548 
HEMODYNAMICS 
terenol on human subjects, observed an in- 
creased cardiac output, stroke volume and 
stroke work of both left and right ventricles. 
The increased stroke volume due to the adminis- 
tration of isoproterenol noted in humans was 
not consistently found in horses. We have ob- 
served a slightly decreased or unchanged stroke 
volume most frequently, while the stroke work 
was unaltered or slightly increased. 
The eifects of epinephrine and isoproterenol 
were quite different from those of norepine- 
phrine. The latter drug caused an increase in 
stroke work without any significant change in 
cardiac output or heart rate. 
The intravenous infusion of norepinephrine 
usually reduces the cardiac output in man. Orig- 
inally, this was shown by Goldenberg and co- 
workers. Barcroft and Starr^'' have shown 
similar effects in man using ballistocar- 
diography. On the other hand, Frank et al.,^*' 
using the same method, noted an increase in 
cardiac output in response to norepinephrine in- 
fusion prior to bleeding but not during hemor- 
rhagic shock in the dog. Using a dye dilution 
technique to measure the cardiac output in the 
dog, Gilmore et al.^''^ arrived at a contrary con- 
clusion. It was apparent in our studies that no 
significant change occurred in cardiac output 
with norepinephrine, even though the left ven- 
tricular contractility was increased significantly 
when judged by the marked increase in stroke 
work which occurred from a smaller end-dias- 
tolic size. 
Glucagon 
The positive inotropic and moderate chrono- 
tropic effect of glucagon in normal cardiac mus- 
cle has been clearly established in various ani- 
mal preparations^^"^^'^*' and in man.-''^-"^^'^'' 
Studies were undertaken in this laboratory to 
evaluate the cardiotonic effects of glucagon in 
horses. Only conscious horses were used in these 
studies. 
Intravenous administration of glucagon in 
awake horses resulted in increased left ventric- 
ular end-diastolic volume, increased stroke vol- 
ume, increased heart rate, increased stroke 
work, increased ejection fraction, a slight in- 
crease in left ventricular peak pressure and a 
virtually unchanged left ventricular end-sys- 
tolic volume (Tables V and VI). The mean left 
ventricular end-diastolic volume (EDV) in- 
creased for the three horses studied from 1,635 
to 1,977 ml. The increase in EDV in the absence 
of a significant change in ESV was reflected in 
an increased stroke volume (from a mean value 
of 821.33 to 1149.8 ml). The increases in heart 
rate and stroke volume resulted in an increase 
in the cardiac output (from a mean value of 
57.69 to 90.80 lit/min). There was also an in- 
crease in stroke work (from 829.13 to 1190.60 
gm M) and ejection fraction (from 50.08 to 
59.64%). 
Kumar et al.^^ reported increased heart rates 
and cardiac output in dogs from glucagon infu- 
sions, but stroke volume decreased. In the pres- 
ent study the stroke volume was increased and 
the resultant increase in cardiac output was due 
to both an increase in heart rate and stroke vol- 
ume. In human studies, it has been shown that 
following glucagon infusion the increase in car- 
diac output was due more to an increase in 
stroke volume than an increase in heart rate.^^ 
In the present study with horses, the onset of 
glucagon action was rapid with significant ef- 
fects seen within 1 to 2 minutes after intrave- 
nous administration of the drugs. However, the 
Table V. — Effect of Glucagon Infusion on Cardiovascular Measurements in Chronic Horses 
Horse No. 
Treatment 
End- 
Diastolic 
Volume (ml) 
End-systolic 
Volume (ml) 
Stroke 
Volume (ml) 
Heart Rate 
(beats/min) 
Cardiac 
Output 
(L/min) 
Ejection 
Fraction 
(% EDV) 
Stroke Work 
(Gm-meters) 
Left 
Ventricular 
Pressure 
PSP 
030 
Control 
2019.7 
1133.3 
889.7 
54 
48.04 
44.05 
895.3 
126 
Glucagon 
2791.0 
1433.3 
1358.0 
63 
76.00 
48.70 
1274.3 
132 
006 
Control 
1929. 
822. 
1107. 
75 
83.0 
57.4 
1084. 
116 
Glucagon 
2109. 
642. 
1464. 
88 
128.8 
69.5 
1592. 
124 
0011 
Control 
957.9 
490.9 
467.0 
90 
42.03 
48.80 
508.1 
124 
Glucagon 
1031.6 
404.1 
627.5 
108 
67.77 
60.82 
705.5 
128 
Mean 
Control 
1635.53 
815.4 
821.23 
73 
57.69 
50.08 
829.13 
122 
Glucagon 
1977.20 
826.8 
1149.80 
86.3 
90.86 
59.67 
1190.60 
128 
