CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 1, January/February 2011
14
AFRICA
The variability of baroreflex sensitivity in juvenile,
spontaneously hypertensive rats
VE VALENTI, LC DE ABREU, E COLOMBARI, MA SATO, C FERREIRA
Summary
In this study the baroreflex sensitivity of conscious, juvenile,
spontaneously hypertensive rats (SHRs) was compared. The
study population consisted of 19 eight-week-old male SHRs.
The baroreflex sensitivity was quantified as the derivative of
the variation in heart rate (HR) and the variation of mean
arterial pressure (baroreflex sensitivity
= ∆
HR/
∆
MAP).
MAP was manipulated with sodium nitroprusside (SNP)
and phenylephrine (PHE), administered via an inserted
cannula in the right femoral vein. The SHRs were divided
into four groups: (1) low bradycardic baroreflex (LB) where
the baroreflex gain (BG) was between 0 and –1 bpm/mmHg
with PHE; (2) high bradycardic baroreflex (HB), where the
BG was
<
–1 bpm/mmHg with PHE; (3) low tachycardic
baroreflex (LT) where the BG was between 0 and 3 bpm/
mmHg with SNP; (4) high tachycardic baroreflex (HT)
where the BG was
>
3 bpm/mmHg with SNP.
We noted that 36.8% of the rats presented with an
increased bradycardic reflex, while 27.8% demonstrated
an attenuated tachycardic reflex. No significant alterations
were noted regarding the basal MAP and HR. There were
significant differences in the baroreflex sensitivity between
SHRs in the same laboratory. One should be careful when
interpreting studies employing the SHR as a research model.
Keywords:
baroreflex, rats, inbred SHR, sympathetic nervous
system, parasympathetic nervous system, autonomic nervous
system
Submitted 17/7/09, accepted 10/3/10
Cardiovasc J Afr
2011;
22
: 14–17
DOI: CVJ-21.006
Diverse factors are involved in the onset of hypertension and
different animal models have been developed in the investigation
of this disease. These are the renovascular model, the DOCA-salt
model, the neurogenic hypertension model and the genetic model
of hypertension in spontaneously hypertensive rats (SHR). The
SHR is a suitable model to study the course of hypertension, as
it shares certain similarities with human essential hypertension.
These similarities include: a genetic predisposition to high blood
pressure with no known aetiology, an increase in total periph-
eral vascular resistance without volume expansion, and similar
responses to drug treatment.
1
It has been described in humans that arterial baroreflex func-
tion is significantly related to the prognosis of acute myocardial
infarction, arrhythmias, heart failure and stroke.
2-6
These obser-
vations indicate that such patients with a lower baroreflex sensi-
tivity exhibit shorter survival times. Recently, it was reported that
arterial baroreflex function or sensitivity plays an important role
in the pathogenesis and prognosis of hypertension, atheroscle-
rosis, aconitine-induced arrhythmia and LPS-induced shock.
5,7,8
Conditions such as ageing, hypertension and radiation therapy
to the neck diminish both arterial compliance and baroreflex
sensitivity, and increased vascular stiffness may be an important
clue to possible impaired baroreflex sensitivity.
An important question for the basic science researcher in
hypertension is: are all spontaneously hypertensive rats (SHRs)
the same? In 1987, it was described that SHRs from two different
laboratories demonstrated significant differences with regard to
growth rate and blood pressure.
9
Although it was previously documented that a portion of
normotensive Sprague-Dawley rats exhibited lower baroreflex
sensitivity than their peers,
6,10
no studies have yet been published
that address the issue of whether there are any differences in
baroreflex sensitivity between other types of rat of the same
strain. It was recently reported that age is an important factor
regarding baroreflex development in the SHR.
11
The purpose of this study was to compare the baroreflex
sensitivity between juvenile SHRs from the same laboratory,
in order to explore the possibility that there may be intra-strain
differences in the baroreflex sensitivity. We analysed the follow-
ing: the baroreflex gain, the bradycardic and tachycardic peak
and the heart rate (HR) range – the difference between the brady-
cardic and the tachycardic peak. Based on pilot studies (data not
published), we expected significant differences between SHR
rats of the same strain and from the same laboratory.
Methods
The experiments were performed on eight-week-old SHRs from
the same laboratory. Rats were housed individually in plastic
cages under standard laboratory conditions. They were kept
under a 12-hour light/dark cycle (lights on at 06:30) and they had
free access to food and water. Housing conditions and experi-
mental procedures were approved by the Institution’s Animal
Ethics Committee. The minimum number of animals was used.
One day before the experiment, the rats were anaesthetised
with ketamine (50 mg/kg i.p.) and xylaxine (50 mg/kg i.m.)
and a catheter was inserted into the abdominal aorta through
Department of Medicine, Cardiology Division, UNIFESP, São
Paulo, Brazil
VITOR E VALENTI, PhD,
CELSO FERREIRA, MD
Department of Public Health, University of São Paulo, Brazil
LUIZ CARLOS DE ABREU, PhD
Department of Morphology and Physiology, School of
Medicine of ABC, Santo André, Brazil
EDUARDO COLOMBARI, PhD
MONICA A SATO, PhD
Cardiology Division, School of Medicine of ABC, Santo
André, Brazil
CELSO FERREIRA, MD
