The response of the newborn rat to intraleural dextran: vascular and cellular aspects.

The development of hind paw oedema, in response to dextran injected in to the pleural cavity of rats, has been shown to differ with the age of rat studied. It was found that newborn rats were less responsive than adults, with respect to oedema formation induced by dextran. Attempts to suppress the dextran-indu.ced foot oedema using mepyramine and cyproheptadine, were successful only in rats from the adult age group. A semiquantitative analysis was made of the inflammatory cellular exudate produced by the intrapleural injection of dextran into rats of different ages. In contrast to the reaction of adult rats, it was found that accumulation of polymorphs in the pleura of newborn animals was delayed. The polymorph was the dominant cell type found in exudates induced either by intrapleural saline or dextran, in rats from the 6-hour age group. This contrasted strikingly with comparable exudates induced in adult rats, whose major cell type was the mononuclear cell (after saline), and the polymorph, followed by the mononuclear cell (after dextran). Fewer cells were observed in the reaction of 6-hour-old rats, compared with 7-day-old animals following intrapleural injection of the same volume of a 6-percent solution of dextran.