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

Using the synthetic androgen R1881 (17β-hydroxy-17α-methyl-estra-4,9,11-trien-3-one) as probe, we identified cytoplasmic androgen receptors in baboon myocardium. The relative binding affinity of selected steroids for the androgen receptor was R1881, 100%; 5α-dihydrotestosterone, 32.6%; testosterone, 29.6%, progesterone, 7.2%; R5020, 1.0%; and estradiol-17β, 5.8%. The androgen receptor migrated on low ionic strength linear sucrose density gradients as a macromolecule with a sedimentation coefficent of 8.5S. Saturation analysis performed at 2°C (available sites) showed that the androgen receptor content of baboon myocardial cytoplasmic extracts were 5.9 ± 1.4 fmol/mg protein and that the dissociation constant for R1881 was 1.16 ± 0.30 nM. These cytoplasmic androgen receptors are indicated to be physiologically functional by previous autoradiographic studies (McGill et al., 1980; McGill and Sheridan, 1981) that showed localization of radioisotope in nuclei of myocardial fibers following injection of baboons with 5α-dihydrotestosterone.