Does chronic prenatal methadone exposure affect beta-receptor subtypes in placental, fetal and maternal brain homogenates?

Methadone treatment during pregnancy

Methadone maintenance has been used for decades to treat opioid-dependent pregnant women. The outcomes of pregnancies thus treated are vastly improved over the outcomes of pregnancies complicated by street drug use. Despite its long history of successful use during pregnancy, little is known about the long-term effects of methadone on the fetus and the newborn. Studies done in animals suggest there may be subtle effects on brain and behavior. Only recently have other treatments for opioid dependency during pregnancy been investigated. There is increasing evidence that altering the traditional methadone maintenance protocols may be beneficial, and that tapered withdrawal can be safely achieved under some circumstances.

Demonstration of physical dependence following chronic continuous methadone delivery via osmotic minipumps in pregnant rats

The effects of a 14-day (gestation days 7-20) chronic methadone (6.3-9.0 mg/kg/day) infusion via osmotic minipumps were studied on the induction of physical dependence in both pregnant and nonpregnant female rats. Following continued methadone exposure, an acute injection of naloxone (2.0 mg/kg, SC) produced the following symptoms of withdrawal in both pregnant and nonpregnant methadone-exposed rats: increased frequency of head shakes, teeth-chattering and face-rubbing episodes, as well as the induction of burrowing, diarrhea, facial tremor, squeaking and vaginal sniffing. Increased fetal movement in the maternal abdomen was also observed in the pregnant rats. In the saline-exposed pregnant controls, naloxone failed to induce a significant effect. In addition, brain and plasma methadone levels during the various stages of pregnancy (gestation days 8-20) were determined. The methadone levels in plasma were initially variable (gestation days 8-12) but became more constant (approximately 50 ng/ml) from gestation day 14 to 20. Methadone brain levels also followed a similar pattern, except that the brain methadone content was at least 20-fold greater than plasma concentrations at any given time. Thus, relative to the high brain levels, the present data suggest that acute changes in methadone plasma concentration may not be a good index of pharmacological effect.