750 
PHARMACOLOGY 
Table I. — Desired Conditions for Use of Animals Yield- 
ing Tissues for in Vitro Study 
1. Definition and knowledge of genotype. 
2. Precise knowledge of morphological and physiological status of 
animal. 
3. Absence of specific pathogenic agents, parasites, and disease 
states. 
4. Standardized environmental conditions. 
6. Knowledge of seasonal or circadian variations in function and 
reactivity. 
forgotten by the physiologist and pharmacolo- 
gist. First, there are questions relating to the 
animal source from which various isolated car- 
diac or vascular preparations are obtained. 
Table I lists some factors which one must con- 
sider in selecting any given species or strain of 
animal, and some known major factors that can 
determine the subsequent responses of isolated 
tissues obtained from these animals. While 
some of these factors have been known or ap- 
preciated for many years, others (e.g., the in- 
fluence of circadian rhythm on drug responses) 
are only now being fully documented and inves- 
tigated. 
Depending on one's perspective, the goals of 
in vitro studies may vary. From the point of 
view of many pharmacologists, however, the 
main objective is to utilize those in vitro tech- 
niques which take advantage of the known di- 
versity of function and morphology of any 
given tissue, derived from a variety of sources, 
and which increases our understanding of gen- 
eral principles of drug action. This then leads to 
the important questions of (1) what are the 
most suitable and meaningful in vitro prepara- 
tions for the assessment of drug action, and (2) 
how valid are these in vitro tests in predicting 
effects in the intact organism? 
Relative to the last question, many important 
positive correlations exist between in vitro tests 
and effects observed in man (e.g., the cardio- 
Table III. — "False Negative" in Vitro Responses to 
Active Agents 
Agent Tissue Effec t Reason 
Cyclic AMP — Heart Weak inotropic Permeability 
barrier 
Bradykinin Human Vein Strip No contraction Species /tissue 
Rabbit Aortic 
Strip 
Angiotensin — Kitten atrium; Weak inotropic Species/tissue 
Frog Vent. No contraction 
Table II. — Examples of Poor Correlation Between in 
Vitro and in Vivo Drug Effects 
Effect 
Agent 
In vivo 
In vitro 
Eledoisin 
Prostaglandin E2 
Ko-592 
Vasodilator 
Vasodilator 
Weak ^-blocker 
in the rat 
Vasoconstrictor 
Vasoconstrictor 
Potent ^-blocker 
tonic effect of cardiac glycosides). Yet major 
disturbing discrepancies exist which indicate 
we must be extremely cautious of extrapolating 
in vitro results to the intact animal. Table II 
shows three types of agents which produce 
qualitatively or quantitatively different results 
depending on the test system. Many more exam- 
ples are available. 
Some of these discrepancies would, of course, 
lead to the discarding or dismissal of many im- 
portant agents, depending on which test might 
be utilized first. For example, in Table III, the 
inotropic effects of cyclic AMP and angiotensin 
would be underestimated by the use of the indi- 
cated in vitro tests because of permeability 
problems, or species/tissue differences. Simi- 
larly, the in vivo vascular effect of bradykinin 
would be missed if one utilized the tissues indi- 
cated. Clearly, the wider the spectrum of in 
vitro/in vivo testing, the less likely one would 
miss meaningful biological activity. Yet, are 
there any clues which allow us to rationally 
choose one test over another ? 
Table IV summarizes some selected studies 
indicating the diversity of results pertaining to 
the inotropic responses of isolated cardiac prep- 
Table IV. — Species Differences in Inotropic Responses 
to Prostaglandins 
Tissue* PG Species Effect Investigator** 
L. Atrium E2 Rabbit + Levy 
L. Atrium E2 Human ±; 0 Levy 
Vent. El Cat 0 Berti et al. 
Vent. El Rat 0 Berti et al. 
L. Atria Ei.Ai.Fs G.P. + Nutter & Ratts 
L. Atria Ei,Ai,F2 Rabbit 0 Nutter & Ratts 
Vent El Toad + Nutter & Ratts 
* Isolated hearts 
** See References 
+ = positive inotropism 
0 = no significant eflect 
± — variable inotropic response 
