DISTRIBUTION OF FOS-IMMUNOREACTIVITY IN RAT-BRAIN FOLLOWING A DIPSOGENIC DOSE OF CAPTOPRIL AND EFFECTS OF ANGIOTENSIN RECEPTOR BLOCKADE

Immunohistochemical techniques were used to detect Fos in the brain fo llowing subcutaneous administration of the angiotensin converting enzy me inhibitors captopril or enalapril at 0.5 mg/kg to conscious rats. I ncreased Fos-Like immunoreactivity was observed in many neurons in the lamina terminalis, and in regions of the hypothalamus. Captopril at t his dose also caused water drinking in other rats. Pre-treatment with the angiotensin AT, receptor antagonist ZD7155 (10 mg/kg) given subcut aneously prevented the captopril-induced increase in Fos in the lamina terminalis. This dose of ZD7155 also prevented captopril-induced drin king in other rats. With a higher dose (50 mg/kg) of captopril or enal april, there was no increase in Fos in the lamina terminalis. This dos e of captopril was not dipsogenic. The results are consistent with the proposal that the lower dose (0.5 mg/kg) of captopril or enalapril in creases circulating angiotensin I levels which are then converted to a ngiotensin II in the organum vasculosum of the lamina terminalis and s ubfornical organ. Stimulation of neurons at these sites may subserve w ater drinking and sodium appetite.