A major role for AT1b receptor in mouse mesenteric resistance vessels and its distribution in heart and neuroendocrine tissues

In mice, angiotensin (Ang) II type-1 (AT1) receptors exist as AT1a, and AT1b subtypes. In an effort to understand the role of AT1b in regulating vascular function, AT1 subtype mRNA and its functional relevance in the mesenteric resistance vessels were determined using wildtype (WT) and AT1a knockout (AT1a-/- mice) mice. With RT-PCR followed by restriction-enzyme digestion, we found that AT1b accounted for almost all (98%) of AT1 receptors in the mesenteric resistance vessels of WT mice. Also, the Ang II response in the vessels of AT1a-/- mice was comparable to that of WT mice, suggesting an important role for AT1b in regulating vasoreactivity. To further characterize AT1b receptor distribution, several other tissues were examined. Among them, AT1b is only predominantly expressed in hypothalamus, whereas AT1a exists exclusively or as a major subtype in heart, pituitary, adrenal glands and brainstem. These results further underscore a tissue-specific role for AT1b receptor in mice.