Effects of prenatal bisphenol-A exposure and postnatal overfeeding on cardiovascular function in female sheep.

Bisphenol-A (BPA) is a widely used endocrine-disrupting chemical. Prenatal exposure to BPA is known to affect birth weight, but its impact on the cardiovascular system has not been studied in detail. In this study, we investigated the effects of prenatal BPA treatment and its interaction with postnatal overfeeding on the cardiovascular system. Pregnant sheep were given daily subcutaneous injections of corn oil (control) or BPA (0.5 mg/kg/day in corn oil) from day 30 to day 90 of gestation. A subset of female offspring of these dams were overfed to increase body weight to ~30% over that of normal fed controls. Cardiovascular function was assessed using non-invasive echocardiography and cuff blood pressure (BP) monitoring at 21 months of age. Ventricular tissue was analyzed for gene expression of cardiac markers of hypertrophy and collagen at the end of the observation period. Prenatal BPA exposure had no significant effect on BP or morphometric measures. However, it increased atrial natriuretic peptide gene expression in the ventricles and reduced collagen expression in the right ventricle. Overfeeding produced a marked increase in body weight and BP. There were compensatory increases in left ventricular area and internal diameter. Prenatal BPA treatment produced a significant increase in interventricular septal thickness when animals were overfed. However, it appeared to block the increase in BP and left ventricular area caused by overfeeding. Taken together, these results suggest that prenatal BPA produces intrinsic changes in the heart that are capable of modulating morphological and functional parameters when animals become obese in later life.

High fat diet affects reproductive functions in female diet-induced obese and dietary resistant rats.

The incidence of ovulatory disorders is common in obese animal models. The mechanism behind this effect is unclear. We hypothesised that a high-fat (HF) diet induces alterations in neuroendocrine mechanisms resulting in anovulation in diet-induced obese (DIO) animals. Adult female DIO and diet-resistant (DR) rats were fed either chow or a HF diet (45% calories from fat) for 6 weeks. Oestrous cyclicity and body weight were monitored regularly. At the end of treatment, rats were implanted with a jugular catheter to monitor luteinising hormone (LH) levels on the day of pro-oestrous. Rats were sacrificed on the next pro-oestrous, and their brains and ovaries were collected. Plasma from trunk blood was analysed for oestradiol and leptin concentrations. Ovaries were fixed and sectioned for histological analysis. Brains were removed, frozen and sectioned, and norepinephrine (NE) concentrations in discrete hypothalamic areas were measured using high-performance liquid chromatography with electrochemical detection. A HF diet exposure affected oestrous cyclicity in both DIO and DR rats, with the effect being more pronounced in DIO animals. HF diet exposure increased leptin levels in both DIO and DR rats. Oestradiol levels were low in the DIO-HF group. NE levels in the hypothalamus were unaffected by HF diet or genotype. A normal LH surge was observed in DR-Chow rats and LH levels were low in the remaining groups. These results lead to the conclusion that DIO rats have an inherently reduced reproductive capacity and exposure to a HF diet decreases it further. A reduction in oestradiol and LH surge levels could contribute to this effect; however, the underlying mechanisms need to be investigated further.

Chronic exposure to a high-fat diet affects stress axis function differentially in diet-induced obese and diet-resistant rats.

OBJECTIVE: Consumption of a high-fat (HF) diet is a contributing factor for the development of obesity. HF diet per se acts as a stressor, stimulating hypothalamo-pituitary-adrenal (HPA) axis activity resulting in elevated glucocorticoid levels; however, the mechanism behind this activation is unclear. We hypothesized that consumption of an HF diet activates HPA axis by increasing norepinephrine (NE) in the paraventricular nucleus (PVN) of the hypothalamus, leading to elevation in corticotrophin-releasing hormone (CRH) concentration in the median eminence (ME) resulting in elevated serum corticosterone (CORT). SUBJECTS: To test this hypothesis, diet-induced obese (DIO) and diet-resistant (DR) rats were exposed to either chow or HF diet for 6 weeks. MEASUREMENTS: At the end of 6 weeks, NE in the PVN was measured using HPLC, CRH in the ME, and CORT and leptin levels in the serum were measured using RIA and ELISA, respectively. The gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in NE synthesis, and leptin receptor in brainstem noradrenergic nuclei were also measured. RESULTS: HF diet increased PVN NE in both DIO and DR rats (P<0.05). However, this was accompanied by increases in CRH and CORT secretion only in DR animals, but not in DIO rats. Leptin receptor mRNA levels in the brainstem noradrenergic areas were not affected in both DIO and DR rats. However, HF diet increased TH mRNA levels only in DIO rats. CONCLUSION: Significant differences occur in all the arms of HPA axis function between DIO and DR rats. Further studies are needed to determine whether this could be a causative factor or a consequence to obesity.

