Stocks closed lower Wednesday as market participants took profits following a red-hot run higher. Indeed, the three main indexes are hovering near record highs and are poised to close out May with solid gains.  

At the close, the Nasdaq Composite was down 0.6% at 16,920 and the S&P 500 was off 0.7% at 5,266. The Dow Jones Industrial Average fell 1.1% to 38,441 as UnitedHealth Group ( UNH ) slumped 3.8% after the health insurer forecast "some disturbance" in its Medicaid business. At roughly $484, UNH stock has the greatest weighting of all 30 stocks in the price-weighted Dow.

ConocoPhillips ( COP ) to buy Marathon Oil ( MRO )

In other single-stock news, Marathon Oil ( MRO ) jumped 8.4% after ConocoPhillips ( COP ) agreed to buy the Texas-based exploration and production company in an all-stock deal valued at $22.1 billion, including debt. The transaction is expected to boost COP's shale assets and could close later this year if all goes as planned. 

This is just the latest in a string of merger-and-acquisition (M&A) news coming from the energy sector. Most recently, Hess (HES, -2.1%) shareholders on Tuesday approved a $53 billion merger with Chevron ( CVX ) – though the deal has a few more hurdles to clear before it closes. 

"Consolidation, especially among oil and gas producers, has been a key dealmaking trigger in the last several months due to reduced oil prices, economic pressures and increased support for achieving net zero plans," says Mark Williams, chief revenue officer for the Americas at dealmaking platform Datasite.

The deals are being driven by large producers looking to strengthen their market positions amid maturing business models, Williams adds, "especially to secure lower-cost reserves." He anticipates this trend will continue into the second half of this year.

Chewy has its best day ever after earnings

Outside of the oil patch, Chewy (CHWY) surged 27.1% – its biggest one-day gain on record – after earnings. For its fiscal Q1, the online pet supplies retailer disclosed higher-than-expected earnings of 31 cents per share, up 55% year-over-year. Revenue increased 3.1% to $2.9 billion. 

Chewy also unveiled a $500 million stock buyback plan, representing more than 5% of its market cap.

American Airlines ( AAL ) dives after cutting Q2 forecast

American Airlines ( AAL ) was another notable mover, diving 13.5% after the air carrier cut its second-quarter guidance and said its chief commercial officer, Vasu Raja, is leaving the company in June.

"Guidance held out as long as it could, but it's clear AAL's long-term strategy will take some time to execute," said Jefferies analyst Sheila Kahyaoglu, who downgraded the stock to Hold from Buy and lowered her price target to $12 from $17.