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PubMed2006

Gene expression changes related to endocrine function and decline in reproduction in fathead minnow (Pimephales promelas) after dietary methylmercury exposure.

BACKGROUND: Methylmercury (MeHg) is a known neurotoxic agent, but the mechanisms by which MeHg may act on reproductive pathways are relatively unknown. Several studies have indicated potential changes in hormone levels as well as declines in vertebrates with increasing dietary MeHg exposure. OBJECTIVES: The purpose of this study was to identify alterations in gene expression associated with MeHg exposure, specifically those associated with previously observed changes in reproduction and reproductive biomarkers. Fathead minnows, Pimephales promelas, were fed one of three diets that were similar to documented concentrations of MeHg in the diets of wild invertivorous and piscivorous fish. We used a commercial macroarray in conjunction with quantitative polymerase chain reaction to examine gene expression in fish in relation to exposure to these environmentally relevant doses of MeHg. RESULTS: Expression of genes commonly associated with endocrine disruption was altered with Hg exposure. Specifically, we observed a marked up-regulation in vitellogenin mRNA in individual Hg-exposed males and a significant decline in vitellogenin gene expression in female fish with increasing Hg concentrations. Other genes identified by the macroarray experiment included those associated with egg fertilization and development, sugar metabolism, apoptosis, and electron transport. We also observed differences in expression patterns between male and female fish not related to genes specifically associated with reproduction, indicating a potential physiological difference in the reaction of males and females to MeHg. CONCLUSION: Gene expression data may provide insight into the mechanisms by which MeHg affects reproduction in fish and indicate how MeHg differs in its effect from other heavy metals and endocrine-disrupting compounds.

Animal Feed↗
PubMed1991

The potential of exposure biomarkers in epidemiologic studies of reproductive health.

To further the development and application of exposure markers in field investigations in reproductive epidemiology, we have synthesized recent examinations of the issues surrounding exposure measurements in reproductive epidemiology. The specific goals of this paper are to define exposure biomarkers and explore their potential uses, particularly as screening tools. The tests for glucaric acid, thioethers, mutagenicity, and porphyrin patterns meet the general criteria for useful exposure screens. For certain xenobiotic agents, these tests accurately differentiate exposure levels, as demonstrated in occupational and environmental epidemiologic studies. As urinary screens, they are noninvasive and applicable on a large scale with current laboratory techniques. For short-term exposure, glucaric acid, thioethers, and mutagenicity tests are useful. Porphyrin patterns may measure cumulative effects as well as current exposure levels. The usefulness of these tests in epidemiologic studies of environmental effects on reproductive health has yet to be studied. To do so, the battery must be standardized for pregnant women, and test results must be correlated with measured adverse reproductive outcomes, such as gestational length and birthweight. This correlation is particularly important because maternal exposure rather than fetal exposure is being measured. The extent to which xenobiotic chemicals cross the placental barrier may vary greatly depending on the type of exposures, timing in pregnancy, and maternal detoxification capability. Without better exposure measures, epidemiologic studies of reproductive health probably will not successfully identify xenobiotic fetotoxic agents in the environment. However, with an adequate battery of nonspecific exposure biomarkers, prospective studies of environmental effects on pregnancy outcomes might be possible.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomarkers↗
PubMed1993

The epidemiology of disasters and adverse reproductive outcomes: lessons learned.

A disaster has been defined as a disruption of human ecology that exceeds the capacity of the community to function normally. Little is known about the adverse effects of natural disasters on reproductive outcomes. Important lessons can be derived from several disasters caused by human factors, such as the Minamata Bay disaster. Adverse reproductive outcomes include infertility, early pregnancy loss, stillbirths, congenital malformations, and serious developmental disabilities such as cerebral palsy and mental retardation. Recent disasters like the Chernobyl and Bhopal explosions have provided important lessons on the need for accurate and sound information about the risk of prenatal exposures for adverse reproductive outcomes. To study questions of adverse reproductive outcomes and disasters requires a well-planned approach. It should include early development of surveillance for adverse reproductive outcomes, analytic studies on the risk of disasters from direct and indirect effects, sensitive methods to measure early pregnancy loss, and long-term follow-up programs to assess outcomes such as developmental disabilities.

Animals↗
PubMed1995

The reproductive toxicology of Great Lakes contaminants.

