The sympathetic nervous system regulates the three glycerol-3P generation pathways in white adipose tissue of fasted, diabetic and high-protein diet-fed rats

Abstract

The aim of the present study was to investigate the participation of the sympathetic nervous system (SNS) in the control of glycerol-3-P (G3P) generating pathways in white adipose tissue (WAT) of rats in three situations in which the plasma insulin levels are low. WAT from 48 h fasted animals, 3 day-streptozotocin diabetic animals and high-protein, carbohydrate-free (HP) diet-fed rats was surgical denervated and the G3P generation pathways were evaluated. Food deprivation, diabetes and the HP diet provoke a marked decrease in the rate of glucose uptake and glycerokinase (GyK) activity, but a significant increase in the glyceroneogenesis, estimated by the phosphoenolpyruvate carboxykinase (PEPCK) activity and the incorporation of 1-[(14)C]-pyruvate into glycerol-TAG. The denervation provokes a reduction (~70%) in the NE content of WAT in fasted, diabetic and HP diet-fed rats. The denervation induced an increase in WAT glucose uptake of fed, fasted, diabetic and HP diet-fed rats (40%, 60%, 3.2 fold and 35%, respectively). TAG-glycerol synthesis from pyruvate was reduced by denervation in adipocytes of fed (58%) and fasted (36%), saline-treated (58%) and diabetic (23%), and HP diet-fed rats (11%). In these same groups the denervation reduced the PEPCK mRNA expression (75%-95%) and the PEPCK activity (35%-60%). The denervation caused a ~35% decrease in GyK activity of control rats and a further ~35% reduction in the already low enzyme activity of fasted, diabetic and HP diet-fed rats. These data suggest that the SNS plays an important role in modulating G3P generating pathways in WAT, in situations where insulin levels are low.

Identification of Suitable Reference Genes for Quantitative Gene Expression Analysis in Innervated and Denervated Adipose Tissue from Cafeteria Diet‐Fed Rats

“…To the best of our knowledge, this is the first study to evaluate 10 candidates commonly used as reference genes for qRT-PCR in innervated and denervated IBAT and RWAT from cafeteria diet-fed or control diet-fed rats by the following algorithms: geNorm, NormFinder, BestKeeper, and comparative ΔC t method. Initially, our efficiency of surgical sympathetic denervation agree with several studies that have demonstrated a similar reduction in IBAT and RWAT NE concentration without changes in tissue weight (Foster et al, 1982;Frasson et al, 2012; -Hagen et al, 1990;Kawashita et al, 2002). The absence of denervation effects in IBAT and RWAT weight demonstrates that the main stimulus for the increase in tissue weight in cafeteria diet-fed rats is hormonal.…”

Cellular mechanisms regulating fuel metabolism in mammals: Role of adipose tissue and lipids during prolonged food deprivation

“…Because GK activity in adipose tissue of humans and rodents is relatively very low, even in the fed state [61, 62], G3P must be derived from either conversion of glucose to dihydroxyacetone (DHA) and then G3P [63], or by glyceroneogenesis using branched chain amino acids (BCAA) or TCA cycle intermediates [64]. However, in rats fasted for 48 hours, adipose tissue glucose uptake decreases by 68% while PEPCK-C activity increases by 400% [65], so glyceroneogenesis may be the preferred method of G3P synthesis during fasting.…”

A computational model of postprandial adipose tissue lipid metabolism derived using human arteriovenous stable isotope tracer data

“…Within the adipocyte, glucose is quickly converted to glucose-6-phosphate (G-6-P) which serves to trap the glucose within the adipocyte. Glucose is the primary source of the glyceraldehyde-3-phosphate (G-3-P) backbone needed for re-esterification of adipocyte NEFA [36].…”