EFFECTS OF IONS ON VASCULAR SMOOTH MUSCLE 



I 147 



hyperexcitability (140), while an increase in K re- 

 versibly abolishes the ability to contract (47). These 

 two rather baffling reports, although stemming from 

 different authors, are united in one major respect: the 

 artery preparation was driven electrically rather than 

 by means of a known physiologically active mediator. 



Although once again we find that it is difficult to 

 equate the complex procedures used and the complex 

 results obtained, several fundamental facts emerge. 



/ ) Vascular smooth muscle, like other types of 

 smooth muscle, responds to the sudden reduction of 

 K,, with little immediate change. 



2) As equilibration in low K„ media proceeds, the 

 responsiveness of vascular smooth muscle and its 

 basal tension progressively decline to reach a new low 

 level which is steadily maintained for long periods. 

 The experiment of continuing to lower K„ by succes- 

 sive washout has apparently not been attempted. 



2) Vascular smooth muscle exposed to high K„ (at 

 least fourfold normal) shows an increase in tension 

 proportionate to the increase in K„ , and this is 

 usually sustained. Responsiveness too is increased in 

 high K„ media. 



^) Time is an important variable in the responses 

 studied — too often an insufficiently considered vari- 

 able. 



j) In general, there is a suggestive inverse relation 

 between K„ and Na„. 



Evidence from Studies of Resistance in 

 Regional I 'ascular Beds 



effects of Na infusions. It is exceedingly difficult 

 to attempt to alter only one constituent of a perfusing 

 solution in an in vivo preparation and still remain 

 within the bounds of physiological decency. Even 

 so, considerable progress has been made in demon- 

 strating that at least some of the in vitro observations 

 have important implications for vascular homeo- 

 stasis. We shall now examine the major lines of these 

 investigations, noting especially where they are 

 consistent with the evidence already cited. 



All workers who have infused Na salts into the 

 arterial circulation have observed peripheral vaso- 

 dilatation. Eliakim et at. (56) observed a fall in 

 systemic blood pressure in the dog on injecting 1 ml 

 per kg of qo per cent NaCl fairly rapidly. We (78) 

 observed that Na salts depress diastolic and systolic 

 blood pressure in the rat even in the presence of a 

 simultaneously administered pressor agent. Katz & 

 Lindner (125) perfused the coronary arterial circula- 

 tion in the dog with defibrinated blood in a classic 



4.01 

 111 



e 30 J 



Potassium 



150 



e 



; 100 



> 



j 50 



> 

 I 



J 



: 1.5 1 



Brachial Artery 



Small Artery 



Small Vein 

 Cephalic Vein 

 Total 



10 - Small VeBfit-l 



s 

 i 



pi 



Arteries 



Veins 



MHmMWHH«M»l»B » tt«Mmwitr-»VWHJM» 



1478 



155.5 1685 



mEij Na/L 



fig. 4. Relation of serum [Na + ] in venous outflow to % as- 

 cular pressures and resistances in the dog forelimb. Average 

 of 1 1 animals. Ten per cent NaCl infused into brachial artery 

 at 0.0, 1.0, 2.3, and 0.0 ml/min in that order. [From Haddy 



(101).] 



series of experiments and observed that even fairly 

 small additions of Na produced vasodilatation. 



Marshall & Shepherd (148), in a beautiful series, 

 used the newly developed ultrasonic flowmeter to 

 monitor flow in the femoral artery of the dog and 

 studied changes in limb resistance in response to Na 

 salts. They found that the rapid injection of 2 ml of 

 10 to 20 per cent NaCl produced vasodilatation. The 

 same effect was obtained with a continuous infusion 

 of the same solutions at 2.3 ml per min. A series of 

 other salts (citrate, lactate, bicarbonate, acid and 

 alkaline phosphate) all produced the same effect. 

 Binet & Burstein (12) obtained similar results in the 

 dog limb isolated from the circulation of the rest of 

 the body, except as perfused under control from the 

 systemic circulation through a constant pressure 

 pump. 



Haddy and his associates have used perhaps the 

 most detailed and elegant technique to study this 

 same problem. Basically, these workers perfuse the 

 forelimb of the dog with arterial blood rerouted from 

 the femoral artery. The connecting polvethylene 

 tubing uniting the femoral to the brachial artery 

 passes through a constant output pump which operates 

 by intermittent compression of the tubing. Pressure 



