Isolation of Ovulation-inducing Factors in the Seminal Plasma of Bactrian Camel (Camelus bactrianus) by DEAE-cellulose Chromatography

Ovulation in the Bactrian camel ( Camelus bactrianus ) depends upon the ovulation-inducing factor in the seminal plasma; however, little research has been conducted to isolate and identify the factor. The current study attempts to isolate and identify the bioactive fractions from the seminal plasma of Bactrian camel. The seminal plasma was fractionated by diethylamino-ethylcellulose (DEAE)-cellulose chromatography and five protein fractions were obtained. The bioactive of each fraction was estimated by rat pituitary tissue culture in vitro and by the intramuscular injection of the bioactive fraction to the female camels in vivo . The concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the pituitary culture media before and 6 h after the addition of each fraction and in the peripheral blood plasma collected from the camel immediately before and hourly after the injection of the active fraction were measured by radioimmunoassay. The results demonstrated that the third fraction (L3) had the bioactive potential to stimulate the release of LH in vitro from 11.82 ± 1.77 to 25.63 ± 3.84 mIU/ml after the addition of L3 to the culture media. The in vivo concentrations of LH in the blood plasma of the camel increased from 6.43 ± 0.14 before to 15.50 ± 2.64 ng/ml 6 h after injection of L3. However, the concentrations of FSH did not show any significant changes either in vitro or in vivo . The results clearly demonstrated the existence of LH-releasing associated fractions in the seminal plasma that appears to be separated by DEAE-cellulose matrix and the isolated L3 fraction might be the ovulation-inducing factor or one of its components.     

初情期前母猪垂体细胞LH和FSH的释放及其对GnRH类似物的反应

利用垂体细胞单层培养模型研究了30，60，90，120和150日龄北京黑猪母猪垂体细胞LH和FSH的释放及其对LRH－A3反应能力。结果表明，猪垂体细胞LH和FSH释放对LRH－A3的反应呈S形剂量依赖型同线。LH基础释放量和LRH－A3刺激的最大释放量在不同日龄间没有显著差异，说明初情期前母猪垂体细胞已达最大LH释放和对GnRH反应的能力。FSH的基础释放量和LRH－A3刺激的最在释放量在30日龄与60日龄之间无差异，但90日龄以后垂体细胞FSH的释施量随日龄增大而降低，提出可能由于垂体在体内时受过抑制素的作用。     

Comparison of the fractionation and assay of domestic duck and fowl pituitary gonadotrophins

1. Pituitary glycoproteins from domestic ducks and fowls were fractionated to separate luteinising hormone (LH) and follicle stimulating hormone (FSH) activities using the same chromatographic steps. 2. Fractions were bioassayed for LH using the release of progesterone from fowl granulosa cells and for thyroid stimulating hormone (TSH) by measuring the release of thyroxine in 3-d-old chicks. Follicle stimulating hormone activity was measured either in a cockerel-testes radioreceptor assay or by the release of oestrogen from cultured rat Sertoli cells. 3. Fractions containing predominantly FSH or LH activity were isolated from the fowl glycoproteins. Duck gonadotrophin did not occur in fractions corresponding to those containing fowl FSH. 4. Duck gonadotrophin was found in a fraction corresponding with the most highly purified fowl LH fraction. A duck LH fraction was found with little FSH activity for which there was no corresponding fowl LH fraction. 5. It is concluded that domestic fowl and duck gonadotrophins have different chromatographic properties. Further study is required to determine whether the purified duck gonadotrophin preparation comprises proteins with similar physico-chemical properties but with separate FSH and LH biological activities.     

The Concentrations of LH,FSH, Oestradiol-17β and Progesterone in the Blood Plasma of the Female Bactrian Camel (Camelus bactrianus) before and after Intramuscular Injection of Seminal Plasma

The concentrations of LH, FSH, oestradiol-17beta and progesterone in the blood plasma of the female Bactrian camel (Camelus bactrianus) before and after intramuscular injection of seminal plasma.     

