Biomedical subjects

M E Wilson

Publications and source records attributed to M E Wilson.

At least 19 recordsLinked to original sources

PubMed2007

Patterns of late embryonic and fetal mortality and association with several factors in sheep.

Embryonic and fetal mortality reduce lambing rates and litter sizes, thus contributing to economic losses in the sheep industry. In the current study, the timing of late embryonic and fetal loss in ewes and the factors with which these losses were associated were examined. Ewes lambing and lambs born were compared with pregnancy diagnosis and counts of embryos by ultrasonography near d 25, 45, 65, or 85 of gestation. Approximately 19.9% of the ewes experienced late embryonic loss, fetal loss, or both; and 21.2% of the embryos or fetuses were lost from d 25 to term. Potential offspring were lost throughout gestation; 3.7% of embryos from d 25 to 45, 4.3% of fetuses from d 45 to 65, 3.3% from d 65 to 85, and 11.5% from d 85 to parturition; thus, approximately 3 to 4% of the potential offspring were lost for each 20-d period of pregnancy beyond d 25. A greater proportion of ewes lost one (36.7%) rather than all (20.5% single; 3.8% multiple) embryos or fetuses. The patterns of loss were similar in ewes mated during the anestrous season and the transitional period and did not vary with service period within breeding season or method of synchronization of estrus. Late embryonic or fetal losses were not related to the temperature-humidity index. Maternal serum collected near d 25, 45, 65, or 85 of gestation was assayed for concentrations of progesterone, estradiol-17beta , and vascular endothelial growth factor (VEGF). The proportions of embryos or fetuses lost were associated with breed type (P < 0.05), as were concentrations of progesterone (P < 0.01), estradiol (P < 0.05), and VEGF (P < 0.01). The relationships of loss or retention of pregnancy to hormonal variables at the 4 stages studied were limited. Complete and partial losses increased rapidly as maternal progesterone at d 25 decreased below 2 ng/mL (P < 0.05). Survival of fetuses within a litter from d 25 to 65 was greater for ewes with medium concentrations of VEGF near d 25 and from d 65 to parturition was greater for ewes with high concentrations of VEGF near d 45 (P < 0.05). In summary, late embryonic or fetal losses occurred from d 25 throughout gestation and varied with breed type and with concentrations of progesterone in maternal serum on d 25.

Abortion, Veterinary↗

PubMed2006

Genome-wide scan for visceral leishmaniasis susceptibility genes in Brazil.

A genome-wide scan was conducted for visceral leishmaniasis (VL) in Brazil. Initially, 405 markers were typed in 22 multicase pedigrees (28 nuclear families; 174 individuals; 66 affected). Non-parametric multipoint analysis detected nine chromosomal regions with provisional evidence (logarithm of the odds (LOD) scores 0.95-1.66; 0.003<P<0.018) for linkage. To confirm linkage, 132 individuals (43 affected) from 19 independently ascertained families were genotyped across these regions. Three regions (6q27, 7q11.22 and 17q11.2-q21.3) retained evidence (LOD scores 1.08, 1.34, 1.14; P=0.013, 0.007, 0.011) for linkage. To determine which genes contribute to linkage at 17q11.2-q21.3, 80 single nucleotide polymorphisms were genotyped in 98 nuclear families with 183 affected individuals. Family-based association test analysis indicated associations at two chemokine genes, CCL1 and CCL16, that lie 1.6 Mb apart, show some extended linkage disequilibrium with each other, but each lie within different clusters of candidate CCL genes. Multiple genes may therefore contribute to the linkage peak for VL at 17q12.

Brazil↗

PubMed2006

Effect of melengestrol acetate as an alternative to induce molting in hens on the expression of yolk proteins and turnover of oviductal epithelium.