The Great Lakes basin is characterized as a heavily populated and industrialized region in which a large number of environmental contaminants have been identified. Both the scientific community and the public have voiced concern that contaminants present in the Great Lakes may pose undue risk to human reproduction. Evidence from animal experiments, wildlife studies, and reports of occupational and accidental human exposures indicate that chemical contaminants can adversely affect reproduction. The purpose of this paper is to review the reproductive toxicity of some of the many contaminants known to be present in the Great Lakes. Since the number of chemicals present in the Great Lakes is far too great for each to be adequately reviewed here, discussion will be limited to those contaminants that have been identified in human serum, ovarian follicular fluid, and semen obtained from people residing in the Great Lakes region. It is concluded that a) the data at present is too limited to support the notion that reproduction, in the general population, has been impaired by exposure to chemicals present in the Great Lakes; b) the lack of data in some cases such as for hexachloroethane and 1,2,4-trichlobenzene does provide reason for concern and underscores the need for further research in this area; and c) the potential for a number of the compounds, including polychlorinated biphenyls (PCBs) and 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT), to disrupt endocrine functions suggests that additive or synergistic effects of these compounds may already be causing adverse effects on reproduction in sensitive individuals, which needs to be explored.

Animals↗
PubMed2003

Estrogen and bone--a reproductive and locomotive perspective.

UNLABELLED: The primary function of the skeleton is locomotion, and the primary function of estrogen is reproduction. When the skeleton is considered within this locomotive context, the onset of estrogen secretion at puberty leads to packing of mechanically excess mineral into female bones for reproductive needs. Accordingly, the unpacking of this reproductive safety deposit at menopause denotes the origin of type I osteoporosis. INTRODUCTION: According to the prevailing unitary model of involutional osteoporosis, female postmenopausal bone loss can be described as having an initial accelerated, transient phase (type I), followed by a gradual continuous phase (type II). Estrogen withdrawal is generally accepted as the primary cause of the type I osteoporosis. Thus, the quest to uncover the origin of type I osteoporosis has focused on the estrogen withdrawal-related skeletal changes at and around the menopause. However, considering that the cyclical secretion of estrogen normally begins in early adolescence and continues over the entire fertile period, one could argue that focusing on perimenopause alone may be too narrow. MATERIALS AND METHODS: This is not a systematic review of the literature on the skeletal function of estrogen(s), but rather, an introduction of a novel structure- and locomotion-oriented perspective to this particular issue through pertinent experimental and clinical studies. RESULTS AND CONCLUSIONS: When considering locomotion as the primary function of the skeleton and integrating the classic findings of the pubertal effects of estrogen on female bones and the more recent hypothesis-driven experimental and clinical studies on estrogen and mechanical loading on bone within this context, a novel evolution-based explanation for the role of estrogen in controlling female bone mass can be outlined: the onset of estrogen secretion at puberty induces packing of mechanically excess bone into female skeleton for needs of reproduction (pregnancy and lactation). Accordingly, the unpacking of this reproductive safety deposit of calcium at menopause denotes the accelerated phase of bone loss and thus the origin of type I osteoporosis.

Adolescent↗
PubMed2001

The effects of assisted reproduction on the trends and zygosity of multiple births in England and Wales 1974-99.

Assisted reproductive techniques have led to an increase in the proportion of maternities that are multiple. Though predominantly dizygotic, they are at greater risk of monozygotic division than those spontaneously conceived. England and Wales data 1974-99 on stillbirths and livebirths were analysed for 4 periods: 1974-80 (pre-assisted reproduction; 1982-8; 1989-91 (pre-redefinition of stillbirth); 1993-9 (post-redefinition of stillbirth). For twin data, Weinberg's rule was applied to estimate the proportions that were mono- (MZ) and dizygotic (DZ). Compared with the period before assisted reproduction, the most recent period shows an increase in twin maternities of 3.81 per 1,000 comprised of 3.22 (95% CI 3.10 to 3.33; p < 0.0001) DZ and 0.60 (95% CI 0.51 to 0.68; p < 0.0001) MZ twins. It is estimated that 15.7% of assisted reproduction twins are MZ. Higher order multiple births showed an increase of 3.06 (95% CI 2.85 to 3.29; p < 0.0001) per 10,000 maternities. Stillbirth rates in MZ twins are of the same order of magnitude as those in higher order multiple births but higher than those in DZ twins. The improvement in stillbirth rates over the 26 year study period is of the same order magnitude in singletons, DZ and MZ twins and higher order multiples. Assisted reproduction has led to a significant increase in the proportion of MZ twins. These are at high risk of fetal death and this needs to be considered when local stillbirth and perinatal mortality rates are used in auditing obstetric services.

