Measurement of the amount of mRNA for gonadotropins during an estradiol-induced preovulatory-like surge of LH and FSH in ovariectomized ewes

The amount of messenger RNA (mRNA) for luteinizing hormone beta-subunit (LH beta), follicle-stimulating hormone beta-subunit (FSH beta) and alpha-subunit was measured during estradiol-17 beta (E) positive feedback in ovariectomized (OVX) ewes. During the anestrous season, OVX ewes were given an i.m. injection of E (25 micrograms: n = 5) or oil (control; n = 4) and hourly blood samples were collected for 16 hr. After blood collection, ewes were killed and anterior pituitary glands were removed for analysis of hormone and mRNA content. Preovulatory-like increases in serum concentrations of LH and FSH were measured in E-treated OVX ewes. In two E-treated OVX ewes the serum concentrations of LH and FSH were still increasing, whereas in the remaining three E-treated OVX ewes, serum concentrations of LH were on the decreasing portion of the E-induced preovulatory-like surge. Pituitary content of LH was lower (P less than .10) in E-treated OVX ewes when serum concentrations of LH were decreasing than that measured in control ewes or E-treated OVX ewes in which serum concentrations were still increasing. Pituitary content of FSH and prolactin were similar (P greater than .05) among all groups. The amount of mRNA for LH beta-subunit was similar (P greater than .05) in ewes in which serum concentrations of LH were increasing and in control ewes, but was lower (P less than .05) in ewes with decreasing levels of LH. The amount of mRNA for FSH beta-subunit was lower (P less than .05) in all E-treated OVX ewes (independent of whether serum concentrations of FSH were increasing or decreasing) than that measured in control ewes. There was no difference (P greater than .05) in the amount of mRNA for alpha-subunit among any groups. Thus, amounts of mRNA for the beta-subunits of gonadotropins are reduced, while amounts of mRNA for alpha-subunit are unchanged during estradiol positive feedback in OVX ewes.     

Basal and GnRH induced secretion of FSH and LH in ovariectomized ewes treated with bovine follicular fluid

Ovariectomized (OVX) ewes were injected with 5 ml of either bovine serum, charcoalextracted bovine follicular fluid (FF), or whole bovine FF. Five hours after this pretreatment, ewes on each pretreatment were injected with either 0, 1, or 5 μg of GnRH. Ewes that were pretreated with either type of FF had decreased concentrations of FSH regardless of dose of GnRH when compared to ewes pretreated with bovine serum. There was no effect of charcoal extraction. There were no differences among the pretreatment groups in LH response to GnRH. In a second experiment, OVX ewes were pretreated (4 ml) with either bovine serum or bovine FF 5 hr prior to GnRH or with bovine FF 42, 30 and 18 hr prior to GnRH. Ewes were injected with either 0 or 5 μg of GnRH. Pretreatment with FF for 5 or 42 hr prior to GnRH resulted in significantly decreased concentrations of FSH both at the time of GnRH treatment and during the following 2 hr. Concentrations of LH did not differ among pretreatment groups. In a third experiment, OVX ewes were pretreated with either bovine serum or bovine FF 30, 18 and 5 hr prior to GnRH. Ewes were injected with either 0, 5 or 50 μg of GnRH. Pretreatment with FF resulted in decreased concentrations of FSH both at the time of GnRH treatment and during the following 2 hr. Concentrations of LH were also decreased at the time of GnRH treatment.     

GDF9基因多态性对山羊血清FSH和LH水平的影响

为了研究GDF9基因多态性与多胎山羊血清促卵泡素(follicle stimulating hormone,FSH)和促黄体素(lutein hormone,LH)水平的关联,试验选择经GDF9基因型鉴定后的自然发情健康经产安徽白山羊母羊80只,采集血样,应用PCR-SSCP检测GDF9基因的多态性,用全自动化学发光免疫分析法(CLIA)测定FSH和LH水平。结果表明:安徽白山羊群体中GDF9基因外显子存在2个SNPs,均出现3种基因型,在EF4461682:c.1956AC位点,不同基因型母羊外周血中FSH水平无明显差异,但CC型外周血中LH水平高于AA型(P005)。CC型和AC型产羔数(LSM)没有差异,但都显著高于AA型(P005);在EF4461682:c.3319GA位点,AA型外周血中FSH水平显著高于GG型(P005);AA型外周血中LH水平极显著高于GA和GG型(P001),GA型外周血中LH水平显著高于GG型(P005)。AA型平均产羔数LSM极显著高于AG型和GG型(P001),AG型平均产羔数LSM极显著高于GG型(P001)。由此得知,GDF9基因作为影响安徽白山羊产羔数的主效基因之一,其功能表达对FSH和LH水平起着重要影响。     