Inducing hens to molt increases egg quality, egg production and extends the productive life of hens. It has been previously demonstrated that melengestrol acetate (MGA), an orally active progestin, decreased gonadotropic support for the ovary, which decreased the steroidogenic support for the oviduct and resulted in the cessation of lay. Estradiol produced by the theca cells of small follicles stimulates the production of the yolk proteins vitellogenin II and apolipoprotein II by the liver and supports the oviductal epithelial cells. The objective of the present experiment was to determine gene expression for yolk proteins and oviductal epithelial cell turn-over in response to a MGA-induced molt. Hy-Line W-36 laying hens were fed either 0 or 8mg MGA per day for 28 days in a balanced diet and then returned to a standard layer ration until day 36. Four birds per treatment on days 1, 8, 16, 28 and 36 were euthanized and the liver was removed and snap frozen in liquid nitrogen until RNA was extracted. Expression of vitellogenin II and apolipoprotein II genes was determined using real-time RT-PCR. A portion of the magnum was removed to determine proliferation and programmed cell death for secretory and ciliated luminal epithelium. Vitellogenin II and apolipoprotein II gene expression was reduced in hens fed 8mg MGA compared to those fed 0mg MGA. There was no effect of day on gene expression of either yolk protein. Cell proliferation was increased in the ciliated epithelial cells of the oviduct in hens receiving 8mg MGA compared to those receiving 0mg. However, programmed cell death of the ciliated epithelial cells was not different between controls and MGA treatment. Programmed cell death and proliferation increased in the secretory epithelial cells in hens receiving 8mg MGA compared to controls. Therefore, utilizing MGA as an alternative method to induce molt results in some, but not all, of the physiological changes previously described for hens molted by feed withdrawal. These findings lead us to suggest that some of the observed physiological changes resulting from feed withdrawal are required to increase egg quality and egg production following molt and other changes are not necessary, but are just a result of nutrient deprivation.

Animal Feed↗

PubMed2006

Diet-induced alterations in progesterone clearance appear to be mediated by insulin signaling in hepatocytes.

Factors that affect progesterone clearance from plasma and by hepatocytes in culture were examined in a series of experiments. In Exp. 1, the objective was to determine whether an increase in hepatic portal blood acetate or propionate could alter progesterone metabolism by the liver. For ewe lambs gavaged orally with sodium propionate compared with those gavaged orally with sodium acetate, serum progesterone concentrations began to diverge as early as 0.5 h after administration and were greater (P < 0.05) at 3 and 4 h after administration. The objective of Exp. 2 was to determine the effect of a single oral gavage of either sodium acetate or sodium propionate on peripheral insulin and glucagon concentrations. Ewes gavaged orally with sodium propionate had greater (P < 0.05) insulin concentrations at 0.5 and 1 h after gavage than ewes gavaged with sodium acetate. Furthermore, glucagon concentrations were greater (P < 0.05) at 0.5, 1, and 2 h for ewe lambs gavaged orally with sodium propionate compared with those receiving sodium acetate. The third experiment investigated the rate of in vitro progesterone clearance by cultured hepatocytes in response to treatment with different concentrations of insulin and glucagon. Progesterone clearance was reduced (P < 0.05) with the addition of 0.1 nM insulin compared with the control. Furthermore, there was a greater reduction (P < 0.05) in progesterone clearance in response to 1.0 and 10 nM insulin compared with the control and 0.1 nM insulin. No change was observed in progesterone clearance in hepatocytes treated with either physiological (0.01 and 0.1 nM) or supraphysiological (1.0 nM) glucagon. Supraphysiological concentrations of glucagon (1.0 nM) negated the effects of either 0.1 or 1.0 nM insulin on progesterone clearance by hepatocytes. However, with physiological concentrations of glucagon (0.1 nM) and 1.0 nM insulin, glucagon was not able to negate the reduction in progesterone clearance caused by insulin. These data are consistent with a paradigm in which elevated hepatic portal vein propionate increases plasma insulin in ruminants, which decreases progesterone clearance, thereby increasing serum progesterone concentrations.

