Control of peripheral free estradiol pool during the menstrual cycle of the olive baboon (Papio anubis)

The role of testosterone-estradiol binding globulin (TeBG) in the control of free estradiol (E₂) and testosterone has been shown in the human but its role in the control of free E₂ in the non-human primate, which is speculative, was examined in sera collected from sex female baboons during a complete menstrual cycle. Total E₂ was estimated by radioimmunoassay, percentage free E₂ by equilibrium dialysis and sex skin monitored daily. The percentage free E₂ showed little alteration over the cycle (4-6%) and TeBG concentration was maximal 8 days before ovulation. Maximum sex skin turgescence coincided with peak total and free E₂ concentrations. TeBG had no apparent control over free E₂. It is speculated that it is controlled by non-specific binding proteins whose low affinity interaction with E₂ would facilitate rapid dissociation, thus maintaining a dynamic equilibrium between the free and bound components at any given concentration of total E₂.