Biomedical subjects

D L Foster

Publications and source records attributed to D L Foster.

At least 37 records · Page 2Linked to original sources

PubMed1998

Glucose availability modulates the timing of the luteinizing hormone surge in the ewe.

To determine if glucose availability modulates the timing of the positive feedback action of oestrogen on gonadotropin secretion, we monitored the estradiol-induced luteinizing hormone (LH) surge in sheep (n = 5/group) made transiently hypoglycemic by insulin. Experiment 1 determined an effective insulin treatment, one which would depress tonic LH secretion. Two injections of insulin (5 IU/kg iv) 4 h apart were found to induce extended hypoglycemia (10-13 h) and to decrease the LH pulse frequency for 8 h (5.0 +/-0.32 pulses/4 h before versus 2.5+/-0.34 pulses/4 h after insulin; P<0.05; mean +/- SEM). Using this same paradigm, experiment 2 determined the influence of the transient hypoglycemia on the LH surge mechanism. In control sheep, estradiol (subcutaneous implants at hour 0) evoked an LH surge with a latency period of 12.4+/-0.5 h. When insulin was administered either before (hours -4 and 0) or after the estradiol stimulus (hours 4 and 8, or 12 and 16), the onset of the LH surge was delayed to 29.0+/-2.4 h (average of all three time groups, P <0.05). Infusion of glucose from hours 12-30, along with insulin, prevented hypoglycemia and restored the normal timing of the oestrogen-induced LH surge to that of controls (15.4+/-0.93 h, P>0.05). These findings suggest that not only is the tonic mode of LH secretion sensitive to metabolic fuel availability, but the surge mode of LH secretion is as well.

Animals↗

PubMed1998

Second trimester screening for Down's syndrome using maternal serum dimeric inhibin A.

OBJECTIVES: To determine the second trimester Down's syndrome screening performance of maternal serum dimeric inhibin A, both alone and in combination with existing serum markers. SETTING: A case-control set of serum samples from patients with Down's syndrome (52) and subjects with matched unaffected pregnancies obtained in a previous cohort study before second trimester amniocentesis and karyotyping. The amniocenteses were performed for reasons other than a positive serum screening test result. METHODS: For each serum from a Down's syndrome pregnancy, five serum samples from pregnancies with a normal karyotype were matched for recruitment centre, gestational age, maternal age, and date of amniocentesis. A specific form of inhibin (dimeric inhibin A) was measured using monoclonal antibodies. Measurements of alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin and its free beta subunit were already available. Screening performance was modelled using distribution variables of the analytes coupled with the 1993 age distribution of pregnant women in the United States. RESULTS: The median dimeric inhibin A level was 2.10 times higher in Down's syndrome pregnancies. When dimeric inhibin A was combined with maternal age and three other serum markers (alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin) the Down's syndrome detection rate increased to 75% (from 66%) at a 5% false positive rate. If dimeric inhibin A could be added for less than $31 (ranging from $16 to $39 depending on the detection rate, markers chosen, and method of dating), the cost of detecting each Down's syndrome pregnancy and the number of procedure related fetal losses would both be reduced. CONCLUSIONS: The addition of dimeric inhibin A to prenatal screening programmes for Down's syndrome should be considered, or possibly it could be substituted for an existing serum marker. One barrier to implementation in the United States, however, is the unavailability of kits with Food and Drug Administration approval.

Case-Control Studies↗

PubMed1998

Evidence for GnRH regulation by leptin: leptin administration prevents reduced pulsatile LH secretion during fasting.

Administration of leptin during undernutrition improves reproductive function, but whether this occurs at the level of the brain, pituitary, or gonads is not yet clear. The present study tested the hypothesis that one important mechanism is the control of pulsatile gonadotropin-releasing hormone (GnRH) secretion. Our approach was to determine if leptin could prevent the marked suppression of pulsatile luteinizing hormone (LH) secretion which occurs during fasting. Leptin (3 micrograms/g i.p.; three times/48 h) or vehicle was administered during a 48-hour fast in adult ovariectomized and estrogen-treated ovariectomized rats (n = 5-7/group). LH was measured in blood samples collected every 6 min for 2 h before and after fasting. In vehicle-treated animals, plasma insulin and leptin levels decreased after fasting. As expected, the LH pulse frequency also decreased markedly. When circulating leptin remained artificially elevated during fasting, the suppression of LH pulse frequency did not occur. Leptin treatment maintained a high LH pulse frequency in the presence or absence of estrogen. The finding that leptin modulates LH pulse frequency indicates that this fat-derived hormone conveys information about nutrition to mechanisms which regulate pulsatile gonadotropin-releasing hormone secretion. Because this occurs in the absence of estrogen, the mechanism does not necessarily involve modulation of negative feedback.