Acetates↗

PubMed2005

Evidence for TeV gamma-ray emission from a region of the galactic plane.

Gamma-ray emission from a narrow band at the galactic equator has previously been detected up to 30 GeV. We report evidence for a TeV gamma-ray signal from a region of the galactic plane by Milagro, a large-field-of-view water Cherenkov detector for extensive air showers. An excess with a significance of 4.5 standard deviations has been observed from the region of galactic longitude l E (40 degrees, 100 degrees) and latitude /b/ < 5 degrees. Under the assumption of a simple power law spectrum, with no cutoff in the EGRET-Milagro energy range, the measured integral flux is phi gamma(>3.5 TeV) = (6.4 +/- 1.4 +/- 2.1) x 10(-11) cm(-2) s(-1) sr(-1). This flux is consistent with an extrapolation of the EGRET spectrum between 1 and 30 GeV in this galactic region.

Journal Article↗

PubMed2005

Atypical American visceral leishmaniasis caused by disseminated Leishmania amazonensis infection presenting with hepatitis and adenopathy.

Leishmania amazonensis is widely recognised as a cause of cutaneous leishmaniasis in Latin America, but it can also disseminate to produce atypical visceral leishmaniasis with hepatitis and lymphadenopathy. The patient, an 8-year-old Brazilian boy, presented with a febrile illness and hepatosplenomegaly, elevated liver enzymes and generalised adenopathy. Serological tests using antigens of L. chagasi, the typical cause of visceral leishmaniasis in Latin America, were inconclusive. Leishmania amazonensis was eventually isolated in a culture of a lymph node. The patient recovered fully after treatment with meglumine antimoniate. As this case illustrates, L. amazonensis produces a spectrum of disease that includes atypical American visceral leishmaniasis with evidence of hepatocellular injury and generalised lymphadenopathy.

Antiprotozoal Agents↗

PubMed2005

Melengestrol acetate in experimental diets as an effective alternative to induce a decline in egg production and reversible regression of the reproductive tract in laying hens. I. Determining an effective concentration of melengestrol acetate.

Induced molting increases egg quality and egg production and extends the productive life of hens. Molting is accomplished by feed withdrawal, which has been criticized for not addressing hen well-being, and current alternatives have resulted in poor postmolt performance and inadequate well-being. Molting leads to regression of follicles on the ovary and causes loss of steroidogenic support for the oviduct, leading to cessation of lay. Melengestrol acetate (MGA), an orally active progestin, may decrease support for the ovary, resulting in loss of support for the oviduct, while hens are fed a balanced diet. In this experiment, a dose response study, Hy-Line W-36 hens were fed 0, 0.1, 1, 4, or 8 mg of MGA per hen/d in a balanced diet for 28 d and then returned to a normal diet. Four birds on d 0 and 4 birds per treatment on d 1, 2, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, and 44 were euthanized. The weight of the ovary with follicles, magnum, shell gland, and oviduct were determined. A decrease in egg production was observed in those groups receiving 4 and 8 mg of MGA, until removal of MGA from the diet. After d 28, egg production increased to the production level of hens fed 0, 0.1, or 1 mg of MGA. The weight of the ovary with follicles, oviduct, magnum, and shell gland were unchanged throughout in groups fed 0, 0.1, or 1 mg of MGA. However, groups fed 4 or 8 mg of MGA exhibited a decrease (P < 0.05) in the weight of the ovary with follicles, oviduct, magnum, and shell gland until d 28. Recrudescence of the large yellow follicles as well as rejuvenation of the oviduct and its components, the magnum and shell gland, in the 4 and 8 mg MGA groups occurred by d 44. Melengestrol acetate, fed to hens on a balanced layer diet, caused reversible regression of follicles and, therefore, removal and return of support for the oviduct.

Aging↗

PubMed2005

Melengestrol acetate as an effective alternative to induce a decline in egg production and reversible regression of the reproductive tract in laying hens. II. Effects on postmolt egg quality.

