It has been demonstrated that nitric oxide play a role in thermoregulation

but very little is known about the mechanism in yeast-induced fever and aminopyrine-evoked hypothermia in rats. We have a hypothesis that Guizhi Tang

a formulum possesses dual thermoregulatory action

may exhibit anapyrexia or anti-hypothermia action via NO. To test the hypothesis

the cytosolic nitric oxide synthase in hypothalamus in both the fever and the hypothermia rats induced by yeast or aminopyrine accordingly was determined using a colorimetric assay. The NOS activity enhanced after a s.c. yeast-injection and decreased after an i.p. treatment of aminopyrine. Reversion in NOS and body temperature were observed in fever rats after the administration of Guizhi Tang orally at a dose dependent manner. While a confusing result obtained from the hypothermia rats treated with Guizhi Tang was that a recover of body temperature paraileled a continual decrease in NOS activity.Data suggested that the cytosolic NOS in hypothalamus participates the thermoregulation in rats and may also play a role in antipyretic action of Guizhi Tang

but not in its anti-hypothermia action.