with CIDR devices during the second trial. This may reflect an increase in the skill level of the TAI technician.