Recent studies have shown that 2-hydroxyestradiol (2-OH-E2) synthesized locally from estradiol (E2) stimulates progesterone production by granulosa cells (GC) and enhances the action of other trophic hormones. A particularly strong synergistic interaction between 2-OH-E2 and beta-adrenergic agonists was observed. Therefore, the present studies were undertaken to determine if this synergism was due to a 2-OH-E2-stimulated increase in the number of beta-adrenergic binding sites in GC. Binding of the 125I-labeled beta-adrenergic ligand iodocyanopindolol ([125I]iodo-CYP) to GC was evaluated and was found to be saturable with time and ligand concentration, and of high affinity (Kd = 29 +/- 8 pM; maximum binding = 0.55 +/- 0.02 fmol/10(6) cells). Rank order potency for agonist/antagonist binding was consistent with a beta-adrenergic receptor: propranolol greater than isoproterenol greater than norepinephrine. 2-OH-E2 did not compete for the [125I]iodo-CYP-binding sites. Incubation of cultured porcine GC with 2-OH-E2 caused a time- and dose-dependent increase in the number of specific [125I]iodo-CYP-binding sites. Averaged over eight separate experiments, 4-day treatment with 4 micrograms/ml 2-OH-E2 increased the number of [125I]iodo-CYP-binding sites 3.1 +/- 0.9-fold above the control value (P less than 0.05). A similar 4-day treatment with 2 micrograms/ml E2 or 200 ng/ml LH or FSH was without effect on [125I]iodo-CYP binding (P greater than 0.05) despite stimulation of progesterone secretion to a degree similar to that seen with 2-OH-E2. These results support the hypothesis that 2-OH-E2 produced by GC may enhance progesterone production stimulated by catecholamines, in part by increasing the numbers of beta-adrenergic binding sites on GC.