Effects of morphine and naloxone on fetal heart rate and movement in the pig.
Cohen, S, N. Parvizi, E. J. H. Mulder, H. A. Van Oord, F.Jonker, F. H. , G. C. Van Der
Weijden, and M. A. M. Taverne.
1Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht
University, 3584 CL Utrecht; 2Department of Obstetrics, Neonatology and Gynecology,
University Medical Center, Utrecht, The Netherlands; and 3Department of Physiology,
Institute for Animal Science and Animal Behavior, FAL, Neustadt, Germany
APStracts 7:0052A, 2000.
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.
Received 16 February 2000; accepted in final form 16 October 2000
APS Manuscript Number A156-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2000 The American Physiological Society.
Published in APStracts on 29 January 2001