The beta adrenergic receptor in septic shock
The myocardial depression found during septic shock has been a subject of intense study for many years. Many theories exist as to the precise cause of this condition but in this thesis the role of the β-adrenergic receptor is examined. Some investigators have found reduced response to β-adrenergic stimulation in models of septic shock in animals. This is of interest to the clinician since adrenergic stimulation is a key manipulation in the management of septic shock. An animal model of septic shock was established using a comparatively small dose of Escherichia coli endotoxin infused into the male Sprague-Dawley rat. Heart function and response to isoprenaline, a β1-agonist, were measured in an in vitro organ bath. A reduction in the force of contraction was found together with a shift in the response curve to the right. These findings were associated with an increase in the number of β-receptors in the ventricular tissue from the same hearts, a measurement made using radioligand binding with I125-(-)-Iodocyanopindolol, a β1-antagonist. The finding of more β-receptors in the context of septic shock raises interesting questions discussed in the thesis. When forskolin, a plant alkaloid that stimulates the adenyl cyclase enzyme, was used to stimulate the atria in vitro the same response was found in the endotoxin treated and the normal groups. This is strong evidence that endotoxin causes a myocardial depressant effect mediated prior to adenylcyclase in the β-receptor transduction cascade.