Fluctuations in plasma oestradiol levels in normal men.

Plasma levels of oestradiol were measured in blood samples obtained from 6 normal men every 12 minutes for two 4-hour periods: between 08.00 and 12.00h and between 18.00 and 22.00h. Circulating oestradiol was measured by radioimmunoassay after chromatographic separation on microcolumns of Sephadex LH-20. Mean values of oestradiol concentrations and coefficients of variation for two 4-hour periods were calculated for each subject and for the whole group. Data were statistically evaluated by means of the Wilcoxon signed-rank test. Rapid fluctuations in plasma oestradiol levels were observed in all subjects. The pattern of the fluctuations was found to be irregular and different in each subject. The mean concentration and coefficient of variation were significantly (p less than 0.05) higher in the morning, suggesting the possibility of a circadian rhythm in the secretion of oestradiol in men.