Comparative Anatomy and Biochemistry

In the stumptail Macaca arctoides) and bonnet (Macaca radiata) monkeys, the cytoplasm of the Clara cells contained abundant mitochondria, a medium-sized Golgi complex, and a moderate amount of granular endoplasmic reticulum (Cast-LEMAN et al. 1975). In bonnet monkeys, the cells frequently contained round secretory droplets, which were homogeneously electron dense. Secretory droplets were less frequently observed in the non-ciliated bronchiolar cells of the stumptail monkey. The non-ciliated bronchiolar cells of the rhesus monkey (Macaca mulatto) were not observed to contain any secretory droplets. 

In the rabbit, the Clara cell is immature at birth, and differentiation occurs primarily during week 3 and 4 of postnatal life (Plopper et al. 1983). 

In the neonate rat, the apical region of the Clara cell lacks the profusion of smooth endoplasmic reticulum typical of the adult (Smith et al. 1974) also, in all but a few neonatal Clara cells there is less smooth and rough endoplasmic reticulum in the middle zone than occurs in the adult. 

The airways of avian species do not contain any Clara cells accordingly, lung microsomes prepared from chickens or Japanese quails were completely unable to catalyse the NADPH-dependent covalent binding of either 4-ipomeanol or benzo[a]pyrene although these reactions occur in liver or kidney 

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