Influence of estradiol, progesterone, and nutrition on concentrations of gonadotropins and GnRH receptors, and abundance of mRNA for GnRH receptors and gonadotropin subunits in pituitary glands of beef cows

Effect of progesterone from corpus luteum, intravaginal implant, or both on luteinizing hormone release, ovulatory response, and subsequent luteal development after gonadotropin-releasing hormone treatment in cows

This study aimed to determine the effect of circulating progesterone (P4) concentrations produced by a corpus luteum (CL) or released by an intravaginal P4 implant (IPI) on GnRH-induced LH release, ovulatory response, and subsequent CL development, after treatment with 100 μg of gonadorelin acetate (GnRH challenge). Nonlactating multiparous Holstein cows were synchronized and GnRH was used to induce ovulation (d -7). Over 4 replicates, cows that ovulated (n = 87) were randomly assigned to a 2 × 2 factorial arrangement (presence or absence of CL and insertion or not of an IPI at GnRH challenge), creating 4 groups: CL_IPI, CL_NoIPI, NoCL_IPI, and NoCL_NoIPI. On d -1.5, NoCL_IPI and NoCL_NoIPI received 2 doses of 0.53 mg of cloprostenol sodium (PGF2α), 24 h apart to regress CL. On d 0, cows were treated with 100 μg of GnRH and, simultaneously, cows from IPI groups received a 2-g IPI maintained for the next 14 d. Diameter of dominant follicle, ovulatory response, and subsequent CL volume were assessed by ultrasonography on d -1.5, 0, 2, 7, and 14. Blood samples were collected on d -1.5, 0, 1, 2, 3, 5, 7, and 14 for analysis of circulating P4 and at 0, 1, 2, 4, and 6 h after GnRH challenge for analysis of circulating LH. In a subset of cows (n = 34), the development of the new CL was evaluated daily, from d 5 to 14. The presence of CL at the time of GnRH challenge affected the LH peak and ovulatory response (CL: 5.3 ng/mL and 58.1%; NoCL: 13.2 ng/mL and 95.5%, respectively). However, despite producing a rapid increase in circulating P4, IPI insertion did not affect LH concentration or ovulation. Regardless of group, ovulatory response was positively correlated with LH peak and negatively correlated with circulating P4 on d 0. Moreover, new CL development and function were negatively affected by the presence of CL and by the IPI insertion. In summary, circulating P4 produced by a CL exerted a suppressive effect on GnRH-induced LH release and subsequent ovulation of a 7-d-old dominant follicle, whereas the IPI insertion at the time of GnRH had no effect on LH concentration or ovulation. Finally, elevated circulating P4, either from CL or exogenously released by the IPI, compromised the development and function of the new CL, inducing short cycles in cows without CL at the time of GnRH treatment.

Effects of different supplemental soya bean oil levels on the performance of prepubertal Saanen goats: Oestrogen and progesterone release

The aim of this study was to investigate the effects of different levels of soya bean oil in the total diet on the growth rate, metabolic changes, and oestrogen and progesterone release in Saanen goats. After dietary adaptation, 21 prepubertal goats (weight of 29.12 ± 0.91 kg, 230 days old) were randomly distributed among three diets of D2: inclusion of 2% soya bean oil in the total diet; D3: basal diet - inclusion of 3% soya bean oil in the total diet; and D4: inclusion of 4% soya bean oil in the total diet. The basal diet (D3) was formulated to promote a daily gain of 0.140 kg. The goats were weighed, and their blood samples were collected weekly. Glucose, cholesterol, triglycerides, total protein, urea, non-esterified fatty acids, beta-hydroxybutyrate, oestrogen and progesterone in the plasma were measured. Prepubertal goats that were fed D4 exhibited a significantly lower dry matter intake, urea and cholesterol levels compared with the goats that were fed D2 and D3. Indeed, goats that were fed D4 displayed a significantly lower final weight than goats that were fed D2 and D3. In contrast, the inclusion of soya bean oil in the diet increased the progesterone and oestrogen concentrations, and goats that were fed D4 released a significantly higher concentration of progesterone than those that were fed D2 and D3. Furthermore, the percentage of goats with a progesterone level greater than 1 ng/ml (functional Corpus luteum) was significantly higher among the goats that were fed D3 and D4 than among those that were fed D2. In this study, although the inclusion of 4% soya bean oil in the diet decreased dry matter intake and growth rate, it increased progesterone concentration and the percentage of goats with a functional Corpus luteum, suggesting that the inclusion of soya bean oil accelerated puberty in prepubertal goats.

