[ ;M. HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



BLOOD PRESSURE 



fig. 12. Results obtained with the 

 preparation seen in fig. i i showing that 

 maximum physiological frequency in vaso- 

 constrictor fibers to the leg muscle is about 

 6-8 per sec. [After Folkow (90).] I, 2, 

 carotid occlusion; ;j, sympathectomy. 4. 

 0.5 stim./sec; 5, ! stim./sec; 6, 2 stim./ 

 sec; 7, 4 stim./sec; 8, 6 stim./sec; 9, 10 

 stim. sec; 10, 15 stim./sec; II, 20 stim./ 

 sec. For further details see text. 



Sympathetic Vasodilator Nerves 



Folkow & Uvnas (102) noticed that after Dibena- 

 mine, stimulation of the abdominal sympathetic 

 chain caused marked vasodilatation in the cat's 

 hind limbs. The reason was sought in a later paper 

 (103). What kind of fibers had they been stimulating? 

 Were they true sympathetic fibers? To decide this 

 they extirpated dorsal root ganglia Lj to L 5 on one 

 side and allowed 10 to 14 days for the sensory fibers 

 to degenerate. However, this did not diminish the 

 vasodilator response in the legs during stimulation 

 of the abdominal sympathetic chain. From this and 

 other elegant experiments they concluded that the 

 increase in blood flow must be due to stimulation of 

 none other than sympathetic vasodilator fibers. 

 That being so they then investigated the where- 

 abouts of this vasodilatation in the hind parts. 

 Stimulation of the abdominal sympathetics did not 

 increase flow in the saphenous vein draining the skin, 

 on the other hand the flow from the vena cava drain- 

 ing skinned hind parts, with the paws tied off, did 

 increase very greatly. They concluded that the in- 

 crease must have been in the muscles. Other investi- 

 gators had shown that the skeletal muscles of the dog 

 are supplied by sympathetic vasodilator fibers (47). 



CHEMICAL TRANSMISSION AT SYMPATHETIC VASODILATOR 



nerve endings in skeletal muscle. These are cho- 

 linergic. Folkow et al. (96) showed this in cats given 

 Dibenamine to block the action of sympathetic vaso- 

 constrictor fibers. They noticed that the vasodilator 

 response to stimulation of the abdominal sympa- 

 thetic chain was much reduced by atropine. Atropine 

 did not reduce the vasodilator action of adrenaline 

 or of histamine. If the abdominal sympathetic vaso- 

 dilator fibers were cholinergic, they argued, the 

 vasodilatation should be potentiated after inactiva- 



tion of cholinesterase by eserine. It was difficult to 

 test this because the combination of Dibenamine and 

 eserine caused almost maximal vasodilatation in the 

 hind legs. Positive results were obtained in only a 

 few experiments. Nor could they test the effect of 

 the venous effluent on the eserinized leech muscle 

 because there were no leeches in Sweden. However 

 the results of tests made with extracts of the venous 

 effluent upon the cat's blood pressure and upon the 

 frog's rectus muscle showed beyond any doubt that 

 sympathetic vasodilator nerve stimulation did re- 

 lease acetylcholine. Folkow & Uvnas (105) could 

 find no evidence for the existence of adrenergic 

 vasodilators to muscle vessels in the cat. In the dog 

 too these vasodilator fibers are cholinergic (46). 



ACTIVATION OF SYMPATHETIC VASODILATOR FIBERS 

 TO SKELETAL MUSCLE BY HYPOTHALAMIC STIMULATION. 



Eliasson et al. (78) were the first to show that stimula- 

 tion of the hypothalamus activated the sympathetic 

 vasodilator fibers to muscle blood vessels. These 

 fibers must have been solely responsible as the re- 

 sponse was abolished by minute doses of atropine or 

 by section of the abdominal sympathetic chains. 

 Figures 1 ; and 14 show the preparation and a typ- 

 ical result. As hypothalamic stimulation caused con- 

 striction in the skin and intestines, tachycardia, 

 constriction of the spleen, and dilatation of the pupils, 

 they thought that activation of the vasodilator fibers 

 to the skeletal muscles must be part of the reaction of a 

 state of emergency in which a sudden increase in 

 muscle blood flow is often needed for muscular activ- 

 ity. Further studies have since been made on the 

 central connections of these fibers (2-4, 79, 139, 140). 



SYMPATHETIC VASODILATOR FIBERS TO HUMAN SKELETAL 



muscles. Observations on man suggest that these 



