Patterns of exposure to glucocorticoid receptor ligand.

Hormones are characteristically secreted in distinct pulses. Corticosterone (in rodents) and cortisol (in human) show profound circadian and ultradian rhythmicity which results in rapid changes in ligand concentration in the circulating blood. The pattern of ultradian glucocorticoid levels shows genetic modulation, can change according to the physiological and pathological status of the animal and can be programmed by neonatal events. Since the tissue response to changes in circulating glucocorticoid levels can be very rapid, changes in ultradian rhythm could allow tissue-specific regulation of glucocorticoid signalling without major changes in mean plasma hormone levels.