England↗
PubMed1978

Factors affecting reproduction in red deer (Cervus elaphus) hinds on Rhum.

In a population of free-ranging red deer hinds on the Isle of Rhum (Inner Hebrides) we investigated relationships between four aspects of reproductive performance (fertility, calf birth weight, birth sex ratio and calving date) and four variables likely to affect the mother's condition: age, reproductive status, home range area and year of calving. Fertility was significantly related to mother's age, reproductive status and home range area as well as to year of calf's birth. Stag calves were heavier than hind calves and birth weight was significantly related to mother's age, home range area and year of (calf's) birth but not to mother's reproductive status. Birth sex ratio did not differ from parity, and was not significantly associated with any of the four variables examined. Birth date was significantly related to the mother's reproductive status, home range area and year of (calf's) birth but not to mother's age or the sex of the calf.

Animals↗
PubMed1979

Male reproductive patterns in nonhibernating bats.

Knowledge relative to the reproduction of nonhibernating bats is reviewed. Events in the male, as they are now understood, are summarized for all families for which data exist. Attention is given to the wide species diversity of male accessory sex oragns in respect to gross structure and glandular complement. Stability or variability or organization of the male reproductive system is noted. Functional relationships between primary and accessory sex organs are considered and any synchrony between these organs and their functional cyclicity identified. Various frequencies of male reproductive cycles are examined for each species within families. Factors influencing male reproductive evens in nonhibernating Chiroptera are briefly considered. It has long been speculation that reproductive cycles under natural conditions are strikingly related to the environment, with such features as temperature, moisture, length of day and available food all implicated. These cues, however, appear to be filtered through varied genetic potential and physiological patterns, since not all species respond similarly, even though residing together in a homogeneous environment. Variation between certain species in frequency and length of the oestrous cycle seem to be accommodated to by parallel adjustments in the male, including extended sperm production or storage and continued secretory activity of accessory sex glands.

Animals↗
PubMed1984

Photoperiod influences the annual reproductive cycle of the male pallid bat (Antrozous pallidus).

Adult pallids bats collected in April or May, were maintained in short or long photoperiods (10 or 14 h light/day) for 3-6 months. In August, the short-day bats had regressed testes, epididymal spermatozoa and fully developed accessory sex glands, corresponding to the autumnal reproductive condition of field animals; long-day bats had testes undergoing spermatogenesis, few epididymal spermatozoa and undeveloped accessory sex glands (summer reproductive condition). Bats in each photoperiod manifested the expected autumnal reproductive pattern in October. We suggest that photoperiod influences the reproductive physiology of male pallid bats by affecting an endogenous circannual reproductive rhythm.

Animals↗
PubMed1986

Effects of reciprocal ovary transplantation on reproductive performance of lethal yellow mice (Ay/a; C57BL/6J).

This study was conducted to determine whether reproductive failures in ageing, obese lethal yellow (Ay/a) females are due primarily to defects within Ay/a ovaries or to systemic defects which may operate outside the ovaries. Reciprocal ovary transplantation between control (a/a) and lethal yellow (Ay/a) females provided an experimental system to test the reproductive potential of not only Ay/a ovaries in control (a/a) females but also control (a/a) ovaries in mutant (Ay/a) females. Results on reproductive performance of all four combinations of grafts between Ay/a and a/a mice proved that Ay-induced reproductive failures are not due to intrinsic ovarian lesions but rather to defects operating extrinsically to the ovary. The hypothalamo-pituitary axis is a likely site for this reproductive lesion.

Aging↗
PubMed2001

Gender differences in the inhibitory effects of a reduction in ambient temperature and a reduction in food quantity on reproduction in the Southern African rodent, Rhabdomys pumilio.

