[Osmotic and ionic homeostasis in insects and vertebrates under extreme influences on water-salt metabolism]

Dehydration which is accompanied by the decrease in the body mass of frogs and pigeons approximately by 10%, results in the corresponding increase in osmolality of the blood serum, as well as in the increase of sodium content of the latter. Under the same conditions, the increase in osmolality and sodium level in rats does not exceed 2% which is associated with the effective renal function. In caterpillars of the insect Vanessa urticae whose haemolymph is rich in organic osmotically active substances and potassium ions, in spite of dehydration and loss of the body mass, osmolality of the haemolymph slightly decreases, while cation concentration in the latter remains essentially constant. Experiments with injections of hyperosmotic solutions to rats and caterpillars, showed that these animals, belonging to different phylogenetic branches, exhibit highly effective physiological mechanisms of ionic and osmotic homeostasis.