I'm researching the possible connection between the dream content and the activity of various organ or hormonal systems within the human body. I'm looking for information on biological cycles within the human body that occur on a 24 hour cycle and may influence the sleep cycle, dream content or the overall state of awareness.

So far I was able to find: Adrenaline, cortisol, testesterone - circadian endogenous cycle.

leptin, glucose, insuline - peak with awakening, decline with bedtime

What else within the human body is functioning on a predictable 24 hour cycle?

Thank you for any information!

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    $\begingroup$ Note that circadian cycle is not exactly 24 hours $\endgroup$ – nico Mar 3 '12 at 0:14
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    $\begingroup$ Also, the fact that an hormone is produced in a circadian manner does not at all involve it in the sleep/wake cycle. I would be extremely careful in concluding anything about that. $\endgroup$ – nico Mar 3 '12 at 0:40
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    $\begingroup$ I agree with nico on both points. Insulin, glucose and leptin (and many if not all the incretin hormones) are not circadian regulated to my knowledge. Insulin generally exhibits 3 major cycles through the day corresponding with 3 meals, and then is not secreted while fasting or sleeping because it is dependent on nutrient intake. Glucose as well, a sugar, naturally exhibits peaks after meals and lows when fasting. These cycles would just as easily be perturbed if I got up in the middle of the night to eat a meal and not regulated with any kind of circadian rhythm, only behaviour. $\endgroup$ – user560 Mar 3 '12 at 13:26
  • $\begingroup$ Thank you for great info! There's anectodal evidence that eating before bed has an impact on the dream content. Would eating within 1 hour of bed trigger insulin/glucose elevation over the course of the entire night? $\endgroup$ – Alex Stone Mar 3 '12 at 15:07
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    $\begingroup$ @leonardo: what I am saying is that just because an hormone is not secreted in a circadian manner it does not imply that its secretion cannot be controlled -or at least modulated- by circadian genes. A colleague of mine has recently published a review on the subject. $\endgroup$ – nico Mar 4 '12 at 11:12

The real answer is probably more than you want, but its easy to do better than the list above.

I took a look through GEO for human circadian expression data and surprisingly I only found 2.

Looking at GSE2703 - the rhesus circadian expression experiment, they have shown 355 genes that are rhythmically expressed. This is not a great experiment because they only looked over a single 24 hour period. Its only the adrenal gland. Nonetheless they found 355 genes which seemed to be circadian. the table is supplemental data to the article, listed below.

I see a fibroblast growth factor receptor, some hydrocarbon nuclear receptor components, sterol regulatory factors, bone morphogenic protein 2, glutamate receptor, thrombonspondin receptor, ryanodine receptor 3 (what is that?) , lysophosphatidic acid G-protein-coupled receptor 2, purinergic receptor P2Y, G-protein coupled. You might find more if you know what you are looking for.

The other circadian study was on human muscle, which will no doubt give different answers. I imagine circadian behavior is highly tissue dependent.

Reference: Lemos DR, Downs JL, Urbanski HF. Twenty-four-hour rhythmic gene expression in the rhesus macaque adrenal gland. Mol Endocrinol 2006 May;20(5):1164-76

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    $\begingroup$ Don't forget that many hormones and cytokines are translated in inactive forms (insulin is a great example) and are later cleaved to release an active peptide. Thus, mRNA production may be constant while active peptide levels may cycle. $\endgroup$ – Larry_Parnell Mar 2 '12 at 21:41
  • $\begingroup$ Maybe there is only 2 in monkey, but the amount of data on mouse is huge. $\endgroup$ – nico Mar 3 '12 at 6:22
  • $\begingroup$ 355 genes is quite a lot to process at once. Thanks for the GEO Ascension viewer link, I'll investigate that! $\endgroup$ – Alex Stone Mar 3 '12 at 15:10
  • $\begingroup$ nico is right - mouse and rat are going to be the strongest organisms to look at... $\endgroup$ – shigeta Mar 5 '12 at 7:48

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