Species differences in cerebral taurine concentrations correlate with brain water content

The notion that taurine (Tau) has an osmoregulatory function in the mammalian brain has not been established, although it has been reported that the severity of hyponatremic edema is proportional to cerebral [Tau]. Tau pools are not easily altered in vivo, but the fact that there are large differences in cerebral taurine levels between mice, rats and guinea pigs offers an opportunity to determine whether endogenous Tau affects volume regulation of the brain in hyposmolal conditions. This issue was investigated by injecting saline or distilled water intraperitoneally at 150 ml/kg in anesthetized mice, rats and guinea pigs. The animals were decapitated 4 h later, and blood osmolality, cortical specific gravity, Na+, K+ and amino acid concentrations were determined. In controls, blood osmolality and specific gravity of the cortex were highest in the mouse (304 +/- 3 mmol/kg; 1.0488 +/- 0.0003 kg/l), followed by the rat (294 +/- 1; 1.0462 +/- 0.0002) and the guinea pig (285 +/- 2; 1.0445 +/- 0.0002). There was a correlation between these measures and cortical Tau levels which were 10.31 +/- 0.36 mmol/kg in mouse cortex, 6.31 +/- 0.18 in rat cortex and 1.37 +/- 0.06 in guinea pig cortex. Despite these differences, water-induced cerebrocortical swelling did not differ between the species studied. Interspecies variation in cortical osmolality did not relate to [Na+] and [K+], since the levels of these electrolytes were higher in the guinea pig cortex than in the rat and mouse cortex. After administration of water, the levels of Na+ and K+ were reduced in rat and guinea pig cortex, while only [Na+] was significantly decreased in mouse cortex.(ABSTRACT TRUNCATED AT 250 WORDS)