Animals↗

PubMed1998

Sexual differentiation of reproductive neuroendocrine function in sheep.

In many species, the timing of puberty is different in males and females. This does not simply reflect differences in the time course of activation of the testes and ovaries. Rather, sex differences in pubertal onset reside within brain mechanisms controlling GnRH secretion, as exemplified by studies conducted in sheep. Exposure of sheep fetuses to testicular steroids alters the timing of puberty, principally by reducing photoperiod responsiveness. This is manifest as an early increase in LH secretion in males or in females exposed experimentally to testosterone before birth. Steroids also act on non-photoperiodic mechanisms to abolish the preovulatory gonadotrophin surge. In view of these multiple organizational actions of steroids to control postnatal gonadotrophin secretion, it is becoming clear that there are many critical periods of brain development for organizing the GnRH neurosecretory system, and that these may be sensitive to different testosterone metabolites. Although GnRH neurones are not sexually dimorphic with respect to number, distribution or gross morphology, fundamental questions remain as to how steroids exert their effects at the cell through actions on GnRH afferents. Teleologically, these early sex-specific changes in mechanisms timing puberty maximize the chance that reproductive activity will ultimately be successful in each sex.

Androgens↗

PubMed1997

Regional differences in the distribution of gonadotropin-releasing hormone cells between rapidly growing and growth-restricted prepubertal female sheep.

Growth retardation induced by dietary restriction in the lamb results in a low GnRH pulse frequency, and thus, puberty is delayed. In our experimental model, in which ovariectomized lambs are maintained at weaning weight (approximately 20 kg BW), hypothalamic GnRH is present and releasable, suggesting that central mechanisms limit the release of GnRH during chronic growth restriction. Our study compared the number and distribution of GnRH-containing neurons in growth-restricted (n = 5) and rapidly growing (n = 5) ovariectomized prepubertal female lambs at 24 weeks of age (normal age of puberty is about 30 weeks). Immunoreactive cells were labeled using LR-1 antiserum (R. Benoit) and an avidin-biotin-immunoperoxidase procedure. GnRH neurons were localized in 60-micron coronal sections from the level of the diagonal band of Broca to the mammillary bodies. The estimated total number of GnRH neurons in the growth-restricted and rapidly growing lambs was similar (3364.8 +/- 513.8 vs. 3151.2 +/- 279.8, respectively). In addition, the percent distributions of GnRH neurons in the diagonal band of Broca, the anterior hypothalamus, the lateral hypothalamus, and the posterior hypothalamus were not different. A trend (P = 0.07) toward a smaller percent distribution in the preoptic area was noted in growth-restricted lambs (30.6 +/- 3.6) compared to rapidly growing lambs (44.0 +/- 5.2). By contrast, the percent distribution of GnRH neurons in the medial basal hypothalamus was significantly greater in the growth-restricted lambs compared with the rapidly growing lambs (17.7 +/- 2.2 vs. 6.7 +/- 1.4, respectively; P < 0.005). It is of interest that the percent distribution of GnRH-containing neurons in the medial basal hypothalamus of the hypogonadotropic growth-restricted lamb is similar to that observed in the fetal lamb, whereas the eugonadotropic rapidly growing lamb is more similar to the adult female. In this context, decreased GnRH secretion and delayed puberty during diet-induced growth restriction may arise from alterations in the GnRH neurosecretory system.

Animals↗

PubMed1997

Prenatal androgens time neuroendocrine puberty in the sheep: effect of testosterone dose.

