Physiological consequences of beta-adrenergic receptor disruption.

Activation of beta-adrenergic receptors (beta-ARs) in vivo is an important means by which animals regulate cardiac performance, vascular tone, lipid and carbohydrate metabolism, and behavior. The advent of targeted gene disruption in mice has led to significant advances in our understanding of the role that beta-AR subtypes play in these processes, and this technique has become an important tool for the study of G protein coupled receptors in general. To date, targeted disruption of both beta1- and beta3-ARs in mice has been reported. Mice lacking beta1-ARs are unresponsive to cardiac beta-AR stimulation, suggesting that neither beta2- nor beta3-ARs couple to inotropic or chronotropic responses in the mouse. Conversely, mice lacking beta3-ARs retain at least some adipose beta-AR responsiveness through remaining beta1- and beta2-ARs, suggesting that all three beta-AR subtypes mediate similar functions in this tissue. While these knockout models have been extremely valuable tools for revealing the roles that individual beta-ARs play in whole animal physiology, it is also useful to integrate the results of experiments derived from either transgenic overexpression of beta-ARs or purely pharmacological approaches to the study of beta-AR function in order to create a comprehensive model of beta-AR function in vivo.