Quantitative studies of APUD cells in airways and gut in the guinea pig

Amine Precursor Uptake and Decarboxylase (APUD) cells have been studied quantitatively to determine their normal distribution in the airways, ileum and cecum of adult guinea pigs utilizing tissues fixed in either Bouin’s or Ito and Karnovsky’s fixative. Cells were detected by four histochemical stains: Grimelius, en-block silver, lead-hematoxylin-en block silver and PAS-lead-hematoxylin. The guinea pig exhibits APUD cells in all airway segments in densities that decrease with decreasing airway size. This distribution is similar to that encountered in adult human, rat and hamster lungs and different from that in fetal or neonatal human, hamster or rabbit lungs in which these cells are more frequent in bronchioles. APUD cell densities in airways are 36–80 times lower that those in the ileum. The detection of airways APUD cells is dependent upon the histochemical stain utilized for their detection with Grimelius double impregnation providing the most sensitive stain. Fixation with the two solutions utilized does not significantly influence the results. Technical differences in staining may explain differences in quantitative studies of APUD cells performed in different laboratories and should be considered when designing future studies concerning the influence of pharmacologic, physiologic and pathologic agents on airways and intestinal APUD cells.