In sheep, prenatal exposure to androgens during a critical period for sexual differentiation of the brain (30-90 days of gestation; 145 days is term) can advance the timing of puberty in females and prevent the preovulatory LH surge. The present study tests the hypothesis that in sheep, the timing of neuroendocrine sexual maturation is related to the amount of prenatal steroid exposure. In addition, we determined if different steroid requirements exist for sexual differentiation of the tonic and surge modes of gonadotropin secretion. Testosterone was administered weekly to three groups of pregnant ewes from days 30-90 of gestation at doses of 200, 80, or 32 mg/week. The resulting androgenized female lambs together with control males and females (n = 5-7/group) were gonadectomized at 3 weeks of age, and gonadal steroids were replaced with a SILASTIC brand estradiol-filled capsule. LH concentrations were measured from biweekly blood samples. Sustained increases in circulating LH were considered to reflect the initiation of neuroendocrine puberty. In male lambs, LH secretion started to increase at 8.3 +/- 0.9 weeks of age (mean +/- SEM). The two highest doses of prenatal androgen advanced the onset of neuroendocrine sexual maturation in females. In the 200 mg androgenized females, the pubertal LH rise (10.2 +/- 2.0 weeks) began about the same time as in males. In the 80 mg treatment group, LH concentrations increased at 16.2 +/- 1.5 weeks, which was later than in males, but well before that in normal females (27.1 +/- 0.7 weeks). For females treated with the lowest dose of androgen (32 mg), the pubertal LH increase (24.6 +/- 1.9 weeks) began about the same time as in normal females. To test the function of the LH surge system, LH was measured every 2 h for 60 h after an acute increase in circulating estradiol was produced by implanting additional estrogen capsules. All control females produced a surge in response to acute estradiol stimulation. LH surges did not occur in males, 200 mg androgenized females, or 80 mg androgenized females. Of six females from the 32 mg treatment group, two produced LH surges in response to the stimulatory feedback action of estradiol. We conclude that the greater the amount of prenatal testosterone, the earlier the initiation of the pubertal LH rise. Moreover, the finding that low doses of testosterone (32 mg/week) are capable of abolishing the LH surge without significantly advancing the timing of puberty supports our hypothesis that different steroid requirements exist for sexual differentiation of tonic and surge modes of LH secretion.

Aging↗

PubMed1996

Defeminization of the reproductive response to photoperiod occurs early in prenatal development in the sheep.

Photoperiod times the transition to sexual maturity in many seasonal breeders. In male and female sheep, photoperiod influences the timing of puberty differentially. Whereas in females, age at sexual maturity is highly dependent on photoperiod, puberty in males begins at the same age regardless of day length. We have determined that this sex difference is due to the organizing action of androgens during prenatal development. In the present investigation, we studied when during gestation (term: approximately 150 days) androgens defeminize the reproductive response to photoperiod. We compared the age at sexual maturity in female lambs treated with testosterone prenatally from Days 30 to 76 (Early, n = 7) or 89 to 135 (Late, n = 8) to that of normal males (n = 8) and normal females (n = 7). To reveal differential responsiveness to photoperiod, all lambs were maintained from birth under constant long days (16L:8D), a treatment that inhibits puberty in normal females. The age at the pubertal LH rise was determined in a standardized experimental model (lambs gonadectomized and treated with estradiol). As expected in the long day photoperiod, only 1 of 7 normal females had a pubertal rise in LH. In contrast, all males increased LH secretion by 6.7 +/- 0.6 wk. Similarly, in the Early group, a sustained increase in LH occurred in all females, but this was delayed relative to the increase in the males (16.8 +/- 1.7 wk; p < 0.001). The Late group had LH patterns similar to those of the normal females, with only 3 of 8 females having sustained elevations in LH. These data suggest that a "critical period" for the defeminization of the reproductive response to photoperiod occurs early in prenatal development. In addition, it appears that this critical period and the period for defeminization of the surge mode of gonadotropin secretion occur at similar stages in development. When challenged with an acute increase in estradiol, all normal and Late androgenized females responded with an LH surge. In contrast, none of the males and only 1 of 7 Early females produced a robust response to estradiol.

Aging↗

PubMed1996

Metabolic interfaces between growth and reproduction. V. Pulsatile luteinizing hormone secretion is dependent on glucose availability.

