The demonstration of oestrogen, androgen and progestagen receptors in the cytosol fraction of canine mammary tumours

The presence of cytoplasmic receptors in canine mammary tumours for oestrogens, androgens and progestagens has been demonstrated. The binding molecules showed low capacity and high affinity for each respective group of hormones with mean dissociation constants (and ranges) of 3.9 × 10 −9 M ( 3.7 × 10 −10 − 9.9 × 10 −9 ) for oestradiol- 17β, 1.37 × 10 −10 M ( 2.2 × 10 −10 − 3.6 × 10 −9 ) for 5α-dihydrotestosterone and 1.28 × 10 −10 M ( 3.4 × 10 −10 − 3.3 × 10 −9 ) for R 5020, a synthetic progestagen. The mean receptor site concentration (and ranges) were 61.7 (13.4–129.1), 15.2 (3.5–30.0) and 30.6 (5.0–80.9) fmole/mg cytosol protein respectively for these steroids. Sucrose density gradient ultracentrifugation analysis revealed that each receptor sedimented with a coefficient of 8S and that they were specific for their group of steroids.