DIURNAL RHYTHM OF PLASMA DELTA-SLEEP-INDUCING PEPTIDE IN HUMANS - EVIDENCE FOR POSITIVE CORRELATION WITH BODY-TEMPERATURE AND NEGATIVE CORRELATION WITH RAPID EYE-MOVEMENT AND SLOW-WAVE SLEEP

Since delta-sleep-inducing peptide (DSIP) was isolated in 1977, numero us reports have suggested that this nonapeptide stimulates asleep [slo w wave sleep (SWS)]. Although DSIP-like immunoreactivity (DSIP-LI) has been found in the serum of many animals and man, its diurnal rhythm a nd relation to sleep stages have not been well defined. We hypothesize d that circulating levels of this putative sleep hormone would be high est at night and would probably be elevated before or during episodes of SWS. We, therefore, measured plasma DSIP-LI levels every 30 min for 24 h in 12 normal volunteers in whom we obtained simultaneous polygra phic recordings. We found a distinct diurnal rhythm for plasma DSIP-LI levels, with the maximum at 1500 and the minimum at 0100 h. DSIP-LI l evels were substantially lower in rapid eye movement sleep (P < 0.005) and somewhat lower in SWS (P < 0.05) compared to awake values. DSIP-L I levels did not rise before, during, or after a significant percentag e of episodes of SWS. We found, however, that the diurnal rhythm of DS IP-LI closely followed that of body temperature with a high degree of correlation (r(2) = 0.66; P < 0.0001). We conclude that endogenous ele vations of circulating DSIP may be associated with suppression of slow wave and rapid eye movement sleep, and that the circadian rhythm of t his peptide is coupled directly or indirectly to that of body temperat ure.