Relationship of follicle size and concentrations of estradiol among cows exhibiting or not exhibiting estrus during a fixed-time AI protocol

Cows exhibiting estrus near fixed-time artificial insemination (AI) had greater pregnancy success than cows not showing estrus. The objective of this study was to determine the relationship between follicle size and peak estradiol concentration between cows that did or did not exhibit estrus during a fixed-time AI protocol. Ovulation was synchronized in beef cows by applying the CO-Synch protocol [GnRH (100 μg) on day-9, prostaglandin F2α (PGF2α; 25 mg) on day-2, and a second injection of GnRH 48 h after PGF2α (day 0)] to both suckled (experiment 1) and nonsuckled (experiment 2) cows. Follicle size (day 0) and ovulation (day 2) was determined by ultrasonography. Blood samples were collected every 3 or 4 h beginning at the time of PGF2α injection (0 h). Estrus was detected by visual observation with the aid of estrus-detection patches, and cows that ovulated were classified as exhibited estrus (n = 46) or did not exhibit estrus (n = 63). In both suckled and nonsuckled cows, there was a positive relationship between all cows (P < 0.05) and among those that exhibited estrus (P < 0.05) between follicle size and peak estradiol concentration, but no linear relationship (P > 0.50) between follicle size and peak estradiol concentration was observed among cows not exhibiting estrus. Cows that exhibited estrus had greater (P < 0.01) peak estradiol concentrations than cows that did not exhibit estrus. Suckled cows exhibiting standing estrus had greater (P < 0.001) preovulatory concentrations of estradiol beginning 6 h (replicate 1) or 4 h (replicate 2) after the injection of PGF2α on day-2 compared with cows not exhibiting standing estrus. Nonsuckled cows exhibiting standing estrus had greater (P < 0.001) preovulatory concentrations of estradiol beginning at the injection of PGF2α on day-2 compared with cows not exhibiting standing estrus. Furthermore, cows that exhibited estrus had an increased (P < 0.01) rate in the rise in concentrations of estradiol following the PGF2α to peak estradiol than cows not exhibiting estrus. In summary, follicle diameter had a positive relationship with peak concentrations of estradiol, but only among cows that exhibited standing estrus, and estradiol increased earlier in cows that exhibited estrus compared with cows that did not.

Influence of ethynylestradiol and methyltestosterone on the hypothalamo-hypophyseal-gonadal axis of adult air-breathing catfish, Clarias gariepinus

Adult male and female air-breathing catfish Clarias gariepinus were treated with ethynylestradiol (EE(2)) and methyltestosterone (MT) at concentrations of 1microg/L, respectively for 21 days. EE(2) treatment caused disappearance of spermatids/sperm from several testicular lumen/lobules in males while MT treatment to females led to precocious ovarian development. EE(2) caused significant fluid retention in all tissues including peritoneal cavity and seminal vesicles. Immunocytochemical localization of catfish GnRH (cfGnRH) and luteinizing hormone (LH) in preoptic area-hypothalamus (POA-H) and pituitary, respectively, revealed decreased immunoreactivity (ir-) following EE(2) treatment in males. MT treatment however caused no observable change in cfGnRH ir- and a significant increase in LH ir- in females. Semi-quantitative RT-PCR analysis indicated that cfGnRH transcripts in POA-H decreased significantly following EE(2) and MT treatment in males and females, respectively. Levels of POA-H dopamine (inhibitory monoamine for gonadotropin [GTH] synthesis and release) increased following EE(2) and MT treatment in males and females while levels of serotonin and norepinephrine (GTH-stimulatory monoamines) decreased significantly. The results demonstrate a direct in vivo effect of sex steroid analogs on cfGnRH-LH axis and monoaminergic system vis-à-vis on gonads in addition to probable direct action on gonads.

