KENNETH KENT, PETER DEMPSEY, ZENA MCCALLUM AND THEODORE COOPER 
623 
(phase 2). Also Bassett et al." have demon- 
strated a diminution of the rate of rise of phase 
0 as canine Purkinje fibers were made hypoxic. 
Although the contractile responses of the ca- 
techolamine-depleted hearts are less impaired 
by hypoxia than the control muscles, the same 
degree of shortening of phase 2 of the TAP oc- 
curred in all muscles studied, control and dener- 
vated. Thus, there appears to be a dissociation 
of the membrane elTects of hypoxia and the ef- 
fects on contractility in catecholamine-depleted 
myocardium. 
SUMMARY 
The technique of extrinsic cardiac denerva- 
tion in cats has made it possible to study catech- 
olamine-depleted isolated whole hearts by using 
a LangendoriT apparatus as well as isolated 
right ventricular papillary muscles. In addition 
to contractility studies, it is possible to assess 
the transmembrane action potential of the 
chronically-denervated myocardium. 
REFERENCES 
1. Donald, D. E., and Shepard, J. T. Response to 
exercise with cardiac denervation. Am. J. Physiol. 
205:393-400, 1963. 
2. Dempsey, p. J., and Cooper, T. Supersensitivity 
of the chronically denervated feline heart. Am. J. 
Physiol. 215:1245-1249, 1968. 
3. Dempsey, P. J., and Cooper, T. Ventricular choli- 
nergic receptor systems. J. Pharmacol. Exp. Ther. 
167:282-290, 1969. 
4. GuTH, L., Dempsey, P. J., and Cooper, T. Main- 
tenance of neurotrophically regulated protein in 
denervated skeletal and cardiac muscle. Exp. Neurol- 
ogy 32:478-488, 1971. 
5. Gaffney, T. E., Braunwald, E., and Cooper, T. 
Analysis of the acute circulatory effects of gu- 
anethidine and bretylium. Circulation Res. 
10:83-88, 1962. 
6. Dempsey, P. J., McCallum, Z. T., Kent, K. M., 
and Cooper, T. Direct myocardial effects of angi- 
otensin II. Am. J. Physiol. 220:477-481, 1971. 
7. Dempsey, P. J., McCallum, Z. T., Kent, K. M., 
and Cooper, T. Dissociation of cardiac inotropic 
and transmembrane action potential effects of oua- 
bain. J. Pharmacol. Exp. Ther. 177:78-84, 1971. 
8. HiRSCH, E. F., Kaiser, L. C, Barnes, H. C, and 
Cooper, T. The innervation of the feline heart. In 
The Innervation of the Vertebrate Heart. Ed. E. F. 
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pp 64-80. 
9. Crout, T. R. Standard Methods in Clinical Chem- 
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10. Kent, K. M., Goodfriend, T., McCallum, Z. T., 
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siol. 206:971-974, 1964. 
13. Trautwein, W., Gottstein, U., and Dudel, J. 
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ACKNOWLEDGMENTS 
The authors wish to express their apprecia- 
tion to Dr. Joseph Pierce for his assistance in 
the development of the operative procedure in 
cats. We also appreciate the technical assistance 
of Mr. James Hopkins and Mr. Everett Hodge 
during the operative procedure. 
DISCUSSION 
J. B. Senturia, Cleveland State University, 
Ohio: There exists an animal model for this 
system that you're talking about in nature : the 
hibernator, which would stand hypoxia. Ani- 
mals like the European hedge hog, ground 
squirrel and so forth seem to lack adrenergic in- 
nervation to the myocardium. There's been 
some dispute about whether the data is com- 
pletely correct or not, but experiments by Ouve- 
man and Nielson in Sweden seem to indicate 
that this is exactly the case. They do lack adre- 
nergic innervation normally, and, of course, 
they withstand hypoxia considerably. All of the 
hibernators seem to be able to withstand hy- 
poxia; so there is a natural animal model for 
this system that does exist. 
Dr. Kent: That's very interesting. The hi- 
bernator, of course, physiologically during hi- 
bernation is probably not hypoxic, but certainly 
they do stand hypothermia, hypoxia, and a lot 