Effects of estradiol on secretion of LH, hypothalamic function and testicular development in bull calves

Two experiments were conducted in order to determine the effects of estradiol (E₂) on the development of the hypothalamic-pituitary-testicular axis in bull calves. In experiment 1, calves were assigned randomly to one of the following groups: 1) intact, 2) intact E₂-treated, 3) castrated, or 4) castrated E₂-treated. Treatments began when the calves were 7.5 wk of age and continued for 16.5 wk. Samples of blood were collected once a week from 3 to 14 wk of age and every 10 min for 6 hr at 8, 12 and 16 wk of age. Concentrations of E₂ in plasma decreased between 3 and 4 wk of age and were further reduced by castration. Maximum concentrations of E₂ (24.3 pg/ml) were observed 72 hr after insertion of E₂ implants, however, plasma E₂ stablized at 5–9 pg/ml by 2 wk after insertion of implants. Treatment with E₂ eliminated the pulsatile secretion of LH in intact and castrated calves and retarded testicular growth. In experiment 2, calves were assigned to a control (n=4) or E₂-treated (n=6) group. Implants of E₂ were inserted at 7.5 wk of age. At 24 wk of age, calves were bled and then sacrificed to collect hypothalamic and pituitary tissues. Age-related changes in testicular weight and secretion of LH were blocked by E₂. Neither the morphology nor the intensity of immunostaining of GnRH nerve cell bodies in the preoptic area (POA) were affected by E₂. However, the density of GnRH fibers and beads in the stalk median eminence (SME), and concentrations of pituitary GnRH receptors were greater (P<.01) in E₂-treated compared to control calves. In addition, concentrations of norepinephrine (NE) in the SME were lower in E₂-treated calves when compared to controls. Based on these observations, it is concluded that administration of E₂ at 7.5 wk of age causes profound alterations in hypothalamic function including, changes in metabolism of NE and suppression of GnRH release.     

Effect of cerebroventricular infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in diet-restricted ewes

The objective was to determine the effect of central infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in the ewe. Twenty-two ovariectomized ewes (32 wk of age) were fitted with two lateral cerebroventricular (LCV) cannulae and fed 33% of NRC requirements for 8 wk. Ewes (n> or =5/group) were then infused, via LCV cannulae, with artificial cerebrospinal fluid (aCSF) or aCSF containing physiological concentrations of insulin (INS), glucose (GLU), or INS + GLU; the mass of each increasing linearly from Day 0 (mass = 0 units/h) to Day 8 (mass of INS = 80 mIU/hr and GLU = 10 mg/hr). Jugular serum was collected every 12 min for 4 hr on Days 0, 2, and 4. Ewes treated with INS or INS + GLU had greater (P<0.06) mean concentrations of LH than aCSF treated ewes on Day 2 (13.8+/-1.8 and 12.5+/-1.3 > 8.0+/-3.3 ng/ml). Furthermore, on Day 4, concentrations of LH in INS treated ewes exceeded that (P<0.07) of aCSF treated ewes (14.8+/-2.0 > 7.4+/-3.0 ng/ml). Expression of NPY mRNA did not differ between treatments (P = 0.87). Leptin receptor mRNA expression was dramatically reduced (P<0.0002) in INS+GLU versus aCSF treated ewes. These data provide evidence to suggest that insulin may be an important component of hypothalamic mechanisms regulating secretion of LH and expression of leptin receptors in undernourished ruminants.     

Gonadal regulation of LH secretion in prepubertal bull calves

In the present study we examined the influence of castration and exogenous estradiol on pulsatile LH release during the transition from infancy to the prepubertal period of development. Bull calves were assigned to treatments (N = 5 treatment) at 6 weeks of age. Treatments consisted of intact controls, castrates and castrates receiving estradiol implants. Plasma LH response was monitored over 8 hr periods at 7, 8, 9, 10, 11 and 13 weeks of age. Castration alone did not alter LH concentrations, compared to controls until 10 weeks of age. At 10, 11 and 13 weeks, mean LH concentration and the number of LH pulses/8 hr period were greater (P less than .05) in castrates than in controls. In castrates with estradiol implants, mean LH concentration and the number of LH pulses/8 hr period were suppressed at all ages compared to controls and castrate treatments. These results indicate that LH release is not inhibited by gonadal factors from 6 to 9 weeks of age in the bull calf. However, estradiol negative feedback on LH secretion is evident during this same developmental period.     

