[Studies for clinical application of ovine corticotropin-releasing factor]

Synthetic ovine corticotropin-releasing factor (o-CRF) stimulated adrenocorticotropin (ACTH) release at the concentration of 10(-10) M or more in monolayer culture of rat anterior pituitary cells. Dexamethasone, 10(-7) M, inhibited this effect. In 5 healthy human subjects, o-CRF, 1 microgram/kg iv bolus, increased plasma ACTH levels from less than 10 pg/ml to 40.4 +/- 11.0 (mean +/- SD) after 30-60 min, and plasma cortisol from 12.8 +/- 2.8 micrograms/dl to 23.6 +/- 3.1 after 45-60 min. Of 7 patients with Cushing's disease (CD), five showed an exaggerated response of plasma ACTH and cortisol, one an exaggerated response of plasma ACTH but low response of plasma cortisol and the other no response of both hormones. The significant positive correlation between the inhibition of plasma cortisol by dexamethasone and the response of plasma ACTH and cortisol to o-CRF in CD was seen. No response of plasma ACTH and cortisol to o-CRF was seen in each one patient with Cushing's syndrome due to an adrenocortical adenoma, ectopic ACTH syndrome (but low response at retesting), isolated ACTH deficiency and Sheehan's syndrome. In one patient with Addison's disease an exaggerated response of plasma ACTH but no response of plasma cortisol was seen. In 4 of 5 healthy subjects and 5 of 7 patients with CD, plasma ACTH and cortisol levels showed a second peak at 120--210 min after o-CRF administration. To clarify the prolonged effect of o-CRF in human in vivo, the disappearance rates of injected o-CRF were evaluated by radioimmunoassay in 3 patients with cured Cushing's syndrome. A biexponential decay curve showed t1/2 values of 9.3 +/- 0.4 min and 79.6 +/- 0.7 min (mean +/- SE). From the chromatographic profile, a portion of injected o-CRF was thought to be bound to macromolecule (s). o-CRF, as a specific secretagogue of ACTH, is thought to be useful tool in evaluating patients with hypothalamo-pituitary-adrenal disorders.