Pharmacokinetic behaviour in polymorphonuclear leucocytes of N,N‐dimethylcarbamoylmethyl α,2‐dimethyl‐5H‐[1]benzopyrano[2,3‐b]‐pyridine‐7‐acetate (Y‐23023), a new prodrug type of antiinflammatory agent, and indomethacin after oral administrations in rats