Eszopiclone stimulates the hypothalamo-pituitary-adrenal axis in the rat

Eszopiclone (Lunesta?) is used for the treatment of insomnia. It is the S (+)-enantiomer of racemic zopiclone, a cyclopyrrolone with no structural similarity to the hypnotic drugs zolpidem and zaleplon or to the benzodiazepines and barbiturates. Although eszopiclone interacts with the gamma-aminobutyric acid A-type (GABA(A)) receptor complex, it has a different binding profile than other sedative/hypnotic agents and modulates the receptor complex in a unique manner. Thus, eszopiclone might produce different pharmacological effects compared to other sedative/hypnotic agents. Beside their behavioral properties, sedative/hypnotic drugs affect the hypothalamo-pituitary-adrenal (HPA) axis. In general, low doses of benzodiazepine-type drugs decrease, whereas high doses increase the activity of the HPA axis. Furthermore, benzodiazepines reduce stress-induced increases in HPA axis activity. The goal of the present study was to characterize the effects of eszopiclone on the HPA axis in the rat. Male rats were injected with saline or eszopiclone and trunk blood was collected for the measurement of plasma levels of adrenocorticotropin (ACTH) and corticosterone by radioimmunoassay. The acute administration of eszopiclone produced dose-dependent increases in plasma levels of ACTH and corticosterone, and tolerance developed to these effects after repeated drug administration. Pretreatment with eszopiclone did not affect stress-induced stimulation of the HPA axis. These results show that eszopiclone and the benzodiazepine-type drugs differentially affect the HPA axis.