Resolve,
"Glycerol, a natural metabolite which is rapidly absorbed, has osmotic action, and is evenly distributed within the body fluid compartments, was tested as a possible hyperhydrating agent (Lyons, Riedesel, Meuli & Chick, 1990)."
"Interstitial glycerol concentrations were measured in the abdominal and femoral subcutaneous tissue in 10 lean and 6 obese subjects. In the lean subjects [waist-hip circumference ratio (WHR) 0.89 +/- 0.01] the fasting interstitial glycerol concentrations in the abdominal and femoral regions were 185 +/- 20 and 160 +/- 15 (SE) microM, respectively, whereas glycerol in venous plasma was considerably lower (66 +/- 5 microM). After an oral glucose load (100 g) the interstitial glycerol concentrations declined but remained higher than in plasma. In obese subjects (WHR 1.1 +/- 0.03) the fasting interstitial glycerol levels were higher, in both regions, than in lean individuals. Furthermore, interstitial glycerol in the abdominal site (291 +/- 32 microM) was significantly higher than in the femoral fat (210 +/- 13 microM; P less than 0.05), while plasma glycerol was similar to that in lean subjects (80 +/- 12 microM). Interstitial glycerol remained higher in the obese than in the lean subjects also after an oral glucose load, but the regional differences were less apparent. Thus interstitial glycerol is higher in the subcutaneous tissue than in venous blood (Jansson, Smith & Lonnroth, 1990)."
Also an increase in Mean Arterial Pressure due to the increased plasma volume "hyperhydration" will trigger arterial baroreceptors. Along with the baroreceptors, peripheral chemoreceptors, sensing electrolyte imbalance, will trigger a negative feedback leading to decreased release of Vasopressin and Aldosterone to begin water excretion. With this process diffusion will occur along the osmotic gradient from the plasma into the extra and intracellular fluids in attempts to normalize blood pressure. Hence the bloating that can be associated with glycerol intake. Glycerol is a metabolite naturally occurring within the body and supplementing with this will saturate and then some. Causing levels within the blood and within the cells and extracellular fluid to rise bringing water along with it.
Lyons, T., Riedesel, M., Meuli, L., & Chick, T. (1990). Effects of glycerol-induced hyper-hydration prior to exercise in the heat on sweating and core temperature. Medicine and Science in Sports and Exercise, 22(4), 477-483. Retrieved from ukpmc.ac.uk/abstract/MED/
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Jansson, P., Smith, U., & Lonnroth, P. (1990). Interstitial glycerol concentration measured by microdialysis in two subcutaneous regions in humans. The American Physiological Society, Retrieved from ajpendo.physiology.o r g/content/
258/6/E918.short