Molucular mechanism in the control of water metabolism : integrated study of hypothalamus and kidney

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Water balance in the body is regulated by the thirst mechanism and vasopressin (AVP) release controlled by the hypothalamus. Antidiuretic action of AVP in the kidney is also regulated by various factors. In the present study, integrated correlation of hypothalamus and kidney in the water homeostasis was examined from the point of molecular aspects. The neural activity of AVP cells in the supraoptic nuclei in the hypothalamus was examined in rats by immuno-staining of c-Fos. Infusion of hypertonic saline to rats intensified its expression and this response was exaggerated by the fall of circulation blood volume after hemorrhage even under the absence of change in its basal activity. This finding indicates the integrated function of AVP cells to both osmotic and volume stimuli. In the rats with hereditary hypothalamic diabetes insipidus, Brattleboro strain, expression of vasopressin dependent water channel, AQP-2, remained low even after vigorous water deprivation. The expression of AQP-2 is intensified in the rats with glucocorticoid deficiency and attenuated under the hyponatremic states resulting in the exaggeration and attenuation of urine concentration ability, respectively. Thus, in the action of AVP in the kidney, the regulation of AQP-2 takes a crucial role in forming a balanced circumstances of water homeostasis in the body.