The time-course of ACTH stimulation of cortisol synthesis by the immature ovine foetal adrenal gland.
The aim of this study was to establish the time-course of foetal adrenal gland activation by ACTH at a period of intra-uterine development during which adrenal function is minimal (100-120 days of gestation). Blood samples for cortisol analysis were collected at 6-h intervals during the 24 h ACTH (0.05, 0.5 and 5.0 micrograms/h) infusion and during the subsequent 24-h period following cessation of the infusion. Plasma cortisol concentrations were measured using a newly developed radioimmunoassay, whose sensitivity was found to be comparable to that of the validated double-isotope dilution derivative method. There was a significant increase in foetal plasma cortisol concentration, from 3.9 +/- 1 to 17.8 +/- 1.9 nmol/l, within 12 h of commencement of the 2 higher doses of ACTH. Values are mean +/- SEM; n = 5. Following termination of the infusion, cortisol levels fell significantly by the first 6 h, returning to basal levels thereafter. An increase in plasma ACTH from 4.6 +/- 0.6 to 8.4 +/- 1.0 pmol/l was sufficient to initiate a significant increase in cortisol production. The results suggest that the normal low values of cortisol at this period of gestation result from inadequate endogenous ACTH production at this stage.
Tangalakis
K
K
Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria, Australia.
Roberts
F E
FE
Wintour
E M
EM
D000311:Adrenal Glands / Q000196:embryology / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000502:physiology*; D000818:Animals; D001784:Blood Gas Analysis; D005260:Female; D006400:Hematocrit; D006854:Hydrocortisone / Q000096:biosynthesis* / Q000097:blood; D007700:Kinetics; D011863:Radioimmunoassay; D012756:Sheep; D016482:Urinalysis
D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone