Exercise prevents whole body type 2 diabetes risk factors better than estradiol replacement in rats

High-fat diet changes the behavioural and hormonal responses to water deprivation in male Wistar rats

NEW FINDINGS

What is the central question of this study? What is the effect of an obesogenic diet on the control of hydromineral balance in rats? What is the main finding and its importance? The results showed that, when dehydrated, rats fed a high-fat diet drink less water than their control-diet-fed counterparts. Changes in aquaporin-7 and peroxisome proliferator-activated receptor α expression in the white adipose tissue might be involved.

ABSTRACT

High-fat diet (HFD) increases fat accumulation, glycaemia and blood triglycerides and is used as a model to study obesity. Besides the metabolic changes, obesity likely affects water intake. We assessed the effects of HFD on behavioural and hormonal responses to water deprivation. Additionally, we measured if the adipose tissue is differentially affected by water deprivation in control and HFD-fed rats. HFD rats showed a decreased basal water intake when compared to control-fed rats. When subjected to 48 h of water deprivation, as expected, both control and HFD rats drank more water than the hydrated rats. However, the increase in water intake was lessened in HFD dehydrated rats. Similarly, the increase in haematocrit in dehydrated rats was less pronounced in HFD dehydrated rats. These results suggest that HFD diminishes drinking behaviour. White adipose tissue weight, glycaemia and plasma glycerol concentration were increased in HFD rats; however, after 48 h of water deprivation, these parameters were significantly decreased in dehydrated HFD rats, when compared to controls. The increase in adipose tissue caused by HFD may mitigate the effects of dehydration, possibly through the increased production of metabolic water caused by lipolysis in the adipocytes. Oxytocin possibly mediates the lipolytic response, since both its secretion and receptor expression are affected by dehydration in both control and HFD rats, which suggests that oxytocin signalling is maintained in these conditions. Changes in mediators of lipolysis, such as aquaporin-7 and peroxisome proliferator-activated receptor α, might contribute to the different effects observed in control and HFD rats.

Estrogen receptor α activation modulates the gut microbiome and type 2 diabetes risk factors

Estradiol and exercise can decrease risk factors associated with type 2 diabetes (T2D) including total body weight gain and abdominal fat gain. Estradiol functions through estrogen receptor (ER) α and ERβ. Some studies suggest that activation of ERα may provide protection against T2D. Female Wistar rats were ovariectomized and fed a high-fat diet for 10 weeks and divided into the following 5 experimental groups: (1) no treatment (control), (2) exercise, (3) estradiol, (4) propylpyrazoletriyl (a selective ERα agonist), and (5) diarylpropionitrile (a selective ERβ agonist). ERα activation decreased the abundance of Firmicutes, and ERα and ERβ activation increased the abundance of Bacteroidetes. ERα activation decreased food consumption, and ERα and ERβ activation increased voluntary activity. Exercise was the only treatment to decrease the blood glucose and serum insulin levels. ERα activation, but not ERβ, increased hepatic protein expression of ACC and FAS and decreased hepatic protein expression of LPL. ERα activation also decreased hepatic mRNA expression of PPARα and PPARγ. This study elucidates the functions of estradiol by assessing specific activation of ERα and ERβ. As obesity increases the abundance of Firmicutes and decreases the abundance of Bacteroidetes, our study shows that ERα activation can restore the gut microbiome to non-obese abundances. This study further provides novel insights into ERα's role in hepatic fat metabolism via regulation of ACC, FAS, LPL, PPARα, and PPARγ.