The developmental effects of exposure to various doses of buprenorphine, me
thadone, or water during the perinatal period were studied in the rat. Rats
were exposed to buprenorphine (0.3, 1.0, or 3.0 mg/kg/day), methadone (9 m
g/kg/day), and/or water prenatally, postnatally, or both pre- and postnatal
ly, via maternally implanted osmotic minipumps. Fetal and maternal mortalit
y and morbidity were assessed, as well as the acquisition of several develo
pmental milestones, pup weight gain, precipitated withdrawal, and the antin
ociceptive effect of morphine. Although perinatal exposure to buprenorphine
failed to produce severe maternal and fetal or neonatal mortality, it was
associated with a significant amount of perinatal mortality and perturbatio
ns of pup development. Pups developed physical dependence to both drugs, as
evidenced by the ability of naloxone challenge to precipitate withdrawal.
Both drugs induced tolerance to the antinociceptive effects of morphine in
the tail-flick test. The effects of buprenorphine varied with the dose used
, and the highest dose did not always produce the greatest effect. There we
re some similarities between the effects of perinatal buprenorphine and per
inatal methadone; however, differences were also observed between the effec
ts of the two drugs, which may be related to the different affinities and e
fficacies of the drugs at different opioid receptor subtypes.