Cocaine selectively inhibits beta-adrenergic receptor binding in pregnant human myometrium.

OBJECTIVE

This study evaluated the in vitro effects of cocaine on the binding characteristics of alpha- and beta-adrenergic receptors from pregnant human myometrium.

STUDY DESIGN

By means of membrane fractions from myometrium obtained from 26 women at term undergoing cesarean section, equilibrium binding assays were performed with tritiated dihydroergocryptine for alpha-adrenergic receptors and iodine 125-cyanopindolol for beta-adrenergic receptors. Equilibrium competition curves were determined with and without cocaine. Results were compared by one-way analysis of variance.

RESULTS

Cocaine inhibited beta-adrenergic receptor binding (inhibition constant = 132 mumol/L) but had little effect on alpha-adrenergic receptor binding (inhibition constant = 1.63 mmol/L). Benzoylecgonine, a stable metabolite of cocaine, had no effect on binding to either receptor.

CONCLUSION

Cocaine selectively inhibits myometrial beta-adrenergic receptor binding. This may alter the contractile equilibrium of the pregnant uterus and could explain, in part, the association of cocaine abuse with premature delivery.