Induced molting increases egg quality and egg production and extends the productive life of hens. Molting is accomplished by feed withdrawal, which has received criticism, and alternatives described thus far result in poor postmolt performance. Melengestrol acetate at a dosage of 4 or 8 mg/d, in a balanced diet, leads to reversible regression of the reproductive tract. However, this alternative must also increase egg quality after rest to be considered an adequate method by the industry. Hy-Line W-36 (n = 497) laying hens were assigned randomly to a diet containing 0 mg of melengestrol acetate (MGA; control) throughout the experiment or 4 or 8 mg of MGA/d for 2, 4, or 6 wk. Upon reaching 50 and 70% lay, after MGA removal, eggs were collected for measurements of egg quality, including Haugh units (i.e., internal egg quality), shell thickness, and breaking strength (i.e., external egg quality). Haugh units were greater (P < 0.05) for eggs laid by hens molted with a diet containing 8 mg of MGA for all durations compared with controls. Shell thickness was greater (P < 0.05) when hens were treated with 4 mg of MGA for 6 wk and 8 mg of MGA for 4 and 6 wk compared with control. Egg breaking strength was greater (P < 0.05) than controls for all hens fed MGA, regardless of dosage or duration of feeding. A subset of hens was fed 8 mg of MGA per hen/d for 2 wk, and eggs were collected for 3 wk. Seven days after MGA was removed from the diet, the amount of MGA in the yolk was below the level of detection of the assay, and the concentration found in the eggs at all time points was 3 orders of magnitude below the Food and Drug Administration's tolerance for MGA in edible tissue. When used as an alterative method to induce a rest, MGA leads to an increase in the internal and external egg quality of hens compared with nonmolted hens.

Aging↗

PubMed2005

Growth hormone at breeding modifies conceptus development and postnatal growth in sheep.

Experiments were performed to determine the effects of components of the GH-IGF axis on conceptus development and postnatal growth in sheep. In Exp. 1, ewes received one of the following treatments: 1) sustained release GH at breeding, 2) sustained release GH at breeding and estradiol-17beta at d 5 and 6, 3) only estradiol-17beta at d 5 and 6, or 4) no treatment. Uteri were flushed on d 7, and flushings were analyzed for content of IGF-I. A single injection of sustained-release bovine GH at breeding increased IGF-I content in uterine luminal flushings compared with control ewes (P < 0.05). Treatment with estradiol-17beta on d 5 and 6 after breeding did not alter IGF-I content compared with control ewes, and it blocked the effect of GH on uterine luminal IGF-I content. In Exp. 2, sustained release GH or no treatment was administered at breeding, and gravid uteri were collected at d 25, 80, or 140 of gestation. On d 80, GH-treated ewes had smaller chorioallantoic weights (P < 0.05) and tended to have more efficient placentae (fetal weight/total placental weight; P = 0.052), with a higher percentage of placental weight as cotyledons (P = 0.068) compared with control ewes. In Exp. 3, ewes were treated with or without sustained release GH at progesterone withdrawal. Lambs from GH-treated ewes were heavier at birth (P < 0.05). Lambs from GH-treated ewes reared as singles, but not lambs reared as multiples, were heavier at 30, 60 (P < 0.05), and 75 d (P = 0.075) of age than lambs from control ewes. In conclusion, ewes treated with sustained-release GH at breeding developed smaller, more efficient placentas, and had larger lambs at birth.

Animals↗

PubMed2004

Reduced growth hormone secretion prolongs puberty but does not delay the developmental increase in luteinizing hormone in the absence of gonadal negative feedback.

