Effects of gonadal steroids on tonic luteinizing hormone (LH) release and luteinizing hormone-releasing hormone-induced LH release from bovine pituitary cells cultured in vitro

Perinatal exposure to low doses of cypermethrin induce the puberty-related hormones and decrease the time to puberty in the female offspring

Pyrethroid insecticides are ubiquitously detected in environmental media, food, and urine samples. Our previous epidemiological study reported a correlation between increased pyrethroid exposure and delayed pubertal development in Chinese girls. In this study, we further investigated the effects of perinatal exposure to low doses of cypermethrin (CP) on pubertal onset and hypothalamic-pituitary-ovarian axis in the female mice offspring. The treatment of CP with 60 μg/kg/day from gestation day 6 (GD6) to postnatal day 21 (PND21) significantly decreased the time to puberty in the female offspring. Exposure of CP increased the serum levels of gonadotropin-releasing hormone (GnRH) and the expression of GnRH genes in a dose-dependent manner in the female offspring. CP also induced the serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), as well as the expression of gonadotropin subunit genes [LHβ, FSHβ, and chorionic gonadotropin α (Cgα)]. Furthermore, CP induced serum estradiol (E₂) levels and the expression of steroidogenesis-related genes [steroidogenic acute regulatory (StAR) and Cytochrome p 450, family 11, subfamily A, polypeptide 1 (CYP11A1)] in the ovary. In accordance with the in vivo tests, administration of CP (6.7, 20, and 60 μg/L) stimulated a dose-dependent increase in the synthesis and secretion of the puberty-related hormones in the explants of hypothalamus, pituitary, and ovary. The interference with calcium channels in the ovary may be responsible for CP-induced pubertal onset. Our study provided evidence that perinatal exposure to low doses of CP induced puberty-related hormones and decreased the time to puberty in the female offspring.

Kisspeptin induces ovulation in heifers under low plasma progesterone concentrations

The objective of the present study was to compare the effect of a single versus multiple doses of a 10-amino acid fragment of human (hKp) or murine (mKp) kisspeptin on LH secretion and the fate of the dominant follicle. In all experiments, a new wave was induced (Day 0) by ultrasound-guided ablation of >5 mm follicles, a progesterone device (CIDR) was placed in the vagina, animals given prostaglandin F2α analog im on Day 3.5 and 4, and hKp or mKp treatment given on Day 6. The experimental design maintained growth and ovulatory potential of the dominant follicle for 12 days and allowed hypothesis testing during the low-progesterone period (plasma progesterone ≤1.8 ng/ml on Day 6) wherein spontaneous wave emergence and ovulation did not occur between Day 6 and Day 12. In Experiment 1, heifers (n = 10/group) were given single iv dose of 45 mg hKp, 45 mg mKp, or 2 ml normal saline (control). Post-treatment plasma LH concentrations from 15 to 90 min were higher (P < 0.01) in hKp group than in the mKp and control groups. Two heifers ovulated in hKp group versus none in other groups. In Experiment 2, heifers (n = 6/group) were given 45 mg hKp over a 2 h period divided into multiple iv doses treatments or 2 ml normal saline (control). Post-treatment plasma LH concentrations were higher (P < 0.01) in all hKp treatment groups than in the control group. The ovulation rate was higher (P = 0.06) after hKp treatments (11/18) than in the control group (0/6). In Experiment 3, heifers (n = 6/group) were given 45 mg mKp over a 2 h period divided into multiple iv doses treatments or a single iv dose of gonadorelin acetate (positive control). Plasma LH concentration was higher (P < 0.01) and the ovulation rate was greater (P = 0.01) in the GnRH group (5/6) than mKp groups (1/12). In summary, hKp was more effective to induce ovulation than mKp. Human kisspeptin-10 given over a 2 h period induced ovulations at a rate similar to that of GnRH treatment in heifers under a low plasma progesterone state.

