The response of the newborn rat to injury. I. Vascular and humoral aspects.

The development of oedema in response to irritants injected into the skin, or pleural cavity of rats, has been shown to differ according to the age of rat studied. It was found that newborn rats were less responsive, with respect to oedema formation, at certain times after the injection of a particular irritant. Attempts to suppress the reactions of these animals using anti-histamines, anti-serotonin and kinin-depleting agents were less successful than in adults. Analysis of serum, plasma and exudate proteins revealed quantitative and qualitative differences between newborn and adult rats. The ability of various agents to cause increased vascular permeability in the skin of newborn rats was found to vary with the age of animal studied. Thus histamine, 5-hydroxytryptomine, cellulose sulphate and prostaglandin E2, all failed to cause increased vascular permeability in the skin of rats younger than 3 wk of age. However, lymph-node permeability factor induced increased vascular permeability in newborn (i.e., 6-hr-old) rats. An attempt was made to correlate these results with those of oedema formation following the infections of certain irritants.