Effect of water restriction on the development of hypothalamic lesions in weanling rodents given MSG. II. Drinking behaviour and physiological parameters in rats (Rattus norvegicus) and golden hamsters (Mesocricetus auratus).

No hypothalamic lesions were found in weanling Sprague-Dawley (SD) rats or in golden hamsters deprived of water and/or food overnight (ON 19.00-09.00 h) and offered monosodium L-glutamate monohydrate (MSG) in up to 10% solution for 30 min subsequently. ON restriction of water resulted in haemoconcentration, with elevation of haematocrit, plasma protein, electrolytes and osmolality in SD rats. Water-restricted rats avidly consumed large volumes of concentrated MSG solution and showed further evidence of haemoconcentration, with delayed restoration of plasma sodium and with high plasma glutamate, but did not develop lesions at up to 5.4 g MSG/kg b.w. Hamsters deprived of water ON consumed smaller volumes of MSG in aqueous solution than did SD rats, and in them no hypothalamic lesions were observed. That SD rats and golden hamsters, which are susceptible to hypothalamic lesions from the parenteral administration of high doses of MSG, did not develop lesions following the voluntary intake of MSG in aqueous solution, even under conditions of severe thirst, is further evidence of the safety of MSG as a food ingredient.