Neuroendocrine control of reproductive function in the aging female rodent

Paternal Fenitrothion Exposures in Rats Causes Sperm DNA Fragmentation in F0 and Histomorphometric Changes in Selected Organs of F1 Generation

The adverse effects of maternal pesticides exposure on the progeny is very well established. However, the impact of paternal exposure to pesticides such as Fenitrothion (FNT) on the histomorphometry of progeny’s organs in unexposed mothers are much less well studied. Therefore, this study aims to evaluate the effects of paternal FNT exposure on the sperm quality of the parent rat and its effects on the histomorphometry of the progeny’s organs. Randomly, male Sprague Dawley rats (n = 24) categorized as F0 were distributed equally into three groups namely Control, FNT-10, and FNT-20. Control received 1 mL/kg corn oil while FNT-10 and FNT-20 received 10 mg/kg and 20 mg/kg of FNT, respectively, via oral force feeding for 28 consecutive days. At the end of the study, male rats were mated with unexposed female rats and the male rats were sacrificed to obtain sperm for sperm characterization and DNA damage evaluation. Meanwhile, the rats’ progeny (F1) namely pControl, pFNT-10, and pFNT-20 were left to grow until postnatal day 70 before being sacrificed to obtain the matured organs for histology and morphometric analysis. Our results showed that both doses of FNT reduced sperm quality and caused DNA fragmentation in F0 rats compared with the control group (p < 0.05). The number of Leydig cells as well as the diameter of the seminiferous tubules and glomerulus of the pFNT-20 group had significantly decreased (p < 0.05) compared with the pControl group. The Bowman’s space of the pFNT-20 group had significantly increased (p < 0.05) compared with the pFNT-10 and pControl groups. Therefore, paternal exposure to FNT reduced the sperm quality and increased sperm DNA fragmentation in F0 male Sprague Dawley rats and altered the histology and morphometry of the selected organs in the F1 progeny.

Plasma levels of kisspeptins in postmenopausal Chinese women do not show substantial elevation

The menopause, defined as the permanent cessation of menstruation resulting from ovarian failure, is characterized by elevated levels of serum gonadotropins. Recent studies have demonstrated that the gonadotropin hypersecretion in postmenopausal women is secondary to increase of KiSS-1 mRNA from the hypothalamus neurons, which encoded kisspeptin peptides. The present study was designed to determine whether plasma kisspeptins levels are altered in postmenopausal women. Blood samples were taken from 145 postmenopausal women, 35 young women and 30 pregnant women control in the first trimester. The plasma concentration of kisspeptins, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and estradiol (E₂) was measured using immunoassay kits. Results indicated that plasma kisspeptins levels in postmenopausal women had higher than those in young women (5.25±0.36; 4.48±0.34 pmol/L), but no significant difference was found between the two groups (p=0.179). Plasma FSH and LH levels were significantly higher in postmenopausal women (124.67±12.78, 57.14±3.57 mIu/mL) than those in young women (9.23±2.78, 7.56±2.71 mIu/mL, p<0.001). However, Plasma kisspeptins levels were not significantly correlated to FSH and LH in postmenopausal women (r=-0.23, 0.324; p=0.927, 0.176, respectively), and also there was no any correlation between plasma kisspeptins and E₂ in postmenopausal women (r=-0.065; p=0.792). Collectively, there was no significant difference in plasma kisspeptins levels between postmenopausal and young women. Our result suggested that kisspeptins' role during menopause might mainly act in central rather than peripheral system and it could not be currently used as a clinical marker for menopause.

Reproductive effects of maternal and pre-weaning undernutrition in rat offspring: age at puberty, onset of female reproductive senescence and intergenerational pup growth and viability

Maternal and/or postnatal undernutrition are widespread in human populations and are components of many experimental developmental and reproductive toxicology bio-assays. This study investigated in utero and/or pre-weaning undernutrition effects on reproductive maturation and senescence in the Sprague-Dawley rat as well as potential intergenerational effects. Pregnant rats were given food ad libitum or at 50% of normal dietary intake throughout pregnancy. Their offspring (control or IUGR) were cross-fostered to control dams with litter sizes of 8 or 16 pups (control and undernourished). Offspring body weights were reduced and onset of male puberty slightly delayed in animals from large postnatal litters. Similar body weight effects were observed in females but there was no difference in the age of vaginal opening. Female reproductive senescence as measured by onset of estrus acyclicity occurred at a younger age in IUGR-8-pup and Control-16-pup groups compared to Control-8-pup or IUGR-16-pup groups. Females were bred to control males and no evidence of adverse reproductive effects was found in any F2 groups. The offspring of the F1 generation did not show an intergenerational effect as documented in humans.

