SOME EFFECTS OF PROSTAGLANDINS E1 AND E2 AND OF ENDOTOXIN INJECTED INTO THE HYPOTHALAMUS OF YOUNG CHICKS: DISSOCIATION BETWEEN ENDOTOXIN FEVER AND THE EFFECTS OF PROSTAGLANDINS

Abstract

1 Prostaglandins E₁ and E₂ elevated body temperature of young chicks when injected into the hypothalamus at thermoneutrality (31°C). In contrast, they lowered body temperature when so injected below thermoneutrality (16°C): 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 ‘O’-somatic antigen of Shigella dysenteriae consistently evoked hyperthermia when injected into the hypothalamus, irrespective of whether 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 O-somatic antigen of Shigella dysenteriae was reduced. 5 The intrahypothalamic injection, below thermoneutrality of prostaglandins E₁, 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.