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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



Herrick et al. (78) measured blood flow through 

 the cranial mesenteric artery of unanesthetized dogs 

 with a thermostromuhr during treadmill exercise and 

 found that the flow was essentially unchanged despite 

 an increase in arterial blood pressure, indicating an 

 intestinal vasoconstriction. Barcroft & Florey (9) 

 observed exteriorized preparations of colonic mucosa 

 of dogs during exercise. Early in the period mucosal 

 pallor was evident but, as the exercise continued, 

 the color returned to normal. 



Several workers (50, 60) have attempted to study 

 the influence of various emotional states such as 

 depression, anxiety, fear, etc., on human intestinal 

 blood flow by making inferences from observations on 

 the degree of mucosal engorgement in colostomies. 

 The possible errors inherent in such inferences have 

 already been alluded to. 



Pancreas 



The information available on the influence of 

 nervous stimulation and of drugs on pancreatic 

 circulation is scanty. Both Anrep (3) and Gayet & 

 Guillaume (52) showed a reduction in venous outflow 

 as a consequence of splanchnic stimulation. The 

 effect of vagal stimulation is not quite so clear. Anrep 

 concluded that the vagus carried neither constrictor 

 nor dilator fibers to the pancreas. Gayet and Guil- 

 laume consistently found a marked increase in blood 

 flow during vagal stimulation. 



Gayet & Guillaume (52), Maltesos & Watson 

 (98), Jones (88), and Bennett & Still (14) all ob- 

 served an increase in blood flow when secretin was 

 administered, in contradistinction to Weaver (136), 

 who could find no change in venous outflow. J ones 

 found that the rise in flow was a function of splanchnic 

 vasomotor tone and could be quite small when the 

 tone was high. Because Bennett and Still observed a 

 secretin-induced rise in blood flow only when the 

 pancreatic duct pressure increased, they proposed 

 that the apparent vasodilator action of the hormone 

 was not due to a direct effect on the vasculature but 

 was the consequence of a reflex initiated by the rise 

 in ductal pressure during secretion. They concluded 

 that a truly "vasodilation-free" secretin may be 

 prepared. 



Recently, Holton & Jones (80) used a photoelectric 

 technique to measure blood content changes in the 

 pancreas and found that acetylcholine, histamine, 

 secretin, and pancreozymin all produce vasodilation, 

 whether or not secondary to a rise in ductal pressure 

 is not clear. 



Spleen 



In most of the investigations on the splenic circula- 

 tion, attention has been directed toward changes in 

 the volume of the organ rather than the blood flow 

 through it. Adrenergic stimulation causes a marked 

 decrease in volume in dogs and cats. As shown by 

 Celander (33) in cats under chloralose anesthesia, 

 sympathetic stimulation is more potent in this regard 

 than epinephrine, which in turn is several times more 

 effective than norepinephrine. Others, such as Ahl- 

 quist et al. (1) and Holtz et al. (81) have demon- 

 strated that epinephrine is also more effective than 

 norepinephrine in the dog. Many other compounds 

 produce splenic contraction; ephedrine, pituitrin, 

 histamine, acetylcholine, and amyl nitrite. Anesthetic 

 agents also exert a profound influence; as shown by 

 Hausner and co-workers (74), ether causes a reduc- 

 tion in size and various barbiturates a marked en- 

 largement over that of the waking animal. Hahn 

 et al. (72) reported that spleens taken from dogs 

 anesthetized with pentobarbital weighed four times 

 those from etherized animals. Almost any change in 

 the environment which can produce a sympathetic 

 discharge in the animal causes splenic contraction. 

 Thus, Hargis & Mann (73) and Barcroft and co- 

 workers (8, 10) observed this in waking dogs sub- 

 jected to a loud noise, tail pinching, hemorrhage, 

 exercise, or exposure to cold. The first mentioned 

 workers thought that most of these responses were 

 reflex, since they occurred so rapidly and were not 

 observed after denervation. Barcroft and Elliott, 

 however, did find contraction of the denervated spleen 

 after a loud noise, although it was delayed and 

 progressed slowly. One of the few maneuvers which 

 increases splenic volume is feeding. 



A number of investigators, for example, Glaser 

 et al. (56), have concluded that the spleen is not an 

 important blood storage organ in the human body, 

 and hence does not change volume as markedly as 

 in the dog or cat. 



With regard to factors influencing the splenic blood 

 flow, Burton-Opitz (28) found that stimulation of the 

 splanchnic nerve or any of the fibers of the splenic 

 plexus caused a reduction in blood flow through the 

 splenic vein. Green and co-workers (67, 104) studied 

 this in more detail and found that splanchnic stimula- 

 tion of short duration decreased arterial inflow but 

 temporarily increased venous outflow, thus accounting 

 for the reduction in volume of the organ. They also 



