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

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.