186 J. C. Stoclet, Y. Cohen 



Calcium Exchanges in the Aorta of the Rat 



J. C. Stoclet, Y. Cohen 

 Laboratoire de Pharmacodynamic, Faculte de Pharmacie, Paris, France 



The present experiments were carried out to study the chemical dynamics of 

 aorta mineral of the non-treated rat. Calcium exchanges were measured in vivo with 

 •*3Ca and the data interpreted by comparison with extracellular ions diffusion spaces: 

 «-Br and ^^Na. 



The marked sensitivity of the wall of the aorta to calcification has been reported 

 in arteriosclerosis (Lansing et al., 1950) and after treatment by vitamine D or 

 dihydrotachysterol (Selye and Renaud, 1959) but until now no quantitative data 

 have been reported on calcium exchange reactions inside the aorta maintained in a 

 physiological state. 



Methods 



The experiments were carried out on male Wistar rats. Their weight averaged 

 200 g and they were between 60 and 70 days old. All animals were freely fed on an 

 equilibrated diet (calcium 1 per cent, inorganic phosphate 0.8 per cent, vitamin D 

 1,270 i. u. per Kg) and tap water. 



High specific activity ^'^Ca CI, (15 //Ci-, 0.02 mg of calcium in 0.25 ml of isotonic 

 NaCl solution) was given intravenously to 50 rats. Groups of five animals each 

 were killed by bleeding under ether anesthesia at varying intervals ranging from one 

 minute to 48 hours after injection. The thoracic and abdominal aorta were dissected 

 out, carefully and rapidly cleaned of adhering tissue and weighed (un-washed, wet 

 weight about 40 mg). Total calcium (Solomon et al., 1946) and ^'^Ca (Comar et al., 

 1951) were determined in blood plasma and aorta samples after wet ashing by nitro- 

 perchloric mixture and addition of 50 //g of Ca. 



-*Na and ^-Br spaces have been measured on two groups of five rats each, killed 

 twenty minutes after intravenous injection of 5 //Ci of one of the radioisotopes 

 ('^NaCl or Na^-Br). Tissue samples were dissolved in concentrated OHNa solution 

 (40 per cent). The volume was adjusted to 1.5 ml and the radioactivity was counted 

 directly. 



For each group of rats the result was expressed as the mean of experimental 

 determinations plus or minus standard error of the mean multiplied by t 0.05 (fiducial 

 limits at a probability of 95 per cent). 



The kinetic study of specific activity of plasma and aorta calcium permits 

 measurement of size and exchange rates of different compartments In which aorta 

 calcium is distributed. It Is assumed that calcium concentration does not vary In the 

 aorta and in blood plasma during the course of the experiment. 



For further details on the collection of samples, analytical methods, counting and 

 calculations, see Stoclet (In press). 



Results 



The wall of the aorta Is surprisingly high in calcium. We found 19.2 ± 2.5 //M 

 per gram of wet aorta, Instead of 2.7/; M/ml in blood plasma and 1.5 //M/g In 

 skeletal muscles. 



