Angiotensin receptors: history and mysteries

Angiotensin receptors became relatively easy to study when radioactive derivatives of the peptide were synthesized for radioimmunoassays. Binding assays in vitro led to the discovery of receptors in many tissues different from those involved in the classic actions of angiotensin. The physiologic significance of receptors in sites such as the gonads, other endocrine organs, peripheral blood cells, and many regions of the brain is still uncertain. Kinetics of the binding reaction are susceptible to intracellular guanine nucleotides, and extracellular cations, fatty acids, steroids, and eicosanoids. Synthesis of receptors is under equally complex control. Receptor binding assays simplified screening for angiotensin antagonists. Nonpeptide antagonists proved so specific they revealed the existence of receptor subtypes. The two principal subtypes are found in different tissues and trigger different postreceptor cascades. Studies of receptors, the genes that code for them, and the drugs that block them have led to a growing awareness of angiotensin’s effects on the structure of the heart, vessels, and kidneys, some of which are pathologic. The existence of receptor subtypes, the different signal transduction cascades they stimulate, the widespread location of receptors, and the range of effects they mediate suggest that the angiotensins are of broad relevance in biology and pathology. This multidimensional matrix also indicates that receptor antagonists may have effects not yet described.