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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



FIG. 1 1 . Upper curves, decentralized nictitating membrane; 

 ■lower curves, denervated nonpregnant uterus of the cat. Con- 

 traction upwards. Time, 30 sec. A: hepatic nerves stimulated. 

 B: right splanchnic nerves stimulated after exclusion of ad- 

 renals. C: same as in B and injection of 1.5 Mg epinephrine. 

 D: duodenohepatic nerves stimulated. E: same as in D after 

 severance of duodenal nerves. [From Cannon & Rosenblueth 

 (19)-] 



the blood-borne action on the denervated heart after 

 reflex excitation, resuhing from struggle, as compared 

 with the rapid and large effect in cases where the 

 adrenals were active may be explained by the gradual 

 and prolonged release of moderate amounts of trans- 

 mitter in the former case. The activation of the 

 adrenals has a tendency to cause an 'explosive' re- 

 lease. A continuous liberation into the blood stream 

 during 'sham rage' has also been noted (136) in 

 decorticate cats showing a quasiemotional state as 

 exidenced by the reduction in the rate of the dener- 

 vated heart after section of the hepatic nerves. Even 

 as a consequence of normal emotions a release of 

 transmitter into the blood has been observed. 



On exposure to cold no sign of continuous effect on 

 the denervated nictitating membrane of the cat was 

 found, however (107). The persistent erection of hairs 

 when the animal is in cold surroundings is apparently 

 not accompanied by a liberation of enough trans- 

 mitter to affect remote organs even if these are sensi- 

 tized. 



During^ypoglycemia there is no evidence for ac- 

 tivation of the sympathetic system as a whole. Only 

 a selective release of epinephrine from the suprarenal 

 has been demonstrated by direct analysis of the 

 venous blood (38). The contention expressed by Can- 

 non and Rosenblueth that "it is characteristic of the 



sympathetic system, when specially excited, to act as 

 a whole; thus adrenine is secreted by splanchnic im- 

 pulses at the same time that sympathetic impulses 

 elsewhere in the body are liberating sympathin" has 

 not been corroborated by later experiments and 

 experience. It is now reasonably certain that the 

 secretion of epinephrine is a process which occurs in- 

 dependently and often during quite other conditions 

 than the activation of other parts of the sympathetic 

 system. It would also appear peculiar if the action of 

 epinephrine in maintaining blood sugar homeostasis 

 should be obligatorily linked with, for instance, a rise 

 of arterial pressure as a result of generalized adrener- 

 gic activity. The statement of Cannon and Rosen- 

 blueth that "adrenine and sympathin collaborate in 

 affecting structures innerv-ated by sympathetic 

 nerves" is only true in a restricted sense and its biolog- 

 ical significance is too limited to be set forth as a gen- 

 eral rule. The statement also illustrates the hazards 

 of using the term 'sympathin' since this may repre- 

 sent either epinephrine or norepinephrine. It may be 

 recalled that the two amines have opposite effects for 

 instance on the vessels of the skeletal muscles (i , 8, 37). 

 Even if the leakage of transmitter into the blood stream 

 is negligible from the point of view of physiological 

 action, this phenomenon has been of great heuristic 

 value as in Cannon and Rosenblueth's work and also 

 in the extensive work dealing with the excretion of 

 the neurotransmitter in urine (67, 129). 



Information about the nerv-e transmitter may also 

 be gained by collecting blood or perfusing fluid from 

 an organ during stimulation of the sympathetic 

 nerves, and by recording the effects of this fluid on 

 suitable test organs. Studies of this kind are in prin- 

 ciple similar to the pioneer experiments by Loewi. 

 Active substances in the effluent have been demon- 

 strated in many instances, such as from the frog's 

 stomach (13), the aqueous humour (3), the rabbit's 

 intestine (45) and the dog's tongue (6). 



By the use of an appropriate testing technique it 

 could be shown later that the active substance re- 

 leased by adrenergic nerve stimulation conformed 

 in its properties with norepinephrine (14, 93, 98, 106, 

 108). In these studies the venous plasma of the stimu- 

 lated organ was tested. Most investigators have also 

 stated that s maller amoujits of epinephrine were 

 sometimes also liberated. The significance of the 

 simultaneous appearance of small amounts of epi- 

 nephrine will be considered below. 



The release of epinephrine-like materials on stimu- 

 lation of the vagus nerve to the atropinized heart has 

 also been reported (65, 94). The former authors con- 