小尾寒羊复旧期子宫组织内胶原纤维的研究

从细胞、亚细胞水平来揭示羊子宫复旧过程中的组织学变化规律。用透射电子显微镜(TEM)对9只产程正常、健康的小尾寒羊子宫复旧期间子宫结缔组织内胶原纤维的变化进行了研究。试验结果表明:在产后1~7d,胶原纤维排列不规则,胶原呈片段存在,其内部溶解形成形态各异的空腔;从分娩第13天开始,胶原片段数量减少,排列较规则;到产后第25天时,胶原纤维束纵横交错排列,横纹清楚,无胶原片段。     

Effects of estradiol-17β, para-chlorophenylalanine and quipazine on tonic and LHRH-induced secretion of luteinizing hormone in ovariectomized ewes

Changes in metabolism of serotonin (5-HT) might mediate the reduced tonic luteinizing hormone (LH) and increased pituitary responsiveness to luteinizing hormone releasing hormone (LHRH) caused by estradiol-17β (estradiol). Two experiments were conducted to determine effects of estradiol, para-chlorophenylalanine (PCPA), an inhibitor of synthesis of 5-HT, and quipazine, an agonist of 5-HT, on tonic and LHRH-induced secretion of LH in ovariectomized ewes during the summer. Tonic levels of LH were reduced, the interval from LHRH to peak of the induced surge was longer and the magnitude of release of LH was greater in ovariectomized ewes treated with estradiol than in controls. Neither PCPA nor quipazine affected tonic secretion of LH. In ovariectomized ewes not receiving estradiol, PCPA and quipazine increased the magnitude of the LHRH-induced release of LH. However, PCPA reduced pituitary sensitivity to LHRH when administered concomitantly with estradiol; treatment with quipazine attenuated this effect of PCPA. The interval to the peak of the induced surge of LH was not affected by PCPA or quipazine in estradiol-treated or control ovariectomized ewes. Based on these results it appears that 5-HT mediates or is required for estradiol to increase pituitary responsiveness to LHRH.     

Effects of estradiol-17 beta, naloxone and gonadotropin releasing hormone on postpartum secretion of luteinizing hormone in fall-lambing ewes

The interaction among exogenous estradiol-17 beta, naloxone and gonadotropin releasing hormone (GnRH) in the control of luteinizing hormone (LH) secretion was studied in intact postpartum ewes nursing their offspring. One-half of 30 fall-lambing ewes were implanted subcutaneously with an estradiol-17 beta containing Silastic capsule between postpartum d 1 and 12 which doubled their serum concentrations of estradiol (16.0 +/- .1 vs 8.4 +/- .1 pg/ml). Blood samples were collected from implanted and non-implanted ewes at 15-min intervals for 5 h on d 3, 8, 13, 20 and 28 postpartum. Pre-injection samples were collected for 1 h, and ewes were injected with saline, naloxone (NAL;1 mg/kg) or GnRH (100 micrograms/ewe). When averaged across all days and implant groups, serum LH in the three post-NAL samples was higher (P less than .05) than in the three pre-NAL samples (3.6 +/- 1.2 vs .6 +/- .2 ng/ml). Post-GnRH concentrations of serum LH were lower (P less than .05) in estradiol-implanted ewes than in non-implanted ewes on d 8 and 13, but there were no differences in any LH characteristics on d 20 and 28 after implant removal on d 12. In non-implanted ewes, serum LH responses to GnRH increased (P less than .05) eightfold from d 3 (3.8 +/- 1.4 ng/ml) to d 8 (31.6 +/- 1.4 ng/ml), remained elevated through d 20, but declined by d 28 (10.8 +/- 1.4 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of orexigenic peptides and leptin on melatonin secretion during different photoperiods in seasonal breeding ewes: an in vitro study

The pineal gland (PG) acts as a neuroendocrine transducer of daily and seasonal time through the nocturnal release of melatonin. Here, we examined the interaction of season, orexin, ghrelin, and leptin on melatonin secretion by pineal explants in short-term culture. Glands were collected after sunset from 12 ewes during long days (LD; April and May) and from an additional 12 ewes during short days (SD; October and November). Glands were transected sagittally into strips, with each equilibrated in 2.5 mL of Dulbecco's modified Eagle's medium for 60 min, followed by a 2-h incubation in control medium or medium containing orexin B (10 and 100 ng/mL), ghrelin (10 and 100 ng/mL), or 50 ng/mL of leptin. After a 3-h incubation, some PG explants treated previously with lower doses of orexin or ghrelin were challenged with 50 ng/mL of leptin and those treated with both doses of orexin were challenged with 300 nM of the β-agonist isoproterenol. One milliliter of medium was harvested and replaced from each well every 30 min. Treatment with the low dose of orexin during LD increased melatonin secretion about 110% (P<0.01); treatment with a high dose increased melatonin secretion about 47% (P<0.001). During the SD period, leptin stimulated (P < 0.05) melatonin secretion slightly compared with mean melatonin concentration in controls. However, together, orexin and leptin depressed (P<0.01) melatonin secretion. Both doses of ghrelin reduced (P < 0.01) melatonin concentration during the SD season compared with control culture. Addition of ghrelin and leptin to culture medium increased (P<0.01) melatonin concentration compared with ghrelin-treated culture and decreased melatonin concentration (P<0.01) compared with leptin-treated culture during SD. Isoproterenol stimulated (P<0.01) melatonin secretion compared with values observed during the pretreatment period. We conclude that orexigenic peptides (orexin B and ghrelin) and an anorectic peptide (leptin) affect PG directly. The responses of PG to those hormones depend on day length. Moreover, secretion of melatonin from the ovine PG is under an adrenergic regulation.     