Circulating nitric oxide metabolites during luteolysis and the effect of luteinizing hormone on circulating nitric oxide metabolites in heifers

Temporal relationships among circulating concentrations of nitric oxide metabolites (NOM), progesterone (P4), and luteinizing hormone (LH) within the hours of a PGFM pulse were studied during luteolysis in heifers. The peak of a PGFM pulse was designated Hour 0. All of the following increases and decreases were significant. Within a spontaneous PGFM pulse (experiment 1; n = 7), concentrations of P4 and LH decreased between Hours -1 and 0 and increased between Hours 0 and 1; NOM increased between Hours -1 and 2. In experiment 2, PGFM pulses were simulated by intrauterine infusion of PGF2α (PGF group, n = 6), and another group was also treated with acyline to inhibit LH secretion (acyline-PGF group, n = 6). Averaged over the two groups, concentration of P4 decreased between Hours -2 and 0, increased (rebounded) between Hours 0 and 1, and decreased after Hour 2. In the PGF group, concentration of LH decreased between Hours -2 and -0.5 and increased between Hour 0 and Hour 1.5 to a maximum at Hour 1.5; NOM decreased between Hours -2 and -1.5 and increased between Hours 0 and 1.5. In the acyline-PGF group, the effect of hour was not significant for concentrations of LH and NOM. The absence of an increase in NOM concentration when LH was inhibited is a novel finding. The hypotheses were supported that concentrations of LH and NOM are temporally related, and LH has a role in the increase in NOM within the hours of a PGFM pulse.

Corpus luteum development and function after supplementation of long-acting progesterone during the early luteal phase in beef cattle

Strategic supplementation of P4 may be used to increase conception rates in cattle, but timing of supplementation in relation to ovulation, mass of supplementary P4 and formulation of the P4-containing supplement has not been determined for beef cattle. Effects of supplementation of long-acting progesterone (P4) on Days 2 or 3 post-ovulation on development, function and regression of corpus luteum (CL) were studied in beef cattle. Cows were synchronized with an oestradiol/P4-based protocol and treated with 150 or 300 mg of long-acting P4 on Day 2 or 3 post-ovulation (6-7 cows/group). Colour-doppler ultrasound scanning and blood sample collection were performed from Day 2-21.5. Plasma P4 concentrations were greater (p < 0.05) from Day 2.5-5.5 in the Day 2-treated groups and from Day 3.5-5.5 in the Day 3-treated cows than in the control group. CL area and blood flow during Day 2-8.5 did not differ (p > 0.05) among groups, suggesting no effect of P4 treatment on luteal development. The frequency of cows that began luteolysis before Day 15 was greater (p < 0.04) in cows treated with 300 mg than in the controls, but there were no differences between non-treated and 150 mg-treated cows. The interval from pre-treatment ovulation to functional and structural luteolysis was shorter (p < 0.01) in the combined P4-treated groups than in the control cows. In conclusion, was showed for the first time that long-acting P4 supplementation on Day 2 or 3 post-ovulation increases P4 concentrations for ≥3 day, has no effect on luteal development, but anticipates the beginning of luteolysis in beef cattle.

Effect of progesterone on magnitude of the luteinizing hormone surge induced by two different doses of gonadotropin-releasing hormone in lactating dairy cows