To test the hypothesis that mechanisms controlling the secretion of LH are modulated by glucose availability, the acute effects of glucoprivation were studied. The model was the gonadectomized male lamb raised on a limited diet of artificial milk. The approach was to monitor LH secretion before and after the administration of a competitive antagonist of glucose metabolism, 2-deoxyglucose (2DG). We first determined whether LH secretion was influenced by glucose availability by administering 2DG at several doses. Peripheral administration of the glucose antagonist (240 and 480 mg/kg 2DG, single iv injection) transiently decreased LH pulse frequency, but not LH pulse amplitude. By contrast, LH secretion (frequency or amplitude) was not affected by lower doses (60 or 120 mg/kg) of the glucose antagonist. A second study was conducted to determine whether either the pituitary gland or the GnRH neurosecretory system per se is directly affected by short term glucoprivation. The competency of the pituitary was assessed by administering GnRH during the time when LH secretion is suppressed by pharmacological glucose blockade. Similarly, the function of the GnRH neurosecretory system was assessed by administering a GnRH secretagogue (N-methyl-D,L-aspartate) under the same glucoprivic conditions. In response to an optimized iv dose of 2DG, LH pulse frequency decreased. However, in lambs that received either GnRH or N-methyl-D,L-aspartate during the period of glucoprivation, LH pulse frequency was sustained at levels comparable to those before 2DG was given. To determine whether the effect of glucoprivation was central in origin, the glucose antagonist was administered into the lateral cerebral ventricle at 1/100th the doses used peripherally. Central administration of 2DG, independent of dose, transiently decreased LH pulse frequency, but not pulse amplitude. However, unlike the case with peripheral injection, plasma glucose values did not change after the administration of any dose of 2DG tested centrally. These findings indicate that glucose availability in the developing sheep influences LH secretion. Moreover, based upon analysis of LH pulse frequency, glucoprivation does not directly impair either the pituitary gland or the GnRH neurosecretory system. Collectively, these results suggest that glucose availability affects LH secretion by acting within the central nervous system at a detection site(s) peripheral to the GnRH neuron.

Animals↗

PubMed1996

Reduction of glucose availability suppresses pulsatile luteinizing hormone release in female and male rats.

Glucose availability controls reproductive activity through modulation of LH secretion. The aim of the present study was to determine whether the glucoprivic suppression is potentiated by gonadal steroids and if glucoprivic suppression of pulsatile LH release is sexually differentiated. Pulsatile LH secretion was examined in rats after peripheral (jugular) administration of the competitive inhibitor of glycolysis, 2-deoxyglucose (2DG). Fourteen days after gonadectomy, blood samples were collected every 6 min for 3 h. One hour after the onset of sampling, 2DG was administered peripherally (200, 400, or 800 mg/kg BW, iv), and food intake was determined after 2DG injection in gonadectomized males and females in the presence or absence of sex steroids (testosterone or estradiol). To test the ability of the pituitary to produce LH under glucoprivic conditions, LHRH was injected every 30 min for 2.5 h in ovariectomized (OVX) rats 30 min after treatment with 400 mg/kg 2DG. At all peripheral doses of 2DG in females and at the middle and high doses of 2DG in males, mean plasma LH and LH pulse frequency decreased (P < 0.05) in the presence of steroids. However, in the absence of sex steroids, the lowest dose in females and the middle dose in males were not effective. Pituitary function appeared normal, because increases in mean plasma LH in response to the exogenous LHRH occurred in OVX rats treated with the middle dose of 2DG. Food intake significantly (P < 0.05) increased after 2DG injection in all groups except estrogen-treated OVX females at the low and high doses of 2DG. These findings suggest that glucoprivic suppression of LH pulses is potentiated by gonadal steroids in both sexes. Moreover, the hypothalamo-hypophyseal axis of the female rat seems to be more sensitive to the decreased glucose availability induced by 2DG than that of the male.

Animals↗

PubMed1996

Suppression of luteinizing hormone pulses by restriction of glucose availability is mediated by sensors in the brain stem.

