Comparative effects of smooth and rough Pasteurella hemolytica lipopolysaccharides on arachidonic acid, eicosanoids, serotonin, and histamine in calves.

Effect of IV infusions of smooth and rough Pasteurella hemolytica lipopolysaccharides (LPS; 24 ng/kg/min for 500 min) on circulating levels of arachidonic acid, prostaglandins (PG), thromboxane B2 (TxB2), histamine, and serotonin in calves was evaluated. Both smooth and rough LPS had no effects on plasma PGE but caused maximal increases in arachidonic acid, TxB2, and PGF2 alpha at 1 hr and 6-keto-PGF1 alpha at 3 hr of infusion, respectively. The increases in arachidonic acid and its metabolites were greater and more prolonged for smooth LPS than for rough LPS. Although both rough and smooth LPS increased plasma serotonin transiently at 25 min of infusion, only rough LPS decreased serotonin in the later period of endotoxemia. In contrast, smooth, but not rough, LPS decreased plasma histamine during endotoxemia. These results indicate that during endotoxemia there is increased PG and TxA2 synthesis secondary to marked arachidonic acid release into circulation. The data also demonstrate that smooth and rough LPS differ in their abilities to release histamine, serotonin, and eicosanoids. These effects might be due to differences in the in vivo mechanisms of action of smooth and rough LPS and may partly explain the differential potency of smooth and rough LPS in producing pathophysiological changes.