Androgen and estrogen binding in rat skeletal and perineal muscles

Abstract

Specific in vitro binding of [3H]testosterone (T), 5α-[3H]dihydrotestosterone (DHT), and [3H]estradiol (E2) was demonstrated in the 30 000 × g supernatant (cytosol) of thigh muscles (TM) and of the levator ani – bulbocavernosus muscle complex (LA–BC) by gel filtration through Sephadex G-25 columns. In TM cytosol, T and E2 [are bound with high affinity (Ka = 1.1 × 109 M−1 and 2.3 × 109 M−1, respectively) whereas DHT binding is of lower affinity (Ka = 5.0 × 107 M−1).] In LA–BC cytosol, T, E2, and DHT are bound with high affinity (Ka = 1.9 × 109 M−1, 0.3 × 109 M−1 and 0.5 × 109 M−1, respectively). Competition experiments suggest that the binding of the three hormones (T, E2, and DHT) is due to different proteins. In addition to TM and LA–BC, T and E2 binding was found in other muscles of male and female rats, including gastrocnemius, the pectoralis, diaphragm, and heart.