Medical device maker Smith & Nephew was a high riser again after reports yesterday suggested that US peer Stryker was working on a bid for the firm. While the rumours were denied by Stryker, Smith & Nephew's share price was continuing to extend gains this morning after Credit Suisse said it sees "merger synergies of about 160-195p/S&N share" if the hypothetical deal were to go ahead.The UK group also this afternoon announced that it has completed the acquisition of ArthroCare Corporation, a medical device company with a highly complementary sports medicine portfolio. The purchase price was $48.25 per share paid in cash.IMI was trading higher after UBS lifted its rating on the stock from 'neutral' to 'buy', saying that growth rates at the engineering group have the potential to double in the medium-term.Morrisons was lifted by a reiteration of its 'buy' rating from Cantor Fitzgerald. WPP Group climbed following Investec's decision to raise its target price from 1,350p to 1,420p and upgrade it from 'add' to 'buy'.Aggreko the temporary power and temperature control services group, was a heavy faller after saying that interim Chief Executive Officer Angus Cockburn will be replaced on a permanent basis by Centrica board member Chris Weston. Cockburn, who stepped in after previous boss Rupert Soames quit earlier this year, is "keen to seek fresh challenges", the company said.DIY retailer Kingfisher dropped despite hailing a "strong start to the year" as 20% growth in retail profits in the first quarter came in shy of analysts' expectations. Group sales growth of 6.1% also failed to impress.Housebuilder Barratt Developments led housebuilders and related companies lower following the release of the latest data on the Help to Buy scheme, which, according to analysts, indicated it has had a limited impact.FTSE 100 - RisersSmith & Nephew (SN.) 1,024.00p +3.07%IMI (IMI) 1,597.00p +2.31%Centrica (CNA) 337.40p +2.00%William Hill (WMH) 351.80p +1.59%Sainsbury (J) (SBRY) 340.80p +1.58%Pearson (PSON) 1,165.00p +1.57%Diageo (DGE) 1,909.00p +1.52%Morrison (Wm) Supermarkets (MRW) 201.90p +1.51%Rolls-Royce Holdings (RR.) 1,031.00p +1.48%British American Tobacco (BATS) 3,589.00p +1.47%FTSE 100 - FallersAggreko (AGK) 1,661.00p -5.03%Kingfisher (KGF) 398.10p -4.60%Barratt Developments (BDEV) 356.40p -3.39%Persimmon (PSN) 1,320.00p -2.65%Johnson Matthey (JMAT) 3,272.00p -2.15%Travis Perkins (TPK) 1,689.00p -1.69%CRH (CRH) 1,655.00p -1.08%Next (NXT) 6,615.00p -0.90%Coca-Cola HBC AG (CDI) (CCH) 1,356.00p -0.88%Prudential (PRU) 1,394.00p -0.85%NR