AN ONTOGENETIC STUDY ON ENDOTHELIN-PRODUCING CELLS IN THE RAT LUNG AND SUBMANDIBULAR GLAND

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We ontogenetically examined endothelin (ET) in the lungs and submandibular glands of Wistar rats at various stages, from fetuses to the aged, using specific polyclonal ET-antibody. In the lung, strong ET-immunopositive cells first appeared at 13 days of gestation in the bronchial epithelia, and the strongest immunoreactivity at 17 days; thereafter, the reactivity gradually decreased, disappearing after birth. However, the gene expression of ET-1, ET-3, the receptor A (ET-AR), and B (ET-BR) was observed continuously throughout all the stages. In the submandibular glands, ET-immunopositive cells were first observed in the duct cells at 18 days of gestation; these cells gradually increased in number after birth. In the adult rat, the immunoreactivity was confined predominantly to the granular convoluted tubule. This reactivity was found in every age group, including the aged (3-year-old) rats. All the gene expression of ET-1, ET-3, ET-AR, and ET-BR was observed in the submandibular glands of postnatal and adult rats. We speculate that the ET in these tissues may possibly act as a growth factor.