April 22 (Reuters) - Dow Inc reported a 69% rise in first-quarter profit on Thursday, as prices for its chemicals used in plastics and packaging rose on the back of tighter supply and higher demand. The company posted a net operating income, which excludes certain items, of $1.02 billion, or $1.36 per share, in the three months ended March 31, compared with a profit of $607 million, or 81 cents per share, in the fourth quarter.