Monosodium l-glutamate-obesity onset is associated with disruption of central control of the hypothalamic-pituitary-adrenal axis and autonomic nervous system

Lactation overnutrition-induced obesity impairs effects of exogenous corticosterone on energy homeostasis and hypothalamic-pituitary-adrenal axis in male rats

AIMS

Litter size reduction on the first days of life results in increased body weight and adiposity, with higher levels of circulating glucocorticoids. Obese rodents are more sensitive to the anabolic effects of glucocorticoids and less responsive to glucocorticoids feedback on hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to evaluate effects of the treatment with corticosterone on metabolic responses and HPA axis in adult male rats reared in small litters.

MAIN METHODS

From postnatal day (PND) 60 to 88, adult male rats of normal (NL- 10 pups/dam) and small (SL- 3 pups/dam) litters received oral treatment with Corticosterone (CORT-15 mg/L) in the drinking water or no treatment, composing the four experimental groups (NL-water; NL-CORT; SL-water and SL-CORT), for the evaluation of energy homeostasis and HPA axis.

KEY FINDINGS

Male rats of SL-water group presented on PND88: glucose intolerance, higher adiposity, plasma triglycerides, free fatty acids, total and low-density lipoprotein (LDL) cholesterol and corticosterone. SL-water animals showed increased mRNA of corticotrophin-releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN) and proopiomelanocortin (POMC) in the pituitary, with decreased mRNA expression of PVN mineralocorticoid receptor. NL-CORT animals presented glucose intolerance, increased body weight, food intake, total and LDL cholesterol. Glucocorticoid treatment reduced corticosterone levels and adrenal cortex thickness in NL group, associated with increased mRNA of PVN CRH and pituitary POMC, without effects on SL animals.

SIGNIFICANCE

Lactation overnutrition promotes hyperreactivity of HPA axis and reduces the responsiveness to glucocorticoids effects on energy balance and negative feedback of HPA axis in adult male rats.

Phenylhydrazine-induced anemia reduces subcutaneous white and brown adipose tissues in hypothalamic obese rats

NEW FUNDINGS

What is the central question of this study? This study aims to assess whether an anemic state could modify adiposity and metabolic parameters in hypothalamic obese rats. What is the main finding and its importance? Our results indicate that hypothalamic obese rats do not display iron deficiency. However, the pharmacological induction of anemia in hypothalamic-obese rats resulted in reduced adiposity, characterized by a decrease in subcutaneous white and brown adipose tissue depots. These findings suggest that iron imbalance in obesity may elevate lipolysis.

ABSTRACT

Iron imbalance is frequent in obesity. Herein, we evaluated the impact of anemia induced by phenylhydrazine on adiposity and metabolic state of hypothalamic obese rats. Hypothalamic obesity was induced by high doses of glutamate monosodium (MSG; 4g/Kg) administered to neonatal male rats (n = 20). Controls (CTL; non-obese rats) received saline equimolar (n = 20). Rats were weaned at 21 days of life. At 70 days, half of the rats received three intraperitoneal doses of phenylhydrazine (PHZ; 40mg/Kg/dose) or saline solution. Body weight and food intake were accompanied for four weeks after PHZ administration. At 92 days, rats were euthanized, blood was collected for microcapillary hematocrit (Hct) analysis and plasma quantification of glucose, triglycerides, total cholesterol, and iron levels. The liver, the spleen, and the white (WAT) and brown (BAT) adipose tissues were excised, weighed, and used for histology. MSG-treated rats developed obesity, hypertriglyceridemia, and insulin resistance, compared to CTL rats, without changes in iron levels and Hct. PHZ administration reduced iron plasma levels and promoted similar tissue injuries in the spleen and liver from MSG and CTL rats. However, in MSG-treated rats, PHZ decreased fasting glucose levels and Hct, as well as diminished the subcutaneous WAT and BAT mass. Although MSG-obesity does not affect iron plasma levels and Hct by itself, PHZ-induced anemia associated with obesity induces a marked drop in subcutaneous WAT and BAT mass, suggesting that iron imbalance may lead to increased lipolytic responses in obese rats, compared to lean rats. This article is protected by copyright. All rights reserved.

