244 



E. Uehlinger: On the Influence of Thyroxine, Thiouracil, Cortisone 



marked dift'erences. A certain degree of unrest is observed in the proliferating zone, 

 which may, however, be ascribed to chance. A distinct impression is obtained that a 

 slightly increased ossification has taken place in the primary ossification zone, but 

 this is in no case certain. However, the labelling process with tritiated thymidine 

 reveals a significant increase of labelling of the preosteoblasts. The proliferation index 

 of preosteoblasts in the normal rat is Z.SVo, (Table 1). In these experiments, in which 



Table 1 



^H-Indcx of the Pre-Osteoblast in °o 



more than 2000 cells were counted per animal, the preosteoblast proliferation-index 

 more than doubled itself with values over H^/o being obtained. In other words, 

 thyroxine practically selectively stimulated the preosteoblasts and thus furthered the 

 endochondral ossification, (Uehlinger et al., in press). 



The experiments utilizing the thyroid inhibitor, thiouracil, were more impressive 

 and significant. These experiments clearly exhibited a remarkably intensive shorten- 

 ing of the epiphyseal cartilage plate, especially In the zone of proliferation and 

 vesicular cartilage. This shortening occurs simultaneously with a certain repositioning 

 of the cartilage columns. In contrast to the inhibitory effect upon the chondrocytes, 

 which is also clinically observed in thyrogenic growth retardation, the effect on the 

 osteoblasts is little different to that of thyroxine. The zone of vesicular cartilage is, as 

 in normal tissue, invaded by capillaries, its cells are loosened, and the cartilaginous 

 ground substance is covered by bone. Remarkably broad primary spongiosa trabeculae 

 result. The preosteoblast counts support this histological observation. The pro- 

 liferation-index is again increased from a norm of ZVo to values over H^/o. Why 

 thyroxine and thiouracil both induce the same degree of preosteoblastic stimulation is 

 as yet not clear. 



Table 2 



By the same technique we Investigated the influence of cortisone, estrogen and 

 testosterone (Rohr, 1964; Holzer, 1965). Wistar rats after 10 days of cortisone 

 treatment showed a reduction of the proliferation-index of the preosteoblasts to 



