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.

Contrasting strategies of osmotic and ionic regulation in freshwater crabs and shrimps: gene expression of gill ion transporters.

Owing to their extraordinary niche diversity, the Crustacea are ideal for comprehending the evolution of osmoregulation. The processes that effect systemic hydro-electrolytic homeostasis maintain hemolymph ionic composition via membrane transporters located in highly specialized gill ionocytes. We evaluated physiological and molecular hyper- and hypo-osmoregulatory mechanisms in two phylogenetically distant, freshwater crustaceans, the crab Dilocarcinus pagei and the shrimp Macrobrachium jelskii, when osmotically challenged for up to 10 days. When in distilled water, D. pagei survived without mortality, hemolymph osmolality and [Cl-] increased briefly, stabilizing at initial values, while [Na+] decreased continually. Expression of gill V-type H+-ATPase (V-ATPase), Na+/K+-ATPase and Na+/K+/2Cl- symporter genes was unchanged. In M. jelskii, hemolymph osmolality, [Cl-] and [Na+] decreased continually for 12 h, the shrimps surviving only around 15-24 h exposure. Gill transporter gene expression increased 2- to 5-fold. After 10 days exposure to brackish water (25‰S), D. pagei was isosmotic, iso-chloremic and iso-natriuremic. Gill V-ATPase expression decreased while Na+/K+-ATPase and Na+/K+/2Cl- symporter expression was unchanged. In M. jelskii (20‰S), hemolymph was hypo-regulated, particularly [Cl-]. Transporter expression initially increased 3- to 12-fold, declining to control values. Gill V-ATPase expression underlies the ability of D. pagei to survive in fresh water while V-ATPase, Na+/K+-ATPase and Na+/K+/2Cl- symporter expression enables M. jelskii to confront hyper/hypo-osmotic challenges. These findings reveal divergent responses in two unrelated crustaceans inhabiting a similar osmotic niche. While D. pagei does not secrete salt, tolerating elevated cellular isosmoticity, M. jelskii exhibits clear hypo-osmoregulatory ability. Each species has evolved distinct strategies at the transcriptional and systemic levels during its adaptation to fresh water.