[Regulation of the fetoplacental unit. 2. Circadian changes in the sensitivity of the fetal hypothalamo-hypophyseal system for the feedback effect of cortisol].

The present study investigates the significance of a circadian changing sensitivity on the feed back action of cortisol for the foetal hypothalamic hypophyseal system. 9 patients with uncomplicated courses of pregnancy in the 37th to 40th week volunteered in this study. All of them delivered healthy babies at term. 5 patients received a continuous infusion of 0.25 mg ACTH1-24 (Synacthen) in the morning from 10 a.m. to 4 p.m. (group I). To 4 patients an analogous ACTH infusion was applied in the evening from 8 p.m. to 2 a.m. (group II). Blood specimens (5 ml) were drawn from 8 a.m. to 5 p.m. in group I and from 5 p.m. to 3 a.m. in group II in 60 and 30 minutes intervals, respectively. Free plasma oestriol was measured by radioimmunoassay, total plasma cortisol by the protein binding method. In group I cortisol increased from 294.3 +/- 52.9 ng/ml to 774.5 +/- 170 ng/ml, whereas oestriol decreased from 13.1 +/- 6.1 ng/ml to 6.8 +/- 2.1 ng/ml (p less than 0.001). In group II cortisol rose from 267.5 +/- 76.2 ng/ml to 1010 +/- 284 ng/ml, whereas oestriol levels were suppressed from 21.7 +/- 10.5 ng/ml to 10.8 +/- 3.2 ng/ml (p less than 0.001). Two hours after starting ACTH infusion rising cortisol and falling oestriol concentrations were negatively correlated (r = -0.9657, p less than 0.001 in the morning; r = -0.9119, p less than 0.001 in the evening). Plasma oestriol levels were in the evening suppressed on an average of 10.9 ng/ml and exceeded the oestriol decrease in the morning (6.3 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)