The availability of metabolic fuels such as glucose is known to influence reproductive function. Peripheral administration of 2-deoxyglucose (2DG), a competitive inhibitor of glycolysis, inhibits pulsatile LH secretion in the rat and growth-retarded lamb. We hypothesized that such glucoprivic suppression of LH secretion is mediated by the lower brain stem, because studies of both ingestive and reproductive behavior implicate lower brain stem structures, such as the area postrema, as a site that is sensitive to glucose availability. In the present study, the effect of a 2DG infusion, targeted to the fourth ventricle, on pulsatile LH secretion was examined in male rats. The males were castrated or castrated and immediately implanted with testosterone. Blood samples were collected through an indwelling atrial cannula every 6 min for 4 h for LH determination. After the first hour of blood sampling, 2DG (4 or 40 mg/kg) was infused into the fourth ventricle at a flow rate of 0.2 microliter/min through a cannula that had been stereotaxically implanted 1 week before sampling. The high dose of 2DG (40 mg/kg), but not the low dose (4 mg/kg), suppressed pulsatile LH secretion and increased food intake in both castrated and testosterone-treated castrated rats. LH secretion and food intake were not affected by the infusion of xylose (40 mg/kg) as an isoosmotic control. The site specificity of the 2DG treatment was confirmed by histological examination after an isovolumetric infusion of dye (0.2 microliter/min). These results suggest that glucose availability could influence LH secretion as well as feeding through a central sensor in the lower brain stem and are consistent with the idea that the area postrema might be an important glucosensor involved in the modulation of LH secretion.

Animals↗

PubMed1996

Paraventricular norepinephrine release mediates glucoprivic suppression of pulsatile luteinizing hormone secretion.

Restriction of glucose availability by 2-deoxyglucose (2DG) suppresses pulsatile LH release. The aim of the present study was to determine whether norepinephrine (NE) release in the paraventricular nucleus (PVN) is involved in the glucoprivic suppression of LH secretion in ovariectomized rats. Twelve days after ovariectomy, animals were stereotaxically implanted with a guide cannula for microdialysis in the PVN. Two days later, the PVN was perfused continuously with Ringer's solution or Ringer's solution containing a catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine (100 microM), through a microdialysis probe inserted in the guide cannula 2 h before the beginning of sampling, which lasted 3 h. Blood samples were collected every 6 min through an atrial cannula, and dialysates were collected every 20 min. One hour after the beginning of sampling, 2DG (400 mg/kg BW) was administered iv through the atrial cannula. Paraventricular NE levels significantly increased immediately after 2DG injection (P < 0.05), and both mean LH concentrations and the frequency of LH pulses decreased. By contrast, when alpha-methyl-p-tyrosine was administered into the PVN, 2DG did not produce an increase in paraventricular NE, and no depression of LH secretion occurred. These results suggest that the PVN mediates the glucoprivic suppression of LH pulses via the release of NE.

Animals↗

PubMed1996

Prenatal androgens defeminize activation of GnRH neurons in response to estradiol stimulation.

To determine if prenatal androgens prevent activation of GnRH neurons in response to estradiol stimulation, Fos colocalization with GnRH was compared in the brains of normal female lambs, normal males, and androgenized females in response to a surge-inducing dose of estradiol. Blood samples were collected every 1-2 h for 6 h before estradiol treatment up to the time of sacrifice at 17-19 h post-treatment. Following perfusion, 60 micrograms coronal brain sections were immunostained for Fos (1:1000, Santa Cruz Biochemicals) and GnRH (1:40,000, LR-1) using NiCl-enhanced and unenhanced DAB, respectively. Although LH secretion increased in females before sacrifice, no increase was observed in males or androgenized females. Despite differences in LH secretion, the number and distribution of GnRH neurons was not sexually dimorphic. Moreover, Fos immunostaining was visible throughout steroid-responsive limbic regions in all three groups of lambs. However, the colocalization of Fos with GnRH was highly sexually dimorphic. In females perfused after the peak of the LH surge, 65.7% of GnRH neurons in the preoptic area, anterior hypothalamus, and mediobasal hypothalamus expressed Fos, whereas only 1.7% of GnRH neurons were Fos-positive in males and androgenized females. These findings indicate that sex differences in the activation of GnRH neurons in response to estradiol are determined prenatally through the actions of testosterone.

Analysis of Variance↗

PubMed1996

Sexual differentiation of the surge mode of gonadotropin secretion: prenatal androgens abolish the gonadotropin-releasing hormone surge in the sheep.

