Sometimes the right treatment for nervous jitters is a jolt of good news. That's what the stock markets got this morning as nervousness about the prospect of further gains gave way to rampant optimism. Both the Dow Jones Industrials (DJINDICES:^DJI) and the S&P 500 moved toward new record highs in the first hour of trading. Strength in U.S. factory orders helped bolster what had already looked to be a positive opening for the market, as European stocks proved surprisingly resilient despite a shrinking eurozone economy. By 10:55 a.m. EDT, the Dow was up 102 points, or 0.7%, with the S&P 500 and other major market benchmarks following suit with similar percentage gains.

But the real popper of the day is UnitedHealth (NYSE:UNH), which has soared 7.4%, adding to yesterday's late-day gains on news that the government agency responsible for Medicare will increase its reimbursement rates by 3.3% for fiscal 2014. Previously, the Centers for Medicare and Medicaid Services had suggested that those reimbursement rates might actually drop by 2.3%, sparking a sell-off among health insurance companies dependent on the government program for a substantial part of their business. The good news cements UnitedHealth's leadership position in the industry even as Obamacare has posed some new questions for health insurers.

On the other hand, Hewlett-Packard (NYSE:HPQ) has dropped 5.2% on a downgrade from Goldman Sachs. Goldman questioned the big bull run that has seen HP's stock soar more than 60% so far in 2013, arguing that any restructuring won't have a material impact on the difficulties HP will face in its sales of PCs and other computer hardware until next year at the earliest. Perhaps most remarkably, Goldman made a downgrade all the way to "sell" -- a rare rating for Wall Street analysts -- but it seems appropriate, given the investment firm's price target of $16, which still implies more than 25% further downside from here.

Finally, beyond the Dow, financial-services and real-estate brokerage company BGC Partners (NASDAQ:BGCP) has soared 43.5% after Nasdaq OMX Group (NASDAQ:NDAQ) bought BGC's eSpeed electronic trading platform in a deal worth about $1.23 billion in cash and stock. Nasdaq shares fell more than 10% on investor concerns that the company overspent for eSpeed, but the move shows just how cutthroat the exchange industry has become in light of high-frequency trading and other lucrative money-making strategies for exchange companies.

Fool contributor Dan Caplinger has no position in any stocks mentioned. You can follow him on Twitter @DanCaplinger. The Motley Fool recommends Goldman Sachs and UnitedHealth Group. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.