哺乳动物精清诱导排卵活性蛋白质研究

在动物的精清里包含一些与动物生殖生理活动密切相关的活性蛋白和多肽。驼科动物的双峰驼、美洲驼、羊驼和澳洲考拉等哺乳动物精清中含有类似促性腺激素释放激素(GnRH)作用的活性蛋白质,诱导排卵因子(ovulation inducing factor,OIF),它能引发外周血液中促黄体素(LH)峰浓度的出现和诱发母畜排卵。OIF被认为是一种新的生物活性蛋白质或潜在的新型激素。甚至报道在牛等自发排卵动物以及人精清中也存在类似的活性蛋白。这类因子的发现对于哺乳动物生殖生理及繁殖的深入研究具有重要的意义,有助于动物克服繁殖障碍及繁殖疾病的治疗等。     

α-Adrenergic control of gonadotropin secretion in the ewe

The effect of the centrally acting α-adrenoceptor agonist, clonidine, on plasma LH and FSH was studied in oestradiol-primed and unprimed ewes and in oestrous ewes. In unprimed anoestrous ewes, clonidine stimulated LH and FSH release after a lag period of 18 h, and noradrenaline intracarotid injection or i.v. infusions immediately stimulated LH release. In oestradiol-infused anoestrous ewes, clonidine produced either a delay or inhibition of the gonadotrophin surge and noradrenaline i.v. infusion advanced the LH surge. In oestrous ewes treated with clonidine, there was marked delay in the LH surge, but the magnitude of the LH and FSH surges were unaffected. Intravenous administration of α-adrenoceptor blockers, phentolamine and phenoxybenzamine, blocked the oestradiol-induced gondotrophin surge in anoestrous ewes. The effect of phenoxybenzamine on gonadotrophin surge was dose dependent in oestrous ewes. Small doses (4 mg/kg i.v.) of phenoxybenzamine delayed the synchronous LH and FSH surges. There was complete blockade of the LH surge and partial blockade of FSH surges in ewes given phenoxybenzamine (8 mg/kg i.v.) before the expected synchronous gonadotrophin surges. After this experiment, the initial rise of plasma progesterone concentrations did not occur until day 6 of oestrous cycle. Administration of phenoxybenzamine before the expected second FSH surge had no effect on the second FSH surge. Gonadotrophin release induced by gonadotrophin-releasing hormone was attenuated by phenoxybenzamine, but not by clonidine. The results suggest that the LH surge is under α-adrenergic control and the first FSH surge is under partial α-adrenergic control, but the second FSH surge is not under α-adrenergic control. The results also suggest oestradiol modulation of α-adrenergic receptor action.     

Effect of unilateral castration and unilateral cryptorchidism on gonadotropin and testosterone response to gonadotropin releasing hormone in the bull

The effects of unilateral castration (UC) and induced unilateral cryptorchidism (UCR) on basal plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, and on the responses of these hormones to gonadotropin releasing hormone (GnRH), were investigated in bulls altered at 3, 6 or 9 months of age. Blood plasma was collected before and after GnRH (200 micrograms) stimulation approximately 1 year following gonadal manipulation. Neither mean baseline concentrations nor GnRH-induced increases in plasma testosterone were altered (P greater than .1) by hemicastration or UCR (P greater than .1). Both mean baseline LH and GnRH-induced LH release were greater (P less than .05) in bulls altered at 3 months of age than in bulls altered at 9 months of age. UC increased (P less than .05) plasma LH response to GnRH over that observed in intact bulls, but not above that in UCR bulls. UCR had no detectable effect on either baseline concentrations or GnRH-stimulated LH release. FSH was increased (P less than .05) in hemicastrates, while UCR had a variable effect on peripheral FSH: FSH was reduced (P less than .05) in UCR animals altered at 3 months of age but increased (P less than .05) in UCR bulls altered at both 6 and 9 months of age when compared to FSH in intact bulls. The results indicate that, compared with intact bulls, UC bulls release increased amounts of both gonadotropins but similar amounts of testosterone in response to GnRH stimulation. UCR had a variable effect on FSH release and did not alter either LH or testosterone.     

Comparison of the ability of the three endogenous GnRHs to stimulate release of follicle-stimulating hormone and luteinizing hormone in chickens

