(Includes Wells Fargo, US Bancorp, KeyCorp and SunTrust results.)Regional banks that have already reported second-quarter results are showing continued strains in their loan portfolios, as the commercial sector sags in the recession. Large money center banks and brokerage firms were able to somewhat offset weak credit metrics during the quarter, thanks to their investment banking arms. Goldman Sachs ( GS), Bank of America ( BAC) and JPMorgan Chase ( JPM) posted impressive trading results and racked up fees revenue as troubled companies looked to recapitalize their balance sheets. BofA, JPMorgan Chase, BB&T ( BBT)and others also benefited from the mortgage refinancing boom earlier in the quarter. Citigroup ( C) had a huge one-time gain from the completion of the Smith Barney- Morgan Stanley ( MS) joint venture, sending its quarterly numbers into the black. But regional banks are tied much more closely to the health of the economy. They depend much more on making money on the spread between the interest rates they offer depositors and the amount at which they lend money to businesses and consumers. This can be particularly stressful as borrowers don't pay their loans back, measured by nonperforming assets, and weak demand for lending as a result of an anemic economy. On Wednesday, US Bancorp ( USB), SunTrust Banks ( STI) and KeyCorp ( KEY) were the latest regional banks to report rising nonperforming assets and continued stress in their loan portfolios. Wells Fargo ( WFC), which has become more of a national bank with its acquisition of Wachovia last year, also reported results. Both SunTrust and Key posted earnings losses for the second quarter. US Bancorp reported substantially lower profit due to higher credit costs.