In sheep, the surge mode of gonadotropin secretion is sexually differentiated, i.e. the LH surge is present in the female, but not in the male. The present study tested the hypothesis that sexual differentiation of the LH surge mechanism reflects a sex difference in the pattern of GnRH, and that prenatal androgens abolish the surge mode of GnRH secretion. We monitored the pattern of GnRH secretion in pituitary portal blood after acute treatment with estradiol in gonadectomized postpubertal males (n = 6), females (n = 6), and androgenized females (exposed prenatally to testosterone from day 30-90 in gestation, n = 7). Four capsules, each containing a 30-mm column of estradiol were implanted s.c. into each lamb to produce high physiologic concentrations of the hormone. Beginning 7 h later, portal and peripheral blood samples were collected hourly for 48 h for measurement of GnRH and LH, respectively. All females exhibited a GnRH surge beginning 13.0 +/- 0.4 h after estradiol treatment; this was accompanied by an LH surge. By contrast, only one male produced a small surge in GnRH (1.7 pg/min) with a latency of 32 h; a corresponding increase in LH occurred in this male. Likewise, among the androgenized females, only one exhibited GnRH and LH surges which began at about 22 h after estradiol treatment. Some of the androgenized females had sporadic increases in GnRH which were of lower amplitude than in the control females, and were unaccompanied by rises in LH. These findings provide the first direct evidence that the sex difference in the surge mode of LH secretion results from the sexual differentiation of the pattern of GnRH release. The study also suggests that androgens during prenatal development abolish the GnRH surge and subsequently, the generation of the LH surge.

Androgens↗

PubMed1995

Melatonin and puberty in female lambs exposed to EMF: a replicate study.

In an earlier study, we found no effects of 60 Hz electric and magnetic fields (EMF) from a 500 kV transmission line on serum melatonin patterns or on puberty in ten female Suffolk lambs (Ovis aries). We conducted a larger replicate study of 15 lambs exposed to a mean electric field of 6.3 kV/m and a mean magnetic field of 3.77 muT and 15 controls exposed to EMF two orders of magnitude weaker than in the line area. The replicate produced essentially the same results as our previous study.

Animals↗

PubMed1995

Prenatal androgens modify the reproductive response to photoperiod in the developing sheep.

In most seasonal breeders, photoperiod influences the timing of the transition to sexual maturity. In sheep, males and females express reproductive maturity under different photoperiods. Spring-born males begin the maturational process during lengthening days (spring), whereas females do so during shortening days (autumn). We hypothesized that photoperiod differentially influences the transition to sexual maturity in each sex, and that this difference results from the presence or absence of androgens prenatally. We monitored the timing of sexual maturity in male and female lambs (n = 8 each) and in prenatally masculinized female lambs (n = 7) maintained under controlled photoperiods (natural-simulate or reverse natural-simulate). Circulating LH was analyzed to reveal the timing of the pubertal gonadotropin rise; lambs were gonadectomized and implanted with estradiol to provide a constant feedback on LH secretion. Under natural-simulate photoperiod, LH increased in males at 7.0 +/- 0.3 wk when days were lengthening. In females treated similarly, sexual maturity occurred at 27.0 +/- 0.8 wk when day lengths were decreasing. The reverse photoperiod had no effect on males, but it delayed the expression of sexual maturity in females. Thus, LH also increased in males at 7.1 +/- 0.9 wk, while none of the females maintained under the same photoperiod had elevated LH secretion when the experiment was terminated (32 wk of age). Prenatal treatment with androgens masculinized the reproductive response to photoperiod; as in the males, LH increased in the androgenized females maintained under a reverse natural-simulate photoperiod at 7.1 +/- 0.4 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1995

Prenatal testosterone differentially masculinizes tonic and surge modes of luteinizing hormone secretion in the developing sheep.