Effects of idazoxan, tolazoline, and yohimbine on xylazine-induced respiratory changes and central nervous system depression in ewes

We compared the ability of 3 alpha 2-adrenoreceptor antagonists, idazoxan (0.05 mg/kg), tolazoline (2 mg/kg), and yohimbine (0.2 mg/kg) to reverse xylazine (0.3 mg/kg)-induced respiratory changes and CNS depression in 6 ewes. Once weekly, each ewe was given a random IV treatment of xylazine, followed in 5 minutes by either an antagonist or 0.9% NaCl solution. Xylazine alone caused recumbency for 54.2 +/- 5.3 minutes (mean +/- SEM). Xylazine also increased respiratory rate and decreased PaCO2 for at least 45 minutes, but did not significantly change arterial pH or PaCO2. Idazoxan and tolazoline were equally effective in reversing the respiratory actions of xylazine; however, yohimbine was less effective in reducing the respiratory rate and was ineffective in antagonizing the decreased PaO2. Idazoxan and tolazoline decreased the duration of xylazine-induced recumbency to 6.3 +/- 0.6 and 9.5 +/- 2.3 minutes, respectively, whereas yohimbine did not significantly change this effect of xylazine. Thus, at the dosages studied, idazoxan and tolazoline appeared to be more effective than yohimbine in reversing the respiratory and CNS depressant actions of xylazine in sheep.     

Regulation of pulsatile LH secretion by ovarian steroids in the heifer

Two experiments were conducted to evaluate relationships among luteinizing hormone (LH), estradiol-17 beta (E2) and progesterone secretion during the preovulatory period in the heifer after prostaglandin F2 alpha (PGF2 alpha)-induced regression of the corpus luteum. A second objective was to elucidate the effects of E2 in regulating LH secretion. In Exp. 1, LH, E2 and progesterone concentrations were determined in serial samples collected during the preovulatory period after PGF2 alpha-induced luteal regression in five Red Angus X Hereford heifers. Progesterone declined to 1 ng/ml by 12 h after the second injection of PGF2 alpha. Frequency of LH pulses increased linearly (P less than .01), whereas no change in amplitude of LH pulses was detected before the preovulatory LH surge. This resulted in a linear increase (P less than .01) in mean LH concentrations. Estradiol also increased in a linear manner (P less than .01), and the rise in E2 was parallel to the increase in mean LH concentrations. In Exp. 2, 12 Angus X Hereford heifers were ovariectomized and administered either 13.5- or 27-cm silastic implants containing E2 at ovariectomy. Four heifers served as nonimplanted controls. Thirty-one days after ovariectomy all heifers were bled at 12-min intervals for 6 h. Frequency of LH pulses declined linearly (P less than .03) while mean LH (P less than .09) and pulse amplitude (P less than .01) increased linearly as E2 dose increased. These results indicate that a reduction in progesterone increases the frequency of LH pulses during the follicular phase of the estrous cycle in cattle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The secretion of luteinizing hormone in ewes of Finnish landrace during estrus

The secretion of luteinizing hormone in ewes of Finnish Landrace during estrus. Acta vet. scand. 1979, 20, 216–223. — Luteinizing hormone immunoreactivity was measured in the venous plasma of four cycling Finnish Landrace sheep during the breeding season in connection with one synchronized estrus and the subsequent one. The ewes were slaughtered after the second estrus to establish the number of ovulations. To determine the LH concentration, a heterologous method of assay was used; this was based on the cross reaction of sheep plasma LH in a human LH radioimmunoassay system.As a result of the investigation, it was found that the peaks of LH were lower during the time of synchronized estrus and that these peaks occurred earlier than in the subsequent estrus. However, the differences were not statistically significant. On account of the limited material, the effect of the occurrence of the LH peak on the number of ovulations could not be established.