16 
CARDIAC MODELS 
In a subsequent experiment Kramsch and 
Hollander fed 12 young Macaca fascicularis 
monkeys a diet containing 1.4% cholesterol by 
weight. The serum cholesterol concentration of 
these animals rose above 350 mg% and all the 
monkeys fed the atherogenic diet developed se- 
vere and extensive atherosclerosis of the proxi- 
mal segments of the coronary arteries. Occlu- 
sive lesions of the coronary arteries resulted in 
the death of tv^o monkeys after 12 months of 
the diet.*3 
STUMPTAIL MACAQUES (Macaca arctoides) 
Stumptail macaques, in the past called Ma- 
caca speciosa, have been of interest because it is 
believed by many that they are more docile than 
other macaques. In our experience it is true that 
the juvenile animals are remarkably more doc- 
ile; how^ever, there is very little difference in 
the tractability of adults as compared v^^ith 
other adult macaques. 
A single study has been reported on the sus- 
ceptibility of these animals to diet-induced 
atherosclerosis.** Macaca arctoides fed choles- 
terol for nine months developed hypercholes- 
terolemia of about 600 mg/100 plasma and had 
atherosclerotic plaques in the aorta and coro- 
nary arteries. 
SQUIRREL MONKEYS (Saimiri sciureus) 
Squirrel monkeys have been found to offer a 
number of advantages as animal models of ath- 
erosclerosis because they are relatively inexpen- 
sive, are easily caged and manipulated, breed 
well in captivity, are susceptible to naturally-oc- 
curring and diet-induced atherosclerosis, and 
share with man several important aspects of 
whole body cholesterol metabolism.*^ 
The natural occurrence of atherosclerosis has 
been studied both in wild-caught squirrel mon- 
keys maintained in the laboratory and among 
free-living animals in the vicinity of Leticia, 
Colombia, South America. In 1964, Middleton 
et al.**' reported on the occurrence of aortic and 
coronary artery atherosclerosis among wild- 
caught adult monkeys that had been maintained 
in the laboratory for periods of three months to 
one year. About 85 % of these animals had fatty 
streaks of the aorta, visible after Sudan IV 
staining, while about 7% had small raised 
plaques primarily in the abdominal aorta that 
were visible without prior staining. Coronary 
artery atherosclerosis, although minimal in ex- 
tent, was present in 30% of these monkeys. 
Since it was not possible to eliminate the possi- 
bility that confinement and diet may have influ- 
enced the lesions an additional study was under- 
taken in which the prevalence and extent of 
arterial lesions in 220 squirrel monkeys autop- 
sied shortly after being trapped in Colombia, 
South America, were determined.*'^ Fatty streak 
lesions of the aorta discernible after staining 
with Sudan IV were infrequent in the juvenile 
monkeys and were common in the adults with a 
higher prevalence in the females than in the 
males. Approximately 10% of the adult mon- i 
keys had lipid containing lesions in the small in- 
tramyocardial arteries. It was apparent that | 
monkeys surveyed in their natural habitat have 
lower prevalence of both coronary and aortic i 
atherosclerosis than did monkeys maintained in ! 
the laboratory for three to twelve months. It 
was of interest that the mean serum cholesterol 
concentration of the free-living monkeys (ap- | 
proximately 100 mg%) was about half that of 
monkeys maintained in our laboratory and fed 
low fat cholesterol-free chow.*^ j 
Because of the differences in serum choles- j 
terol concentration between free-living squirrel i 
monkeys and those in the laboratory it seemed [ 
of interest to study the changes in serum choles- I 
terol concentration and lipoprotein cholesterol 
during the process of capture, confinement, 
transport, and laboratory acclimation.*^ Blood 
samples were obtained from a group of adult 
squirrel monkeys shortly after being trapped 
and at subsequent intervals during the labora- 
tory acquisition and acclimation process. There 
were increases in serum cholesterol concentra- ; 
tion with each of these processes and increases j 
were noted from the usual 100 mg% noted i 
among free-living animals to concentrations of 
about 200 mg% in the laboratory. Investigators ! 
using these animals, especially in diet or drug 
studies, should recognize that a significant hy- 
percholesterolemia may exist at the start of the 
experiment. 
Atherosclerosis can be markedly exacer- 1 
bated by the addition to the diet of fat and 
