U.S. corporate debt markets fluctuated between losses and gains after Federal Reserve officials raised interest rates by 75 basis points (bps) for the third consecutive time and stoked expectations among debt investors for even tighter policy ahead.

A key measure of perceived U.S. credit risk, the Markit CDX North American Investment Grade Index, which declines as credit risk drops, widened 2.11 bps, to 100.6, as of 4:31 p.m. in New York, to the highest on an intraday basis since July 6, after initially tightening. The CDX high-yield index, which rises as credit risk declines, fell 0.5 points to 98.5.

"I believe 75 is the new 25 until something breaks, and nothing has broken yet," said Bill Zox, a high-yield portfolio manager at Brandywine Global Investment Management. "The Fed is not anywhere close to a pause or a pivot. They are laser-focused on breaking inflation. A key question is what else might they break."