Circadian rhythm of corticotropin (ACTH) secretion

Top panel: Pulse analysis of plasma ACTH concentrations in samples obtained at 10-minute intervals for 24 hours. The line represents the plasma ACTH concentration at any moment as predicted by a computer-generated deconvolution program. Bottom panel: Computer-calculated ACTH secretion rate at any moment. The circadian rhythm in plasma ACTH concentrations and, therefore, of cortisol secretion and plasma cortisol concentrations is a function of the variation in the amplitude, not the frequency, of ACTH secretory pulses. To convert pg/mL to pmol/L, multiply by 0.22.