Cardiovascular Research 45 (2000) 215–219
www.elsevier.com / locate / cardiores
www.elsevier.nl / locate / cardiores
Historical note
The elusive coypu: the importance of collateral flow and the search for an
alternative to the dog
David J. Hearse*
Cardiovascular Research, Rayne Institute, St Thomas’ Hospital, London SE1 7 EH, UK
Keywords: Blood flow; Collateral circulation; Coronary circulation; Coronary disease; Infarction; Ischemia
1. Introduction
There are several ‘villains’ in this story: (i) researchers
who convinced themselves that myocytes could stay alive
without blood; (ii) authors who discarded (or journal
editors who refused to publish) negative studies; (iii) dogs
that had too much and too variable a collateral flow; (iv)
legislation and animal suppliers that made the use of
canine preparations (and an intriguing alternative, see Fig.
1) impossible or prohibitively expensive; and (v) a UK
government plot to exterminate the coypu (nutria).
2. Infarct size reduction? no problem!
For anyone interested in myocardial injury and protection, the 1970s and 1980s were both confusing and
exciting. Almost every copy of every journal contained a
new paper in which yet another drug reduced infarct size
in a canine model of coronary artery occlusion and
myocardial infarction. The interventions ranged from the
well known (beta blockers, calcium antagonists, vasodilators and glucose) through the surprising and sometimes
disasterous (steroids) to the bizarre (rutosides, cobra venom
and hyaluronidase). Opinion leaders in the field vigorously
promoted the concept that just because myocardial tissue
lay within the distribution of a recently occluded coronary
artery did not mean that it was necessarily condemned to
death — despite the absence of reperfusion. For those of us
who believed that early reperfusion was an absolute
prerequisite for the salvage of severely ischemic tissue this
seemed like heresy!
*Tel.: 144-171-922-8133; fax: 144-171-928-0658.
3. It’s negative, we won’t publish it . . . . unless it’s a
clinical trial!
Astounding claims resounded from the dog labs but,
despite this, clinical trials were consistently disappointing
and no single intervention was ever adopted for widespread clinical use as an anti-infarct agent in patients with
myocardial infarction. Clearly, something was wrong —
possibly the design of the trials, the choice of experimental
models or the concept upon which tens of thousands of
experimental animals (mostly dogs) met an untimely end.
There were, in fact, many negative studies but these were
often consigned to the sponsors’ archives or were very
difficult to get published and those that were published
usually appeared in lesser journals. However, one laboratory in particular (that of Robert Jennings and Keith
Reimer) did manage to publish negative studies in reputable journals and indeed, with a few exceptions, every
drug they studied appeared to have no beneficial effect on
infarct size.
4. Understand your model and its pathology before
you use it!
With hindsight we now know that the Jennings and
Reimer laboratory was one of the few that: used adequate
numbers of animals, measured infarct size after several
days, used a morphological assessment of infarct size and
took full account of the baseline variables influencing the
rate and extent of infarction. Ironically the understanding
of the vital importance of these baseline variables (particularly collateral flow) received major impetus from a
well publicised case of scientific fraud that came to light in
a multi-centre canine infarct size reduction trial (the
AMPIM study). This trial [1] rapidly became a landmark
publication, representing the cornerstone of our under-
0008-6363 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved.
PII: S0008-6363( 99 )00331-4
216
Species variation in coronary collateral circulation during ischemia
Fig. 1. Myocastor coypus molina (known as the coypu or nutria). A giant rat-like beast about 60 cm long and weighting up to 9 kg. Photo: courtesy of
Michael Haramis of the Maryland Department of Natural Resources.
standing of the factors which determine the amount of
tissue that will infarct within an ischemic risk zone. It
precipitated some long overdue realism in relation to the
(in)ability of drugs to protect against cell death in severe
sustained ischemia. Researchers began to acknowledge the
key distinction between the undoubted ability of some
drugs to slow the rate of cell death as opposed to their
questionable ability to reduce its ultimate extent [2–4]. To
make the critical distinction between injury slowing and
injury delaying required eventual infarct size to be measured several days after an episode of ischemia and
reperfusion (as Jennings and Reimer) and not after a few
hours as practised by many investigators.
tion process greatly), the failure to distinguish injury
slowing versus injury preventing and the frequent use of
inadequate animal numbers often made the outcome of
studies more a matter of chance than good science. The
need to interpret results in the light of collateral flow gave
rise to the ‘Reimer-gram’ — the acid test of the ability of a
drug to reduce infarction. As shown in Fig. 3, collateral
flow in a typical dog heart study may vary between 2%
and 40% and infarct size may occupy 90% to 40% of the
area at risk. It is only on the rare occasions when the
regression line for the treated group falls significantly
below that of the controls that drug-induced infarct size
reduction can be claimed with any degree of confidence.
5. Collaterals — the key to the problem
6. Problem solved? The challenge of the $1000 dog
Of the many variables that can influence the rate of
evolution of infarction the extent and distribution of
collateral or residual flow delivered to the ischemic zone is
undoubtedly the most important. Unfortunately, the dog
(which was the favoured species of most infarct size
reducers) has a very variable and often substantial collateral flow (see Fig. 2) — particularly in the case of the ‘failed
greyhound’ (regular losers at the greyhound race track who
were wanted no more!). This strain, with its enormous
hypertrophied heart, often exhibited collaterals capable of
providing 30% or more of normal flow to the perfusion
bed of the LAD despite a total occlusion. The variability in
collateral flow (with high levels slowing down the infarc-
The application of rigorous methodology and the distinction between delaying and reducing infarction led to a
severe decline in the number of papers claiming miraculous drug-induced infarct size reductions. At last we were
in a position to study infarct size limitation properly — but
unfortunately, for most investigators animal legislation and
soaring costs now made canine studies impossible. The
search was on for an alternative to the dog — pigs were
used quite often and offered the advantage of being devoid
of collaterals (see Fig. 4) thereby effectively eliminating
the most troublesome variable from the experiment and at
the same time (not surprisingly), leading to many negative
studies. However, pigs are not the most delightful of
Key publication: M.P. Maxwell et al. / Cardiovascular Research 1987
217
Fig. 2. Collateral vessels in the canine heart. This photograph shows multiple anastomoses connecting epicardial coronary arteries between adjacent
perfusion bed. Photo: courtesy of Wolfgang Schaper.
