BLOOD SUPPLY TO THE HEART 



'Sj 1 



heart rate, cardiac output, blood pressure, length of 

 systole and diastole, each of which could alter cardiac 

 metabolism, work and coronary flow separately or in 

 combination. Actually, in experiments with adequate 

 flow methods, a) increase in intragastric or intrabiliary 

 tension gives a variable flow response (bubble flow- 

 meter and rotameter) but always in the same direction 

 as the blood pressure change (90, 285, 405); b) dermal 

 contact with ice water in the anesthetized dog fails to 

 produce reflex constriction of the coronary arteries 

 (24, 347). The sight, smell, and ingestion of food and 

 tilting the head down all increase coronary flow 

 (electromagnetic flowmeter) concurrently with an 

 augmented heart rate and blood pressure (301). It is 

 therefore unreasonable to maintain, as has been done, 

 that such agents have caused active vasoconstriction 

 or vasodilatation in the coronary bed and that such 

 changes are necessarily largely controlled through 

 nervous reflexes. This is especially so since in each 

 experiment the effects of the stimuli were not generally 

 tested after as well as before the cutting of the car- 

 diac nerves. 



Thus, while reflexes to the coronary circulation from 



the heart or extracardiac visceral structures certainly 

 do exist and may be important in normal physiology 

 and pathological physiology, we must wait for the 

 future to show their exact function. 



Hormones 



norepinephrine and epinephrine. Since the generally 

 accepted theory of autonomic nerve transmission is 

 based on the liberation of acetylcholine and epineph- 

 rine-like substances, the coronary flow effects with 

 these agents are of particular interest in connection 

 with coronary innervation. 



The action of epinephrine on the coronary blood 

 flow has been investigated extensively. In most dog 

 preparations, including the fibrillating heart (27), 

 heart-lung preparation (179), the open-chest dog (82, 

 83, 1 12, 146), and the unanesthetized dog a few days 

 postoperative to flowmeter implantation (301), 

 intracoronary artery injection of epinephrine and 

 norepinephrine increases coronary blood flow. In 

 the latter two preparations, their effect on the coro- 



6 fiq EPINEPHRINE I V 

 CONTROL ] 12 ! 



16 SEC 



RECOVERY 



90 

 123 

 197 

 2 2 

 162 

 35 



120 

 120 

 196 

 1.6 



163 

 33 



114 

 114 

 119 

 1.0 

 90 

 29 



fig. 10. Reproduction of sections from original record taken in a conscious resting dog some days 

 postoperative, showing the effect of rapid intravenous injection of 6 /xg epinephrine on phasic arterial 

 blood pressure and stroke left circumflex How, using a strain gauge and electromagnetic flowmeter 

 as in fig. 6. [Rayford el a/. (301).] 