Ovulation to the first GnRH injection of Ovsynch-type protocols is lower in cows with high progesterone (P4) concentrations compared with cows with low P4 concentrations, suggesting that P4 may suppress the release of LH from the anterior pituitary after GnRH treatment. The objectives of this study were to determine the effect of 1) circulating P4 concentrations at the time of GnRH treatment on GnRH-induced LH secretion in lactating dairy cows and 2) increasing the dose of GnRH from 100 to 200 μg on LH secretion in a high- and low-P4 environment. A Double-Ovsynch (Pre-Ovsynch: GnRH, PGF(2α) 7d later, GnRH 3d later, and Breeding-Ovsynch 7d later: GnRH, PGF(2α) 7d later, and GnRH 48 h later) synchronization protocol was used to create the high- and low-P4 environments. At the first GnRH injection of Breeding-Ovsynch (high P4), all cows with a corpus luteum ≥ 20 mm were randomly assigned to receive 100 or 200 μg of GnRH. At the second GnRH injection of Breeding-Ovsynch (low P4) cows were again randomized to receive 100 or 200 μg of GnRH. Blood samples were collected every 15 min from -15 to 180 min after GnRH treatment, and then hourly until 6h after GnRH treatment. As expected, mean P4 concentrations were greater for cows in the high- than the low-P4 environment. For cows receiving 100 μg of GnRH, the LH peak and area under the curve (AUC) were greater in the low- than in the high-P4 environment. Similarly, for cows receiving 200 μg of GnRH, the LH peak and AUC were greater in the low- than the high-P4 environment. Cows receiving 100 or 200 μg of GnRH had greater mean LH concentration in the low- than the high-P4 environment from 1 to 6h after GnRH treatment. On the other hand, when comparing the effect of the 2 GnRH doses in the high- and low-P4 environments, cows receiving 200 μg of GnRH had a greater LH peak and AUC than cows treated with 100 μg of GnRH both in the high- and low-P4 environments. For the high-P4 environment, mean LH was greater from 1.5 to 5h after GnRH treatment for cows receiving 200 μg of GnRH than for those receiving 100 μg of GnRH. In the low-P4 environment, mean LH was greater for cows receiving 200 μg of GnRH than for those receiving 100 μg of GnRH from 1 to 2.5h after GnRH treatment. We conclude that the P4 environment at GnRH treatment dramatically affects GnRH-induced LH secretion, and that a 200-μg dose of GnRH can increase LH secretion in either a high- or a low-P4 environment.

Physiology and Endocrinology Symposium: Harnessing basic knowledge of factors controlling puberty to improve synchronization of estrus and fertility in heifers

The development of replacement heifers is a major economic investment for all beef and dairy operations. The costs associated with heifer development cannot be recovered if heifers do not conceive and remain productive in the herd; therefore, heifers need to conceive early in the breeding season or risk being culled. Previous research has reported up to a 21% increase in fertility from pubertal estrus to the third estrus of a heifer. The use of reproductive tract scores to determine pubertal status has demonstrated that peripubertal and pubertal heifers have increased pregnancy success to estrous synchronization compared with heifers that were prepubertal. The development of RIA has allowed accurate measurement of peripheral blood hormone concentrations associated with the pubertal process and luteal formation. This basic knowledge has increased our understanding of the mechanisms that control puberty in heifers. In addition, understanding the hormonal changes that occur during the estrous cycle has allowed for the development of estrous synchronization protocols that result in increased control of follicular growth, regression of luteal tissue, and ovulation. Transrectal ultrasonography has increased our understanding of follicular waves; this understanding led to research investigating the endocrine regulation of follicular waves and development of methods to synchronize follicular waves for purposes of fixed-time AI. Current topics of research include the effect of antral follicle count on fertility and the effect of maternal nutrition (on the fetus in utero) on subsequent reproductive potential of a heifer (i.e., fetal programming). Advancements in genomic technologies will likely provide a powerful tool for selecting heifers at birth that will have a greater probability of being reproductively successful if managed correctly. Therefore, knowledge gained through basic research on factors that control puberty has improved and will continue to improve heifer development and fertility.

Effect of dose of estradiol-17β on prominence of an induced 13,14-dihydro-15-keto-PGF(2α) (PGFM) pulse and relationship of prominence to progesterone, LH, and luteal blood flow in heifers

