Hormones of the hypothalamo-pituitary-adrenocortical (HPA-) axis are considered to be of physiological and clinical relevance in regulating spontaneous growth hormone (GH) secretion. To further investigate interdependencies between both systems, we studied the effects of adrenocorticotropin [ACTH(1-24)] and human corticotropin-releasing hormone (h-CRH) upon spontaneous GH secretion in 10 male volunteers. Administration of 1 microgram ACTH (1-24), 10 micrograms h-CRH or saline (control: CTL) every hour from 9.00 to 6.00 p.m. resulted in significant differences of cortisol secretion during the entire observation period (8.00 a.m.-3.00 a.m.) between the three groups (p less than 0.001, Friedman two-way ANOVA). Mean area under the time course curve (AUC) values (+/- SEM) for cortisol expressed as ng x 1,000 x min/ml showed also significant differences between the three treatments from 8.00 a.m. to 3.00 a.m.: CTL 64.0 +/- 6.4, ACTH(1-24) 178.5 +/- 9.4 (p less than 0.01, Wilcoxon test), h-CRH 88.5 +/- 5.6 (p less than 0.01). The main portion of cortisol was released during daytime from 8.00 a.m. to 11.00 p.m., where the most significant differences in the AUC values emerged: CTL 59.6 +/- 5.8, ACTH(1-24) 171.5 +/- 8.8 (p less than 0.01, Wilcoxon test), h-CRH 80.2 +/- 5.1 (p less than 0.01). With regard to GH secretion, significant differences became obvious between the three treatments during daytime from 8.00 a.m. to 11.00 p.m. and the sleep-related period from 11.00 p.m. to 3.00 a.m. (p less than 0.01 and p less than 0.02, Friedman two-way ANOVA).(ABSTRACT TRUNCATED AT 250 WORDS)