Previous studies have shown that the growth hormone (GH) axis is important for timing the later stages of puberty in female monkeys. However, it is not clear whether these growth-related signals are important for the initiation of puberty and early pubertal events. The present study, using female rhesus monkeys, used two approaches to answer this question. Experiment 1 tested the hypothesis that reduced GH secretion would blunt the rise in nocturnal LH secretion in young (17 mo; n = 7) but not older adolescent ovariectomized females (29 mo; n = 6). Reduced GH secretion was induced by treating females with the sustained release somatostatin analogue formulation, Sandostatin LAR (625 microg/kg). Morning (0900-0930 h) and evening (2200-2230 h) concentrations of bioactive LH were higher in older adolescent compared to young adolescent females. However, diurnal concentrations were not affected by the inhibition of GH secretion in either age group when compared to the placebo-treated, control condition. Experiment 2 tested the hypothesis that reduced GH secretion induced in young juvenile females would delay the initial increase in nocturnal LH secretion and subsequent early signs of puberty. In order to examine this hypothesis, puberty in control females (n = 7) was compared to those in which puberty had been experimentally arrested until a late adolescent age (29 mo) by the use of a depot GnRH analogue, Lupron (750 microg kg(-1) mo(-1); n = 7). Once the analogue treatment was discontinued, the progression of puberty was compared to a group treated in a similar fashion but made GH deficient by continuous treatment with Sandostatin LAR (n = 6). Puberty occurred as expected in control females with the initial rise in evening LH at 21 mo, menarche at 22 mo, and first ovulation at 30 mo. As expected, Lupron arrested reproductive maturation, but elevations in morning and evening LH and menarche occurred within 2 mo of the cessation of Lupron in both Lupron and Lupron-GH-suppressed females. In contrast, first ovulation was delayed significantly in the Lupron-GH-suppressed females (41 mo) compared to the Lupron-only females (36 mo). These data indicate that within this experimental model, reduced GH secretion does not perturb the early stages of puberty but supports previous observations that the GH axis is important for timing the later stages of puberty and attainment of fertility. Taken together, the data indicate that factors that reduce GH secretion may have a deleterious effect on the completion of puberty.

Animals↗

PubMed2004

Optotype acuity and re-operation rate after unilateral cataract surgery during the first 6 months of life with or without IOL implantation.

AIMS: To compare optotype acuities and re-operation rates in children corrected with a contact lens (CL) compared with an intraocular lens (IOL) following unilateral cataract extraction during infancy in a non-randomised, retrospective case series. METHODS: 25 infants with a unilateral congenital cataract underwent cataract surgery with (IOL group, n = 12) or without (CL group, n = 13) IOL implantation when <7 months of age. Optotype acuities were assessed in 19 of these children at a mean age of 4.3 years (range 3.3-5.5 years). The number of re-operations were assessed in 21 children. RESULTS: The visual acuity results were similar in the two treatment groups (p = 0.99); however, two of the four (50%) children in the IOL group compared with two of the seven (28%) children in the CL group undergoing surgery during the first 6 weeks of life had 20/40 or better visual acuity. The children in the IOL group had more re-operations than the children in the CL group (mean 1.1 v 0.36). Most of the re-operations in the IOL group were membranectomies performed during the first year of life (median 8.0 months) whereas all of the re-operations in the CL group were the implantation of a secondary IOL later in childhood (mean 2.2 years). CONCLUSION: Optotype acuities were similar for the children corrected with a CL compared with IOL, while the children in the IOL group underwent more re-operations .

Cataract↗

PubMed2004

Estradiol negative feedback regulates nocturnal luteinizing hormone and follicle-stimulating hormone secretion in prepubertal female rhesus monkeys.

