E. Uehlinger: On the Influence of Thyroxine, Thiouracll, Cortisone 243 



From these two experiments we gather that: 



1. Calcitonin does not act by inhibition of the parathyroid hormone. 



2. Its action on plasma phosphate can occur without an effect on calcium. 



3. It cannot lower plasma calcium below a certain level. 



Summary 



1. Calcitonin is a thyroid hormone which lowers plasma calcium and phosphate. 



2. It is extremely potent. 



3. Its site of action seems to be the bone. 



4. It does not act by inhibition of the parathyroid hormone; concurrent synthesis 

 of RNA is not necessary for its acute actions. 



5. It appears to have therapeutic potentialities. 



6. Calcitonin will change our views on calcium homeostasis and bone physiology. 



Reference 



Bernstein, D., C. R. Kleeman, and S. Pine: The effect of thyro-parathyroid perfusion with 

 hyper- and hypocalcaemic blood on calcium, phosphorus and magnesium metabolism. 

 Clin. Res. 13, 105 (1965). 



On the Influence of Thyroxine, Thiouracil, Cortisone, Estrogen 



and Testosterone on Endochondral Ossification Utilizing 



Autoradiography 



E. Uehlinger 

 Pathologisches Institut, Universitat Zurich, Schweiz 



The experiments which will be dealt with in my report have as their goal a 

 further clarification of the influence exerted by hormones on endochondral ossi- 

 fication. Tritiated thymidine was employed in separate studies in conjunction with 

 the various individual hormones and my report will deal primarily with the results 

 obtained with thyroxine and thiouracil. Tritiated thymidine, a precursor of DNA, is 

 presently being utilized to label the mitotic activity of various tissues. During a 

 40 minute period after intravenous or intraperitoneal application, tritiated thymidine 

 is incorporated by all those cells which are actively synthesizing DNA so that they 

 may double their chromosomes during mitosis. The number of labelled cells is there- 

 fore proportional to the proliferation of a specific tissue or a group of cells. This 

 allows the calculation of the proliferation index (Hg-Index), which is the ratio of the 

 labelled cells to the total number of identical cells in percent (Rohr, 1963). 



Two month old, 250 — 300 gram, male Wistar rats received daily during the entire 

 experiment 0.05 mg (50 y) thyroxine subcutaneously, or 50 mg thiouracil enterally. 

 The animals were then killed at regular intervals of 7, 14, 21 and 28 days. 40 min. 

 prior to death each rat also received a single intraperitoneal injection of 25 uQ of 

 tritiated thymidine. 



The experiments with thyroxine yielded the following results: A comparison of 

 the cartilaginous proliferation of the epiphyseal plate with control animals showed no 



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