Lipid A fever in cats.

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Abstract
In unanesthetized cats the effect of (Salmonella lipopolysaccharide) lipid A on rectal temperature and on prostaglandin E2 (PGE2) activity in cisternal cerebrospinal fluid (c.s.f.) was examined. Lipid A was injected either i.v. or into the cerebral ventricles. Lipid A injected i.v. in a dose of 1-4 .mu.g/kg produced long-lasting fever which was more often biphasic than monophasic. With a 2nd injection a much shorter but usually higher monophasic response was produced. The cat was then for a time insensitive to i.v. lipid A but when the injections were repeated at 24 h intervals brisk monophasic fevers were again produced. The threshold dose of i.v. lipid A lay between 0.1 and 0.3 .mu.g/kg. Lipid A injected into the cerebral ventricles in a dose of 100 ng or 1 .mu.g produced long-lasting monophasic fever. No tolerance developed; the same or only slightly diminished responses occurred on repeated injections. The threshold dose was between 5 and 20 ng. A cat rendered insensitive to i.v. lipid A gave its normal fever response to injection of lipid A into the cerebral ventricles. The fever produced by lipid A injected i.v. or into the cerebral ventricles was associated with the appearance of, or a rise in PGE2 activity in c.s.f. Both the fever and the PGE2 activity in c.s.f. produced by lipid A injected i.v. or into the cerebral ventricles were brought down and prevented by i.p. injections of aspirin, paracetamol, or indomethacin.