DSIP (Delta Sleep-Inducing Peptide) vs Melatonin

DSIP (Delta Sleep-Inducing Peptide)

DSIP, or delta sleep-inducing peptide, is a nine-residue peptide first described in rabbits during experimentally induced sleep. It was isolated from blood drawn from animals in which sleep had been produced by electrical stimulation of the brain, and the name comes from the slow-wave activity reported when that material was transferred to other animals. Later studies in animals and small human studies gave inconsistent findings on sleep, and the name describes how the peptide was found rather than an agreed function. No gene encoding DSIP and no dedicated receptor have been found. Work continued on its possible roles in stress hormones and other systems, but the literature is fragmented, and much of it is several decades old.

Melatonin

Melatonin (N-acetyl-5-methoxytryptamine) is a small indoleamine made from tryptophan, chiefly in the pineal gland; it is not a peptide. It is made from serotonin in two steps, acetylation and then methylation, in the pineal gland and in smaller amounts in the retina, gut and other tissues. Pineal production follows a daily rhythm set by the suprachiasmatic nucleus of the hypothalamus: it rises in darkness and is suppressed by light. Human research is substantial and concentrates on circadian physiology and sleep, alongside a large animal literature that includes seasonal breeding. Work on its chemistry as a free-radical scavenger is mostly in vitro or in animals, often at concentrations well above those found in blood.

How DSIP (Delta Sleep-Inducing Peptide) acts

Without an identified receptor or gene, DSIP's standing as a signalling molecule in its own right is uncertain, and its mechanism is described through scattered observations. Animal and tissue studies have reported interactions with GABA and glutamate transmission, including NMDA receptors, with opioid signalling, and with the hypothalamic–pituitary–adrenal axis, where release of ACTH and corticosterone has been examined. Immunoreactive material resembling DSIP has been reported in the brain and in peripheral tissues. These reports come from different models and methods, and no single pathway has emerged that ties them together.

How Melatonin acts

Two high-affinity melatonin receptors, MT1 and MT2, have been characterised. Both are G-protein-coupled receptors that couple mainly to Gi, lowering cyclic AMP, and both are expressed in the suprachiasmatic nucleus, where rodent studies have linked MT1 to suppression of neuronal firing and MT2 to shifts in the timing of the circadian clock. They are also found in the retina, blood vessels and several peripheral tissues. A third binding site, once labelled MT3, was later identified as the enzyme quinone reductase 2. Apart from receptor signalling, melatonin and several of its metabolites react directly with reactive oxygen and nitrogen species in chemical systems.

The records side by side

• Type: DSIP (Delta Sleep-Inducing Peptide), Nonapeptide; Melatonin, Amino acid derivative (non-peptide)
• Length: DSIP (Delta Sleep-Inducing Peptide), 9 amino acids; Melatonin, not recorded
• Molecular weight: DSIP (Delta Sleep-Inducing Peptide), 848.8 g/mol; Melatonin, 232.28 g/mol
• Molecular formula: DSIP (Delta Sleep-Inducing Peptide), C35H48N10O15; Melatonin, C13H16N2O2

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.