Oestradiol-17 beta and prolactin levels in rat peripheral plasma.

Radioimmunoassay methods for the determination of oestradiol-17 beta and prolactin have been examined for their reliability and applied to the measurement of hormone concentrations in the plasmas from male and female rats. Prolactin was detectable in all samples (greater than 7 ng RP-1 ng/ml) but the concentration of oestradiol-17 beta was below the sensitivity of the method (greater than 0-10 ng/100 ml) in ovariectomized females. Plasma oestradiol-17 beta concentration rose gradually from metoestrus to proestrus and fell to barely detectable levels in oestrus. Plasma prolactin concentration was very variable even for rats in the same stage of the oestrous cycle but values were minimal in the afternoon of diestrus and a surge in secretion occurred in the afternoon of proestrus. In addition to the stage of the oestrous cycle, the prolactin concentration was influenced by mode of blood collection, degree of haemolysis and choice of serum or plasma. There was no correlation between the concentration of prolactin and that of oestradiol-17 beta in the same sample of plasma.