Effects of alteration in fluid balance on angiotensinogen gene expression in the rat

The renin-angiotensin system (RAS) functions in circulatory and fluid homeostasis. There is evidence that genes encoding the protein elements of this system (renin and angiotensinogen) are expressed in a variety of tissues and that interaction of the products of these genes within tissues may represent part of the physiological function of this system. Using a solution hybridization assay for rat angiotensinogen (Ao) gene which incorporates a quantitative sense RNA standard we have measured angiotensinogen gene expression (AGE) in rat liver, brain (basal forebrain and brain stem), kidney and heart (atrium and ventricle) from individual animals. The effect of a 48hr period of dehydration on gene expression was compared with age and sex-matched animals which had water available ad libitum. Dehydration lead to a significant increase in plasma osmolality (pOsm) and plasma angiotensin II immunoreactivity (pAII). AGE was unaffected by dehydration in liver, brain stem, kidney, atrium and ventricle. However, significant increases AGE were observed in basal forebrain. In individual animals there was a significant positive correlation between pOsm and basal forebrain gene expression regardless of hydration state. This selective activation of the Ao gene in the forebrain during dehydration supports other observations which suggest that an intra-cranial RAS may participate in hypothalamic mechanisms of fluid homeostasis.