With the use of [125I]iodocyanopindolol as a β-receptor ligand, β-receptors were identified and characterized in human amnion tissue. [125I]Iodocyanopindolol was found to bind to a total particulate fraction prepared from amnion tissue obtained at term. At low concentrations of [125I]iodocyanopindolol, more than 80% of total [125I]iodocyanopindolol bound was at specific high-affinity sites and could be displaced by an excess of (±)-propranolol. The Kd and Bmax for binding of [125I]iodocyanopindolol to amnion β-receptors were 10.1 ± 1.1 pM and 46.8 ± 3.2 fmol/mg protein, respectively. Analysis of the competition for binding to amnion β-receptors between [125I]iodocyanopindolol and ligands that discriminated between β1- and β2-receptors revealed that the β-receptors of human amnion were almost entirely of the β2-subtype. The density of β-receptors found in the amnion at term was approximately three times that found early in the second trimester of gestation. The β-receptors in human amnion appear to be functional since the in vitro exposure of amnion tissue pieces to isoproterenol (10-5M), resulted in a fivefold increase in the intracellular concentration of cyclic adenosine monophosphate. The presence of β-receptors in the amnion is in keeping with the proposed importance of the catecholamines found in amniotic fluid in the regulation of prostaglandin production by the amnion.
ASJC Scopus subject areas
- Obstetrics and Gynecology