Melatonin secretion related to side-effects of beta-blockers from the central nervous system.

In two studies of hypertensive patients the relationship between beta-blocker-induced CNS side-effects and the nightly urinary secretion of melatonin was analysed. In one group (n = 10) placebo, atenolol (mean dose 86 mg/day) or propranolol (mean dose 305 mg/day) were given in a double-blind, randomised design. In the other (n = 13) 100-400 mg metoprolol was given daily (mean dose 197 mg). After 4 weeks of treatment all beta-blockers reduced melatonin excretion, but the effect was significant only for metoprolol. Sleep disturbance records revealed more disturbed nights in the metoprolol group compared with the propranolol and the atenolol groups, even when the difference in age between the groups was controlled for. In the metoprolol group a significant relationship (p less than 0.05) was found between the fall in melatonin and the percentage of disturbed nights. Severe CNS side-effects, such as nightmares, occurred only in patients treated with metoprolol (21%), which in all cases were accompanied by low levels of melatonin. Our data suggest that the CNS side-effects during beta-blockade are related to a reduction of melatonin levels.