Kinin receptor subtypes.

Bradykinin, kallidin, and some of their metabolites exert potent biological effects in a variety of organs and tissues. These effects are mediated by specific receptors, of two different types B1 and B2, according to the classification proposed in 1980 by Regoli and Barabé. This classification has recently been challenged by several authors on the basis of data obtained with a variety of synthetic analogs (both agonists and antagonists) of bradykinin and kallidin. B2-receptor subtypes and even a new receptor type, B3 have been considered. Other workers have shown that some of the kinins' biological effects, such as the activation of prostaglandins or histamine release, may occur through nonreceptor mechanisms. Recently, a variety of new kinin-related peptides have been prepared and tested. In particular, new selective agonists for both B1 and B2 receptors have been identified and used for receptor characterization, particularly in complex biological systems. Antagonists are critically reviewed, because several of them are in effect partial agonists. Pure antagonists have been obtained and used for receptor characterization in various organs. Activation of receptors and nonreceptor mechanisms by kinins bring about direct effects on smooth muscles and other cells and indirect effects mediated by endothelium-derived relaxing factor, or by prostacyclin, prostaglandins, leukotrienes, histamine, etc. Interaction of kinins with their receptors activates second messengers that may be different from one cell to another (in the same tissue) and that are activated either by kinins or by other endogenous mediators released by kinins.(ABSTRACT TRUNCATED AT 250 WORDS)