Chronic exposure to low levels of oestradiol-17beta affects oestrous cyclicity, hypothalamic norepinephrine and serum luteinising hormone in young intact rats.

Chronic exposure to oestrogens is known to inhibit the secretion of luteinising hormone (LH) in rats, leading to anovulation. Hypothalamic catecholamines, norepinephrine and dopamine play an important role in LH regulation. However, the effects of chronic exposure to low levels of oestradiol on hypothalamic catecholamines have not been investigated thoroughly. In the present study, adult female Sprague-Dawley rats were either sham implanted or implanted with 17beta-oestradiol (E(2)) pellets (20 ng/day) for 30 (E-30), 60 (E-60) or 90 (E-90) days. E(2) exposure affected oestrous cyclicity and ovarian morphology in a duration-dependent manner. There was no change in oestrous cyclicity in E-30 rats; however, 75% of E-60 and 95% of E-90 rats were acyclic (P < 0.05). Cycling rats from E-30 or the control group were killed at different time points on the afternoon of pro-oestrous. E-30 rats in oestrous, constant oestrous rats in the E-60 and E-90 groups and a group of old constant oestrous (OCE) rats were killed at 12.00 h. LH was measured in the serum by radioimmunoassay. Individual hypothalamic nuclei that are involved in LH regulation were microdissected and analysed for norepinephrine and dopamine levels using high-performance liquid chromatography/electrochemical detection. Norepinephrine levels in the hypothalamic nuclei increased significantly in control and E-30 groups during the afternoon of pro-oestrous, which was accompanied by a rise in LH levels (P < 0.05). On the day of oestrous, norepinephrine concentrations in hypothalamic nuclei and serum LH were significantly lower in E-60, E-90 and OCE rats compared to E-30 and control rats. On the other hand, dopamine levels declined significantly in one hypothalamic nucleus. These results indicate that chronic E(2) exposure affects hypothalamic catecholamine and serum LH levels in a duration-dependent manner. This coincides well with the loss of cyclicity observed in these animals. These results suggest that repeated exposure to endogenous oestrogens could play a role in reproductive senescence.

Effect of L-dopa on interleukin-1 beta-induced suppression of luteinizing hormone secretion in intact female rats.

BACKGROUND: The cytokine, interleukin-1 beta (IL-1 beta), increases during immune stress and is known to suppress the preovulatory luteinizing hormone (LH) surge in female rats by decreasing hypothalamic norepinephrine (NE). We hypothesized that IL-1 beta could produce this effect by decreasing NE biosynthesis. METHODS: Female Sprague-Dawley rats were implanted with a push-pull cannula in the medial preoptic area (MPA) of the hypothalamus and a catheter in the jugular vein. They were treated i.p. with the vehicle or 5 microg of IL-1 beta, the NE precursor, L-dopa, or a combination of L-dopa and IL-1 beta at 1300 hours on the day of proestrus. They were subjected to push-pull perfusion and serial blood sampling. Perfusates were analyzed for NE levels and serum samples for LH. RESULTS: IL-1 beta treatment blocked the increase in NE levels in the MPA and the LH surge. Treatment with L-dopa was able to partially restore both NE and LH levels during the afternoon of proestrus. IL-1 beta treatment caused failure of ovulation and this effect was also reversed by L-dopa. CONCLUSIONS: These results suggest that IL-1 beta could decrease NE levels in the MPA to suppress reproductive functions and L-dopa can be used to counter this effect.