TISSUE-SPECIFIC EXPRESSION OF TYPE-1 ANGIOTENSIN-II RECEPTOR SUBTYPES - AN IN-SITU HYBRIDIZATION STUDY

The angiotensin II type 1 (AT(1)) receptor in murine species exists as two isoforms (AT(1A) and AT(1B)) encoded by two different genes. Both subtypes have a 9/10 homology in the coding sequence of their mRNA. We examined organs of adult rats (liver, pituitary gland, adrenal gland, kidney, heart, and lung) to study the differential expression of these two genes in target tissues for angiotensin II. AT(1A) and AT(1B) mRNAs were detected by in situ hybridization using specific riboprobes for the 3' noncoding region of the mRNAs that have the lowest homology (approximately 6/10). Only AT(1A) was expressed in the liver, heart, and lung, and only AT(1B) was expressed in the anterior pituitary, where most cells were positive. In the adrenal gland, AT(1A) mRNA was detected in the zona glomerulosa and medulla and AT(1B) in the glomerulosa. In the kidney, AT(1A) mRNA was the predominant isoform (mesangial and juxtaglomerular cells, proximal tubules, vasa recta, and interstitial cells), but AT(1B) was also detected in mesangial and juxtaglomerular cells and in the renal pelvis. The results of this in situ detection suggest a tissue-selective regulation of AT(1A) and AT(1B) mRNAs. This tissue specificity may constitute a prerequisite condition if the two angiotensin II receptor subtypes, which are pharmacologically similar, are to selectively modulate the Various effects of angiotensin II in the different target tissues.