Vol 9, No 3 - Chronobiology in Psychiatry
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www.dialogues-cns.org Poster Individuality and stability of nocturnal secretion patterns for eight hormones in healthy young men Methods Six young males, 20 to 30 years of age, were included in a protocol where repeated blood sampling was carried out over a whole night, from 20:00 to 08:00. They were considered to be healthy on the basis of their physical and psychiatric medical history, and physical examina- tion. Routine laboratory blood tests were performed before inclusion in the study; all values were in the nor- mal range. The protocol had been accepted by the local ethical committee. Early in the evening of the study, a short cannula was inserted into a forearm, and blood was subsequently   sampled   every   20   minutes.   Subjects received a light standardized meal at 18:00. Lights were turned off at 21:30 and on again at 06:30. During the night, the light in the room was kept very dim (less than 50 Lux), and the subjects did not wake up during sam- pling. This protocol was repeated once in all 6 subjects. There was an interval of at least 7 days between each study night, and each study was performed on the same day  of  the  week  for  a  given  subject. Blood  was  cen- trifuged, and plasma rapidly frozen.A total of eight hor- mones  were  measured  using  commercially  available immunoassays.These assays had intra-assay and interas- say coefficients of variation of <5 and <10%, respectively. The hormones measured were cortisol, TSH, prolactin (PRL), luteinizing hormone (LH), GH, melatonin, aldos- terone, and testosterone. 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 hor- mones, 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 interindividual differences in nocturnal and ultradian rhythms of these hormones. The second was to see how stable the individual patterns of nocturnal hor- mone secretion could be. Our results indicate that the temporal organization of hormone secre- tion 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.