Fasting as a metabolic stress paradigm selectively amplifies cortisol secretory burst mass and delays the time of maximal nyctohemeral cortisol concentrations in healthy men

Abstract

Serum cortisol concentrations are increased in fasted or malnourished human subjects. The dynamic mechanisms underlying this adaptive response have been investigated in eight normal men by analyzing serum cortisol concentrations measured in blood obtained at 5-min intervals over 24 h on a control (fed) day and on the fifth day of a fast (water only) assigned in randomized order. A multiple parameter deconvolution method was used to simultaneously resolve endogenous cortisol secretion and half-life. Five days of fasting induced a 1.8-fold increase in the 24-h endogenous cortisol production rate (fed, 2504 +/- 308; fasted, 4528 +/- 488 nmol/L distribution volume; P < 0.006). This enhanced cortisol production rate was accounted for by a 1.6-fold increase in the mass of cortisol secreted per burst (fed, 115 +/- 12.1; fasted, 183 +/- 17.3 nmol/L; P < 0.02). Cortisol secretory event amplitudes (maximal rates of cortisol release attained within a burst) increased in seven of eight men, and mean secretory burst durations remained unchanged by fasting. Moreover, the number of computer-resolved cortisol secretory bursts per 24 h (fed, 22 +/- 1.4; fasted, 25 +/- 2.0; P = NS) and the interburst interval (fed, 65 +/- 4.0; fasted, 57 +/- 4.4 min) did not change significantly during a 5-day fast. The calculated half-life of endogenous cortisol was not significantly altered by fasting (fed, 108 +/- 9.7; fasted, 129 +/- 11 min). There was no significant change in the nyctohemeral pattern of v…