AJP - Endocrinology and Metabolism, Vol 242, Issue 5 317-E322, Copyright © 1982 by American Physiological Society
Morphine suppresses plasma catecholamine responses to laparotomy but not to 2-deoxyglucose
G. J. Taborsky Jr, J. B. Halter and D. Porte Jr
The increase of plasma catecholamines that occurs during surgery can be
reduced by administration of morphine. To test the hypothesis that morphine
specifically blocks nociceptive stimulation during surgery, we compared the
effects of morphine administration on the plasma catecholamine response to
a laparotomy in pentobarbital-anesthetized dogs with the effect of morphine
on the plasma catecholamine response to the neuroglucopenic agent,
2-deoxy-D-glucose (2DG, 300 mg/kg iv). In control dogs, plasma epinephrine
(Epi) and plasma norepinephrine (NE) both increased progressively with time
following a midline laparotomy (delta Epi by 50 min, +133 +/- 42 pg/ml, P
less than 0.01 and delta NE by 50 min, +108 +/- 38 pg/ml, P less than 0.01,
mean +/- SE, n = 12). 2-Deoxy-D-glucose produced a similar increase of both
plasma NE and Epi. In dogs that received the anesthesia alone, plasma
catecholamines did not increase from base line during the experiment. The
analgesic morphine (15 mg iv), given 15 min after the completion of
laparotomy, not only prevented the progressive rise of plasma
catecholamines after laparotomy, but also caused a small but significant
decline (P less than 0.05). Naloxone (0.4 mg iv) totally reversed the
suppressive effects of morphine, restoring both catecholamines to the
levels of their time-related control. In marked contrast, neither morphine
nor naloxone affected the plasma NE and Epi increases following the
administration of 2DG. These data suggest that morphine suppression of
plasma catecholamines during surgery is not due to a generalized
attenuation of sympathetic outflow, but rather to a specific interaction
with an opiate receptor that either mediates analgesia or lies within the
neural pathway stimulated by laparotomy but not by 2DG.
