Distribution of adrenergic receptors does not explain regional differences in blood flow in the pregnant rabbit uterus.

The increase in uterine blood flow during pregnancy is maximal at the placental implantation site, but the mechanisms of this increase are poorly understood. Adrenergic receptor activation may influence blood flow both directly and indirectly. We therefore asked whether distribution of myometrial adrenergic receptors within the rabbit uterus could explain the increased blood flow to smooth muscle under the placenta. alpha-Adrenergic and beta-adrenergic receptor concentrations and affinities were measured in myometrium from under the placenta and compared to myometrium between placentas and distant from the placentas. There were no differences in receptor concentrations or affinities in different parts of the uterus. We therefore conclude that the distribution of adrenergic receptors in the pregnant rabbit uterus cannot explain the preferential blood flow to myometrium at the placental implantation site.