Various doses of estradiol-17β (E(2)) were used in heifers to induce a pulse of 13,14-dihydro-15-keto-prostaglandin F(2α) (PGFM). The effect of E(2) concentration on the prominence of PGFM pulses and the relationship between prominence and intrapulse concentration of progesterone (P(4)), LH, and luteal blood flow were studied. A single dose of 0 (vehicle), 0.01, 0.05, or 0.1 mg of E(2) was given (n = six/group) 14 d after ovulation. Blood samples were collected, and luteal blood flow was evaluated hourly for 10 h after the treatment. The 0.05-mg dose increased and the 0.1-mg dose further increased the prominence of the induced PGFM pulse, compared with the 0.0-mg dose and the 0.01-mg dose. The PGFM pulses were subdivided into three different prominence categories (<50, 50 to 150, and >150 pg/mL at the peak). In the 50 to 150 category, P(4) concentration increased (P < 0.05) between -2 h and 0 h (0 h = peak of PGFM pulse). In the >150 category, P(4) decreased (P < 0.05) between -1 h and 0 h, LH increased (P < 0.05) at 1 h, and luteal blood flow apparently decreased (P < 0.05) at 2 h of the PGFM pulse. The novel results supported the following hypotheses: (1) an increase in E(2) concentration increases the prominence of a PGFM pulse, and (2) greater prominence of a PGFM pulse is associated with a greater transient intrapulse depression of P(4) at the peak of the PGFM pulse. In addition, the extent of the effect of prostaglandin F(2α) on the increase in LH and changes in blood flow within the hours of a PGFM pulse was related positively to the prominence of the PGFM pulse.

Luteinizing hormone and growth hormone secretion in early lactating Spanish beef cows

The episodic release of luteinizing hormone (LH) and growth hormones (GH) was studied in three suckling regimens and two breeds of Spanish suckled cows. Parda de Montaña (PA) cows (n = 21) were assigned to once-daily, twice-daily or ad libitum (ADLIB) suckling. Pirenaica (PI) cows (n = 7) were used to evaluate the breed effect in twice-daily suckling. Coccygeal blood samples were collected twice weekly during lactation to determine the interval from calving to first ovulation through peripheral progesterone. On day 32 ± 3 post-partum, jugular blood samples were drawn at 15 min intervals during 8 h to analyse circulating LH and GH. The interval to first ovulation was greater in PA cows suckling ADLIB than in restricted suckling treatment (RESTR1), whereas in RESTR2 it did not differ from the other two treatments. There were no differences between PA and PI cows in the interval to first ovulation. RESTR1 cows showed a tendency to have shorter LH peak widths than ADLIB cows. PA cows showed a tendency to have longer LH peak widths than their PI counterparts. There were no differences across treatments or breeds in any of the GH measures of secretion. The LH release was more affected by breed than by suckling frequency, whereas that of GH was not influenced by any of these parameters. The variables that best allowed discrimination between ADLIB and restricted nursing systems were the interval to post-partum first ovulation, LH peak number and the mean GH concentration.

Effect of the timing of controlled internal drug-releasing device insertion on the gonadotropin-releasing hormone-induced luteinizing hormone surge and ovulatory response

Concentrations of progesterone have been reported to influence GnRH-induced LH surges. At the beginning of many synchronization protocols, GnRH is used to synchronize follicular growth. Therefore, the objective of this study was to determine the effect of elevated concentrations of progesterone from a controlled internal drug-releasing device (CIDR) on the GnRH-induced LH surge and ovulatory response. Angus-cross beef heifers (n = 113; 41 pubertal and 72 prepubertal) were assigned to 1 of 3 treatments: 1) GnRH at CIDR insertion (CIDR-0), 2) GnRH 6 h before CIDR insertion (CIDR-6), or 3) GnRH 48 h after CIDR insertion (CIDR+48). Follicle size was determined before GnRH administration, and ovulatory response was determined 2 d later. Blood samples were collected from a subset of 60 heifers at -30, 0 (GnRH administration), 30, 60, 90, 120, 150, 180, 210, 240, 300, and 360 min after GnRH. Heifers receiving CIDR+48 had greater (P < 0.01) concentrations of progesterone compared with those receiving CIDR-0 and CIDR-6. There was no difference (P > 0.76) between treatments in concentrations of estradiol. There tended to be a cycling status x ovulation interaction on concentrations of progesterone (P = 0.11), and there was a cycling status x ovulation interaction on concentrations of estradiol (P = 0.02). The estradiol-to-progesterone ratio was significant because of treatment (P = 0.002), cycling status (P = 0.001), and a treatment x cycling status interaction (P = 0.02). Cycling status tended (P = 0.11) to have an influence on ovulation (29/41 and 42/72 for pubertal and prepubertal heifers). Ovulation was induced in more (P < 0.05) CIDR-0 (26/38) and CIDR-6 (28/37) heifers than CIDR+48 (17/38) heifers. There was no influence of treatment (P = 0.19), concentrations of estradiol (P = 0.90), or the estradiol-to-progesterone ratio (P = 0.21) on concentrations of LH, but there was an effect (P < 0.01) of progesterone on LH concentrations. Heifers with elevated progesterone at GnRH administration had a reduced LH surge compared with heifers with decreased concentrations of progesterone. Heifers that ovulated tended to have a greater (P = 0.11) magnitude of LH surge than heifers that did not ovulate. In summary, elevated concentrations of progesterone at GnRH administration decreased the GnRH-induced LH surge, and heifers in the CIDR+48 treatment had a decreased ovulatory response. However, there tended to be a difference in the magnitude of the LH surge only between heifers that did and did not ovulate.

Effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given GnRH

The effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given 100 microg of GnRH im were determined in three experiments. In Experiment 1, heifers were given GnRH 3, 6 or 9 days after ovulation; 8/9, 5/9 and 2/9 ovulated (P<0.02). Mean plasma concentrations of progesterone were lowest (P<0.01) and of LH were highest (P<0.03) in heifers treated 3 days after ovulation. In Experiment 2, heifers received no treatment (Control) or one or two previously used CIDR inserts (Low-P4 and High-P4 groups, respectively) on Day 4 (estrus=Day 0). On Day 5, the Low-P4 group received prostaglandin F(2alpha) (PGF) twice, 12 h apart and on Day 6, all heifers received GnRH. Compared to heifers in the Control and Low-P4 groups, heifers in the High-P4 group had higher (P<0.01) plasma progesterone concentrations on Day 6 (3.0+/-0.3, 3.0+/-0.3 and 5.7+/-0.4 ng/ml, respectively; mean+/-S.E.M.) and a lower (P<0.01) incidence of GnRH-induced ovulation (10/10, 9/10 and 3/10). In Experiment 3, 4-6 days after ovulation, 20 beef heifers and 20 suckled beef cows were given a once-used CIDR, the two largest follicles were ablated, and the cattle were allocated to receive either PGF (repeated 12h later) or no additional treatment (Low-P4 and High-P4, respectively). All cattle received GnRH 6-8 days after follicular ablation. There was no difference between heifers and cows for ovulatory response (77.7 and 78.9%, P<0.9) or the GnRH-induced LH surge (P<0.3). However, the Low-P4 group had a higher (P<0.01) ovulatory response (94.7% versus 61.1%) and a greater LH surge of longer duration (P<0.001). In conclusion, although high plasma progesterone concentrations reduced both GnRH-induced increases in plasma LH concentrations and ovulatory responses in beef cattle, the hypothesis that heifers were more sensitive than cows to the suppressive effects of progesterone was not supported.

Immunoreactive galanin expression in ovine gonadotropin-releasing hormone neurones: no effects of gender or reproductive status

The neuropeptide, galanin, has been implicated to play a significant role in numerous physiological functions, including reproduction. Studies on several species have shown that galanin enhances gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone secretion. In rodents, a subset of GnRH neurones expresses galanin in a sexually dimorphic manner and it has been suggested that this may underpin the differences in GnRH secretion observed between the sexes. However, there are few data available for other species. Previous studies in sheep have shown that the distribution of GnRH neurones overlaps with galanin cells. The primary objectives of our study were to determine whether GnRH and galanin coexist in the sheep brain and, importantly, if a sex difference is apparent in the colocalization of these two peptides. Using immunocytochemistry coupled to high temperature antigen retrieval, we found that all GnRH neurones in the ovine brain colocalize with galanin. There is also a distinct population of galanin neurones that do not secrete GnRH. In addition, the distribution of galanin-immunoreactive cells was similar to that previously reported for colchicine treated ewes and, in agreement with earlier studies, the number of GnRH neurones did not differ between rams and ewes or between ewes killed at different stages of the oestrous cycle. These results suggest that, in sheep, GnRH and galanin may be cosecreted but the functional significance of this coexpression and possible cosecretion remains to be elucidated.