Local renal ischemia during burn shock in rat effected by thromboxane A2 and serotonin

Intermittent patchy ischemia in the renal cortex during traumatic shock has previously been observed in dogs and rats. In recent experiments on rats a high rate of abrupt changes in local blood flow was observed after scalding. To try to reveal endogenous factors causing such ischemic episodes, we scalded six series of anesthetized rats (50% of body surface for 30 s in 80 degrees C water) and measured arterial pressure (AP), hematocrit (Hct), and local renal cortical blood flow (RCF). RCF was recorded by the local H2 washout technique. After scalding, RCF decreased markedly in all series whereas AP was relatively well preserved. In accordance with previous experiments, 11% of the washout curves recorded 0-75 min after scalding showed abrupt changes in local blood flow, rising to 27% during the next 60 min in drug-untreated rats. In contrast, blocking of serotonin S2 receptors with Ketanserin abolished the phenomenon. However, in rats treated with the prostaglandin synthesis blockers, indomethacin (general) or 3-ethyl pyridin (thromboxane A2 blocker), the phenomenon was observed in only 2-3% of the washout curves. Furthermore, after blocking the AngII receptors by saralasin or alpha receptors by phentolamine in separate series, the frequency of abrupt flow shifts was reduced in comparison to the frequency in untreated rats. The results indicate that intermittent, patchy vasoconstriction is mediated by serotonin and thromboxane A2 (TxA2), probably released from platelets. The occurrence of ischemic episodes also depends on the local AngII and alpha-adrenergic tonus present after scalding.