FLOW OF BLOOD IN MESENTERIC VESSELS 



'445 



iooju. The fraction of injected spheres which passed 

 through was not determined in these investigations. 



MESENTERIC BLOOD VOLUME 



Attempts to measure the volume of blood in the 

 mesenteric organs of the dog are complicated by the 

 presence of the spleen, the quantity of blood in this 

 organ varying greatly with the nature of the anes- 

 thetic agent. Further, since its hematocrit is much 

 higher than that of the body as a whole, estimates of 

 mesenteric blood volume from the distribution of 

 labeled red cells can be expected to be too high and 

 those made with labeled plasma constituents too low. 

 A correct value can be obtained only if both red cell 

 and plasma volume are measured simultaneously. 



Although such a direct study has not been made, 

 it is possible to approximate the mesenteric blood 

 volume by combining the results of several different 

 investigations. One of the most pertinent of these is 

 Johnstone's (87). He placed ligatures around the 

 esophageal-gastric junction and the rectum of dogs 

 anesthetized with sodium pentobarbital, and in- 

 jected P' i2 -labeled red cells. After a 5-min mixing 

 period, he clamped the celiac axis, mesenteric arteries, 

 and portal vein, simultaneously. By analyzing these 

 organs for P 32 , he found that they contained 22 per 

 cent of the injected red cells. 



To calculate the blood volume from this observa- 

 tion, the hematocrit of the mesenteric organs, es- 

 pecially the spleen, must be known. Allen & Reeve 

 (2) determined both the red cell and plasma volume 

 of spleens from pentobarbital-anesthetized dogs. 

 They found the blood volume to be 4 to 10 per cent 

 of the total body blood volume and the hematocrit 

 1.7 times that of the large vessels. The ratio of the 

 large vessel hematocrit to that of the whole body is a 

 variable quantity as pointed out by Baker & Reming- 

 ton (7); however, in dogs anesthetized with pento- 

 barbital like those of Allen and Reeve, Reeve et al. 

 (108) found the ratio to be about 0.9; that is, the 

 splenic hematocrit would be about 50 per cent greater 

 than that of the whole body. The dogs of Allen and 

 Reeve were only lightly anesthetized and other 

 studies have shown that the spleen in more deeply 

 anesthetized animals may contain more than 10 

 per cent of the total blood volume. A reasonable 

 estimate, though, would be that the spleens of dogs 

 anesthetized with pentobarbital have 10 per cent of 

 the total blood volume and 15 per cent of the total 

 red cell mass. Combining this with Johnstone's 



observations, the other mesenteric organs would 

 contain 7 per cent of the body's red cells and, as- 

 suming their hematocrit to be about the same as the 

 body's, 7 per cent of the total blood volume. Thus, 

 the mesenteric organs would hold 1 7 per cent of the 

 total blood volume, or about 15 ml per kg body wt 

 in dogs under pentobarbital anesthesia. Under ether 

 anesthesia, with the spleen essentially empty of 

 blood, this value would drop to nearly 7 per cent 

 (6 ml/kg). In unanesthetized animals, the volume 

 should be between these two extremes. Friedman 

 (49) has shown that the spleens of unanesthetized 

 mice contains about one-half as much blood as those 

 of animals under pentobarbital anesthesia. 



Horvath et al. (82) used the "exclusion technique" 

 of Delorme and co-workers (39) to determine the 

 volume of blood in the mesenteric organs plus the 

 liver. They found this to be 21 per cent of the total 

 blood volume, 6 per cent in the hepatic, 6 per cent 

 in the splenic, and 9 per cent in the mesenteric 

 artery beds. Most of their experiments were with 

 I 131 -labeled albumin and hence probably gave under- 

 estimates of the blood volume, particularly of the 

 splenic artery distribution. Their findings do not, 

 therefore, disagree significantly with the estimate 

 given above. 



Measurement of the volume of blood contained in 

 the minute vessels of some of the mesenteric organs 

 was made by Gibson et al. (55) in dogs under light 

 morphine narcosis. These workers determined both 

 the red cell and plasma content of the drained organs 

 and found the stomach and intestine to contain 0.04 

 ml blood per g tissue and the spleen 0.5 ml per g. 

 The blood volume of organs of the rat was determined 

 by Everett et al. (43) with Fe 59 -labeled cells and 

 I 131 -labeled plasma in quick-frozen animals. For the 

 small intestine they obtained a blood content of 

 0.034 ml per g and for the spleen, 0.17 ml per g 

 Rieke & Everett (in) made similar measurements 

 with rats under pentobarbital anesthesia and found 

 0.047 ml per g of intestine and 0.32 ml per g of 

 spleen. 



If the minute vessels of the stomach and intestine 

 contain about 0.04 ml per g of blood, these organs 

 in a 1 5-kg dog would contain about 30 ml of blood, 

 2-3 in the intestine. Thus, a dog not too deeply anesthe- 

 tized with pentobarbital would have a total mesen- 

 teric blood volume of some 200 to 250 ml, 60 per 

 cent of which would be in the spleen, 10 to 15 per 

 cent in the minute vessels of the other organs, and 

 the remaining 25 to 30 per cent in the large gastric 

 and intestinal vessels. This partition as well as the 



