Association of cPLA2- and COX-1 using the Golgi equipment of A549 individual lung epithelial cells. (more affordable dosage) or a short hypothermia accompanied by fever (larger dosage). SC-236 (2.5 mg/kg iv) obstructed the fever induced by either LPS dose, whereas SC-560 (5 mg/kg iv) altered neither the febrile response to the low LPS dose nor the fever element of the response to the bigger dose. Nevertheless, SC-560 blocked the original hypothermia due to the bigger LPS dosage. At a subneutral Ta (22C), the rats taken care of immediately LPS with early (70C90 min, nadir) dose-dependent hypothermia. The hypothermic response to either dosage was improved by SC-236 but obstructed by SC-560. The hypothermic response to the bigger LPS dosage was associated with a fall in arterial blood pressure. This hypotensive response was attenuated by either SC-236 or SC-560. At the onset KT 5823 of LPS-induced hypothermia and hypotension, the functional activity of the COX-1 pathway (COX-1-mediated PGE2 synthesis ex lover vivo) increased in the spleen but not liver, lung, kidney, or brain. The expression of splenic COX-1 was unaffected by LPS. We conclude that COX-1, but not COX-2, mediates LPS hypothermia, and that both COX isoforms are required for LPS hypotension. 0111:B4 LPS was purchased from Sigma-Aldrich (St. Louis, MO). A stock suspension of LPS (5 mg/ml) in pyrogen-free saline was stored at ?20C. On the day of the experiment, the stock was diluted to a final concentration of either 10 or 1,000 g/ml. The diluted LPS suspension or saline was bolus KT 5823 injected (1 ml/kg) through the extension of the venous catheter 20 min after completion of the 10-min-long infusion of SC-560, SC-236, or their vehicle. The resultant doses of LPS (10 or 1,000 g/kg iv) have been repeatedly shown to cause a moderate polyphasic fever (the lower dose) or a brief hypothermia followed by fever (the higher dose) at a neutral Ta, whereas they cause a dose-dependent hypothermia at C-FMS a subneutral Ta (68C71, 79). Functional Activity of the COX-1 Pathway and COX-1 Expression COX-1 pathway activity was assessed on the basis of the ex vivo production of PGE2 that is blocked by SC-560. We selected the COX-1-mediated synthesis of PGE2 as a measure of the functional activity of the COX-1 pathway because the immediate product of the reaction catalyzed by COX-1, PGH2, is usually unstable. Among the multiple products synthesized in the next step (by several PGE, D, F, and I synthases and by thromboxane synthases), PGE2 is reasonably stable and the most robustly produced during inflammation in a wide spectrum of organs and tissues throughout the body (35). Furthermore, at least in some situations, the crucial, rate-limiting step of inflammation-associated PGE2 KT 5823 synthesis seems to be the one catalyzed by COX and not the one catalyzed by terminal synthases (8). If one accepts that LPS-induced hypothermia is usually mediated by PGD2 (which may not be the case; observe Refs. 27, 44), an alternative approach would be to use the COX-1-mediated PGD2 synthesis as a measure of COX-1 pathway activity. However, PGD2 is much less stable than PGE2, whereas some more stable products of PGD2, such as 15-deoxy-12,14-PGJ2, increase (rather than decrease) deep Tb in rats (A. A. Steiner, A. S. Dragic, J. Pan, A. A. Romanovsky; unpublished observation). Hence, the stability of PGE2 and the robustness of its synthesis under inflammatory conditions provide a solid justification for the use of COX-1-mediated PGE2 synthesis as a measure of COX-1 pathway activity. It should be understood, however, that this measure displays the enzymatic activity not only of COX-1, but also that of several PGE terminal synthases, and depends both on how COX-1 is coupled with each synthase and on which enzyme in each COX-1-synthase pair catalyzes the crucial step. Tissues for the functional activity assay were harvested from rats 50 min after injection of.