Sex steroid binding proteins in the plasma of the green frog, Rana esculenta: changes during the reproductive cycle and dependence on pituitary gland and gonads.

Sex steroid binding proteins (SSBP) have been reported in the plasma of female and male Rana esculenta. In both sexes SSBP bind [3H]estradiol and [3H]testosterone with medium-high affinity and high specificity. Using ion-exchange chromatography SSBP resolve into two peaks eluting at 0.27 M (peak I) and 0.36 M (peak II) NaCl. Both peaks bind [3H]estradiol and [3H]testosterone equally well. Isoelectrofocusing showed that peak I focused at pH 6.0 and 7.5, whereas peak II focused at pH 6.0. SSBP capacity for [3H]estradiol and [3H]testosterone changes throughout the reproductive cycle, showing low levels during the nonbreeding period and increasing levels during the breeding period. Hypophysectomy and/or gonadectomy result in small changes in SSBP capacity. Short-term steroid hormone treatment of gonadectomized animals does not modify SSBP capacity.