April 21 (Reuters) - Russian consumer electronics retailer M.Video-Eldorado on Thursday reported a jump in first-quarter transaction volumes and online sales but warned of challenges ahead, as Russian companies adapt to Moscow's growing isolation due to sanctions over Ukraine.

Rouble volatility and supply chain disruptions have plagued the Russian market since President Vladimir Putin sent tens of thousands of troops into Ukraine on Feb. 24 and many foreign companies have ceased or suspended their Russian operations.

"In Q1 2022 we saw unprecedented changes in the Russian home appliances and consumer electronics market," Group CEO Enrique Fernandez said in a statement.

He said the company was used to dealing with rouble volatility and supply chain disruptions, but was now facing now big structural shifts, "from strong demand fluctuations to the transformation of brands' very cores."

"Consumer demand is currently declining following a brief surge of sales in late February and early March," Fernandez said.

Check Index, which analyses consumer trends in Russia based on transaction receipts, said that spending on electronics and appliances had jumped 80% from Feb. 21-27 in comparison with the previous week.

M.Video said the demand for goods such as fridges, computers and TV sets increased in particular, a trend it put down to the volatile rouble, unstable supplies and multiple manufacturers leaving the Russian market.

It said the group’s gross merchandise value (GMV), a measure of transaction volumes, rose 28.1% to 177.2 billion roubles ($2.2 billion) in the first quarter and online sales increased by 29.8% to now account for just over two-thirds of the company's total sales.

Activity had levelled off by mid-April and remained below year-ago levels, Fernandez said.

"We are negotiating better lease terms for our retail network, considering closures of inefficient stores and do not rule out scaling back our investment program going forward," Fernandez said.

M.Video said it was also taking steps to tame price growth. Annual inflation in Russia is at its highest since early 2002, hitting 17.6% as of April 15.

(Reporting by Reuters Editing by Mark Trevelyan)