Steroid-binding proteins and testosterone level in the badger plasma during the annual cycle

Steroid-protein interactions were studied in the male badger Meles meles L. during a seasonal sexual cycle. Specific steroid-binding plasma proteins were determined by equilibrium dialysis. This study demonstrates the existence of two high-affinity steroid-binding proteins: one which has high affinity for corticosterone and saturable binding sites and resembles a transcortin-type protein, and the other which has a high affinity and limited capacity for binding DHT and could be a protein of the sex-hormone-binding protein type. The plasma concentrations of these two binding proteins fluctuate throughout the year. Transcortin concentration is not significantly higher in winter and spring than in summer and autumn. The SBP binding capacity is difficult to correlate with testosterone concentrations.