The Vagus Nerve and Spleen: Influence on White Adipose Mass and Histology of Obese and Non-obese Rats

The vagus nerve (VN) and spleen represent a complex interface between neural and immunological functions, affecting both energy metabolism and white adipose tissue (WAT) content. Here, we evaluated whether vagal and splenic axis participates in WAT mass regulation in obese and non-obese male Wistar rats. High doses of monosodium glutamate (M; 4 g/Kg) were administered during the neonatal period to induce hypothalamic lesion and obesity (M-Obese rats). Non-obese or Control (CTL) rats received equimolar saline. At 60 days of life, M-Obese and CTL rats were randomly distributed into experimental subgroups according to the following surgical procedures: sham, subdiaphragmatic vagotomy (SV), splenectomy (SPL), and SV + SPL (n = 11 rats/group). At 150 days of life and after 12 h of fasting, rats were euthanized, blood was collected, and the plasma levels of glucose, triglycerides, cholesterol, insulin, and interleukin 10 (IL10) were analyzed. The visceral and subcutaneous WAT depots were excised, weighed, and histologically evaluated for number and size of adipocytes as well as IL10 protein expression. M-Obese rats showed higher adiposity, hyperinsulinemia, hypertriglyceridemia, and insulin resistance when compared with CTL groups (p < 0.05). In CTL and M-Obese rats, SV reduced body weight gain and triglycerides levels, diminishing adipocyte size without changes in IL10 expression in WAT (p< 0.05). The SV procedure resulted in high IL10 plasma levels in CTL rats, but not in the M-Obese group. The splenectomy prevented the SV anti-adiposity effects, as well as blocked the elevation of IL10 levels in plasma of CTL rats. In contrast, neither SV nor SPL surgeries modified the plasma levels of IL10 and IL10 protein expression in WAT from M-Obese rats. In conclusion, vagotomy promotes body weight and adiposity reduction, elevating IL10 plasma levels in non-obese animals, in a spleen-dependent manner. Under hypothalamic obesity conditions, VN ablation also reduces body weight gain and adiposity, improving insulin sensitivity without changes in IL10 protein expression in WAT or IL10 plasma levels, in a spleen-independent manner. Our findings indicate that the vagal-spleen axis influence the WAT mass in a health state, while this mechanism seems to be disturbed in hypothalamic obese animals.

Whole-body vibration promotes lipid mobilization in hypothalamic obesity rat

OBJECTIVES

This study aimed to analyze the effect of whole-body vibration (WBV) on metabolic parameters using the monosodium l-glutamate (MSG) model of obesity.

METHOD

MSG-obese rats that were exposed to WBV on a vibrating platform with 60 Hz frequency, 2 mm amplitude, three times/week, 10 min/day, during eight weeks (from postnatal day (PN) 80 to PN136). Blood glucose, creatine kinases (CK and CK-MB) and lipid profile through plasma and liver levels of lipids and lipoproteins were evaluated. Morphology and oxidative stress of adipose and hepatic tissues were further evaluated.

RESULTS

When performing a WBV exercise, animals showed contrasting metabolic responses. Vibration Control group (CTL-WBV) presented a reduction in CK and liver triacylglycerol, an increase in glucose, lactate, total cholesterol, liver cholesterol, and LDL while MSG Vibration group (MSG-WBV) showed an increase in total triacylglycerol, VLDL, lactate, CK, liver cholesterol, additional liver lipid peroxidation and LDL, total cholesterol and CKMB reduction.

CONCLUSION

Even although the MSG is a model of impacting injury, the metabolic demand of WBV exercise was able to induce mobilization of substrates, highlighting the lipid mobilization in obese animals, it should be used as a metabolic rehabilitation tool in patients with metabolic diseases, such as obesity and diabetes.