EFFECT OF ACTH AND DEXAMETHASONE ON THE DIURNAL RHYTHM OF UNCONJUGATED OESTRIOL IN PREGNANCY

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Abstract
The present study is concerned with the role of maternal cortisol in regulating diurnal rhythm of unconjugated estriol in 9 pregnant women. Blood was drawn at 30 min intervals between 5 p.m. and 3 a.m. In 5 patients endogenous ACTH-secretion was simultaneously suppressed by 12 mg dexamethasone over 48 h. Between 8 p.m. and 2 a.m., 0.25 mg ACTH1-24 (Synacthen) was infused into the subjects. Free estiol was measured by radioimmunoassay, and the total plasma cortisol by the protein binding method. Patients without dexamethasone demonstrated high estriol levels (21.5 .+-. 9 ng/ml) and episodic secretion between 5 p.m. and 8 p.m. At the same time cortisol concentrations were relatively low (274.1 .+-. 66 ng/ml). Ninety minutes after starting ACTH-infusion, plasma estriol decreased in negative correlation to rising cortisol (r = -0.916, P < 0.001). Between 11 p.m. and 2 a.m. estriol levels were significantly below the control values (12.9 .+-. 3 ng/ml, P < 0.001) and were associated with high cortisol levels (887 .+-. 312 ng/ml). Episodic estriol production did not occur during the period of elevated cortisol levels. Under dexamethasone both estriol (2.1 .+-. 1.2 ng/ml) and cortisol values (36.5 .+-. 24 ng/ml) were markedly suppressed. Only cortisol production could be stimulated during ACTH-infusion (374 .+-. 80 ng/ml), whereas estriol concentration remained in the range of the controls (1.91 .+-. 0.5 ng/ml). These results suggest that diurnal rhythm of unconjugated estriol is predominantly regulated by feedback action of maternal cortisol on the fetal hypothalamus.

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