I446 HANDBOOK OF PHYSIOLOGY -~ CIRCULATION II 



total volume can, of course, vary greatly in both 

 physiological and pathological states. 



FACTORS AFFECTING THE BLOOD FLOW 

 AND ITS DISTRIBUTION 



Stomach 



Stimulation of the splanchnic nerves decreases the 

 blood flow through the gastric vessels. This has been 

 demonstrated by Burton-Opitz (29) in the ether- 

 anesthetized dog, by Lim et al. (94) in the blood- 

 perfused canine stomach, by Thompson & Vane 

 (131) in cats anesthetized with chloralose, and by 

 Walder (134) in Ringer-perfused human stomachs. 

 Friesen & Hemingway (51), using a calorimetric 

 method, showed that the mucosal flow decreased 

 during sympathetic stimulation in unanesthetized 

 dogs. In the rat, Schnitzlein (117) observed blanching 

 of the gastric mucosa during splanchnic stimulation 

 and Arabehety et al. (5) found engorgement following 

 block or section of the same nerves. The latter ob- 

 servations, it should be emphasized, are of the 

 mucosal blood volume and do not necessarily demon- 

 strate that the blood flow through this tissue is de- 

 creased by sympathetic stimulation. 



Care should be exercised in the interpretation of 

 the many observations of changes in mucosal color, 

 labeled red cell content, India ink density, etc. 

 produced by nervous stimulation or drug administra- 

 tion. Blanching may well occur without significant 

 change in the blood flow or even in face of an in- 

 creased blood flow. Engorgement may accompany an 

 increase in flow resistance, especially if that occurs as 

 a consequence of venular constriction. Such observa- 

 tions can properly be taken as indicating changes in 

 blood volume only. 



Many of the investigations cited above (18, 94, 

 131, 134) have shown that the influence of epineph- 

 rine on the gastric circulation is quite similar to that 

 of splanchnic stimulation. In addition, Henning 

 et al. (76) using an acetylene clearance method 

 observed an apparent reduction in human mucosal 

 blood flow in response to administration of sympatho- 

 mimetic drugs. Peters & Womack (105) found that 

 epinephrine produced mucosal blanching in the dog. 

 They also injected glass microspheres into the arterial 

 supply and, finding more large spheres in the venous 

 outflow than in control studies, concluded that adren- 

 aline dilated arteriovenous anastomoses. This latter is 

 not in agreement with the findings of Walder (135), 



who concluded that the increase in arteriovenous 

 anastomotic flow was due only to increased resistance 

 in the capillary system rather than anastomotic 

 dilation. Miller & Haszczyc (101 ) found that epineph- 

 rine reduced the number of blood-filled capillaries 

 in biopsy specimens from human gastrostomies. 

 Dolcini et al. (40) made similar observations in the 

 rat. Schnitzlein (117) observed mucosal engorgement 

 in rats given ergotoxine to block adrenergic influences, 

 although the same drug in Walder's (134) exper- 

 iments did not alter the perfusion rate significantly 

 from control values. 



Burton-Opitz (29), Lim et al. (94), Boenheim (18), 

 Friesen & Hemingway (51) all found little or no 

 effect of vagal stimulation on gastric blood flow 

 unless peristaltic activity appeared, in which case 

 blood flow declined. Schnitzlein (117) did observe 

 mucosal engorgement in the rat with vagal stimula- 

 tion. He also found that the application of acetyl- 

 choline to the gastric muscularis produced contrac- 

 tions and mucosal blanching. Necheles et al. (102) 

 found that acetylcholine usually produced vasocon- 

 striction in Ringer-perfused rat stomachs. It was 

 stated that this was not the consequence of increased 

 motor activity, although the latter was not recorded. 

 Walder (134) reported that acetylcholine in some 

 cases reduced and in others increased the rate of 

 perfusion through human stomachs. He made no 

 comments concerning motor activity. 



In the studies already referred to by Lim et al., 

 Thompson and Vane, and Walder, histamine caused 

 a vasodilation in the stomach. Cutting et al. (37) 

 also observed increased gastric blood flow in cats 

 with this compound. Richards et al. (no), using a 

 calorimetric method, found that histamine increased 

 mucosal flow in the human stomach. In contra- 

 distinction, Necheles et al. (102) could observe no 

 effect of histamine in their Ringer-perfused rat 

 stomachs; and Boenheim (18) reported a decrease in 

 etherized dogs, although the arterial pressures of his 

 animals were very low. Peters & Womack (105) 

 observed a marked increase in the mucosal content 

 of arterially injected starch granules and India ink 

 during histamine administration in the dog. Miller 

 & Haszczyc (101) also saw an increase in filled capil- 

 laries in human mucosa as a consequence of the 

 drug. Kimbel et al. (90), on the other hand, found a 

 marked decrease in the P 32 -labeled red cell content 

 of the gastric mucosa of polycythemic patients given 

 histamine. 



The influence of several other chemicals on gastric 

 blood flow has also been studied. Cutting et al. (37) 



