The response of the newborn rat to injury. II. Histopathological aspects and mononuclear cell turnover.

Histopathological investigations of skin lesions induced by subcutaneous implantation of glass coverslips were carried out in rats between birth and adulthood. Differences were found between the cellular reactions of newborn and adult rats to this irritant. An increased number of cells was found in the skin lesions of newborn rats, compared with adults. Uptake of a 30-min. pulse of tritiated thymidine by mononuclear cells was found to be higher in newborn skin lesions than in those of adult rats. The reverse was observed for the mononuclear cells adherent to implanted glass coverslips. Giant cells were less evident on coverslips removed from the skin of newborn rats.