[NO synthetase in the cells of different tissues and organs of the mouse]

Cellular NO synthase was assayed in bone marrow, spleen, thymus, lymph nodes, epidermis, hypodermic connective tissue, small gut, peritoneal exudate, liver, kidney, and heart by cytochemical and immunofluorescent methods. As a rule the enzymatic activity was found in differentiated cells that finished proliferation (mature hemopoietic cells, epithelium of gut villi, etc.). The enzyme activity was undetectable in actively reproducing low-differentiated cells (basal layer of the epidermis, crypt cells of the small gut, or blast hemopoietic forms). NO is proposed to participate in regulation of tissue-specific terminal differentiation (maturation) of the cells.