It is well established that GnRH can stimulate the release of LH and FSH in mammals. Two GnRHs have been found in the chicken hypothalamus, cGnRH-I and -II. There is controversy as to whether either peptide can stimulate release of FSH in birds. The present studies compared the ability of cGnRH-I and -II to stimulate the release of FSH and LH in chickens. Lamprey (l) GnRH-III may be a specific-releasing factor for FSH, as it selectively stimulates FSH release in rodents and cattle, and has been detected in the hypothalamus of rodents, sparrows and chickens. Therefore, the ability of lGnRH-III to stimulate LH and FSH release was also examined. In our first experiment, the effects of cGnRH-I and -II were studied using 17-week prepubertal females. Intravenous injection of cGnRH-II at 1 and 10 microg/kg BW significantly increased LH secretion more than did cGnRH-I. Neither peptide significantly increased plasma FSH levels. In our second study, we administered cGnRH-I, -II or lGnRH-III to mature males maintained on a short photoperiod. cGnRH-II was again more potent than cGnRH-I in stimulating LH release, while lGnRH-III produced a modest LH rise. No GnRH peptide provided specific or potent stimulus to FSH secretion, although the high dose of cGnRH-II modestly enhanced FSH levels in the adult male (P < 0.05). Our results are not consistent with the view that lGnRH-III is a specific FSH-releasing hormone across multiple classes of vertebrates. We conclude that the mechanism by which independent release of FSH occurs in chickens remains unresolved.     

双峰驼精清及其活性组分凝集素寡糖的初步研究

应用植物血凝素与寡糖结构相同或相似的糖复合物专一凝集的原理与方法,结合小鼠排卵试验,间接观察了公驼精清及其经ＤＥ－５２离子交换层析和高效液相层析提取分离的活性组分的蛋白组成。结果表明,公驼精清内糖蛋白含有２种以上的寡糖,其内的活性组分及诱导排卵因子与所试植物血凝素不发生反应     

复方中草药添加剂对辽宁绒山羊种公羊生殖激素的影响

将15只年龄(2.60±0.25)岁、体重(43.48±1.46)kg的辽宁绒山羊公羊随机分为3组,试验一组和试验二组分别饲喂10 g/d和15 g/d的复方中草药添加剂,对照组不喂,目的是研究中草药添加剂对种公羊促卵泡素、睾酮和促黄体素的影响。结果表明:试验一组在75 d后,精浆LH、FSH和T均显著(P<0.05)高于对照组,试验二组在75 d后,精浆FSH和T显著(P<0.05)高于对照组;在75 d后,两个试验组血浆FSH极显著(P<0.01)高于对照组,血浆LH、T显著(P<0.05)高于对照组。相关分析表明精浆T(y,ng/l)与LH(x,μg/l)存在显著相关关系,并且对照组、试验一组和试验二组拟合的对数曲线相似;对血浆进行同样分析表明,血浆以上两种激素的变化趋势与精浆相似;从曲线的位置分析试验一组T水平最高。这表明对于本复方中草药添加剂而言,辽宁绒山羊种公羊按照10 g/d的剂量应用即达到了提高生殖激素水平和生产性能的效果。     

HMG和FSH一次性注射青年黄牛的药代动力学比较研究

[目的]人绝经期促性腺激素(HMG)是一种具有促卵泡素(FSH)和促黄体素(LH)活性的蛋白质激素,为了比较HMG和FSH一次性注射青年母牛的药代动力学差异和参数。[方法]本研究选择处于发情间期健康状况良好的青年母黄牛20头,随机分成两组,每头牛按4IU/kg体重肌肉注射HMG或FSH,于激素注射后不同时间段采集血样,分离血清后用放射免疫法测定血液中FSH和LH浓度。[结果]表明注射HMG或FSH后血液中FSH与LH水平呈现先升高后下降的趋势,注射HMG后血液中FSH和LH激素水平达峰时间为6h,然后呈缓慢下降趋势,药代半衰期为18h;注射FSH后血液中FSH和LH激素水平在注射后激素血药达峰时间为0.5h,之后呈下降趋势,药代半衰期为6h。单次注射HMG后,0至144h监测期血液中FSH和LH的血药曲线下面积分别为971.21±342.06和176.28±81.80mIU*hr/mL(P0.05),均显著高于单次注射FSH后同期内血液中FSH和LH的血药曲线下面积(分别为39.81±18.01和32.00±20.92mIU*hr/mL,P0.05)。[结论]在青年黄牛体内HMG比FSH的代谢稳定,其活性成分FSH和LH起作用的时间也较长。     