In recent years, animal models of puberty in children have focused on factors responsible for the developmental increase in gonadotropin secretion independent of gonadal negative feedback. Although the testis may play little if any role in timing the initial increase in gonadotropin secretion in the male, the situation may be different for the female. The present study tested the hypothesis that removal of endogenous estradiol by ovariectomy would produce an immediate increase in nocturnal but not daytime LH and FSH concentrations, an effect reversed by estradiol replacement. Morning (1000 and 1030 h) and evening (2200 and 2230 h) concentrations of bioactive LH and, in selected samples, immunoreactive FSH were evaluated in young juvenile female rhesus monkeys (n = 7) before and after ovariectomy at 13 months of age. Evening but not morning concentrations of gonadotropins were significantly increased within 2 wk of ovariectomy, whereas estradiol replacement returned these to presurgical levels and to those observed in age-matched, gonadally intact females (n = 7). By 145 d after ovariectomy, or approximately 17 months of age, evening as well as morning concentrations of LH were significantly higher than concentrations seen immediately after surgery. Estradiol replacement at approximately 18 months of age suppressed both morning and evening LH but not to the degree seen during a similar treatment after ovariectomy. These data support the hypothesis that, for the female, the developmental rise in diurnal gonadotropin secretion is controlled by a gonad-independent mechanism as well as a gonadal negative feedback inhibition. The importance of gonadal restraint on gonadotropin secretion in young juvenile females is evident only in samples obtained during the evening. These data underscore the notion that, for the female puberty, onset, at least in terms of gonadotropin secretion, is a misnomer and that puberty reflects a progression in multiple control mechanisms that ultimately time the attainment of fertility.

Animals↗

PubMed2004

The reproductive performance and factors affecting on-farm application of low-dose intrauterine deposit of semen in sows.

The objective of this experiment was to determine the reproductive performance and factors that affect on-farm application of low-dose intrauterine insemination (IUI) in sows. Four hundred twenty-two sows were used in a simple arrangement of four treatments to determine the effect of spermatozoa per dose (0.5 x 10(9), 1 x 10(9), or 4 x 10(9) IUI, and 4 x 10(9) with a conventional catheter) on the main effects of conception, litter size, and farrowing rate. Following weaning at approximately 18 d after parturition, estrus detection was performed daily in the presence of a mature boar. At the time of estrus detection, sows were blocked for parity (1, 2, or 3+), weaning-to-estrus interval (WEI; 3, 4, or 5 d), and assigned randomly to be serviced twice with semen from the same boar(s). Treatment services were equally divided among three technicians. Delivery of acceptable numbers of spermatozoa per dose with either device (IUI or conventional) produced similar reproductive performances; however, farrowing rate, total pigs born, and total born alive decreased (P < 0.05) when suboptimal numbers (< or = 1 x 10(9)) of spermatozoa were used with IUI. Treatment interactions with parity were not detected and were removed from the final model. Treatment interactions with WEI on farrowing rate were detected (P < 0.05), and sows with WEI of 3 d had a markedly lower (P < 0.05) farrowing rate than all other treatment groups. The results from this experiment suggest that placement of semen at the beginning of the uterine horn with conventional volumes and spermatozoa numbers produces results similar to placement of semen in the cervical cavity with a conventional AI catheter. Although there is little published evidence of reproductive performances in a commercial setting with suboptimal numbers of spermatozoa, these results suggest that insemination beyond the cervix does not offset effects of suboptimal numbers of spermatozoa.

Animals↗

PubMed2003

The traveller and emerging infections: sentinel, courier, transmitter.

The movement of populations shapes the patterns and distribution of infectious diseases globally. The consequences of travel are seen in the traveller and in places and populations visited and may persist long after travel. The traveller can be seen as an interactive biological unit who picks up, processes, carries and drops off microbial genetic material. A traveller can introduce potential pathogens in the absence of signs or symptoms of illness. Travellers can serve as a sentinel population; study of them can provide insights into the presence and level of risk of transmission of infections in other geographical regions. Travellers can also be seen as couriers who inadvertently ferry pathogens and microbial genetic material to regions where researchers can carry out detailed analyses that can help to map the location and movement of strains, genotypes and resistance patterns. The laboratory plays a key role in the identification and characterization of pathogens, which can inform management of individual patients and the public health response. The connectedness and mobility in the world today facilitate the emergence of infectious diseases in humans and also in animals and plants. Many traditional barriers have been breached by travel, roads and technology. Population size and density favour spread of many infections. The rapid generation time of microbes and their capacity to adapt to changes in the physico-chemical and immunological environment will pose continuing challenges.