Progesterone and the distribution of pituitary gonadotropin isoforms in cattle

The objective of the present study was to determine the relative proportion of gonadotropin isoforms in bovine pituitary glands affected by progesterone. Twelve postpubertal heifers (Swiss-Zebu) were assigned to three groups (n=4): intact animals in the luteal phase of the estrous cycle (diestrus group); ovariectomized heifers with (OVXP) or without progesterone treatment (OVX). Prior to pituitary gland collection, a blood sample was taken from each animal to determine the circulating progesterone concentration. Pituitary protein extractions processed by chromatofocusing were eluted with a pH gradient ranging from 10.5 to 3.5. The LH and FSH eluent was grouped on the basis of the following three criteria: (1) as either a basic (pH>or=7.5), neutral (pH 7.4-6.5) and acid (pH<or=6.4); (2) according to the pH unit (pH>or=10.5-3.5); (3) on the basis of distinct isoforms 12 peaks of which (A-L) were identified for LH and 11 (I-XI) for FSH. The analysis by range of pH and by pH of elution in the OVX and OVXP groups showed no difference in the LH and FSH isoform ratio, but diestrus cattle differs having a greater ratio (p<0.05) of basic LH isoforms (87.5+/-0.4%) and lesser ratio (p<0.05) of acid isoforms (5.4+/-0.7%). In the diestrus group, the ratio of acid FSH isoform increased (62.1+/-1.7%), while neutral isoforms decreased (5.7+/-0.4%, P<0.05). The analysis by isoform type of LH revealed a greater proportion of isoforms C (pH 9.4) and E (pH 9.0) in the groups with circulating progesterone when compared to the OVX group. The heterogeneity of FSH was quantitatively similar in most isoforms in the three groups, with the exception of the predominant isoform (VIII, pH 4.9) that was more abundant in the diestrus group (p<0.05). These results indicate that progesterone with other gonad factors influence the pituitary glicosylation altering the relative proportions of gonadotropin isoforms.

Development and validation of a sensitive radioimmunoassay procedure for estimating FSH in mithun (Bos frontalis) plasma

The present study was designed to develop and validate a simple and sensitive radioimmunoassay (RIA) procedure to estimate FSH in mithun (Bosfrontalis) plasma. The assay was carried out in 100 [L of mithun plasma. The bovine FSH standards (10 to 5000 pg/100 microL/tube) in hormone-free plasma were used in the assay. The sensitivity of the assay was 20 pg/100 microL/tube, which corresponded to 0.20 ng/mL plasma. The 50% relative binding sensitivity of the assay was 80 pg/100 microL/tube, which corresponded to 0.80 ng/mL plasma. The intra- and inter-assay coefficients of variation were 4.6% and 12.4%, respectively. The biological validation of the assay was carried out in plasma samples that were collected during different stages of the estrous cycle. In the entire estrous cycle, plasma FSH concentration (p < 0.01) attained two peaks (on day 3 to 4 before estrus 5.1 +/- 0.3 ng/mL and on the day of estrus 6.9 +/- 0.2 ng/mL). FSH concentration remained at basal level (1.3 +/- 0.1 to 1.6 +/- 0.2 ng/mL) during day 4 to 16 of the estrous cycle. The concentration of plasma FSH was found to be significantly (p < 0.05) higher (4.9 +/- 0.3 to 6.8 +/- 0.5 ng/mL) until 48 h following the estrus onset. In conclusion, the RIA procedure that was developed in the current study is sufficiently reliable and sensitive to estimate different physiological levels of FSH in mithun plasma.

Influence of estradiol on adrenal activity in ovariectomized cows during acute stress

Stress-dependent activation of the hypothalamo-pituitary-adrenal axis (HPA) can compromise reproductive function in animals and humans. In addition, it has been shown that estrogens are also capable of influencing the activity of the adrenal cortex. The objective of this study was to evaluate the effect of estradiol (E2) on adrenocortical secretion of cortisol and progesterone as well as on pituitary LH-release in cows during stress. Five ovariectomized Brown Swiss cows were exposed to acute restraint stress (2-h immobilization in a trimming chute), either with or without E2 treatment. Blood samples were taken every 15 min during a 5-h period for determination of cortisol progesterone and LH. Our results demonstrate that during the 2-h stress period mean cortisol concentrations significantly (P < 0.05) increased in all cows independent of E2 treatment. Mean progesterone concentrations also increased during stress, but the effect was only significant in E2-untreated cows. In contrast to cortisol and progesterone, mean LH values decreased in all animals during stress, but the decline was not significant. However, significantly lower mean LH values were seen at the end of the stress period comparing to values before stress. In cows without stress, E2 treatment had no significant effect on mean values of all three hormones analyzed. From our results it can be concluded that in ovariectomized cows (a) acute stress increases cortisol and progesterone secretion but decreases LH release and (b) the stress induced adrenocortical and pituitary responses were clearly attenuated under the influence of estradiol.

