Am J Physiol Heart Circ Physiol. 2012 Mar 9. [Epub ahead of print]
Diet-induced obesity severely impairs myelinated aortic baroreceptor reflex responses.
Source
1Oregon Health and Science University.
Abstract
Diet-induced obesity (DIO) attenuates the arterial cardiac baroreceptor reflex, but the mechanisms and sites of action are unknown. This study tested the hypothesis that DIO impairs central aortic baroreceptor pathways. Normal chow control (CON), and high fat chow obesity-resistant (OR) and obesity-prone (OP) rats were anesthetized (inactin, 120mg/kg) and underwent sinoaortic denervation. The central end of the aortic depressor nerve (ADN) was electrically stimulated to generate frequency-dependent baroreflex curves (5-100Hz) during selective activation of myelinated (A-fiber) or combined (A&C-fiber) ADN baroreceptors. A mild stimulus (1V) that activates only A-fiber ADN baroreceptors induced robust, frequency-dependent depressor and bradycardic responses in CON and OR rats, but these responses were completely abolished in OP rats. Maximal activation of A-fibers (3V) elicited frequency-dependent reflexes in all groups, but a dramatic deficit was still present in OP rats. Activation of all ADN-baroreceptors (20V) evoked even larger reflex responses. Depressor responses were nearly identical among groups, but OP rats still exhibited attenuated bradycardia. In separate groups of rats, the reduced HR response to maximal activation of ADN A-fibers (3V) persisted in OP rats following pharmacological blockade of β(1)-adrenergic or muscarinic receptors, suggesting deficits in both PNS- and SNS reflex pathways. However, the bradycardic responses to direct efferent vagal stimulation were similar among groups. Taken together, our data suggest that DIO severely impairs the central processing of myelinated aortic baroreceptor control of HR, including both PNS and SNS components.
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