U.S. regulators including the Federal Reserve warned banks to guard against possible losses from an end to low interest rates and reduce exposure or raise capital if needed. ... Several U.S. central bankers have called for raising interest rates at a faster pace than increases in the past, while the Fed hasn’t said when or how quickly it plans to lift borrowing costs from a record low. The regulators told banks to run stress tests with scenarios including “instantaneous and significant changes” in rates and “substantial changes in rates over time,” including shifts of as much as 4 percentage points.