Angiotensin II AT₂ receptor mRNA and AT₂ receptor binding in rat tissues.

<p>(A) Expression of mRNAs was studied by RT-PCR in adrenal gland, spleen, kidney cortex, liver, cerebellum, pituitary and inferior olive of adult male Sprague Dawley rats. Gene expression was normalized to the level of GAPDH, and represents the mean ± S.E.M. of three individual determinations. Note that AT₂ mRNA is only expressed in adrenal glands, inferior olive and cerebellum, and it is not detectable in the spleen, kidney, liver and pituitary. (B) AT₂ receptor expression was studied by quantitative autoradiography in sections from adrenal gland and spleen, incubated in the presence of 0.25 nM [¹²⁵I] Sar¹-Ile⁸-Angiotensin II as described in Materials and Methods. Figures represent a typical result repeated in three different rats. Note abundant receptor binding in the adrenal medulla and spleen, and lower expression in adrenal zona glomerulosa and kidney cortex. In the kidney cortex, binding was localized to the glomeruli. Binding was partially displaced in the adrenal cortex, and completely displaced in the spleen and kidney cortex, by incubation with the AT₁ receptor-specific antagonist losartan. Non-specific binding was the result of incubation in the presence of non-radiolabeled Angiotensin II. The results indicate that most of the receptor binding in the adrenal medulla, and part of the binding in the adrenal cortex is insensitive to losartan expression, revealing the expression of AT₂ receptors. Conversely, binding in the spleen and kidney cortex was completely displaced by losartan, indicating that spleen and kidney cortex receptors are exclusively of the AT₁ subtype (B).