Effects of chronic dehydration on angiotensin II receptor binding in the subfornical organ, paraventricular hypothalamic nucleus and adrenal medulla of Long-Evans rats.

Angiotensin II (AII) is an important peptide known to regulate blood pressure and body fluid. In the present study we used a potent AII antagonist, 125I-(Sar1,Ile8)-AII (125I-SI-AII), to study AII receptor binding in Long-Evans rats 5 days after water deprivation. Specific structures evaluated include the subfornical organ (SFO) and adrenal gland. With quantitative autoradiography, we have found that there is an increase of 125I-SI-AII binding in the SFO, whereas there is a decrease in AII binding in the adrenal medulla. These observations suggest that central and peripheral AII target tissues are affected differently by dehydration. The increase in SI-AII binding in the SFO may indicate participation of this structure during dehydration, as angiotensin stimulation of SFO causes thirst and vasopressin release.