Hormone receptors of the baboon cardiovascular system. Biochemical characterization of aortic cytoplasmic androgen receptors

Cytoplasmic androgen receptors were identified in the aorta of the baboon (Papio sp.). Using the synthetic androgen R1881 (17β-hydroxy-17α-methyl-estra-4,9,11-trien-3-one) as probe, androgen receptors were demonstrated only when the incubation mixtures contained 1.0 μM triamcinolone acetonide (TA). The relative binding affinity of selected steroids for the aortic androgen receptor was R1881, 100%, 5α-dihydrotestosterone, 46.1%; testosterone, 60.7%; progesterone, 9.1%; R5020, 3.1%; and estradiol-17β, 7.5%. The androgen receptor migrated on low-ionic-strength linear sucrose density gradients as a macromolecule with a sedimentation coefficient of 8.0S. Saturation analysis performed at 2°C (available sites) showed that the androgen receptor content of baboon aortic cytoplasmic extracts was 12.9±2.4 fmoles/mg protein and that the dissociation constant for R1881 was 1.47±0.07 nM. The observation that TA was required in the cytoplasmic extracts in order to identify androgen receptor indicates the presence of progesterone receptor-like binding components. These aortic cytoplasmic androgen receptors are indicated to be physiologically functional by previous autoradiographic studies that showed localization of radioisotope in the nuclei of aortic smooth muscle cells following injection of baboons with 5α-dihydrotestosterone.