Animals↗

PubMed2003

Paediatric cataract blindness in the developing world: surgical techniques and intraocular lenses in the new millennium.

Paediatric cataract blindness presents an enormous problem to developing countries in terms of human morbidity, economic loss, and social burden. Managing cataracts in children remains a challenge: treatment is often difficult, tedious, and requires a dedicated team effort. To assure the best long term outcome for cataract blind children, appropriate paediatric surgical techniques need to be defined and adopted by ophthalmic surgeons of developing countries. The high cost of operative equipment and the uneven world distribution of ophthalmologists, paediatricians, and anaesthetists create unique challenges. This review focuses on issues related to paediatric cataract management that are appropriate and suitable for ophthalmic surgeons in the developing world. Practical guidelines and recommendations have also been provided for ophthalmic surgeons and health planners dealing with childhood cataract management in the developing world.

Accommodation, Ocular↗

PubMed2003

Tamoxifen is an estrogen antagonist on gonadotropin secretion and responsiveness of the hypothalamic-pituitary- adrenal axis in female monkeys.

The selective estrogen receptor modulator, tamoxifen, effectively slows the progression of estrogen-positive breast cancer and reduces the possibility of this cancer developing in women at high risk. Despite the widespread acceptance of tamoxifen as a therapeutic agent for this disease, its effects on other estrogen-dependent pathways, particularly on neural circuits regulating brain function and peripheral hormone secretion, are poorly understood. The present study, using previously ovariectomized rhesus monkeys, examined the effects of tamoxifen, in both the presence and absence of estradiol replacement, on the reproductive and hypo-thalamic-pituitary-adrenal (HPA) axes. In Experiment 1, monkeys randomly assigned to three groups (n = 8 each) were treated with placebo and either two doses of estradiol, two doses of tamoxifen alone, or two doses of tamoxifen plus high-dose estradiol to assess the effects on negative feedback suppression of luteinizing hormone (LH). Both doses of tamoxifen effectively antagonized the negative feedback efficacy of estradiol on LH secretion. In contrast, neither the low- or high-dose tamoxifen alone had any effect on LH secretion, as concentrations during tamoxifen treatments were indistinguishable from those during placebo. In Experiment 2, females were randomly assigned to one of four treatment groups (placebo, n = 6; estradiol, n = 5; tamoxifen only, n = 5; or tamoxifen plus estradiol, n = 6) to assess the effects on glucocorticoid negative feedback and pituitary and adrenal responsiveness to exogenous corticotropin- releasing hormone (CRH). Tamoxifen also antagonized the facilitating effects of estradiol on basal and CRH-induced ACTH and cortisol secretion. However, this antagonism produced basal and CRH-stimulated cortisol and ACTH concentrations that were lower than placebo-treated females. Interestingly, tamoxifen in the absence of estradiol produced a similar diminution in ACTH and cortisol response. These data suggest that, in the presence of estradiol, tamoxifen not only antagonized estrogenic facilitation of HPA responsivity but also actually attenuated the response compared with the placebo-treatment condition. Taken together, these data indicate that tamoxifen acts as an estrogen antagonist on the neural circuits controlling the neuroendocrine regulation of the hypothalamic-pituitary-ovarian and adrenal axes in ovariectomized macaque females.

Adrenocorticotropic Hormone↗

PubMed2002

Impacts on conceptus survival in a commercial swine herd.

