Angiotensin II binding in area postrema and nucleus tractus solitarius of SHR and WKY rats

The distribution of angiotensin II (AII) binding sites in the area postrema (AP) and adjacent nucleus tractus solitarius (NTS) was compared in spontaneously hypertensive (SHR) rats and normotensive Wistar-Kyoto (WKY) rats. 125I[Saralasin-1-Isoleucine8]-Angiotensin II (125I[SI]-AII) binding density was quantitated from autoradiographic images by computer-assisted image analysis. Seventeen 30 microns serial coronal sections inclusive of the entire AP were analyzed as either individual sections or as groups of sections designated as caudal, middle, or rostral area postrema regions. 125I[SI]-AII binding density was greatest in caudal AP and declined progressively in the rostral direction in both strains; however, binding density in SHR was significantly higher than in WKY rats at each level of the AP analyzed. 125I[SI]-AII binding in the entire area postrema was approximately 46% higher in SHR rats. In the NTS, however, there were no differences in binding density between strains. At the middle level of the AP, 125I[SI]-AII binding was highest in the ventral midline and lowest in the dorsolateral region. In the NTS, the highest 125I[SI]-AII binding density was found in the pars commissuralis and pars medialis. In conclusion a) 125I[SI]-AII binding density was nonhomogeneous in the AP and NTS of both strains, b) qualitatively similar patterns of nonhomogeneity of binding in the AP and NTS were noted in both strains; however, c) the SHR strain consistently had higher density AII binding than WKY in AP, but not in NTS.