Fig. 3. The relationship between collateral flow and infarct size. Each point on this ‘Reimer-gram’ represents the individual infarct size in relation to the
mean transmural residual blood flow within a risk zone. The figure illustrates how, with a fixed ischemic duration, infarct size decreases as collateral flow
increases. In addition, evidence of drug-induced infarct size limitation is provided by the downward shift of the regression lines for each group.
218
Species variation in coronary collateral circulation during ischemia
Fig. 4. Collateral vessels in the porcine heart. This figure shows the clear separation between the coronary arteries of adjacent perfusion beds with no
evidence of significant anastamoses. Photo: courtesy of Wolfgang Schaper.
experimental subjects, anaesthesia and arrhythmias can be
a problem and costs were again very high. Surely small
mammalian hearts could be used for the rapid, cheap and
effective screening of the ability of drugs to limit the
evolution of infarction.
7. Defining species difference in collateral flow
Many workers switched to the rat and rabbit for their
studies, some even undertook infarct size studies in the
mouse. However, before the St Thomas’ group were
prepared to switch from our previously used dog, pig and
baboon models, we felt it imperative to be fully aware of
the cardiac collateral status of various small mammalian
heart. Hence the study cited in this special issue of
Cardiovascular Research in which we characterised the
extent and the distribution of collateral flow within zones
of regional ischemia in isolated perfused hearts from the
guinea pig, dog, cat, rat, ferret, baboon, rabbit and pig. In
the light of the classical work by Schaper [5], our findings
(Fig. 5) were not unexpected with the dog and the cat
having extensive collateral connections which delivered
flow preferentially to the epicardial tissue, thus explaining,
in part, the greater vulnerability of the endocardium to
necrosis and the phenomenon of the ‘wave front of cell
death’ [6]. Interestingly, the guinea pig heart was found to
be totally collateralised making it impossible to induce
infarction in this species — how great it would be if the
human had the coronary artery anatomy genes of the
guinea pig!
8. So what about the coypu?
Whilst small mammalian hearts can undoubtedly be
used as a fast and economical test bed for assessing
infarction, they do suffer from the difficulty of reliably
Key publication: M.P. Maxwell et al. / Cardiovascular Research 1987
219
Fig. 5. Species differences in collateral flow. The amount of flow delivered to an ischemic zone following the occlusion of a major branch of the LAD
(expressed as a percent of that delivered to non-ischemic tissue).
measuring flow (and its all important regional distribution)
in a pretty small piece of meat. Surely, we thought, there
must be a low cost, large, readily available mammalian
heart. Eureka! What about the coypu?
In 1939, myocastor coypus molina (known in some
countries as nutria) was introduced from South America to
the UK for fur farming — a giant rat-like beast (an aquatic
rodent, related to the guinea pig and the porcupine) about
60 cm long and weighting up to 9 kg (see Fig. 1). By 1939
there were 40 coypu farms in the UK and inevitably some
inmates escaped. By the 1960s they had infested much of
the UK, ravaging crops and done great damage to river
banks. At this stage the government instituted a control
and eradication programme — it became illegal to own or
breed a coypu but surely we could use them for infarct
sizing? Just imagine the potential — big hearts, easy to
breed (gestation period of 132 days, litters of up to 9 born
with their fur and their eyes open) and inexpensive, maybe
even free from the trappers who were receiving a bounty
for their capture. Enter bureaucracy — transporting a
coypu turned out to be more difficult than moving a
nuclear warhead or international terrorist through the
centre of London. Thus, despite relentless efforts, we were
never able to study the collateral circulation of the coypu
— for better or for worse, the coypu is now eliminated
from the UK (other than a stuffed one in a Cambridge
museum!) and the cardiological community has been
spared what might have been a series of papers in
Cardiovascular Research extolling the virtues of the coypu
for studies of infarct size.
References
[1] Reimer KA, Jennings RB, Cobb FR et al. Animal models for
protecting ischemic myocardium: results of the NHLBI cooperative
study. Circ Res 1985;56:651–665.
[2] Hearse DJ. Critical distinctions in the modification of myocardial
cell injury. In: Opie LH,, editor, Calcium antagonists and cardiovascular disease, New York: Raven Press, 1984, pp. 129–145.
[3] Hearse DJ. The protection of the ischemic myocardium: surgical
success versus clinical failure? Progress in Cardiovascular Diseases
1988;30:381–482.
[4] Hearse DJ, Yellon DM. Why are we still in doubt about infarct size
limitation? the experimentalists view point. In: Hearse DJ, Yellon
DM, editors, Therapeutic approaches to myocardial infarct size
limitation, New York: Raven Press, 1984, pp. 17–41.
[5] Schaper W. Infarcts and the microcirculation. In: Hearse DJ, Yellon
DM, editors, Therapeutic approaches to myocardial infarct size
limitation, New York: Raven Press, 1984, pp. 79–90.
[6] Reimer RA, Jennings RB. The ‘wavefront phenomenon’ of myocardial ischemic cell death. Transmural progression of necrosis within
the framework of ischemic bed size (myocardium at risk) and
collateral flow. Laboratory Investigation 1979;40:633–644.