Experimental fever. Pyrogenalum is a highly potent nonprotein exogenous pyrogen consisting of LPS

Pyrogenalum is a highly potent nonprotein exogenous pyrogen consisting of LPS. It may be synthesized or produced by Pseudomonas aeruginosa bacteria and by Salmonellae of Typhus-Paratyphus group. The onset of fever in response to pyrogen injection begins after a certain latent period whose duration is shorter in the case of an endogenous pyrogen injection. The latent period depends on the nature and potency of pyrogen, and the way of injection. In the case of intravenous injection the latent period is 15 – 40 minutes, in the case of subcutaneous injection it is 30 to 80 minutes, in the case of injection into cerebral ventricles – it is considerably less than 15 minutes. Repeated injections of exogenous pyrogens produce tolerance, while repeated injections of endogenous ones do not. The blockade of the system of mononuclear phagocytes with Indian ink prevents development of fever after introduction of exogenous pyrogens.

Hyperthermia, unlike fever, is a temporary increase of body temperature due to the disturbance of thermoregulatory mechanisms and brake-down of the balance between thermogenesis and heat emission (loss). Hyperthermia is extremal heat stress, when the ability of the organism to emit heat is lower than heat production, hence an abnormal rise of body temperature against the background of thermoregulatory failure. Hyperthermia results in dehydration, circulatory disorders and hypoxia. Fever does not produce either of the aforementioned changes characteristic of hyperthermia.