Melatonin and zopiclone: the relationship between sleep propensity and body temperature

The sleep promoting effects of the sedative-hypnotics, melatonin and temazepam, have been associated with a decline in core body temperature (Tc). To determine whether changes in body temperature are a general feature of sedative-hypnotics, the present study compared the sleep inducing, core and peripheral temperature effects of melatonin, with those of zopiclone.

Subjects were supine from 08:00-21:30 h and received melatonin, zopiclone or placebo at 14:00 h.

Individual, light and temperature controlled bedrooms.

12 healthy, young, adults (7m, 5f; 20.3 +/- 0.6 years).

Melatonin (5mg), zopiclone (Imovane; 7.5 mg) and placebo were administered in a double-blind, crossover design.

From 11:00-20:00 h, modified hourly multiple sleep onset latency tests (MSLT) of a 20-min duration were conducted and heart rate (HR) was recorded. Tc and foot temperature (T(Ft)) were recorded continuously using thermistors. Compared with placebo, melatonin and zopiclone significantly reduced sleep onset latency (SOL) to stage 1 (by 3.50 +/- 0.73 min and 6.80 +/- 0.61 min, respectively) and reduced Tc (by 0.22 +/- 0.02C and 0.14 +/- 0.02C, respectively). For melatonin, Tc declined as the result of an increase in peripheral heat loss (increase in T(Ft) of 1.65 +/- 0.43 degrees C), and possibly a reduction in heat production as indicated by a decrease in HR (4.56 +/- 0.94 bpm). Zopiclone increased heat loss (increase in T(Ft) of 1.43 +/- 0.68C) and had no cardiac effects. For melatonin, a negative association was found between Tc (mean r=-0.43), however, this association was only weak for zopiclone (mean r=-0.23).

These results suggest that body temperature changes may be a general feature of sedative-hypnotics. The potential role of this effect in the promotion of sleep appears to vary between agents.