An estimated 30 to 40% of potential piglets are lost before farrowing in U.S. or European pig breeds. Because these studies were conducted in limited numbers of university research herds, we decided to characterize the timing, pattern, and extent of conceptus loss in a commercial swine herd in Iowa (Pig Improvement Company; Camborough Line). Sows (parities 2 to 14) were slaughtered on d 25 (n = 83), 36 (n = 78), or 44 (n = 83) of gestation. These days coincide with periods before, during, and after uterine capacity becomes limiting to conceptus survival. At slaughter, numbers of corpora lutea (CL) and uterine horn length were determined, and conceptuses were removed and evaluated. Uterine horn length and CL number did not differ among these days of gestation, averaging 217 cm and 26.6 CL, respectively. In contrast, numbers of conceptuses decreased (P < 0.05) from 15.8 on d 25 to 12.9 on d 36, then remained relatively constant through d 44 (12.1). Thus, conceptus survival averaged 60.2% on d 25, 50.1% on d 36, and 46.3% on d 44, based on numbers of CL present. There was a positive correlation (P < 0.001; r = 0.50) between numbers of viable conceptuses on d 25 and ovulation rate, but this association was completely lost by d 36 (P > 0.10) when uterine capacity becomes limiting. In agreement with this premise, uterine horn length and conceptus number were not associated on d 25 but exhibited positive correlations (P < 0.05) on d 36 (r = 0.36) and d 44 (r = 0.40). On all 3 d examined, the numbers of viable conceptuses were not associated with fetal weight but were negatively correlated (P < 0.05) with placental weight. Compared with the commonly reported values for ovulation rate and percentage conceptus loss in university research herds, values from these production animals were extremely high. Data suggest that throughout this period, larger litters were associated with conceptuses exhibiting small placentae. These data lend support to the concept that increased placental efficiency (fetal weight/placental weight) may contribute to increased litter size in the pig.

Abortion, Veterinary↗

PubMed2002

Conceptus competition for uterine space: different strategies exhibited by the Meishan and Yorkshire pig.

Our laboratory has demonstrated that Yorkshire placentae increase in size and surface area during the final third of gestation. In contrast, Meishan placental size remains constant during late gestation, but the density of blood vessels at the placental-endometrial interface increases markedly. Preliminary observations from our laboratory suggest that if one of two adjacent Meishan fetuses dies, the placenta of the remaining Meishan conceptus fails to increase its length of implantation or its placental weight or surface area. In contrast, if one of two adjacent Yorkshire fetuses dies, the adjacent conceptus accelerates its placental growth. The objective of this experiment was to document that Yorkshire, but not Meishan, conceptuses accelerate placental growth when adjacent fetuses are experimentally destroyed on d 40 of gestation. Straightbred Meishan (n = 5) and Yorkshire (n = 5) females were laparotomized and one uterine horn was randomly assigned to receive fetal crushing (treated horn); the other uterine horn served as a within-animal control. In the treated horn, every other fetus was then crushed through the uterine wall and the animals were allowed to recover. On d 111, animals were killed, uteri were recovered, and fetal weight, crown-rump length (CRL), placental weight, implantation site length, and placental surface area were recorded. Although there were no statistically significant differences in fetal weight or CRL observed between treated or control horns of females of either breed, there was a tendency for the fetuses in the treated uterine horn to be longer and heavier in both breeds. There were no differences in placental weight, placental surface area, or implantation site length between conceptuses in Meishan treated and control horns, which averaged 173.8+/-6.4 g, 1,162.7+/-35.9 cm2, and 19.0+/-0.4 cm, respectively. In contrast, placental weight, placental surface area, and implantation site length were increased (P < 0.05) in Yorkshire treated horns compared to Yorkshire control horns (306.1+/-26.0 g, 1,835+/-93.9 cm2, and 33.4+/-1.5 cm vs 253.7+/-13.4 g, 1,474.3+/-50.4 cm2, and 27.2+/-0.8 cm; respectively). These data confirm that Yorkshire conceptuses, but not Meishan conceptuses, accelerate placental growth when adjacent littermates perish as late as d 40 of gestation. These data indicate that differences exist in the strategies employed by Meishan and Yorkshire conceptuses in the competition for nutrients during gestation.

Animals↗