The past, present and future of angiotensin II type 2 receptor stimulation.

Studying the angiotensin type 2 receptor (AT(2)) has been problematic in the past because a pharmacological tool for direct, specific in vitro and in vivo stimulation of the receptor has been lacking. Consequently, current knowledge about AT(2) receptor signalling and function had to be obtained by indirect approaches, like studying animals or cells with genetically altered AT(2) receptor expression levels, inhibitory experiments using specific AT(2) receptor antagonists, stimulation with angiotensin II under concomitant angiotensin II type 1 receptor blockade or stimulation with the peptide agonist CGP42112A, which has additional AT(2) receptor antagonistic properties. The recently developed non-peptide AT(2) receptor agonist Compound 21 now, for the first time, allows direct, selective and specific AT(2) receptor stimulation in vitro and in vivo. This new tool will certainly revolutionize AT(2) receptor research, enable many new insights into AT(2) receptor function and may also have the potential to become a future medical drug. This article reviews milestone findings about AT(2) receptor functional properties obtained by 'conventional' experimental approaches within the last 20 years. Moreover, it provides an overview of the first results obtained by direct AT(2) receptor stimulation with Compound 21, comprising effects on alkaline secretion, neurite outgrowth, blood pressure and post-infarct cardiac function.