The effects of a reduction in ambient temperature (from 26 degrees C to 15 degrees C) and a 10% reduction in daily food consumption on reproductively active male and female four-striped field mice ( Rhabdomys pumilio) were investigated. In male R. pumilio, both reduced ambient temperature and a reduction in food quantity had an inhibitory effect on spermatogenesis and on size of the reproductive organs, and this was greatest when the two factors were combined and the effect of fat was removed. Female R. pumilio responded differently and reproduction was inhibited by a reduction in food quantity, irrespective of ambient temperature. The masses of the ovaries and uterus, the numbers of developing follicles and corpora lutea, and the development of the uterine wall were all reduced by food deprivation at 26 degrees C to levels similar to those that resulted from a reduction in ambient temperature to 15 degrees C with a reduction in food quantity. It is concluded that reproduction in R. pumilio from the Eastern Cape Province of South Africa is opportunistic, that reproduction will be inhibited by an energetic challenge and that there is sexual dimorphism in the response to ambient temperature and food supply.

Animals↗
PubMed2001

Maternal nutrition and reproduction of daughters in wild house mice (Mus musculus).

Food deprivation after weaning often has greater effects on the reproductive success of females than of males. However, if animals are deprived prenatally (that is, through food deprivation of the mother during gestation), the reproductive success of males may be more adversely affected than that of females because of a disruption in the organizational effects of testosterone in neonatal male mice. The hypotheses that daughters of female mice deprived of food during gestation would have lower reproductive success than control daughters, but that the impact of maternal food deprivation would be lower for daughters than it would be for sons, was tested. There was no difference in the proportion of daughters of food-deprived and control mothers that produced one or two litters. However, the mean number of pups weaned in the second litters by daughters of control females (5.9 +/- 0.57 SEM) was greater than the number of pups weaned by daughters of food-deprived females (4.5 +/- 0.65 SEM). There were no differences in the mean birth or weaning body weights of offspring. Therefore, maternal food deprivation in mice may have a small but significant effect on the reproductive success of daughters. However, studies of sons born to females that were subjected to the same food deprivation protocol indicate that maternal food deprivation may have a much greater effect on the reproduction of sons than on that of daughters.

Animals↗
PubMed2003

Type II gonadotrophin-releasing hormone (GnRH-II) in reproductive biology.

Humans may be particularly unusual with respect to the gonadotrophin-releasing hormone (GnRH) control of their reproductive axis in that they possess two distinct GnRH precursor genes, on chromosomes 8p11-p21 and 20p13, but only one conventional GnRH receptor subtype (type I GnRH receptor) encoded within the genome, on chromosome 4. A disrupted human type II GnRH receptor gene homologue is present on chromosome 1q12. The genes encoding GnRH ligand precursors and GnRH receptors have now been characterized in a broad range of vertebrate species, including fish, amphibians and mammals. Ligand precursors and receptors can be categorized into three phylogenetic families. Members of each family exist in primitive vertebrates, whereas mammals exhibit selective loss of ligand precursor and receptor genes. One interpretation of these findings is that each ligand-cognate receptor family may have evolved to fulfil a separate function in reproductive physiology and that species-specific gene inactivation, modification or loss may have occurred during evolution when particular roles have become obsolete or subject to regulation by a different biochemical pathway. Evidence in support of this concept is available following the characterization of the chromosomal loci encoding the human type II GnRH receptor homologue, a rat type II GnRH receptor gene remnant (on rat chromosome 18) and a mouse type II GnRH ligand precursor gene remnant (on mouse chromosome 2). Whether type I GnRH and type II GnRH peptides elicit different signalling responses in humans by activation of the type I GnRH receptor in a cell type-specific fashion remains to be shown. Recent structure-function studies of GnRH ligands and GnRH receptors and their expression patterns in different tissues add further intrigue to this hypothesis by indicating novel roles for GnRH such as neuromodulation of reproductive function and direct regulation of peripheral reproductive tissues. Surprises concerning the complexities of GnRH ligand and receptor function in reproductive endocrinology should continue to emerge in the future.

Amino Acid Sequence↗
PubMed2005

Molecular interactions of the aryl hydrocarbon receptor and its biological and toxicological relevance for reproduction.

