ATF4 and acute respiratory distress syndrome: Furthermore, we pretreated rats with a potent ER stress inhibitor, 4-phenylbutyrate (4-PBA), before the rats were subjected to CLP surgery, and we found that 4-PBA markedly alleviated the CLP-induced ALI, reduced the upregulation of the p-PERK protein level, and downregulated the elevation of PERK, eIF2-α, ATF4, and CHOP mRNA levels.