AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 2 359-R364, Copyright © 1986 by American Physiological Society
Characteristics of myocardial beta-adrenergic receptors during endotoxicosis in the rat
F. D. Romano and S. B. Jones
The effects of in vivo endotoxin administration on beta-adrenergic
receptors in rat ventricle membranes were studied using
[3H]dihydroalprenolol as a radioligand. Nonlinear regression analysis of
saturation binding indicated one-site binding of antagonist in both control
and endotoxic tissues. There was no change in maximum binding or
dissociation constant of [3H]dihydroalprenolol at 0.5 or 3 h after
endotoxin administration or when the rats were in the agonal stage of
shock. Isoproterenol competition studies revealed that there was an
increase in the slope of the curve from endotoxic tissues at the agonal
stages (0.6 +/- 0.06 vs. 0.91 +/- 0.12, control and endotoxic,
respectively, P less than 0.05) and that there was a decrease in affinity
for isoproterenol binding. Control binding modeled to a two-state fit,
whereas binding to endotoxin-exposed membranes modeled to one state of
lower affinity. These data suggest that there is an alteration in
receptor-adenylate cyclase coupling, which may account for an attenuation
of agonist-stimulated cyclase activity. A modification in the
beta-adrenergic receptor may contribute to the decrease in myocardial
performance during shock.
