β-Adrenoceptors in the extraorbital lacrimal gland of the Syrian hamster characterization with [¹²⁵I]-iodopindolol and evidence of sexual dimorphism

Saturation and competition experiments with the radiolabeled β-adrenergic antagonist (-)-[¹²⁵I]-iodopindolol were used to characterize β-adrenoceptor density (B_max) and receptor affinity in the extraorbital lacrimal gland of male and female Syrian hamsters. Specific binding to the receptor was saturable. Scatchard analysis of saturation isotherms revealed a single population of receptor sites. Male glands had a significantly higher B_max (38.9±5.0 vs. 23.3±2.1 fmole/mg protein, -x±SEM, p< 0.02) and receptor affinity (expressed in a lower dissociation constant K_d: 0.065±0.013 vs. 0.120±0.015 nM, p<0.02) than female glands. Binding of the radiolabeled ligand in competition with various adrenergic antagonists showed the receptor to be stereospecific and of the β₂-subtype.