Inhibition of Na(+),K(+)-ATPase in the hypothalamus, pons and cerebellum of the offspring rat due to experimentally-induced maternal hypothyroidism

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

Effects of gestational thiamine-deprivation and/or exposure to ethanol on crucial offspring rat brain enzyme activities

OBJECTIVE

The fetal alcohol spectrum disorder (FASD) is a group of clinical conditions associated with the in utero exposure to ethanol (EtOH). We have recently examined the effects of a moderate maternal exposure to EtOH on crucial brain enzyme activities in offspring rats, and discussed the translational challenges arising when attempting to simulate any of the clinical conditions associated with FASD.

MATERIALS AND METHODS

In this current study, we: (i) address the need for a more consistent and reliable in vivo experimental platform that could simulate milder cases of FASD complicated by simultaneous thiamine-deprivation during gestation and (ii) explore the effects of such a moderate maternal exposure pattern to EtOH and a thiamine-deficient diet (TDD) on crucial enzyme activities in the offspring rat brains.

RESULTS

We demonstrate a significant decrease in the newborn and 21-day-old offspring body and brain weight due to maternal dietary thiamine-deprivation, as well as evidence of crucial brain enzyme activity alterations that in some cases are present in the offspring rat brains long after birth (and the end of the maternal exposure to both EtOH and TDD).

CONCLUSIONS

Our findings provide a preliminary characterization of important neurochemical effects due to maternal exposure to EtOH and TDD during gestation that might affect the offspring rat neurodevelopment, and that characterization should be further explored in a brain region-specific manner level as well as through the parallel examination of changes in the offspring rat brain lipid composition.

The effects of vitamin C on hypothyroidism-associated learning and memory impairment in juvenile rats

In this study the effects of Vitamin C (Vit C) on hypothyroidism-associated learning and memory impairment in juvenile rats was investigated. The pregnant rats were kept in separate cages. After delivery, they were randomly divided into six groups and treated: (1) Control; (2) Propylthiouracil (PTU) which 0.005% PTU in their drinking; (3-5) Propylthiouracil- Vit C groups; besides PTU, dams in these groups received 10, 100 and 500 mg/kg Vit C respectively, (6) one group as a positive control; the intact rats received an effective dose, 100 mg/kg Vit. C. After delivery, the pups were continued to receive the experimental treatments in their drinking water up to 56th day of their life. Ten male offspring of each group were randomly selected and tested in the Morris water maze (MWM) and passive avoidance (PA) which were started at 63th day (one week after stopping of the treatments). Brains were then removed for biochemical measurements. PTU increased time latency and traveled distance during 5 days in MWM while, reduced the spent time in target quadrant in MWM and step-trough latency (STL) in PA. PTU decreased thiol content, superoxide dismutase (SOD) and catalase (CAT) activities in the brain while, increased molondialdehyde (MDA). In MWM test, 10, 100 and 500 mg/kg Vit C reduced time latency and traveled distance without affecting the traveling speed during 5 days. All doses of Vit C increased the spent time in target quadrant in probe trail of MWM and also increased STL in PA test. Vit C increased thiol, SOD and CAT in the brain tissues while, reduced MDA. Results of present study confirmed the beneficial effects of Vit C on learning and memory. It also demonstrated that Vit C has protective effects on hypothyroidism-associated learning and memory impairment in juvenile rats which might be elucidated by the antioxidative effects.

The Effects of Altered Membrane Cholesterol Levels on Sodium Pump Activity in Subclinical Hypothyroidism

BACKGROUND

Metabolic dysfunctions characteristic of overt hypothyroidism (OH) start at the early stage of subclinical hypothyroidism (SCH). Na⁺/K⁺-ATPase (the sodium pump) is a transmembrane enzyme that plays a vital role in cellular activities in combination with membrane lipids. We evaluated the effects of early changes in thyroid hormone and membrane cholesterol on sodium pump activity in SCH and OH patients.

METHODS

In 32 SCH patients, 35 OH patients, and 34 euthyroid patients, sodium pump activity and cholesterol levels in red blood cell membranes were measured. Serum thyroxine (T₄) and thyroid stimulating hormone (TSH) levels were measured using enzyme-linked immunosorbent assays. Differences in their mean values were analysed using post hoc analysis of variance. We assessed the dependence of the sodium pump on other metabolites by multiple regression analysis.

RESULTS

Sodium pump activity and membrane cholesterol were lower in both hypothyroid groups than in control group, OH group exhibiting lower values than SCH group. In SCH group, sodium pump activity showed a significant direct dependence on membrane cholesterol with an inverse relationship with serum TSH levels. In OH group, sodium pump activity depended directly on membrane cholesterol and serum T₄ levels. No dependence on serum cholesterol was observed in either case.

CONCLUSION

Despite the presence of elevated serum cholesterol in hypothyroidism, membrane cholesterol contributed significantly to maintain sodium pump activity in the cells. A critical reduction in membrane cholesterol levels heralds compromised enzyme activity, even in the early stage of hypothyroidism, and this can be predicted by elevated TSH levels alone, without any evident clinical manifestations.