In organ cultures of chick embryonic limb rudiments the mean length of explants treated with 25μg/ml prostaglandin B1(PGB1) was significantly smaller than that of paired controls (P<0.001) after 4, 6 and 8 days in vitro. The deceleration of linear growth was constant during 8 days in vitro. Growth inhibition was confirmed by a statistically significant decrease in explant dry weight after 8 days of culture. However, PGB1caused no observable alteration in the histological structure of the explants. The possible role of PGB1in the physiological control of cartilage growth is postulated. Explants similarly treated with prostaglandin A1(PGA1) at concentrations of 15 μg/ml for 8 days or 20μg/ml for 4 and 8 days exhibited “comma” and “inverted commas” phenomena, caused by the intermingling of chondroblasts from the epiphyseal and flattened-cell zones, which thus ceased to be distinct entities. Adenylate cyclase in the plasma membrane may be involved in this disturbance of cartilage diffe
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