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 [H-3]estradiol and [H-3]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 [H-3]estradiol and [H-3]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 [H-3]estradiol and [H-3]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. (C) 1994 Academic Press, Inc.