Correlation of plasma non-conjugated oestriol and plasma cortisol in late human pregnancy

The present study concerns the diurnal variations of free plasma oestriol and their relationship to maternal plasma cortisol in late human pregnancy. Four pregnant women volunteered for the study. According to the half-life time of oestriol blood was drawn at intervals of 30 and 60 minutes, respectively, over a period of 24 hours. Free oestriol was measured by radioimmunoassay and cortisol was quantitated by a protein binding method. All patients exhibited a circadian rhythm for free oestriol with higher values in the evening and early night (14.4 +/- 3.7 ng/ml) than in the morning (11.3 +/- 2.3 ng/ml, P less than 0.001). The course of oestriol followed plasma cortisol in a significant negative correlation (r = -0.566, P less than 0.001). During the period of low cortisol concentration oestriol levels demonstrated the phenomenon of episodic secretion. The results suggest that the maternal adrenals predominantly regulate the circadian rhythm of free oestriol by a negative feed-back action on the foetal hypothalamus.