DSIP (Delta Sleep-Inducing Peptide)
DSIP is the nonapeptide Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu, first isolated from rabbits as a factor that enhances slow-wave (delta) and spindle EEG activity, and later studied in rat models of stress hormones and pineal circadian enzymes; the research catalog lists it at https://onesourcepeptides.com/product/dsip.
The peptide was defined by its EEG signature. Schoenenberger and Monnier, PNAS, 1977 (PMID 265572) isolated a peptide from rabbits that enhanced slow-wave (delta) and spindle EEG patterns after intraventricular infusion, sequenced it as Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu, and synthesized it alongside five fragments, two exchanged-residue analogues and a related tripeptide. Under double-blind conditions in 58 rabbits including controls, with Fourier-transformed neocortical and archicortical EEG, only synthetic DSIP produced significant, specific enhancement of delta and spindle activity.
Work in rats then extended DSIP beyond sleep EEG. Graf et al., Neuroendocrinology, 1985 (PMID 2995861) reported that intravenous DSIP significantly reduced corticosterone release stimulated by corticotropin-releasing factor, with no effect on release triggered by ACTH itself, pointing to an action at the pituitary level. In the pineal gland, Graf, Kastin and Schoenenberger, Journal of Neurochemistry, 1985 (PMID 3838100) found that evening injection of DSIP or two of its analogs significantly reduced the nocturnal rise in serotonin N-acetyltransferase, the enzyme that starts melatonin synthesis, while morning injections left it unchanged, a time-of-day dependence that ties the peptide to circadian signaling.
The broader body of early animal and tissue work, including the distribution of DSIP-like immunoreactivity across the body, is collected in Graf and Kastin, Peptides, 1986 (PMID 3550726). Related neuropeptide notes cover Selank and Semax, and lot identity belongs on the certificate of analysis for the vial in hand (see Are research peptides third-party tested?). DSIP on the catalog is laboratory research supply only. This note summarizes published animal and tissue research and is not dosing, reconstitution, or human-use guidance.