Estrous behavior and initiation of estrous cycles in postpartum Brahman-influenced cows after treatment with progesterone and prostaglandin F2α1,2

Spring-calving, crossbred (1/4 to 3/8 Brahman) primiparous (n = 56) and multiparous (n = 102) beef cows were used to evaluate the effects of progesterone, delivered via a controlled internal drug-releasing (CIDR) device, and prostaglandin F(2alpha) (PGF(2alpha)) on estrous behavior, synchronization rate, initiation of estrous cycles, and pregnancy rate during a 2-yr period. To determine luteal activity, weekly blood samples were collected 3 wk before initiation of a 75-d breeding season. Treated cows received a CIDR for 7 d beginning on d -7 of the breeding season. On d 0, CIDR were removed, and cows receiving CIDR were administered PGF(2alpha); control cows received no treatment. Cows were exposed to bulls, and estrous activity was monitored using a radiotelemetry system for the first 30 d of the breeding season. Treatment with CIDR-PGF(2alpha) increased (P < 0.05) the number of mounts received (22.5 +/- 3.0 vs. 13.7 +/- 3.9 for CIDR-PGF(2alpha) vs. untreated control cows, respectively) but did not influence duration of estrus or quiescence between mounts. Number of mounts received and duration of estrus were greater (P < 0.05) in multiparous compared with primiparous cows. Synchronization of estrus was greater (P < 0.05) in cows treated with CIDR-PGF(2alpha) (56%) compared with control cows (13%) during the first 3 d of the breeding season. More (P < 0.05) anestrous cows treated with CIDR-PGF(2alpha) than anestrous control cows were in estrus during the first 3 d (59 vs. 12%) and 30 d (82 vs. 63%) of the breeding season. Treatment with CIDR-PGF(2alpha) decreased (P < 0.05) the interval to first estrus after treatment during the first 30 d of the breeding season compared with control cows (5.5 +/- 1.1 vs. 9.0 +/- 1.4 d). First service conception rate was greater (P < 0.05) in CIDR-PGF(2alpha)-treated cows compared with control cows. Cyclic cows at initiation of the breeding season had an increased (P < 0.05) 75-d pregnancy rate compared with anestrous cows, and the pregnancy rate tended (P = 0.10) to be greater in multiparous compared with primiparous cows. We conclude that treatment of Brahman-influenced cows with progesterone via a CIDR for 7 d, along with administration of PGF(2alpha) at CIDR removal, increases the number of mounts received, improves synchronization and first service conception rates, decreases the interval to first estrus after treatment, and may be effective at inducing estrous cycles in anestrous cows.

Ovine serum and pituitary isoforms of luteinising hormone during the luteal phase

The relative abundance of the different isoforms of pituitary and circulating luteinising hormone (LH) in ewes, at different times after the administration of gonadotrophin-releasing hormone (GnRH), during the luteal phase of the oestrous cycle was investigated. Sixteen ewes on Day 9 of their cycle were divided into four groups (n = 4). The control group (T0) received saline solution; the remaining animals received 100 μg GnRH (i.m.) 30, 90 or 180 min (T30, T90 and T180, respectively) before serum and pituitary gland collection. Luteinising hormone polymorphism was analysed by chromatofocusing (pH 10.5–3.5). The LH eluted from each chromatofocusing was grouped on the basis of the following three criteria: (1) according to the pH of elution (pH ≥ 10–3.5); (2) as either a basic (pH ≥ 7.5), neutral (pH 7.4–6.5) and acidic (pH ≤ 6.4) elution of LH of serum and hypophyseal origin; and (3) on the basis of distinct isoforms, of which 10 (A–J) were identifiable in hypophyseal extracts and four (A–D) were found in the serum. In general, the most abundant forms of LH in both the pituitary and serum, at all times, were basic. However, that proportion was greater in hypophyseal extracts (84 ± 3%, 81 ± 4%, 82 ± 3% and 83 ± 2% at T0, T30, T90 and T180, respectively) than in serum (51 ± 5%, 48 ± 10% and 54 ± 6% at T30, T90 and T180, respectively). Neutral and acidic LH made up a larger proportion of the total LH in sera (neutral: 17 ± 4%, 20 ± 6% and 23 ± 3% at T30, T90 and T180, respectively; acidic: 32 ± 8%, 32 ± 11% and 23 ± 6% at T30, T90 and T180, respectively) than in the pituitary extracts (neutral: 4.0 ± 0.7%, 10 ± 4%, 7 ± 2% and 5.0 ± 0.5% at T0, T30, T90 and T180, respectively; acidic: 12 ± 3%, 11 ± 2%, 12 ± 2% and 12 ± 2% at T0, T30, T90 and T180, respectively) at all times. These data reveal that the relative composition of the LH present in the pituitary gland and the LH secreted into the circulation is different, with more neutral and acidic isoforms being secreted. The pattern of circulating LH isoforms changes between 30 and 180 min after GnRH peak induction, with a greater proportion of isoform C (eluting between pH 7.0 and 6.5) at T180 compared with T30 and T90.

