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Involvement of the Cytoskeleton in Oxytocin Secretion by Cultured Bovine Luteal Cells¹

Laboratory of Reproductive Endocrinology,³ Faculty of Agriculture, Okayama University, Okayama 700-8530, Japan Division of Reproductive Endocrinology and Pathophysiology,⁴ Institute of Animal Reproduction & Food Research, PAS, Olsztyn 10-747, Poland

A number of substances have been implicated in the regulation of oxytocin (OT) secretion from bovine corpus luteum in vivo. However, isolated bovine luteal cells cultured in a monolayer lose the ability to secrete OT in response to stimulatory substances. The present study investigated how cell-to-cell contact and the cytoskeleton affect OT secretion by isolated bovine luteal cells. In experiment 1, bovine midluteal cells (Days 8–12 of the estrous cycle) were stimulated with prostaglandin F₂ (PGF₂; 1 µM), noradrenaline (NA; 10 µM), or growth hormone (GH; 5 nM) in two culture systems: In one system, cell monolayers were incubated in 24-well culture plates, and in the other system, aggregates of cells were incubated in glass tubes in a shaking water bath. The cells cultured in a monolayer underwent considerable spreading and showed a variety of shapes, whereas the cells cultured in glass tubes remained fully rounded during the experimental period and soon formed aggregates of cells. Although PGF₂, NA, and GH did not stimulate OT secretion by the monolayer cells, all tested substances stimulated OT secretion by the aggregated cells (P < 0.01). In experiment 2, the monolayer cells were pre-exposed for 1 h to an antimicrofilament agent (cytochalasin B; 1 µM) or two antimicrotubule agents (colchicine or vinblastine; 1 µM) before stimulation with PGF₂, NA, or GH. Although PGF₂, NA, and GH did not stimulate OT secretion by the monolayer cells in the presence of colchicine or vinblastine, they all stimulated OT secretion in the presence of cytochalasin B (P < 0.001). The overall results show that OT secretion by bovine luteal cells depends on microfilament function and cell shape. Moreover, the aggregate culture system that allows three-dimensional, cell-to-cell contact seems to be a good model for studying OT secretion by isolated bovine luteal cells.

¹ Supported by Grants-in-Aid for Scientific Research from the Polish Ministry of Scientific Research and Information Technology (PBZ-KBN-084/ P06/2002), the Japan Society for the Promotion of Sciences (JSPS; 14360168), and the Japanese-Polish Joint Research Project under an agreement between JSPS and the Polish Academy of Sciences.

² Correspondence. FAX: 48 89 524 0347; skadar{at}pan.olsztyn.pl