Vol. 90, Issue 4, 1577-1583, April 2001
Effects of morphine and naloxone on fetal heart rate and
movement in the pig
S.
Cohen1,
N.
Parvizi3,
E. J. H.
Mulder2,
H. A.
Van
Oord1,
F. H.
Jonker1,
G. C.
Van Der Weijden1, and
M. A. M.
Taverne1
1 Department of Farm Animal Health, Faculty of Veterinary
Medicine, Utrecht University, 3584 CL Utrecht;
2 Department of Obstetrics, Neonatology and Gynecology,
University Medical Center, 3584 EA Utrecht, The Netherlands; and
3 Department of Physiology, Institute for Animal Science and
Animal Behavior, FAL, 31535 Neustadt/Rbge, Germany
To test the hypothesis that an increasing opioid tonus
is involved in decreases in fetal heart rate (FHR) and movement (FM) during late gestation, we studied the effects of intravenous bolus injections of morphine (1 mg) and naloxone (1 mg) on FHR and FM in the
fetal pig. Twenty-one fetuses (1 per sow) were catheterized at
90-104 days of gestation (median 100 days). Recordings of FHR (electrocardiograph or Doppler-derived signals) and FM
(ultrasonography) were made from 15 min before to 45 min after
treatment. Morphine administration significantly decreased FHR, but it
increased FHR variation and forelimb movements (LM). LM were clustered,
and this stereotyped behavior has never before been observed in any mammalian fetus. Naloxone administration increased gross body movements
and FHR without significant changes in FHR variation. It is concluded
that FHR and motility are under opioidergic control in the pig fetus.
Both morphine and naloxone induce hypermotility, suggesting that
naloxone does not act as a pure opioid antagonist in the fetal pig.
fetus; opioids; motility; ultrasound
