DECREASED DELTA-SLEEP AND PLASMA DELTA-SLEEP-INDUCING PEPTIDE IN PATIENTS WITH CUSHING SYNDROME

To evaluate the sleep disturbances of patients with Cushing syndrome a nd to examine the relationship between the sleep disturbances and plas ma levels of delta-sleep-inducing peptide-like immunoreactivity (DSIP- LI), we performed three polysomnographic/endocrinological studies in p atients with Cushing syndrome. In study 1, polysomnography was studied in 12 patients and 12 matched normal volunteers. In addition, DSIP-LI was measured every 30 min for 24 h in 9 patients with Cushing syndrom e and 12 normal volunteers. The percentage of time spent in delta slee p (stages 3 and 4) was significantly reduced in patients with Cushing syndrome(5.8 +/- 1.4%; mean +/- SEM) compared to normal volunteers (14 .0 +/- 2.5%) (p < 0.01). REM sleep indices, however, were not signific antly different between the two groups. There was a significant negati ve correlation between amount of delta sleep and 08.00 h DSIP-LI (r = -0.43, p < 0.05), which is against the notion of a causal relationship between DSIP-LI and delta sleep. The circadian rhythm of plasma DSIP- LI was found to be similar in Cushing patients and normal volunteers. In study 2, we measured plasma levels of delta-sleep-inducing peptide- like immunoreactivity (DSIP-LI) at 08.00 h in 65 patients with Cushing syndrome and 49 normal volunteers. The 08.00 h DSIP-LI concentrations of 797 +/- 57 pmol/l (mean +/- SEM) in the patients with Cushing synd rome were significantly reduced compared to the level of 1,062 +/- 99 pmol/l found in the normal volunteers (p < 0.05). In study 3, plasma w as drawn simultaneously from the petrosal sinuses and peripheral veins of Cushing patients. No central-toperipheral gradient for plasma DSIP -LI was noted and neither peripheral, nor central plasma DSIP-LI was a ffected by administration of intravenous ovine CRH. We conclude that p atients with Cushing syndrome have less delta sleep and lower plasma c oncentrations of DSIP-LI than normal controls, however a causal relati onship between the two appears to be unlikely. The pituitary does not appear to be the site of synthesis of plasma DSIP, whose source remain s unknown.