95 2 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



Fic. 22. Plots similar to those in fig. 

 21 showing the responses to an intra- 

 arterial infusion of acetylcholine at the 

 rate of 25 jug/min, /; and to an intra- 

 arterial influsion of acetylcholine at 

 the rate of 100 Mg/min, 2. Arterial 

 pressure was held constant at 75 mm 

 Hg for /, at 105 mm Hg for 2. 



PRESSURE - mm Hg 

 40 80 120 160 200 



1 1 1 1 r 



Periph Venous 

 Press vs Flow 



40 80 120 160 



ART PRESS - PERIPH. VENOUS PRESS mm Hg 



■ Control 



■Infusion of Acetylcholine 



o - Control 



A— During Infusion 



a— Post Infusion 



ence increased. These findings suggest a dual effect of 

 epinephrine, i.e., an initial small artery or arteriolar 

 constriction, or both, and a subsequent small to 

 intermediate vein constriction as the arterioles dilate 

 [(55) and Rapela and Green, unpublished data]. 

 Similar changes were recorded in dog's leg during 

 sympathetic stimulation (13). 



Acetylcholine, infused into a dog's paw, caused 

 effects opposite from those of epinephrine. Small doses 

 had no effect on the arterioles (fig. 22C, 1) but in- 

 creased the small vein resistance (fig. 22.<4, 1); larger 

 doses decreased the arteriolar resistance (fig. 22C, 2), 

 but only slightly increased small vein resistance (fig. 

 22.4, 2) [(52) and Rapela and Green, unpublished 

 data]. 



Intermediate artery and vein behavior has been 

 studied by inserting fine (0.5 mm) catheters centrally 

 into a small artery and a small vein at the dog's 

 ankle and recording the pressures during a control 

 state and during strong stimulation of the peripheral 

 homolateral lumbar sympathetic chain (15, 70). 

 During stimulation pressure in the small artery fell 

 dramatically while that in the small vein rose. These 

 findings suggest a marked increase in the resistances 

 to flow in the artery and vein between the points of 

 cannulation and the more proximal points of pressure 

 measurement in the larger arteries and veins. The 

 stimulations were repeated as the catheters were fed 

 into the artery or vein toward the knee (15). In the 

 control state the arterial pressure was the same at all 

 levels of the catheter tip but, during sympathetic 



stimulation, a marked drop in pressure was noted in 

 the artery at all points distal to 15 cm proximal to the 

 ankle. These findings indicate that strong vaso- 

 constriction occurred in the arterial tree midway 

 between knee and ankle sufficient to stop flow and 

 pulsations. Similar closures were recorded in the 

 veins midway between knee and ankle. The morpho- 

 logical background for this was described by Shadle 

 et al. (104); they noted that the dorsal foot veins were 

 thick walled and difficult to distinguish from small 

 arteries while veins from thigh muscles were thin 

 walled. 



In a subsequent paper, Davis & Hamilton (16) 

 studied the responses further by a "cross-perfusion" 

 method which allowed the blood to flow out of the 

 proximal cut end of a small artery of the foot through 

 a flowmeter and into the distal cut end of the corre- 

 sponding artery of the opposite foot. Similar cross 

 perfusion was arranged in the veins. Thus stimulation 

 of the sympathetics on one side could affect flow only 

 by causing constriction of the intermediate size vessels 

 proximal to the ankle, whereas, stimulation of the 

 sympathetic fibers on the opposite side of the body 

 could affect flow only by causing constriction of small 

 distal arteries, arterioles, venules, and small distal 

 veins. They found that sciatic nerve stimulation 

 produced intense constriction in both proximal 

 intermediate and distal small arteries and veins which, 

 in either case, was sufficient to stop flow. Lumbar 

 sympathetic stimulation produced similar effects but 

 they were slightly less intense in the paw than with 



