PARTIAL PROSTAGLANDIN-MEDIATED MECHANISM CONTROLLING THE RELEASE OF CORTISOL IN PLASMA AFTER INTRAVENOUS ADMINISTRATION OF ENDOTOXINS

In a first series of experiments we studied the influence of E. coli endotoxins or lipopolysaccharides (LPS) administered either intravenously (i.v.) or intramammarily (i.mam.) to lactating goats on plasma cortisol and rectal temperature (RT). Differences in the magnitude of the cortisol release and shape of the fever curve were observed. In both models maximal pyrexia and fever index (FI) were comparable. In a second series of experiments the influence of LPS on the plasma cortisol and RT was studied after i.v. injection of increasing doses of LPS : low (25 ng/kg), moderate (200 ng/kg) and relatively high (500 ng/kg). Although the cortisol response was dose dependent, the effect was not correlated with FI. The administration of flurbiprofen, a non steroidal anti-inflammatory drug (NSAID), resulted in a complete inhibition of fever at all LPS doses and the cortisol release after administration of low doses LPS. This indicates a prostaglandin mediation. With moderate and high doses LPS the cortisol release was only partially inhibited and delayed suggesting a non prostaglandin mediated mechanism. In a third series of experiments the influence of flurbiprofen on fever and cortisol release was studied after i.mam. LPS administration. The observed increase of plasma cortisol and RT were completely abolished after flurbiprofen treatment. It is concluded that: 1) the increase of plasma cortisol after LPS administration in lactating goats is not related to hyperthermia per se, 2) the control of fever and cortisol release may, to some extent, differ according to the LPS dose and method of administration, 3) the cortisol release observed after moderate and high doses of LPS is probably controlled by two phenomena. The first being induced by cyclo-oxygenase metabolites, the second by intermediary mediators other than prostaglandins or by LPS itself. 4) Although an eight-fold higher dose of LPS was given i.mam., a cortisol release comparable to the lowest dose of LPS (25 ng/kg) was observed. These differences in cortisol release can be ascribed to 1) a detoxification of LPS at the level of the mammary gland or 2) a slower resorption of LPS from the mammary gland.