Rising interest rates, regulatory uncertainty and strategic shifts by mortgage lenders appear to have taken a toll on the market for interest-only loans, where volume was down in the first half of 2006.Inside Alternative Mortgages estimates that $270 billion in new IO loans were originated through the end of June. That marked a 17.4 percent drop from the estimated $317 billion in new IO loans that were originated during the same period...[One data table included]