Allopregnant IgG binds and modulates the activity of uterine beta adrenoceptors.

Female Balb/c mice were mated to C3H male mice, to obtain an allopregnant IgG. This allopregnant IgG con activate beta-adrenoceptors of C3H uterus. Here we show that allopregnant IgG interacts with beta-adrenoceptors in uterus of C3H mice and produces a decrease of the spontaneous motility and an increase of the intracellular cAMP concentration. Both effects are blocked by propranolol, a beta-adrenergic antagonist. Allopregnant IgG interferes with the binding of a specific beta adrenergic radioligand 3H-dihydroalprenolol behaving as a non competitive inhibitor. All these data indicate that allopregnant IgG could modulate the activity of uterine beta-adrenoceptors.