Study on Regulation of Reproductive Hormones in Danzhou Chicken by FSH and LH

To investigate the regulation of reproductive hormones in Danzhou chicken by follicle-stimulating hormone (FSH) and luteotropic hormone (LH),the concentration of FSH and LH in Danzhou chicken blood were changed by different treatments and the concentration of FSH,LH, prolactin (PRL), progesterone (P), and estradiol (E₂) in the blood were determined using the enzyme-linked immunosorbent assay (ELISA).The results showed that exogenous FSH and LH could improve the concentrations of FSH and LH,respectively. When one of FSH and LH increased alone,the concentration of PRL was significantly decreased (P < 0.05),while it was significantly increased when FSH and LH were both increased (P < 0.05).The high level of the FSH could result the significant increase of E₂ and P (P < 0.05),and it would expand the increasing effect in cooperation with the high concentration of LH. While the high level of the LH could elevate the concentration of E₂ and P,but effect was not significant (P > 0.05).In conclusion,the study suggested that the increase level of FSH or LH could reduce the concentration of PRL in Danzhou chicken,meanwhile,it could increase the concentration of E₂ and P in varying degrees. However,both of the FSH and LH increase in the blood could result the significant increase of E₂ and P as the synergy. When the concentration of E₂ and P were too high,it could stimulate the release of PRL which could adjust the concentration of FSH and LH,and rebalance the concentrations of E₂ and P in the blood.     

Lamprey gonadotropin-releasing hormone-III selectively releases follicle stimulating hormone in the bovine

Recent studies have shown that lamprey gonadotropin-releasing hormone (l-GnRH) is localized in the mammalian brain, and that l-GnRH-III, can selectively induce FSH secretion in the rat both in vivo and in vitro. Consequently, the purpose of this study was to determine if l-GnRH-III could elicit selective FSH release in cattle and compare this response with that to mammalian luteinizing hormone releasing hormone (m-LHRH). Cattle were chosen as the animal model because previous studies have demonstrated that FSH and LH are secreted by separate gonadotropes in that species. For these studies, crossbred cycling heifers were implanted with jugular cannulae and l-GnRH-III was infused either between Days 9–14 or on Day 20 of the estrous cycle. Blood samples were collected both before and following peptide infusion. Our results demonstrate that during Days 9–14 of the estrous cycle (luteal phase), when progesterone levels averaged between 4 and 5 ng/ml, a dose of 0.25 mg of l-GnRH-III induced the release of FSH (P < 0.05), but not LH. A 0.5 mg dose of l-GnRH-III caused a greater release of FSH (P < 0.01), but still did not induce LH release. Higher doses of the peptide were capable of significantly releasing both gonadotropins. Importantly, during the luteal phase, doses of 0.5 and 2 mg of m-LHRH were ineffective in stimulating FSH, but did elicit marked increases (P < 0.001) in LH. Again, progesterone levels averaged 4–5 pg/ml. In order to assess gonadotropin releasing ability of l-GnRH-III at a different phase of the estrous cycle, some animals were administered the peptide on Day 20, when progesterone levels were below 1.0 pg/ml. At this time, the l-GnRH-III induced the release of LH (P < 0.01), but not FSH. Overall, our results demonstrate that l-GnRH-III can selectively induce FSH in cattle during the luteal phase, whereas m-LHRH was ineffective in that regard. Furthermore, the fact that l-GnRH-III can selectively stimulate FSH when serum progesterone is high, and LH when serum progesterone is low, suggests its actions are under strong control of this steroid. We suggest the FSH releasing capacity of l-GnRH-III in cattle could render this peptide useful for enhancement of reproductive efficiency in this species.     

A comparative study on the chemical composition of plasma from the cauda epididymidis, semen fractions, and whole semen in boars