The dioxin/aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor responsive to both natural and man-made environmental compounds. AhR and its nuclear partner ARNT are expressed in the female reproductive tract in a variety of species and several indications suggest that the AhR might play a pivotal role in the physiology of reproduction. Furthermore, it appears to be the mediator of most, if not all, the adverse effects on reproduction of a group of highly potent environmental pollutants collectively called aryl hydrocarbons (AHs), including the highly toxic compound 2,3,7,8-tetrachlor-odibenzo-p-dioxin (TCDD). Although a large body of recent literature has implicated AhR in multiple signal transduction pathways, the mechanisms of action resulting in a wide spectrum of effects on female reproduction are largely unknown. Here we summarize the major types of molecular cross-talks that have been identified for the AhR and linked cell signaling pathways and that are relevant for the understanding of the role of this transcription factor in female reproduction.

Animals↗
PubMed2006

Deconstructing mammalian reproduction: using knockouts to define fertility pathways.

Reproduction is the sine qua non for the propagation of species and continuation of life. It is a complex biological process that is regulated by multiple factors during the reproductive life of an organism. Over the past decade, the molecular mechanisms regulating reproduction in mammals have been rapidly unraveled by the study of a vast number of mouse gene knockouts with impaired fertility. The use of reverse genetics to generate null mutants in mice through targeted disruption of specific genes has enabled researchers to identify essential regulators of spermatogenesis and oogenesis in vivo and model human disorders affecting reproduction. This review focuses on the merits, utility, and the variations of the knockout technology in studies of reproduction in mammals.

Animals↗
PubMed2006

Circadian rhythms and reproduction.

There is a growing recognition that the circadian timing system, in particular recently discovered clock genes, plays a major role in a wide range of physiological systems. Microarray studies, for example, have shown that the expression of hundreds of genes changes many fold in the suprachiasmatic nucleus, liver heart and kidney. In this review, we discuss the role of circadian rhythmicity in the control of reproductive function in animals and humans. Circadian rhythms and clock genes appear to be involved in optimal reproductive performance, but there are sufficient redundancies in their function that many of the knockout mice produced do not show overt reproductive failure. Furthermore, important strain differences have emerged from the studies especially between the various Clock (Circadian Locomotor Output Cycle Kaput) mutant strains. Nevertheless, there is emerging evidence that the primary clock genes, Clock and Bmal1 (Brain and Muscle ARNT-like protein 1, also known as Mop3), strongly influence reproductive competency. The extent to which the circadian timing system affects human reproductive performance is not known, in part, because many of the appropriate studies have not been done. With the role of Clock and Bmal1 in fertility becoming clearer, it may be time to pursue the effect of polymorphisms in these genes in relation to the various types of infertility in humans.

Animals↗
PubMed1999

Role of reproductive technologies and genetic resource banks in animal conservation.

In combination with modem reproductive technologies, there is potential to use frozen and stored germplasm (genetic resource banks) to support conservation measures for the maintenance of genetic diversity in threatened species. However, turning this idea into reality is a complex process, requiring interdisciplinary collaboration and clearly defined goals. As the number of species deserving the attention of conservation scientists is overwhelmingly large, yet detailed knowledge of reproductive physiology is restricted to relatively few of them, choosing which species to conserve is one of the most difficult issues to be tackled. Besides the direct application of technologically advanced reproductive procedures, modern approaches to non-invasive endocrine monitoring play an important role in optimizing the success of natural breeding programmes. Through the analysis of urine and faecal samples, this type of technology provides invaluable management information about the reproductive status of diverse species. For example, it is possible to diagnose pregnancy and monitor oestrous cycles in elephants and rhinos without causing stress through restraint for sample collection. In this review, we identify the potential contribution of reproductive biology and genetic resource banks to animal conservation, but also highlight the complexity of issues determining the extent to which this potential can be achieved.

Animals↗
PubMed1999

Influence of social factors on immune function and reproduction.

Animals are presented with continuous energy demands that vary seasonally. For example, during the winter many small mammals and birds inhibit reproduction and growth and funnel energy into thermogenesis or cellular maintenance. As energy shortages become more severe, survival may become compromised because processes such as immune function and thermogenesis are impaired. Thus, there are trade-offs between energetically expensive processes such as reproduction and immune function. In this review, the immune function and reproduction of seasonally breeding species are evaluated in relation to social interactions. It is proposed that individuals maintain the highest degree of immune function that is energetically possible within the constraints of other survival needs, as well as growth and reproduction, in habitats in which energy requirements and availability often fluctuate. It is hypothesized that extrinsic factors, such as social environment, modulate energy allocation to reproductive and immune function and that hormonal mechanisms underlie the partitioning of energy to various physiological components.

Animals↗