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Preclinical screening methods of
(for MD Pharmacology)
- Dr. Advaitha M V
• The animal models of hypertension share many
features which are common to human
• Many of these models have been developed by
utilizing the etiological factors that are presumed
to be responsible for human hypertension.
Excessive salt intake.
Hyperactivity of renin-angiotensin- aldosterone
system (RAAS) and
An ideal animal model of hypertension criteria
• It should be feasible in small animals.
• Simple to perform and uniformly reproducible.
• Should be able to predict the potential
antihypertensive properties of an agent.
• Consume minimal quantities of compounds.
• It should be comparable to some form of human
• In the past, most studies
on experimental hypertension were carried
out on Dogs.
• Currently, rat is the preferred animal species.
• Spontaneous hypertensive rat (SHR), the
genetic strain of hypertensive rat, is the
animal of choice.
Types of animal models of
1. Renovascular hypertension
2. Dietary hypertension
3. Endocrine hypertension
4. Neurogenic hypertension
5. Psychogenic hypertension
6. Genetic hypertension
7. Other models
• This is a very commonly used model of
• Experimentally, renal hypertension is
produced by constriction of renal artery.
• This activates peripheral RAAS and
sympathetic nervous system.
Methods of inducing renovascular
Goldblatt et al (1934)
• He reported that a partial constriction of renal
arteries in dogs produced hypertension.
• This type of hypertension has also been
induced in rabbits, rats and monkeys.
• Rats weighing from 120 to 200 g are
anaesthetized with hexobarbitone sodium (40
mg/kg body weight).
• A silver clip of 0.2 mm internal diameter is
placed on the left renal artery close to the
• The renal artery in rats can also be ligated
with 4-0 silk suture.
• Constriction of renal artery should be more
• The animal is considered hypertensive if
systolic BP is more than 160 mm Hg for two
consecutive days after 4 weeks of
ligation/application of clip.
• Three variants of hypertension produced by
• Two kidney one clip (2K1C) hypertension
• One kidney one clip (1K1C) hypertension
• Two kidney two clip (2K2C) hypertension
Two kidney one clip (2K1C) hypertension
• The renal artery is constricted on only one side
with the other artery (or kidney) left untouched.
• This results in a sustained increase in BP.
• Initially , there is no salt and water retention
because of the other normal kidney being intact.
• So , the resultant hypertension at this stage is
• After about 6 weeks, the increased angiotensin-
II releases aldosterone from adrenal cortex
leading to gradual retention of salt and water.
• Retention of salt and water leads to decreased
• From this stage onwards, hypertension is
One kidney one clip (1K1C) hypertension
• Constriction of renal artery is done on one side
and the contra lateral kidney is removed.
• There is an increase in BP within a few hours.
• Since there is no contra lateral kidney, there is
no pressure diuresis and natriuresis.
• So there is rapid salt and water retention.
• Plasma renin activity is usually normal.
• Hypertension soon becomes volume
Two kidney two clip (2K2C) hypertension
• Constriction of aorta or both renal arteries is
• There is a patchy ischemic kidney tissue, which
secretes renin leading to increased BP.
• The remaining kidney tissue retains salt and
• one of the most common causes of renal
hypertension in human beings is (such) a patchy
ischaemic kidney disease.
Hypertension induced by external
compression of renal parenchyma
• In this method, kidney tissue is compressed by
securing a 'figure of 8' ligature.
• It is of two types:
• Two kidney one ligature (2K1L)
• One kidney one ligature (1K1L)
Reduced renal mass
• Reducing renal tissue to five-sixth (5/6th) by
renal mass ablation produces hypertension.
• Here , the right kidney is removed and 2 or 3
branches of left renal artery are ligated.
• This is to produce infarction of approximately
2/3rd of the left kidney.
I. Increased salt intake:
• Chronic ingestion of excess salt produces
hypertension in rats, which mimics human
• High salt intake hypertension has been
produced in rats, rabbits and chicks by replacing
drinking water with 1-2% sodium chloride for 9-
• This method is also used to cause Accelerated
high pressure in renal hypertension.
DOCA-Salt induced HTN
• Selye et al was the first to demonstrate that
deoxycorticosterone acetate (DOCA) produces
hypertension in rats.
• There is increased DOCA-induced reabsorption of
salt and water leading to increased blood volume
and hence increased BP.
• There is also increased secretion of vasopressin
leading to water retention and vasoconstriction.
• In addition, altered activity of RAAS leads to
increased sympathetic activity
• Rats, especially female and young, are prone
to DOCA-salt induced hypertension.
• DOCA induced hypertension is salt dependent
(neither administration of DOCA nor partial
removal of renal mass is effective in increasing
BP when applied without salt Administration).
To produce hypertension,
• Rats weighing about 100 g are kept on a diet
high in sodium chloride and drinking water is
replaced by 2% sodium chloride solution.
