Angiotensin II type-1 receptor subtype cDNAs: differential tissue expression and hormonal regulation

A rat angiotensin, type 1A (AT1A) receptor cDNA was cloned recently and shown to be a member of the 7-transmembrane, G-protein coupled family of receptors. Here, we report the cloning, sequencing, and expression of a previously unsuspected second form of the type 1 receptor (AT1B) in the rat which exhibits high similarity with the AT1A receptor relative to amino acid sequence (95% identity), binding of angiotensin II analogs, and utilization of Ca+2 as its intracellular second messenger. The adrenal and pituitary gland express primarily AT1B mRNA whereas vascular smooth muscle and lung express primarily AT1A mRNA. Estrogen treatment suppressed AT1B but not AT1A mRNA levels in the pituitary gland. Thus, the unexpected existence of two putative AT1 receptor genes appears to be related to the differential regulation of their expression rather than to different functional properties of the encoded receptor proteins.