INCREASED AFFINITY OF HISTAMINE H-1 BINDING TO MEMBRANES OF HUMAN MYOMETRIUM AT THE END OF PREGNANCY

1. The characterization of H-1 binding sites in membrane preparations of human myometrium obtained from pregnant and non-pregnant women was performed by using H-3-mepyramine as the radioactive ligand. 2. Satura tion curve analysis revealed that H-3-mepyramine is bound to a single class of binding sites. Changes in the H-1 site binding parameters wer e observed at the end of pregnancy, resulting in an increased affinity relative to non-pregnant tissue (K-d: 131.0 +/- 8.8 (non-pregnant) an d 72.5 +/- 7.5 (pregnant) nM, n = 6, P < 0.01). 3. A reduction in rece ptor concentration at the end of pregnancy was also observed, [B-max: 565.2 +/- 43.7 (non-pregnant) and 309.6 +/- 25.9 (pregnant) fmol/mg pr ot, n = 6, P < 0.01]. It is possible that this reduction in B-max coul d be attributed to a dilution factor due to the increase in membraneou s proteins that occurs during gestation.