I Prostaglandins El and E2 elevated body temperature of young chicks when injected into the hypothalamus at thermoneutrality (31 0C). In contrast, they lowered body temperature when so injected below thermoneutrality (160C): the relation of the fall in body temperature to increased heat loss and decreased heat production was examined. 2 The above effects below thermoneutrality were potentiated by pretreatment with inhibitors of prostaglandin synthetase and possible reasons for this potentiation are given. 3 The '0'-somatic antigen of Shigella dysenteriae consistently evoked hyperthermia when injected into the hypothalamus, irrespective ofwhether the chicks were within or below thermoneutrality. 4 Pretreatment with prostaglandin synthetase inhibitors failed to prevent the onset of endotoxin fever; however, duration of the fever, induced by intrahypothalamic injection of the 0-somatic antigen of Shigella dysenteriae was reduced. 5 The intrahypothalamic injection, below thermoneutrality of prostaglandins E,, E2, noradrenaline, 5-hydroxytryptamine or carbachol reversed endotoxin fever, inducing even substantial falls in body temperature.6 While the results cast some doubts on the role of prostaglandins of the E series as mediators of endotoxin fever in chicks, they cannot be eliminated as mediators until the significance of the reduction in duration of the pyrexic response by indomethacin and 5,8,11,14-eicosatetraynoic acid, and the degree of synthesis inhibition attained, are known.
I The effects of intravenous prostaglandin E, and endotoxin were studied in young chickens (11-17 days old).2 At a thermoneutral ambient temperature (31 0C), intravenous prostaglandin E, produced behavioural and electrocortical sleep, increased oxygen consumption and, after an initial fall, elevated body temperature. Below thermoneutrality (160C), the initial hypothermic effect was more marked and oxygen consumption was lowered.3 The soporific actions of prostaglandin E, were sufficient to counteract dexamphetamine-induced behavioural and electrocortical arousal and vocalization. 4 Intravenous injection of the 0-somatic antigen of Shigella dysenteriae evoked, after a latent period, long lasting hyperthermia. This indicates that in young chicks the blood brain barrier is probably permeable to endotoxins.
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