Benzodiazepine receptors in the human fetus

The existence of benzodiazepine receptors in the human fetal brain, liver and placenta has been studied. At 12-15 weeks of gestation specific binding to fetal brain occurs. The dissociation constant of [3H]-flunitrazepam-specific binding was 1.5-2 nM and the maximum number of binding sites was 2.3-3.8 fmol/mg of total brain tissue. In the fetal liver and placenta some specific binding exists, yet the nonspecific binding is more extensive.