- Investors await UK GDP data- RSA, Pru, Anglo among ex-div stocks providing a drag- Kenmare, Petropavlovsk lead rise on FTSE 250London's blue chip index opened cautiously on Wednesday with ex-dividend stocks registering heavy losses, while concerns over the outlook for US economic growth weighed on sentiment. Markets were also awaiting UK gross domestic product (GDP) data for the fourth quarter, due to be released by the Office for National Statistics later this morning.In an exclusive interview with US television station ABC, Federal Reserve Chairman Ben Bernanke said that the increase in gas prices could boost inflation in the following months, decrease consumer income and cause a "hit on growth". He said that while the labour market looks to be improving, employment remains too high and its "far too early to declare victory" on the economy recovery.Meanwhile, French GDP increased by 0.2% quarter-on-quarter in the last three months of 2011, slowing down from the 0.3% growth seen in the preceding quarter. This meant that GDP increased by 1.7% in 2011 as a whole, up from 1.4% growth in 2010.Italy's Prime Minister Mario Monti has appeared to backtrack on comments he made about Spanish contagion risks earlier this week. He said today that the country is on a "steady course of budget consolidation". As for the Eurozone as a whole, he said that the worst of the crisis is now over.EX-DIV STOCKS TUMBLESome heavyweights on the Footsie fell steeply early on after trading without the right to their latest dividends, including RSA Insurance, Prudential, Anglo American, Schroders and Eurasian Natural Resources Corp (ENRC). Miners on the whole were providing a drag, with Antogasta, Randgold Resources and Xstrata losing at least 2% each. Russian steel giant Evraz fell into the red after saying that it expects the global steel industry to remain challenging in 2012. Nevertheless, Evraz reported a pre-tax profit of $873m, up from $633m in 2010. Inter-dealer broker ICAP said it has seen an increase in risk appetite in some markets this year, but has left full year guidance unchanged from that given at the time of its last update at the beginning of February. Shares fell over 1%.FTSE 250: KENMARE, PETROPAVLOVSK BUCK THE TRENDDespite mining stocks falling by an average 1.2% early on, second-tier mining peers Kenmare Resources and Petropavlovsk bucked the trend after their full-year results. Kenmare reported revenues of $167.5m in 2011, up from $91.6m the year before, helped by rising prices. The group swung to a pre-tax profit of $23.7m versus a loss of $16.3m in 2010.Gold producer Petropavlovsk rose after seeing revenue double in 2011 on the back of higher production and soaring gold prices. The group also said it expects production to rise a further 8% in 2012 and admitted that forecast was "conservative".African energy firm Ophir was also a high riser after it said it wants to raise up to £7.6m to help finance its expanding drilling programme. The firm said it would offer up to 30.5m new ordinary shares of 0.25 pence each, which help it to maintain its equity position in its successful Tanzania sites.BCFTSE 100 - RisersHargreaves Lansdown (HL.) 493.50p +1.09%WPP (WPP) 876.00p +0.98%GlaxoSmithKline (GSK) 1,435.50p +0.91%Reckitt Benckiser Group (RB.) 3,588.00p +0.87%Meggitt (MGGT) 402.60p +0.85%SSE (SSE) 1,356.00p +0.82%Reed Elsevier (REL) 565.00p +0.80%Wolseley (WOS) 2,454.00p +0.78%G4S (GFS) 278.50p +0.69%Compass Group (CPG) 655.50p +0.69%FTSE 100 - FallersRSA Insurance Group (RSA) 110.00p -5.01%Prudential (PRU) 773.00p -3.07%Schroders (Non-Voting) (SDRC) 1,254.00p -2.11%Schroders (SDR) 1,610.00p -1.95%Anglo American (AAL) 2,395.00p -1.92%British Land Co (BLND) 491.90p -1.56%Vedanta Resources (VED) 1,284.00p -1.53%GKN (GKN) 208.50p -1.47%Eurasian Natural Resources Corp. (ENRC) 610.50p -1.37%Randgold Resources Ltd. (RRS) 5,550.00p -1.33%FTSE 250 - RisersPetropavlovsk (POG) 651.50p +5.08%Kenmare Resources (KMR) 49.41p +4.57%Ophir Energy (OPHR) 509.00p +4.28%Computacenter (CCC) 445.70p +1.97%Stagecoach Group (SGC) 265.70p +1.80%UK Commercial Property Trust (UKCM) 72.10p +1.62%Northgate (NTG) 217.80p +1.30%Ruspetro (RPO) 208.60p +1.26%Travis Perkins (TPK) 1,100.00p +1.20%Cobham (COB) 227.00p +1.11%FTSE 250 - FallersCentamin (DI) (CEY) 72.40p -7.54%Petra Diamonds Ltd.(DI) (PDL) 181.50p -3.56%F&C Asset Management (FCAM) 67.25p -3.24%Atkins (WS) (ATK) 771.00p -2.65%Domino's Pizza UK & IRL (DOM) 459.30p -2.59%Law Debenture Corp. (LWDB) 379.00p -2.52%Avocet Mining (AVM) 190.00p -2.11%JD Sports Fashion (JD.) 770.50p -2.10%Moneysupermarket.com Group (MONY) 127.30p -2.08%Hansteen Holdings (HSTN) 73.00p -1.95%