Hj. Burgess et al., Effects of bright light and melatonin on sleep propensity, temperature, and cardiac activity at night, J APP PHYSL, 91(3), 2001, pp. 1214-1222
Melatonin increases sleepiness, decreases core temperature, and increases p
eripheral temperature in humans. Melatonin may produce these effects by act
ivating peripheral receptors or altering autonomic activity. The latter hyp
othesis was investigated in 16 supine subjects. Three conditions were creat
ed by using bright light and exogenous melatonin: normal endogenous, suppre
ssed, and pharmacological melatonin levels. Data during wakefulness from 1.
5 h before to 2.5 h after each subject's estimated melatonin onset (wake ti
me +/- 14 h) were analyzed. Respiratory sinus arrhythmia (cardiac parasympa
thetic activity) and preejection period (cardiac sympathetic activity) did
not vary among conditions. Pharmacological melatonin levels significantly d
ecreased systolic blood pressure [5.75 +/- 1.65 (SE) mmHg] but did not sign
ificantly change heart rate. Suppressed melatonin significantly increased r
ectal temperature (0.27 +/- 0.06 degreesC), decreased foot temperature (1.9
8 +/- 0.70 degreesC), and increased sleep onset latency (5.53 +/- 1.87 min)
. Thus melatonin does not significantly alter cardiac autonomic activity an
d instead may bind to peripheral receptors in the vasculature and heart. Fu
rthermore, increases in cardiac parasympathetic activity before normal nigh
ttime sleep cannot be attributed to the concomitant increase in endogenous
melatonin.