Actin is unevenly distributed in the pituitary gland

In view of the suggestion that actin-like proteins might be involved in the final steps leading to hormone secretion, the actin content of pituitary glands of adult rats was determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis (for total actin), by the DNAse method (which measures predominantly monomeric actin) and by immunocytochemistry. The amount of actin present in the neural lobe, expressed per mg total protein, was found to be comparable to that of other neural tissues. In contrast, in the anterior lobe, the ratio was significantly lower. The intensity of immunofluorescent staining with anti-actin antibodies was higher in the neural lobe than in either anterior or intermediate lobes. The intensity and distribution of tubulin immunofluorescent staining with anti-tubulin antibodies resembled that of anti-actin antibodies. Thus, three independent methods point to an uneven distribution of actin in the subdivisions of the pituitary gland, although all these subdivisions are believed to secrete their hormones by exocytosis. These data suggest that the bulk of actin present in pituitary cells is unlikely to be involved only in exocytosis, but may be implicated also in the intracellular translocation of secretory products.