High salt intake differentially regulates kidney angiotensin IV AT4 receptors in Wistar-Kyoto and spontaneously hypertensive rats

Functional angiotensin IV (Ang IV) receptors (denoted AT(4)) are localized to the outer stripe of the medulla in the rat kidney, and may play a critical role in salt homeostasis. The purpose of this study was to determine if AT(4) receptor binding in the kidney is differently regulated in the salt-sensitive spontaneously hypertensive (SH) rat compared to Wistar Kyoto (WKY) controls. AT(4) receptor binding was determined using in vitro receptor autoradiography. AT(4) receptor binding in the outer stripe of the medulla was similar in WKY and SH rats maintained on a 1% salt diet. A high salt diet (8%) resulted in a statistically significant increase (28%) in AT(4) receptor binding in kidneys from WKY rats. However, there was no change in AT(4) receptor binding in the kidneys of SH rats fed the same diet. The present data indicate that AT(4) binding sites are regulated by salt intake. In addition, regulation of this receptor may be impaired in the kidneys of SH rats, explaining in part the salt-sensitivity of this strain.