Journal of Applied Physiology, Vol 57, Issue 1 40-43, Copyright © 1984 by American Physiological Society
Morphine stimulates rapid, regular, deep, and sustained breathing efforts in fetal lambs
R. E. Sheldon and P. L. Toubas
We gave morphine (1-4 mg) to 11 unanesthetized lamb fetuses at 123-141 days
of gestation. After a delay of 28 +/- 7 min (mean +/- SE), the fetuses
began forceful, frequent, regular, and sustained inspiratory efforts
lasting continuously for 105 +/- 15 min and continuing intermittently for a
total of 155 +/- 13 min. The induced breathing motions are more forceful,
frequent, and regular than the naturally occurring efforts of the fetus and
resemble neonatal breathing motions. The phenomenon is blocked by 0.5 mg of
naloxone but not by 0.1 mg of atropine. We conclude that the mechanism of
action involves the opiate receptor system. We speculate that endorphins
may have a role in the regulation of breathing in the fetal and newborn
lamb.
