Beta Receptor Sensitivity Testing in Humans

Abstract

Understanding of beta receptor function in vitro and at the molecular level has advanced enormously in the last five years. With that improved understanding has come the recognition that some of the changes seen in certain pathophysiological states may be related to altered function of the beta receptor in vivo. For example changes in beta receptor function have been described following catecholamine administration (1), with altered sodium intake (2), pseudohypoparthyroidism (3), propranolol withdrawal (2, 4), corticosteroid administration (1), cardiac failure (5), hypertension (6), exercise (7), aging (9, 11) and recently endogenous depression (8). However prior to extrapolating the findings from ex vivo studies of receptor function to the in vivo setting it is necessary to correlate the ex vivo changes to in vivo in sensitivity. Unfortunately in contrast to the plethora of studies reporting changes in receptor function ex vivo the number of studies which have demonstrated a correlation between ex vivo change in beta receptor function and some in vivo change in sensitivity are relatively few. To some extent this reflects the difficulty in defining beta receptor sensitivity in vivo in patients or normal volunteers. The purpose of this paper is to briefly review the available techniques for assessing beta receptor sensitivity in man and suggest a potential improvement.

When assessing beta receptor sensitivity the first issue to be determined is the tissue of interest. Traditionally the response which has been evaluated is the chronotropic response of the heart (10) to a beta agonist such as isoproterenol. However, the response of other tissues including the lungs and vasculature have also been used.