Further studies on the role of prostaglandin in fever.

1. Experiments were carried out in unanaesthetized cats to find out if a prostaglandin is the mediator (a) for the long lasting fever which often follows injections of phsyiological salt solutions into the cerebral ventricles or into the cisterna magna, as well as their perfusions through the cerebral ventricles, and (b) for the sodium fever which occurs during a perfusion of the cerebral ventricles with calcium-free artificial c.s.f. A fever mediated by prostaglandin should be accompanied by an increase of prostaglandin activity in cisternal c.s.f., and be abolished or prevented by antipyretics like paracetamol or indomethacin which inhibit prostaglandin synthesis. Both criteria were applied.2. The fever which follows injections or perfusions of physiological salt solutions appears to be mediated by a prostaglandin of the E series, probably E(2) (PGE(2)) because it was accompanied by increased prostaglandin E-like activity in the c.s.f. and abolished by paracetamol and indomethacin. During the first few days after pre-treatment of the cats with intramuscular chloramphenicol the injections were rarely followed by fever.3. The fever which occurs during a perfusion with calcium-free artificial c.s.f. appears not to be mediated by prostaglandin, because it was not associated with increased prostaglandin activity in the cisternal effluent, and not prevented by paracetamol or indomethacin, although these antipyretics usually attenuated the fever.4. A perfusion of the cerebral ventricles with artificial c.s.f. containing calcium in an abnormally high concentration (6.25 mM) brought down fever produced by PGE(1), or PGE(2), or bacterial pyrogen.