A comparative study was carried out on the chemical composition of plasma from the cauda epididymidis, semen fractions, and whole semen of boars. A total of 22 boars were used in this study. The boars, which ranged in age from 8 to 14 months, were of Swedish Landrace and Swedish Yorkshire breed. All boars used presented a normal semen picture. A dummy sow and an artificial vagina were employed for semen collection. The semen was collected as whole semen and as semen fractions in 10 nil volumes. The contents of the cauda epididymidis was removed post mortem.The following parameters were investigated: sperm concentration, dry weight of spermatozoa and of seminal plasma, osmotic pressure, sodium, potassium, chloride, inorganic phosphorus, calcium, magnesium, total protein, GOT, GPT, and alkaline phosphatase in seminal plasma. Paper electrophoresis was carried out on seminal plasma. Tlxe results of the analysis are summarized in Tables 1–6.The sperm concentration was approximately 3.2 mill./mm3 in the cauda epididymidis, 1 mill./mm³ in the sperm-richest fraction (II) and 0.25 mill./mm3 in whole semen. The dry weight (expressed in per cent dry matter) of spermatozoa was highest in the cauda epididymidis (25.47 %), showing a tendency to decreasing in semen fractions I—IV and was lowest in whole semen (15.29 %). The per cent dry weight in plasma was higher in the cauda epididymidis (4.56 %) than in semen fraction I (2.20 %). In semen fractions I—IV the per cent dry weight rose from 2.20 (U to 4.51 % and reached the level of approximately 3.80 % in the sperm-free fractions V—VII. The osmotic pressure was significantly higher in the cauda epidi-dymal plasma than in the whole seminal plasma or the seminal plasma fractions. The same phenomenon was observed in a boar where the cauda epididymal content was collected in vivo from a patent established fistula. There appears to be a connection between the per cent dry weight of spermatozoa and the osmotic pressure, which means that the per cent dry weight of the cauda epididymal spermatozoa decreases when mixed with the accessory gland secretions, which have a lower osmotic pressure. The fall in per cent dry weights is thought to be caused by an intake of water.The amount of sodium, chloride and magnesium was higher in ejaculated seminal plasma than in cauda epididymal plasma. The reverse was true for inorganic phosphorus and potassium. Moreover the sperm-free fractions contained more sodium, chlorides and magnesium than the sperm-containing fractions, while the concentration of potassium and inorganic phosphorus was comparatively higher in the sperm-containing fractions. A connection is apparent between sperm concentration and the potassium, inorganic phosphorus and magnesium levels. Statistical analysis of the values of chloride and magnesium revealed significant differences between individual boars for most of the semen fractions.The concentration of plasma proteins in the cauda epididymidis was approximately the same as in whole semen and in the semen fractions except for fraction I, which contained a relatively low concentration. As regards total protein there were significant differences between individual boars in most of the semen fractions as well.The paper electrophoretic pattern of epididymal plasma was different from that of semen plasma. Thus there were three or four distinct components in the cauda epididymidis numbered 1, 2, 3, and 4, and three distinct components in whole seminal plasma numbered 3, 4, and 5, while the sperm-richest semen fractions contained four components (2, 3, 4, and 5) and the others three components, namely 3, 4, and 5.The level of GOT was high in the cautlu cpiflidymill contents (99.1 i. u./ml) compared with that for whole seminal plasma (99.1 i.u/ml). In semen fractions there was a clear positive correlation between the level of GOT and the sperm concentration. The GPT concentration wis as a whole low and. in contrast to GOT. somewhat higher in the sperm-free fractions than in the sperm-containing fractions. The concentration of alkaline phosphatase was very high in cauda epididymal plasma (31,463 i. u./ml) as well as in the sperm-rich fractions (e.g. 7,096 i. u./ml in fraction II). Preliminary investigation has moreover revealed a very low alkaline phosphatase concentration in seminal plasma of vasectomized boars, which condition suggests thai the main origin for alkaline phosphatase in boars is the testis and epididymis.     

Increased secretion of luteinizing hormone in prepuberal ewes treated with an antagonist of opiates

The effect of intramuscular injection of naloxone, an antagonist of opiatergic actions, on serum concentrations of luteinizing hormone (LH) and ovarian activity in prepuberal ewes was investigated. Naloxone stimulated release of LH over a period of approximately 3 h. Subsequently, serum concentrations of LH did not differ from controls. Serum concentrations of estradiol-17β were elevated 8 h after treatment with naloxone. Ewe lambs did not ovulate. Endogenous opioid peptides may be involved in the regulation of secretion of LH in immature female sheep.     

Induced gonadotropin release in adrenocorticotropin-treated bulls and steers

The effect of adrenocorticotropin hormone (ACTH) on plasma cortisol and on gonadotropin releasing hormone (GnRH)-induced release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone was determined in nine Holstein bulls and 12 Holstein steers. Treatments consisted of animals receiving either GnRH (200 micrograms, Group G), ACTH (.45 IU/kg BW, Group A) or a combination of ACTH followed 2 h later by GnRH (Group AG). Group G steers and bulls had elevated plasma LH and FSH within .5 h after GnRH injection and plasma testosterone was increased by 1 h after GnRH injection in bulls. In Group A, plasma cortisol was elevated by .5 h after ACTH injection in both steers and bulls, but plasma LH and FSH were unaffected. In Group A bulls, testosterone was reduced after ACTH injection. In Group AG, ACTH caused an immediate increase in plasma cortisol in both steers and bulls, but did not affect the increase in either plasma LH or FSH in response to GnRH in steers. In Group AG bulls, ACTH did not prevent an increase in either plasma LH, FSH or testosterone in response to GnRH compared with basal concentrations. However, magnitude of systemic FSH response was reduced compared with response in Group G bulls, but plasma LH and testosterone were not reduced. The results indicate that ACTH caused an increase in plasma cortisol, but did not adversely affect LH or FSH response to GnRH in steers and bulls. Further, while testosterone was decreased after ACTH alone, neither ACTH nor resulting increased plasma cortisol resulted in decreased testosterone production in the bull after GnRH stimulation.     

