PHYSIOLOGY OF RADIATION INJURY 985 



capillary bed in the irradiated area (Jenkinson and Brown, 1944). Since 

 clinical irradiation is invariably confined to persons in ill health and since 

 the immediate clinical response has a large psychosomatic component, it 

 is not always easy to evaluate the results of such exposure. It is well 

 known that the clinical response is influenced by the nutritional status of 

 the person undergoing radiotherapy (Bean et al., 1944). The mechanisms 

 responsible for reactions in clinical radiation sickness and in the acute 

 radiation syndrome may be quite different. 



The initial anorexia of whole-body irradiation need not be a conse- 

 quence of a direct action on the gastrointestinal tract, since exposure of 

 only the head of the rat results in a comparable early diminution in food 

 intake (Smith, Tyree, Patt, and Bink, 1951). This is not observed when 

 irradiation is confined to the extremities. Weight loss during the first 

 day or two is also rather similar in abdomen-shielded and abdomen- 

 exposed rats (Bond et al., 1950). These facts suggest that the early 

 anorexia may be neurogenic or humoral in origin. Delayed gastric 

 emptying (Ely and Ross, 1947; Mead et al., 1950), perhaps as a result of 

 increased tone of the pyloric sphincter, may be responsible for the 

 anorexia. Subsequent effects on food consumption, however, are prob- 

 ably related more directly to injury of the intestinal mucosa. When the 

 abdomen is shielded, late effects may possibly be attributed to damage of 

 oral and esophageal structures. 



Intestinal motility and tonus are increased by irradiation (Hall and 

 Whipple, 1919; Martin and Rogers, 1923; Swann, 1924; Toyoma, 1933a; 

 Conard, 1951). This has been observed in intestinal loops and in the 

 intact animal. The increase in tonus and amplitude of contraction can 

 be detected during irradiation. With small dosages of X rays tonus 

 returns to normal a few minutes after the exposure is terminated. Large 

 dosages lead to a greater and more prolonged rise in tone, and a spastic 

 contraction, analogous to that seen after other forms of intestinal injury, 

 may be evident. Augmented contraction and hypertonicity are largely 

 prevented by parasympatholytic drugs and ganglionic blocking agents 

 (Conard, 1951). Vagotomy and body shielding afford only a slight 

 reduction of the intestinal response, which is considered to be a conse- 

 quence of direct action of radiation on cholinergic elements in the intes- 

 tinal tract. Increased synthesis of acetylcholine by brain (Torda and 

 Wolff, 1950) and a reduction in blood choline esterase (Barnard, 1948) 

 have been observed after exposure to X rays. 



Irradiation of the stomach reduces gastric acidity and results in exten- 

 sive atrophy of the gastric glands (Miescher, 1923; Ivy et al., 1924; Ely 

 and Ross, 1947; Simon, 1949; Hedin et al., 1950; Douglas et al., 1950). 

 A transitory rise in acidity preceding the depression may occur after 

 exposure of the whole abdomen (Ivy et al., 1924). Secretory depression 

 has been observed with X rays, /3 rays, and neutrons and appears to be a 



