Prostaglandin D2 Regulates Physiological Sleep

Prostaglandin (PG) D2 is identified as a natural constituent in brains of various mammals and its synthesis (6) and degradation (8) in brain have been investigated in detail. The central actions of PGE2 and PGF2α were widely examined and it has been demonstrated that several hypothalamic functions such as regulations of body temperature (3) and food intake are closely related to the production of PGE2 or PGF2α in the brain. However, the central actions of PGD2, which is the major substance among prostaglandins in rat brain, have remained unclear. Recently, we found using the intracerebral microinjection technique that PGD2 elicited several central actions. Although PGD2 is an isomer of PGE2, PGD2 had specific actions on inducing hypothermia (9, 10) and bradycardia (10) which were quite different from the central actions of PGE2. Another specific action of PGD2 was the sleep-inducing effect (1, 2, 10, 11). In this paper, we demonstrate the results concerning the role of the prostaglandin on sleep regulation. Further, we discuss the possible role of endogenous PGD2 in the regulation of physiological sleep.