DUBAI, May 23 (Reuters) - Profit-booking swept across the Saudi Arabian bourse in early trade on Tuesday as investors cashed out ahead of Ramadan, while Abu Dhabi and Qatar were buoyed by gains among constituents of the MSCI emerging market index.

Riyadh's index fell 0.6 percent in the first 40 minutes as 151 shares declined and only eight rose.

"This is the cash-out before Ramadan, and it is not uncommon to see some unwinding ahead of the quieter period," said a Jeddah-based trader. Trading volumes often shrink during the holy month, which is expected to start this Saturday.

In Dubai, the index was down 0.1 percent as theme park operator DXB Entertainments lost 1.2 percent.

MSCI constituents were strong elsewhere, however. They lifted Abu Dhabi's index 0.5 percent with First Abu Dhabi Bank up 0.5 percent. In Doha, the index rose 0.2 percent on the back of gains in companies most exposed to foreign funds; Qatar National Bank was up 0.8 percent.

(Reporting by Celine Aswad; Editing by Andrew Torchia) ((celine.aswad@thomsonreuters.com)(+9715 62247653)(Reuters Messaging: celine.aswad.thomsonreuters.com@reuters.net))