* Overall quarterly net gaming revenue jumps 31%, online slips 8%

* U.S. sports betting venture now live in 23 markets

* Shares down 1.5%

April 7 (Reuters) - Ladbrokes owner Entain saw a rise in first-quarter revenue, boosted by a rebound in its retail betting shops and an expansion of its U.S. joint venture, but shares slipped as online sales fell for the second straight quarter.

The London-listed gambling company, which also owns Coral betting shops and the bwin and partypoker online brands, said on Thursday total net gaming revenue jumped 31% for the three months to March 31 despite an 8% fall in revenues from online.

Shares in the company listed on the FTSE 100 index were down 1.5% at 1030 GMT.

Gambling firms profited during the lockdowns as stay-at-home punters went online for entertainment, but online demand has slowed since economies reopened and people ventured out again, with inflation worries also pressuring spending.

Many firms, including Entain, are also turning to the U.S. market as it opens up to sports betting. Entain's U.S. joint venture with MGM Resorts, BetMGM, is now live in 23 markets with four new additions in the period, Entain said.

"In the U.S., BetMGM is firmly established as the number two operator, and our market launches during Q1 mean that we now have access to over 41% of the U.S. adult population," Entain Chief Executive Jette Nygaard-Andersen said in a statement.

BetMGM is expected to turn a core profit this year compared to a loss a year ago on revenues of more than $1.3 billion, Entain said in January.

"Very impressive BetMGM looks to be ticking over nicely," Hargreaves Lansdown analyst Matt Britzman said, adding that increased online demand, which brings in better margins, also seems to be faring well for Entain despite the return to retail.

Entain, previously known as GVC, has withheld dividend payments in the past two years, and last month said it would use excess cash on acquisitions. It said in January it was considering developing products for virtual reality systems. (Reporting by Amna Karimi in Bengaluru; Editing by Sherry Jacob-Phillips and Jan Harvey)