Oh

Figure 13.6 Possible chemical structure of (6)-gingerdione in solution. (From Kimura et al., 1989a.)

The intensity of absorption at 235 nm decreased after 5 hours, whereas the intensity at 280 nm increased. The shift in the intensity of absorption spectrum was only slight because of its extremely low concentrations. It is possible that the conversion of diketone to enol might have increased during incubation, thus causing the observed transfer of effect from inhibition to potentiation of PGF2a-induced contractions.

Previous investigations (Collier et al., 1975, Landolfi and Steiner, 1984) have shown that ethanol can differentially affect the contractile responses to a variety of prostaglandin compounds in vascular smooth muscles. Low concentrations of ethanol can enhance prostaglandin-induced contractions in isolated blood vessels. The gingerol derivatives containing the hydroxyl group in the alkyl part of the chemical structure potentiated the PGF2a-induced contractions in the same manner as ethanol. In addition, a significant potentiating effect of (±)-(6)-gingerol was also observed upon other types of prostanoid-induced contractions.

Modulation of Eicosanoid-Induced Contractions by (±)-(6)-Gingerol in Isolated Blood Vessels

Eicosanoids are lipid mediators containing 20 carbon fatty acid derivatives. They are derived from phospholipase-released arachidonic acid. In the membrane, the arachidonic acid released by phospholipase A2 from phospholipids is metabolized by cyclooxygenase to prostaglandins and thromboxanes or by lipoxygenase to leukotrienes. The eicosanoids are involved in numerous biological functions such as pain, fever, and inflammation (Rang et al., 1999).

Physiologically active eicosanoids such as the prostaglandins, thromboxane (TX), and leukotrienes (LTs) either dilate or constrict the vasculatures. PGI2, PGF2a, PGD2, and TXA2 are synthesized in the blood vessels (Fostermann et al. 1984) and are involved in the modulation of contractions in vascular smooth muscles. Similarly, LTC4 and LTD4 induce contractions of mesenteric vascular tissues (Feigen, 1983).

The gingerols have been reported to inhibit the synthesis of prostaglandins and leukotrienes in vascular smooth muscles (Kiuchi et al. 1992). Subsequently Kimura et al. (1989a) investigated the effects of gingerols on the contractions induced by various eicosanoids on isolated blood vessels. Such studies will provide new insights into the pharmacological action of gingerols as a modulator of eicosanoid responses in vascular smooth muscles.

Effects of (±)-(6)-Gingerol on PGF2a-Induced Contractions in Isolated Mice and Rat Blood Vessels

The effects of gingerol were compared between species (mouse and rat), between veins (mesenteric vein and vena cava), and arteries (mesenteric artery and aorta) and between longitudinal and circular segments (Table 13.4). (±)-(6)-Gingerol potentiated PGF2a-induced contractions in longitudinal segments of mouse and rat veins and decreased PGF2a-induced relaxation in longitudinal segments of rat artery. In contrast, (±)-(6)-gingerol inhibited PGF2a-induced contractions in circular segments of rat aorta and longitudinal segments of mouse mesenteric artery.

Table 13.4 Effects of (±)-(6)-gingerol on PGF2a-induced contractions in isolated blood vessels of mice and rats

Blood vessel (muscle segment)

0.3 mM PGF2a

+ (±)-(6)-gingerol % (mM)

Mouse mesenteric vein (L)

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