IDENTIFICATION OF BETA-ADRENOCEPTORS IN MOUSE MYOMETRIUM BY RADIOLIGAND BINDING STUDY

The binding of radioligand to cell membrane prepared from mouse myomet rium was used to identify the characteristics of beta-adrenoceptors. U teri were taken from mature mice (Kunming Strain) weighing 40 +/- 5 g pretreated with estradiol benzoate 1 mg . kg(-1) . d(-1) ip for 2 d. T he binding of [H-3]dihydroalprenolol ([H-3]DHA) to uterine membrane wa s saturable, having a B-max of 378 fmol/mg protein and a K-D of 3.1 nm ol . L(-1). The slope of Hill plot (n(H) = 1.03) indicated the absence of cooperative interactions. IC50 and K-1 values of l-norepinephrine (NE), dl-propranol (Pro), d-timolol (d-Tim), and l-Tim competed for th e [H-3]DHA binding sites were 171 +/- 10, 10.3 +/- 4.3, 6.5 +/- 2.1, 0 .40 +/- 0.23 nmol . L(-1) and 113 +/- 6, 6.3 +/- 2.8, 4.0 +/- 1.3, 0.2 5 +/- 0.14 nmol . L(-1), respectively. These 4 agents competed for the [H-3]DHA binding sites in an order of potency: l-Tim > d-Tim > Pro > NE. Atenolol (Ate) did not compete for [H-3]DHA binding sites. The res ults suggested that these binding sites for [H-3]DHA in mouse myometri um appeared to be beta(2)-adrenoceptor.