In sheep, prenatal exposure to androgens during a critical period for sexual differentiation can masculinize tonic luteinizing hormone (LH) secretion and defeminize the LH surge. The present study investigated the possible independent control of these two modes of LH secretion, as revealed by their developmental history. Specifically, we tested the hypothesis that separate critical periods exist for androgenization of tonic and surge LH secretion. Pregnant ewes were treated weekly with testosterone cypionate (200 mg in oil). As a control and to induce robust masculinization of reproductive neuroendocrine function, one group of females received testosterone from day 30 to 86 of gestation (LONG group). To determine if masculinization of tonic LH secretion develops separately from that of the LH surge, two additional groups were treated from day 30 to 51 (EARLY group) or 65-86 (LATE group). At birth, the external genitalia of the LONG- and EARLY-treated females were masculinized; those of the LATE-treated group were normal. At 2 weeks of age, all androgenized females, together with normal males and females (n = 8 each), were gonadectomized and steroids replaced using an estradiol-filled Silastic capsule. First, to determine the timing of the pubertal decrease in steroid sensitivity, circulating LH was monitored twice weekly. Second, to test the function of the LH surge system, LH was measured every 1-2 h for 60 h after an acute increase in estradiol at 9 months of age. With regard to tonic LH secretion, in control males and LONG-treated females, a sustained increase in tonic LH in the presence of constant steroid feedback occurred at 7.1 +/- 0.3 and 10.9 +/- 1.7 weeks of age, respectively (mean +/- SE). In control females, tonic LH increased at 27.1 +/- 0.8 weeks. Despite the differences in their genitalia, EARLY and LATE testosterone treatment produced intermediate effects: LH secretion increased at 19.3 +/- 1.2 and 20.4 +/- 0.8 weeks, respectively. In response to acute estradiol stimulation, all control females produced a surge of LH that peaked 18.4 +/- 0.6 h after steroid treatment. For the control males and LONG-treated females, LH concentrations were not sustained above unsuppressed pretreatment levels throughout the 60-hour sampling period. All but 4 of the 18 EARLY- and LATE-treated females responded to estradiol stimulation with a surge of LH that peaked at 29.8 +/- 1.6 and 31.8 +/- 1.3 h, significantly later than that of control females.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗

PubMed1995

Complete inhibition of endotoxin-induced coagulation activation in chimpanzees with a monoclonal Fab fragment against factor VII/VIIa.

Gram-negative sepsis is oftentimes complicated by activation of coagulation with disseminated intravascular coagulation and microthrombosis. This may contribute to the associated morbidity, multiple organ failure and death. Recent studies have established that the tissue factor-dependent pathway of blood coagulation has a significant participatory role in the initial endotoxin-induced activation of coagulation. Tissue factor (TF), expressed on the surface of activated monocytes and endothelial cells forms cell surface complexes with free circulating factors VII and VIIa. The latter complex proteolytically activates factors X and IX. Recent in vivo experiments have shown that a rapidly neutralizing TF monoclonal antibody prevents and arrests the endotoxin-induced activation of coagulation and similar studies have shown to reduce mortality in baboons. In this study we describe the preparation of a factor VII/VIIa neutralizing monoclonal Fab fragment and characterize its effect on in vivo activation of coagulation during experimental endotoxemia in chimpanzees. Four chimpanzees received a bolus intravenous injection of 4 ng/kg endotoxin in combination with Fab fragments of a factor VII/VIIa neutralizing murine monoclonal antibody (12D10) at a dose of either 50 micrograms/kg (n = 2) or 100 micrograms/kg (n = 2). Four control animals received a bolus injection of endotoxin alone. Administration of the 12D10 Fab fragments, immediately preceding the endotoxin bolus injection, effectively blocked the endotoxin-induced activation of coagulation. Plasma levels of products of in vivo activation, namely F1 + 2, TAT complexes and FpA remained at baseline values. The administration of 12D10 resulted in a rapid decline in factor VII/VIIa antigen levels which remained below 5 ng/ml for 180-240 min, followed by a rapid return to baseline levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

A hookworm glycoprotein that inhibits neutrophil function is a ligand of the integrin CD11b/CD18.

The chronic survival of many endoparasites is dependent on the ability of these organisms to escape the host immune response. Identification of the molecular mechanisms by which these organisms evade this response may yield novel approaches in the development of anti-inflammatory agents. We describe here the discovery and characterization of a novel 41-kilodalton glycoprotein from the canine hookwork (Ancylostoma caninum) that potently inhibits CD11/CD18-dependent neutrophil function in vitro. Neutrophil inhibitory factor (NIF) blocks the adhesion of activated human neutrophils to vascular endothelial cells as well as the release of H2O2 from activated neutrophils, over a similar concentration range (IC50 10-20 nM). Studies aimed at determining the nature of the NIF binding site on neutrophils revealed selective, high affinity binding of this protein to the integrin CD11b/CD18. A cDNA encoding NIF was isolated from a canine hookworm cDNA library. NIF comprises a mature polypeptide of 257 amino acids, preceded by a 17-amino acid leader. The mature protein has 10 cysteines and has seven potential N-linked glycosylation sites. NIF has no significant sequence homologies to any previously reported protein. As such, NIF represents a prototype of a novel class of leukocyte function inhibitors.

Amino Acid Sequence↗