A study has been conducted on the influence of nucleosides and nucleotides to induce the formation of pinocytic vesicles in cultured mouse macrophages.

Extremely high levels of cytoplasmic vesicles were found after exposure of macrophages to adenosine 5'-phosphate, ADP, and ATP. A limited vesicle response was obtained with adenosine 2'-. and 3'-phosphate, 3',5'-adenosine-phosphate, and deoxyadenosine 5'-phosphate. The di- and triphosphates of guanosine, inosine, cytidine, and uridine were stimulatory but much less active than the adenosine derivatives.

Adenosine administration resulted in high levels of pinocytic activity whereas other nucleosides, including inosine, guanosine, cytidine, and uridine, yielded little or no stimulatory effect.

Adenosine and its 5'-phosphates produced morphological effects on macrophages characterized by increased spreading, a thin, peripheral cytoplasmic veil with denser cores of oriented mitochondria and contraction of the centre-sphere region. Large numbers of pinosomes were seen in association with mitochondria-containing portions of the cytoplasm.

The stimulatory effects of adenosine and ATP were rapid and involved the majority of cells in the culture. Adenosine was unable to reverse the pinocytosis inhibition produced by 2,4-DNP, whereas ATP raised vesicle counts to high levels. Possible mechanisms for these effects are discussed.

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