Journal of Applied Physiology, Vol 58, Issue 5 1415-1420, Copyright © 1985 by American Physiological Society
Endogenous opioids and ventilatory responses to hypercapnia in normal humans
S. E. Weinberger, R. A. Steinbrook, D. B. Carr, E. R. von Gal, J. E. Fisher, D. E. Leith, V. Fencl and M. Rosenblatt
Though administration of opioid peptides depresses ventilation and
ventilatory responsiveness, the role of endogenous opioid peptides in
modulating ventilatory responsiveness is not clear. We studied the
interaction of endogenous opioids and ventilatory responses in 12 adult
male volunteers by relating hypercapnic responsiveness to plasma levels of
immunoactive beta-endorphin and by administering the opiate antagonist
naloxone. Ventilatory responsiveness to hypercapnia was not altered by
pretreatment with naloxone, and this by itself suggests that endogenous
opioids have no role in modulating this response. However, there was an
inverse relationship between basal levels of immunoactive beta-endorphin in
plasma and ventilatory responsiveness to CO2. Furthermore, plasma
beta-endorphin levels rose after short-term hypercapnia but only when
subjects had been pretreated with naloxone. We conclude that measurement of
plasma endorphin levels suggests relationships between endogenous opioid
peptides and ventilatory responses to CO2 that are not apparent in studies
limited to assessing the effect of naloxone.
