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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



tivity anticipated from the smooth muscle of the 

 vasculature. That a vital phenomenon is involved is 

 supported by the action of a number of agents known 

 to impair smooth muscle activity: papaverine will 

 eliminate autoregulation (306, 308), as will K.CN 

 (188, 207, 233) and theophylline (121). Procaine has 

 been cited earlier. Certain anesthetics, such as numal 

 (120, 121) and chloralhydrate (330) impair auto- 

 regulation as will ethanol (260). 



Both cooling and perfusion of the kidney with oil 

 remove autoregulation (328, 330). Hemorrhage de- 

 presses autoregulation (73, 271, 331). Anoxia created 

 by perfusion of the kidney with perfusion fluid [20 9i 

 plasma-80 % polyvinylpyrollidone (PVP)-Locke's solu- 

 tion] subjected to helium rather than oxygen appeared 

 to impair autoregulation somewhat; flow increased 

 more with pressure increments than with comparable 

 increments during the control (331 ). 



It is well to point out that autoregulation may be 

 impaired in another manner and may, in part, ex- 

 plain the apparent loss of response in hemorrhage. 

 Under this circumstance and with adrenaline and 

 hypertonic fluid infusions, the smooth muscle of the 

 vasculature becomes highly tonic, and responses to 

 increments in pressure become much reduced (307). 

 Then the pressure-flow curve becomes convex to the 

 pressure axis and resembles the pressure-flow curves 

 obtained in the hind limb and other organs, which 

 usually have a higher resistance than the kidney. 



aberrant resltlts. Several investigations may be 

 cited in which typical autoregulation was not ob- 

 served, but in which pressure-flow curves were linear 

 or convex to the pressure axis. This includes the work 

 of Ohler et al. (235) in the rat. Indications of a high 

 degree of vascular tone are seen in the low flows in 

 many preparations and the high flow intercepts on the 

 pressure axis. It will be recalled that others have re- 

 ported the more common concave-to-pressure-axis 

 curve in the rat (333), indicating autoregulation. 



Likewise, the work of Langston et al. (172, 173) 

 manifested a convex-to-pressure-axis relationship of 

 flow in dogs. Again, flow per gram of tissue was low 

 (less than 2 ml min g) at normal pressure, suggesting 

 a highly tonic preparation. The high pressure inter- 

 cept for flow also suggested this. In the first report 

 (172) flow appeared to be only about 10 ml per min 

 (total per kidney) at 60 mm Hg. In the second report 

 (173), in the control series, the zero flow intercept 

 lay between 20 and 40 mm Hg; flow at 100 mm Hg 

 in most preparations was less than 1 .5 ml per min per 

 g. Furthermore the method of perfusion suggested the 



possibility of a source of technical error. The kidney 

 was perfused via an isolated segment of aorta at the 

 level of the renal artery. Hardin et al. (130) used a 

 similar technique, and found the same convex rela- 

 tionship. However, when they carefully tied small 

 lumbar arteries leaving this segment of the aorta, the 

 pressure-flow curve assumed the more commonlv 

 found contour, concave to the pressure axis (fig. 31). 



SIGNIFICANCE OF THE MYOGENIC RESPONSE. Bayliss ( I 3), 



a number of years ago, called attention to a myogenic 

 response to sudden changes in pressure both in de- 

 nervated organs and segments of artery (carotid), and 

 attributed it to alterations in tonus of smooth muscle 

 in the arteries in response to change in tension. 

 Wachholder (324) studied isolated segments of equine 

 carotid, and observed contractions following sudden 

 increases in pressure occurring with a latency of 

 usually 10 to 20 sec (8 sec was the shortest). The con- 

 traction phase lasted 20 to 60 sec. Burgi (44) utilized 

 bovine mesenteric artery segments, but saw distinct 

 responses in only 23 per cent of his tests; weak re- 

 sponses occurred in 9 per cent, and in 12 per cent the 

 response had so great a latency that it was deemed 

 questionable; 56 per cent showed no response. 



Folkow (89, 90) has placed the suggestion of Bayliss 

 and others on a firmer footing. His experiments, 

 utilizing the dog hind limb preparation, under condi- 

 tions which apparently controlled possible neurogenic 



25 50 75 OO 125 150 175 200 



fig. 31. Perfusion pressure as a function of rate of blood flow 

 through both kidneys of a dog before and after occlusion of the 

 lumbar arteries. Numbers are renal vascular resistance in mm 

 Hg/ml/min. (After Hardin et al. (130).] 



