Figure 10.

Mean (+SEM) profiles of plasma cortisol (top panels), insulin secretion rates (ISR, middle panels), and plasma glucose (lower panels) in nine healthy young men each of whom participated in four studies performed in randomized order. In all four studies, endogenous cortisol levels were suppressed by metyrapone administration, and caloric intake was exclusively in the form of a constant glucose infusion. Dark horizontal bars represent the scheduled sleep periods. The daily cortisol elevation was restored by oral administration of hydrocortisone (or placebo—data not illustrated) either at the normal time of the circadian peak (5 am, left panels) or 12 hours out of phase (5 pm, right panels). Vertical arrows show the timing of hydrocortisone administration in each study. Horizontal lines on the ISR and glucose graphs show, respectively, the mean ISR and glucose levels at the time of hydrocortisone ingestion to facilitate the visualization of post-hydrocortisone changes. The initial effect of the hydrocortisone-induced cortisol pulse was a short-term inhibition of insulin secretion without concomitant glucose changes, and the magnitude of this acute effect was similar in the evening and in the morning. At both times of day, starting 4–6 hours after hydrocortisone administration, there was a delayed hyperglycemic effect that was minimal in the morning but much more pronounced in the evening, when it was associated with a robust increase in insulin secretion. [Redrawn from L. Plat et al: Metabolic effects of short-term elevations of plasma cortisol are more pronounced in the evening than in the morning. J Clin Endocrinol Metab. 1999;84(9):3082–3092 (279), with permission. © The Endocrine Society.]