Time Course of Release in vivo of PGE2, PGF2α, 6-Keto-PGF1α, and TxB2 into the Brain Extracellular Space after 15 Min of Complete Global Ischemia in the Presence and Absence of Cyclooxygenase Inhibition

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Abstract
The time-dependent release of prostaglandin E2 (PGE2), prostaglandin F2α (PGF2α), thromboxane (Tx) B2, and 6-keto-PGF1α (6-keto) from brain was measured before, during, and after a 15-min interval of total ischemia (four-vessel occlusion) in halothane-anesthetized cats using the technique of cerebroventricular perfusion. Resting levels of PGE2, PGF2α, 6-keto, and Tx were: 253 ± 75, 953 ± 300, 650 ± 200, and 550 ± 170 pg/ml, respectively. During the 15-min ischemia, all prostanoids rose significantly, yet the highest levels were not observed until the first 15–60 min of the reflow at which time levels of PGE2, PGF2α, 6-keto, and Tx, as compared with the preischemic baseline, rose ∼8, 3.4, 3, and 55-fold, respectively. Significantly, although all prostanoids showed increases relative to baseline, the ratios of PGF2α/6-keto and PGE2/6-keto remained stable throughout the experiment in both groups of animals. In contrast, the Tx/6-keto ratio rose from ∼1 to ∼ 30 during the 60 min after reflow in untreated cats. Treatment with zomepirac sodium (5 mg/kg, i.v.), a cyclooxygenase inhibitor, resulted in highly significant reductions in the levels of all prostanoids during the preischemic period. In zomepirac sodium-treated animals, there were also highly significant reductions in the prostanoid response to ischemia. Of particular interest was that the degree of inhibition of Tx as compared with 6-keto, during the post-ischemic period of peak secretion was such that the Tx/6-keto ratio fell from 30 in the control ischemic animal to 0.3 in the zomepirac sodium-treated animal, suggesting a selective blockade of the formation of Tx as compared with prostacyclin.