620 
PHYSIOLOGY 
titia and separated from the main pulmonary 
artery and its branches. Electrocautery was 
used for most of this dissection to further aid in 
the destruction of nerve fibers. 
The left phrenic and vagus nerves v^^ere iden- 
tified across the mediastinum and dissected in 
the same manner as on the right side. The left 
vagal cardiac branches were identified and cut. 
The superior vena cava was isolated. At this 
point all of the structures which had previously 
been identified — both vagus and phrenic nerves, 
aortic arch and its branches, pulmonary artery 
and its branches, and superior vena cava, esoph- 
agus and trachea — were retained, and the re- 
maining structures in the superior mediastinum 
were ablated with electrocautery. The pericar- 
dium was cut dorsally on the left side down to 
the left atrium. Careful hyperinflation of the 
lungs was performed, and the chest was closed. 
After closure of the chest 10 to 30 ml of air 
were evacuated with a blunt 16 gauge needle 
carefully inserted in the sixth to eighth inter- 
costal space. The animal was given 50 ml of bal- 
anced salt solution subcutaneously and allowed 
to recover from general anesthesia. Benzathine 
penicillin 300,000 units and procaine penicillin 
300,000 units were given intramuscularly on 
the operative day, and 5 days later 300,000 
units of benzathine penicillin was given. Nitro- 
fuazone powder and an aerosal spray bandage 
was applied postoperatively. Occasionally gas- 
trointestinal complications were evident in the 
postoperative period which probably were a re- 
sult of vagal nerve manipulation. Therefore no 
attempt was made to feed the animals until 36 
to 48 hours postoperatively. Rarely, feeding had 
to be started with a gastric tube on the fourth 
postoperative day. 
Catecholamine stores of the heart were deter- 
mined by the trihydroxy indole method.^ 
Isolated Whole Heart 
Adult male cats, 2 to 3.5 kg, were anesthe- 
tized with sodium thiamylal (Surital) 30 
mg/kg intrapleurally and their hearts were re- 
moved quickly and mounted on a cannula. Re- 
trograde perfusion of the coronary arteries was 
carried out at a constant flow rate (20 cc/min) 
with a modified Krebs-Ringer solution of the 
following composition per item: Na+, 146 mM; 
K+, 3.6 mM; H2PO4-, 1.2 mM; Ca++, 2.5 
mM; Mg++, 1.2 mM; CI", 128 mM; S04=, 1.2 
mM; HCOg", 25 mM; and glucose, 5.6 mM. 
The pH was 7.4, and the temperature was 34 ± 
0.5° C; the solution was oxygenated with 95% 
02 — 5% CO2. Fluid was not recirculated. 
Mean perfusion pressure was monitored with 
a Statham P23 Db strain gauge through a side 
arm on the perfusion cannula and varied from 
25 to 32 mm Hg. Peak pressure developed by 
the isovolumically beating left ventricle was 
used as an index of contractility. For this pur- 
pose a small latex rubber balloon mounted on an 
18-gauge cannula was introduced through a 
purse-string suture into the left ventricle and 
filled with a small amount of saline. The pres- 
sure developed in the balloon was measured by 
means of a Statham P23Db strain gauge. A pre- 
vious study demonstrated that within a wide 
range, variation in balloon pressure was not an 
important determinant of the percent change of 
the observed responses.^ The first derivative of 
the pressure tracing (dp/dt) was monitored 
on-line by means of an active R-C circuit differ- 
entiator with a time constant of 1 msec. The 
perfusion pressure, balloon pressure, and dp/dt 
were recorded simultaneously on a direct writ- 
ing oscillograph. Heart rate was maintained 
constant by right ventricular pacing. 
With the perfusion pressure monitored 
closely, these preparations were stable for up to 
three hours, although the experiments reported 
seldom extended over two hours. The reactivity 
of the Langendorff preparation was verified by 
reproducibility of dose-response curves to 
standard inotropic agents, such as calcium after 
varying lengths of time. 
Isolated Papillary Muscle 
The cats were anesthetized in the same man- 
ner as above, the hearts were quickly removed, 
and right ventricular papillary muscles (0.9 to 
2.2 mm in diameter) were removed after the 
tendinous end was tied with 5-0 Mersiliene su- 
ture. The muscles were then mounted in a 25 ml 
flow-through Lucite bath. The cut mural end 
was inserted in a spring loaded clip which was 
attached to a Minneapolis Honeywell #762025 
isometric force-displacement transducer. The 
tendinous end was tied to a fixed post in the 
