Delta-Sleep Inducing Peptide (DSIP) Delta-sleep inducing peptide (DSIP) was first detected in the cerebral venous blood of rabbits that had been subjected to sleep by electric stimulation of the intralaminal thalamic area. Promotion of SWS after DSIP was reported in several species, although not all preclinical studies reproduced these effects. Only one study has investigated the effects of DSIP on sleep EEG in normal men and found only minor effects. Studies on the efficiency of DSIP in the treatment of insomnia produced conflicting results. DSIP-like immunoreactivity was compared in young men between baseline sleep, sleep deprivation, and recovery sleep. Plasma DSIP-like immunoreactivity decreased at the transition from wakefulness to sleep in both evening sleep and morning recovery sleep. These results suggest that DSIP is induced by mechanisms that are involved in the initiation of sleep