Abstract
Previous studies have shown that the size of the population of bronchopulmonary endocrine (Feyrter) cells appears to be greatest in fetal and neonatal life. This has led to the logical assumption that these cells are important during this period and undergo a subsequent decline in number thereafter. In this study endocrine cells containing calcitonin or a closely related cross reacting peptide have been demonstrated in the lungs of fetal and neonatal rats by immunoenzyme histochemistry. They appear first about three days before birth and their number, expressed as immunoreactive cells per cm2 of histological section, remains relatively constant for up to three weeks after birth. It has been shown previously in this department that endocrine cells immunoreactive for calcitonin are present in the lungs of the normal adult rat. Their number in these adult animals is closely similar to the numbers of cells in the lungs of the developing animals of the present study. It is suggested that, at least in the rat, bronchopulmonary endocrine cells immunoreactive for calcitonin have a role that is not confined merely to the period of transition from fetal to neonatal life.