Atrazine and reproductive function: mode and mechanism of action studies

Atrazine, a chlorotriazine herbicide, is used to control annual grasses and broadleaf weeds. In this review, we summarize our laboratory's work evaluating the neuroendocrine toxicity of atrazine (and related chlorotriazines) from an historic perspective. We provide the rationale for our work as we have endeavored to determine: 1) the underlying reproductive changes leading to the development of mammary gland tumors in the atrazine-exposed female rat; 2) the cascade of physiological events that are responsible for these changes (i.e., the mode of action for mammary tumors); 3) the potential cellular mechanisms involving adverse effects of atrazine; and 4) the range of reproductive alterations associated with this pesticide.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

Effects of combined estrogen and progesterone on brain infarction in reproductively senescent female rats

Recent data from the Women's Health Initiative have highlighted many fundamental issues about the utility and safety of long-term estrogen use in women. Current hormone replacement therapy for postmenopausal women incorporates progestin with estrogen, but it is uncertain if combined therapy provides major cerebrovascular risks or benefits to these women. No experimental animal stroke studies have examined combined hormone administration. The authors tested the hypothesis that combined hormone treatment reduces ischemic injury in middle-aged female rat brain. Reproductively senescent female rats underwent 2-hour middle cerebral artery occlusion (MCAO) followed by 22 hours reperfusion. Estrogen implants were placed subcutaneously at least 7 days before MCAO, and progesterone intraperitoneal injections were given 30 minutes before MCAO, at initiation, and at 6 hours of reperfusion. Rats received no hormone, a 25-microg estrogen implant, a 25-microg estrogen implant plus 5 mg/kg intraperitoneal progesterone, or 5 mg/kg intraperitoneal progesterone. Cortical, caudoputamen, and total infarct volumes were assessed by 2,3,5-triphenyltetrazolium chloride staining and digital image analysis at 22 hours reperfusion. Cortical and total infarct volumes, except in the acute progesterone-treated group, were significantly attenuated in all estrogen-alone and combined hormone-treated groups. There were no significant differences in caudoputamen infarct volumes in all hormone-treated groups as compared with untreated rats. These data have potential clinical implications relative to stroke for postmenopausal women taking combined hormone replacement therapy.

Altered regulation of pituitary luteinizing hormone secretion by GnRH and inhibin in the aged persistent-estrous female rat

The physiologic regulation of pituitary LH secretion is under the direct control of hypothalamic GnRH as well as feedback control via ovarian steroid and peptide hormones. Changes within the hypothalamic-pituitary-ovarian axis during reproductive aging lead to the gradual attenuation and the eventual loss of cyclic LH release that is seen in the old persistent-estrous rat. In the following studies, we determined whether changes in the pituitary response to regulation by hypothalamic GnRH and/or ovarian inhibin could be involved in age-related deficits in LH release by examining the direct effect(s) of GnRH and inhibin on LH release in old persistent-estrous (PE) and young female rats using an in vitro pituitary cell culture system. Both pituitary LH content and LH release were significantly lower in PE pituitary cells compared to young pituitary cells. GnRH (10 ng/ml) significantly increased LH release above basal levels in young and PE pituitaries. However, the magnitude of LH release was significantly lower in PE pituitaries compared to young pituitaries. Treatment with recombinant inhibin (0.1, 1, or 5 ng/ml) did not significantly affect basal or GnRH-stimulated LH release from young rat pituitaries under our culture conditions. In contrast, there were significant decreases in the levels of both basal LH and GnRH-stimulated LH release from PE pituitaries after treatment with 1 or 5 ng/ml human recombinant inhibin, as well as with inhibin plus 10 ng/ml GnRH, respectively. These results suggest that there are significant changes in the pituitary response to GnRH and ovarian inhibin regulation that may lead to significant alterations in LH secretion during aging.