INITIAL X-RAY EFFECTS ON THE AORTIC WALL 211 



LAMBERTS: 1,000 T is the dose with which we have an effect in almost all experiments, but 

 sometimes an effect can be found with a dose of a few hundred r. From experiments with 

 sj^novial fluid in which we measured the X-ray effect on the viscosity, I might say that 

 the dose reduction factor is about 2 or more. 



MOLE: May I ask one or two questions about the technique? This stems from an interest 

 in whether oxygen was present at the place where the irradiation was producing its 

 effect. In the in vitro experiments, were the aortae in a bath or were they in air, and how 

 deep was the needle within the aortae? 



LAMBERTS: There is an oxygen effect in this system, but it is a negative one. In experi- 

 ments with synovial fluid and solutions of pure hyaluronic acid, we found a larger drop in 

 viscosity by irradiation under anoxic conditions than under hyperoxic conditions. In 

 Professor Bacq's laboratory the effect of X-irradiation on the injection pressure in the 

 rat's skin was studied under complete anoxia. The effect was at least as strong as in the 

 presence of oxygen. In the in vitro experiments the aortae were kept in air and the depth 

 of the needle in the injection experiments varied, but was usually less than 1 mm. 

 CURTIS: I was going to ask about the injection experiments. The effect that you get is 

 very rapid there, a matter of seconds as I mterpreted it. Could not this be a smooth 

 muscle reaction? 



LAMBERTS: Certainly not. The needle is inserted m the intima where practically no 

 muscle is present. Furthermore the effect is still present in aortae that had been kept in 

 the 'fridge for several days. 



CURTIS: Nevertheless, the fluid has to go somewhere. As the smooth muscle contracts 

 would not that increase the resistance? 



LAMBERTS: The amount of injected fluid is a few mm^. Sometimes a small bubble is 

 formed on the intima. Smooth muscle contraction would cause a rise in injection pressure 

 but the effect after irradiation is a decrease. 



COTTIER: My first question concerns the reversibility of the effect. The second question — 

 you have shown these atheromata and in correlation with your findings here, how strong 

 are your feelings that these two are strongly correlated? Atheroma is a focal process and 

 it is still in discussion what part in its pathogenesis is played by local thrombosis, I think 

 that irradiation can also produce local thrombi; either due to endothelial, or some other, 

 damage. 



LAMBERTS: In our experiments Ave used excised dead pieces of aortae, so the drop of 

 injection pressure was not reversible. In the skin of living rats j^ou do find reversal — 

 rebuflding of your injection pressure in about 4-5 hours, and then if you u-radiate 

 again you get the same effect. As for your second question, I was afraid somebody would 

 ask that. I myself am not quite certain about the relationship between these effects, but 

 I thuik the most important thing here is to prove that something is produced m this field 

 by irradiation. If the development of atheromatous lesions has something to do with 

 endothelial damage or with the production of thrombi or the depolymerization of 

 mucopolysaccharides under the endothehum well, they aU might play a part in this 

 process, I think. 



UPTON: This is to observe that radiation has been noted to cause lipaemia in irradiated 

 animals, and this effect coupled with some injury to the endothehum might conceivably 

 be additive or synergistic m setting up the cholesterol plaques. 



