Identification of beta-adrenoceptors in mouse myometrium by radioligand binding study

The binding of radioligand to cell membrane prepared from mouse myometrium was used to identify the characteristics of beta-adrenoceptors. Uteri 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. The binding of [3H]dihydroalprenolol ([3H]DHA) to uterine membrane was saturable, having a Bmax of 378 fmol/mg protein and a KD of 3.1 nmol.L-1. The slope of Hill plot (nH = 1.03) indicated the absence of cooperative interactions. IC50 and K1 values of l-norepinephrine (NE), dl-propranol (Pro), d-timolol (d-Tim), and l-Tim competed for the [3H]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, 0.25 +/- 0.14 nmol.L-1, respectively. These 4 agents competed for the [3H]DHA binding sites in an order of potency: l-Tim > d-Tim > Pro > NE. Atenolol (Ate) did not compete for [3H]DHA binding sites. The results suggested that these binding sites for [3H]DHA in mouse myometrium appeared to be beta 2-adrenoceptor.