• After they attain a weight of about 250 g, they
are given DOCA dissolved in sesame seed oil
at a dose of 10 mg/kg SC, twice weekly for 4
• One of the most important negative feedback in
the control of BP originates from baroreceptors
in the carotid sinus and aortic arch.
• Afferents of baroreceptors travel along 9th and
10th cranial nerves.
• Sectioning of the baroreceptor nerves leads to
persistent rise in BP.
• Suitable in dogs, cats and rabbits
• Repeated exposure to stressful situation may
lead to a state of persistent hypertension.
• Borderline hypertensive rats (BHR) are useful
for psychogenic hypertension.
• BHRs that were exposed to daily sessions of
either short (20 min) or long (120 min)
duration air-jet stimulation developed
hypertension within 2 weeks.
• Stress plays an important part in development
of human hypertension.
• So, This model is also very frequently used to
study the pathophysiology of hypertension.
• The so called ‘spontaneous hypertensive rat
(SHR)’ was developed by meticulous genetic
inbreeding by Okamoto and Aoki.
• This inbreeding resulted in 100% of the
progeny having naturally occurring
How are SHR ?
• In SHRs, BP gradually increases until it is
maintained at a markedly elevated level after
approximately 12 weeks of age.
• In unrestrained male SHRs, mean arterial
pressure is approximately 190- 200 mm Hg as
compared to 115-130 mm Hg in normal rats.
• During the early stable stages and
developmental phase of hypertension-
elevated BP is maintained in large part by
enhanced central sympathetic outflow.
• In the later stages
Increased total peripheral resistance.
normal cardiac output
decreased permeability of the glomerular
Forms the basis for the long term maintenance of
• SHRs also develop typical complications of
• There are Stroke prone SHRs (SHRSP), which are
selectively bred among SHRs.
• These develop cerebrovascular lesions
spontaneously in over 80% of rats.
• Because of apparent similarities of the SHR to
SHR models are highly recommended for
screening potential drug candidates for
• Wistar fatty rats (WFR) are derived from cross
between obese Zucker and Wistar Kyoto rats.
• These show persistent hyperinsulinemia and
hypertension after 16 weeks of age.
• A good model to elucidate the relationship
between hyperinsulinemia and hypertension.
Transgenic rat (TGR) models
• Transgenic models of hypertension have
revolutionized the experimental work on
• Here , an additional renin gene, the murine
Ren-2 gene, is introduced into the germ line of
• This results in transgenic hypertensive rat
strain, TGR (mREN2).
• It has an overexpression of renin.
• Linkage has been described for the
angiotensinogen gene in human hypertension.
• TGR model are also useful for studying the
role of local RAAS system in hypertension.
How to measure BP ?
Direct Method :
• It is a invasive procedure.
• A week before the drug adminstration, The
animals are anesthetized.
• Femoral/Carotid Cannula is inserted.
• On the day of screening, cannula is connected to
a mercury manometer or a pressure transducer.
• BP is measured
• A week before the experiment, each rat is
anaesthetised with 40 mg/kg pentobarbital.
• Left or right carotid artery or femoral artery is
cannulated under aseptic conditions with
polyethylene cannula filled with 1% heparin in
• Free end of the cannula is passed under the skin
and allowed to protrude 3-4 cm from the skin
behind the ears of the rat.
• The skin incisions are sutured and a plastic
skin dressing is applied.
• After recovery from anaesthesia (2-2.5 h) each
rat is placed in an individual cage for 24 h
• On the day of expt., Cannula is connected to
a pressure transducer then to the
• BP is recorded on the polygraph or
Non-Invasive/ Indirect method :
Tail cuff Method :
• It is a common and convenient method.
• Tail cuff is inflated and then deflated.
• Pulsations disappear when cuff is inflated.
• When cuff is deflated, pulsations start
appearing when pressure in the cuff equals
• The cuff is attached to a tail cuff
sphygmomano-meter or pressure transducer
and BP is recorded on a chart.
• Tail swelling method.
• Foot swelling method.
Effects of antihypertensive agents
• Antihypertensive drugs, according to their
mode of action, will affect the blood pressure
in certain types of experimental hypertension,
and not in all !
• Vasodilators like minoxidil, hydralazine and
diazoxide are effective in renal hypertensive
• CCB, ACE inhibitors and AT-1 antagonists
decrease BP in 5/6 nephrectomised SHR
• Diuretics, are active in mineralocorticoid or
salt induced hypertension.
• Sympathomimetic Drugs decrease BP in both
endocrine and neurogenic hypertension.
• D.K. BADYAL, H. LATA , A.P. DADHICH. ANIMAL MODELS OF
HYPERTENSION AND EFFECT OF DRUGS. Indian Journal of
Pharmacology 2003; 35: 349-362.
• Journal of Visualized Experiments videos
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