Abstract
BACKGROUND: Brain water content represents a major endpoint in studies of hepatic encephalopathy and liver failure.1 However, none of the current methods for evaluating brain water content fulfills the ideal requirements of a measuring technique, being complex, expensive, lengthy, qualitative or insensitive.2 Our AIM was to evaluate a novel protocol for measuring brain water content using a moisture analyzer in a rodent model of hyponatremia-induced brain edema. METHODS: Female Sprague-Dawley rats (248 ± 41 g bw) undergoing a 3-hour protocol for inducing hyponatremia-related brain edema (HypoNa group) were compared with a group of normonatremic rats (Control group). All rats were anesthetized with sevoflurane and mechanically ventilated. Body temperature was maintained at 37 ºC and major physiological parameters (heart rate, oxygen saturation, mean arterial pressure) were monitored. Acute hyponatremia was induced by administering desmopressin (DDAVP 1 ug/rat s.c.) and two i.p. injections of 140 mmol/L glucose solution (an injection of 12% of b.w. at the beginning and of 6% of b.w. 30 minutes later). At the end of the experiments, blood was collected from aorta, the rats were decapitated, and the brain was quickly dissected. Frontal cortex was immediately frozen and stored in liquid nitrogen. The frontal cortex was pulverized frozen with a metal mortar, and the frozen powder was placed in a moisture analyzer (MB120, Ohaus Corporation) between two glass-fiber filters for measuring water content by the wet-to-dry weight method. Dry weight (g) was determined when there was no change in 1 mg for 3 minutes. RESULTS: Compared with the Control group, rats in the HypoNa group presented lower sodium (134.0 ± 1.0 vs. 104.8 ± 1.0 mmol/L, P < 0.0001), calcium (1.27 ± 0.04 vs. 1.15 ± 0.03 mmol/L, P < 0.05), and effective osmolality (281.2 ± 2.10 vs. 229.8 ± 3.8 mOsm/L, P < 0.0001), and a trend to increased concentrations of potassium (4.10 ± 0.15 vs. 4.75 ± 0.40 mmol/L, P = 0.25) and lactate (2.23 ± 0.38 vs. 6.23 ± 2.18 mmol/L, P = 0.22) in plasma. Frontal cortex water content was higher in the HypoNa group (Control: 82.20 ± 0.74 vs. HypoNa: 85.01 ± 0.97 %, P < 0.01). Measuring time of water content using the moisture analyzer was <15 minutes per sample. CONCLUSIONS: These results suggest that the present protocol using a moisture analyzer is a convenient and sensitive method for measuring brain water content in rats.
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