促卵泡素和促黄体生成素对儋州鸡生殖激素调控规律的研究

为研究促卵泡素（FSH）和促黄体生成素（LH）对儋州鸡体内其他生殖激素的调控规律,本试验通过改变FSH和LH在儋州鸡血液中的浓度,并采用双抗体一步夹心法酶联免疫吸附试验（ELISA）对处理前后儋州鸡血液中FSH、LH、催乳素（PRL）、孕酮（P）、雌二醇（E₂）的浓度进行测定。结果发现,注射外源性FSH和LH分别能提高儋州鸡血液中FSH和LH浓度;当儋州鸡血液中FSH或LH浓度显著升高时则均能引起PRL浓度显著降低（P < 0.05）,但当FSH和LH浓度同时显著升高时,PRL浓度显著升高（P < 0.05）;当儋州鸡血液中FSH浓度显著升高时,E₂及P浓度显著提升（P < 0.05）,且在高浓度LH的协同下提升幅度更大;当儋州鸡血液中LH浓度显著升高时E₂及P浓度升高但不显著（P > 0.05）。本研究结果表明,儋州鸡血液中FSH或LH浓度的提高均能降低PRL的浓度,并能不同程度的提升E₂及P的浓度,但FSH与LH浓度同时提高则能通过协同作用刺激E₂及P浓度的大幅提升,当E₂及P浓度过高时能通过刺激PRL的释放,负反馈调节血液中FSH与LH,并恢复血液中E₂及P浓度。     

An improved method for the purification of blood cells of turkeys

Methods were developed to purify monocytes, heterophils, or erythrocytes from the whole blood of turkeys. After the bulk of thrombocytes was removed by centrifugation, blood was fractionated over a Ficoll-Hypaque discontinuous gradient. Five fractions were harvested separately, and two were further purified by attachment to a plastic surface and/or by lysis of erythrocytes. The monocyte fraction contained 41% +/- 1% monocytes, and the heterophil fraction contained 96% +/- 1% heterophils. The erythrocyte fraction showed a purity of 99.4% +/- 0.3%. These methods would be useful for various in vitro studies that require purified populations of blood cells.     

On the negative feedback regulation of gonadotropins in castrate and intact cattle with comparison of two FSH radioimmunoassays

Two homologous radioimmunoassays for bovine follicle stimulating hormone (bFSH) were utilized in comparing the differential regulation of FSH and luteinizing hormone (LH) in response to ovariectomy or administration of gonadal steroids in cattle. There appeared to be significant LH cross-reactivity in one of the bFSH systems (bFSH-HS-2-17), but not in the other (bFSH-BP3). Concentrations of FSH in plasma measured by these two systems suggested both qualitative and quantitative differences. Following ovariectomy in heifers, LH concentrations in plasma were increased by 7.5 h, while FSH (measured in the bFSH-BP3 system) was not significantly elevated until 18 h. Administration of 200 micrograms of estradiol-17 beta to ovariectomized heifers inhibited levels of FSH in plasma but large doses of testosterone (100 mg), androstenedione (400 mg) and dihydrotestosterone (800 mg) had no effect. Similarly, LH was not affected by the androgens, while estradiol induced LH surges, leading to increased mean LH concentrations. In contrast to the results in heifers, LH concentrations in plasma from steers were inhibited by administration of androgens as well as by estradiol. In steers, FSH (bFSH-BP3) was marginally inhibited by estradiol and not at all by the androgens. Differences in the secretory patterns of FSH and LH also occurred in intact heifers during the estrous cycle. The 72-h period preceding estrus (follicular phase) was characterized by rapidly declining serum progesterone concentrations, followed by concurrent increases in both LH and estradiol. The circulating levels of bFSH (BP3) tended to decline during this interval. Overall, during the estrous cycle, progesterone levels were positively correlated with bFSH-BP3 (r = .37) and negatively correlated with LH (r = -.39). The gonadotropins were not significantly related (r = -.15). These relationships are consistent with the concept that LH controls the final stages of follicular development in cattle and that FSH may exert only a permissive effect.