Regulation of expression of mammalian gonadotrophin-releasing hormone receptor genes

Gonadotrophin-releasing hormone (GnRH), acting via its cognate GnRH receptor (GnRHR), is the primary regulator of mammalian reproductive function, and hence GnRH analogues are extensively used in the treatment of hormone-dependent diseases, as well as for assisted reproductive techniques. In addition to its established endocrine role in gonadotrophin regulation in the pituitary, evidence is rapidly accumulating to support the expression and functional roles for two forms of GnRHR (GnRHR I and GnRHR II) in multiple and diverse extra-pituitary mammalian tissues and cells. These findings, together with findings indicating that mutations of the GnRHR are linked to the disease hypogonadotrophic hypogonadism and that GnRHRs play a direct role in neuronal migration and reproductive cancers, have presented new therapeutic targets and intensified research into the structure, function and mechanisms of regulation of expression of GnRHR genes. The present review focuses on the current knowledge on tissue-specific and hormonal regulation of transcription of mammalian GnRH receptor genes. Emerging insights, such as the discovery of diverse regulatory mechanisms in pituitary and extra-pituitary cell types, nonclassical mechanisms of steroid regulation, the use of composite elements for cell-specific expression, the increasing profile of hormones involved in regulation, the complexity of kinase pathways that target the GnRHR I gene, as well as species-differences, are highlighted. Although further research is necessary to understand the mechanisms of regulation of expression of GnRHR I and GnRHR II genes, the GnRHR is emerging as a potential target gene for facilitating cross-talk between neuroendocrine, immune and stress-response systems in multiple tissues via autocrine, paracrine and endocrine signalling.

Body condition at parturition and postpartum weight changes do not influence the incidence of short-lived corpora lutea in postpartum beef cows1

Seventy-seven multiparous beef cows (Hereford and Angus x Hereford) with thin to moderate BCS at calving were used to evaluate the effects of body condition at parturition and BW change after calving on duration and occurence of luteal activity before and after first estrus. Blood samples were collected twice weekly after parturition to determine the occurrence of the first postpartum luteal activity (LA, progesterone > or = 0.5 ng/mL). Weight changes and BCS were determined at 2-wk intervals. Cows were exposed to bulls and observed twice daily for behavioral estrus. Luteal activity was classified as normal if plasma concentrations of progesterone were > or = 0.5 ng/mL for at least 11 d, or short if concentrations of progesterone were > or = 0.5 ng/mL for 10 d or less. The interval from parturition to first normal LA was shorter (P < 0.001) for moderate condition (BCS > or = 4.5) than for thin (BCS < or = 4) cows (58.3 +/- 3.2 vs. 93.3 +/- 5.1 d, respectively). Interval to first estrus also was shorter (P < 0.001) for moderate than for thin cows (53.3 +/- 3.7 vs. 89.3 +/- 5.6 d, respectively). Before the first normal LA, 78% of cows had an increase in progesterone for < 11 d. Postpartum weight change and BCS at calving did not influence the incidence of estrus associated with first normal LA. After the first estrus, 72% of cows had normal LA, 16% had a short luteal phase, and 12% lacked LA. Postpartum weight change and BCS did not influence the length of LA associated with the first estrus. Cows with normal LA had increased (P < 0.05) maximal concentrations of progesterone compared with cows that had a short luteal phase. When a transient increase in progesterone occurred before first behavioral estrus, 81% of cows had normal luteal function after estrus. We conclude that when beef cows are in thin to moderate body condition at calving, postpartum BW change and BCS at calving do not influence the duration of luteal activity before or after the first postpartum estrus.