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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 96/5/1761    most recent 00528.2003v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Ray, C. A. Articles by Monahan, K. D. Search for Related Content PubMed PubMed Citation Articles by Ray, C. A. Articles by Monahan, K. D.

Aging, opioid-receptor agonists and antagonists, and the vestibulosympathetic reflex in humans

Division of Cardiology, Departments of Medicine and of Cellular and Molecular Physiology, General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033

Submitted 16 May 2003 ; accepted in final form 8 January 2004

Animal studies indicate that opioids inhibit the firing rate of vestibular neurons, which are important in mediating the vestibulosympathetic reflex. Furthermore, this inhibition appears to be greater in more mature rats. In the present study, we tested the hypotheses that opioids inhibit the vestibulosympathetic reflex in humans and that endogenous opioids contribute to the age-related impairment of the vestibulosympathetic reflex. These hypotheses were tested by measuring muscle sympathetic nerve activity (MSNA), arterial blood pressure, and heart rate responses to otolith organ engagement during head-down rotation (HDR) in young (24 ± 2 yr old) and older (63 ± 2 yr) subjects before and after administration of either an opioid-receptor antagonist (16 mg naloxone in 9 young and 8 older subjects) or an opioid-receptor agonist (60 mg codeine in 7 young and 7 older subjects). Naloxone did not augment the reflex increase in MSNA during HDR in young (7 ± 2 vs. 4 ± 2 bursts/min and 81 ± 23 vs. 60 ± 24% change in burst frequency and total MSNA before and after naloxone, respectively) or older subjects (2 ± 2 vs. 1 ± 2 burst/min and 8 ± 7 vs. 8 ± 9% before and after naloxone). Similarly, codeine did not attenuate the increase in MSNA during HDR in young (8 ± 1 vs. 7 ± 2 bursts/min and 53 ± 4 vs. 64 ± 16% before and after codeine) or older subjects (6 ± 4 vs. 3 ± 3 bursts/min and 38 ± 21 vs. 33 ± 20%). Mean arterial blood pressure and heart rate responses to HDR were not altered by either naloxone or codeine. These data do not provide experimental support for the concept that opioids modulate the vestibulosympathetic reflex in humans. Moreover, endogenous opioids do not appear to contribute the age-associated impairment of the vestibulosympathetic reflex.

autonomic nervous system; blood pressure regulation; otolith organs; naloxone; codeine

This article has been cited by other articles:

				J. R. Carter and C. A. Ray Sympathetic responses to vestibular activation in humans Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2008; 294(3): R681 - R688. [Abstract] [Full Text] [PDF]