Individuality and stability of nocturnal secretion patterns for eight hormones in healthy young men

The concentration of hormones in the bloodstream shows oscillations, reflecting the fact that endocrine physiology is structured over time. In many cases, these oscillations have an ultradian configuration that can be superimposed on a circadian rhythm. Secretion of hormones can be linked to the phases of sleep, as is the case with growth hormone (GH); can depend strongly on the circadian pacemaker, as in the case of cortisol; or be under the influence of both, as seen for thyroid-stimulating hormone (TSH). Thus, the temporal pattern of secretion of several hormones, and the resulting plasma concentration (also influenced by hormone tissue distribution and clearance), depends on impulses from biological clocks and is influenced by endogenous and exogenous masking factors. The extent of interindividual differences in the phenotypes of temporal patterns of hormone secretion is not well known. In this study, a series of eight hormones were measured over one night, and these measurements were repeated over another night. The study had two goals. The first was to explore the extent of inter individual differences in nocturnal and ultradian rhythms of these hormones. The second was to see how stable the individual patterns of nocturnal hormone secretion could be. Our results indicate that the temporal organization of hormone secretion into the blood is highly individual, and that these intraindividual patterns are conserved over time. This is relevant in view of the changes in secretion of several hormones that have been described in biological psychiatry research.