Prostaglandin physiological actions

Prostaglandins and terpenes are still other classes of lipids. Prostaglandins, which are found in all body tissues, have a wide range of physiological actions. Terpenes arc often isolated from the essential oils of plants. They have an immense diversity of structure and are produced biosynthetically by head-to-tail coupling of two five-carbon isoprene equivalents —isopentenyl pyrophosphate and dimethylallyl pyrophosphate. 

The functional significance of thromboxane A2 inhibition by kava is not certain. More needs to be understood about the functions of prostaglandins in the CNS, but given the inhibition of GABAA by thromboxane A2, kava s suppression of thromboxane A2 synthesis could conceivably contribute to its anxiolytic and sedative effects. More research is needed to determine if this mechanism of action is physiologically significant at normal kavalactone concentrations. 

In Box 7.13 we saw that the widely used analgesic aspirin exerted its action by acetylating the enzyme cyclooxygenase (COX) which is involved in the production of prostaglandins. Prostaglandins are modified C20 fatty acids synthesized in animal tissues and they affect a wide variety of physiological processes, such as... 

Pro-inflammatory cytokines (see p. 432 et seq.) can also induce sleep, the effect depending on the concentration of the cytokine and the time of day. The effect on the sleep profile (increased non-REM and decreased REM sleep) appears to depend on the increased synthesis of prostaglandin D2 and nitric oxide which then alter the circadian rhythm. It is also known that some pro-inflammatory cytokines can affect the reuptake of 5-HT which plays an important role in regulating the sleep-wake profile. The endogenous fatty acid, oleamide, can cause sedation and induce sleep by activating cannabinoid receptors but also by potentiating the action of benzodiazepines on their receptor sites. Whether such action is of physiological relevance is presently unknown. 

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