Download Gaining new insights into mechanisms of essential hypertension

Central control of blood
pressure. What is wrong in
patients with essential
hypertension?
Dr. Sergey Kasparov
Kasparov
M.D., PhD
Department of Physiology
E9
[email protected]
SK
SK Teaching
Teaching Website:
Website: http://www.bris.ac.uk/Depts/Physiology/Staff/Pysk/Teaching/
%age of Men & Women
with hypertension in England
%
with
high
blood
pressure
40
35
30
25
20
15
10
5
0
Data
Data Source:
Source: www.heartstats.org
www.heartstats.org
Men
34%
Women
30%
Financial Burden of Hypertension
For 2005:
The cost of cardiovascular diseases
(including high blood pressure) in the USA
alone is estimated to be $393.5 billion
Are We Good at Treating High
Blood Pressure?
%
% with
with
Un-controlled
Un-controlled
hypertension
hypertension
90
80
70
60
50
40
30
20
10
0
Data Source: www.heartstats.org
78%
Men
67%
Women
Evidence for higher sympathetic tone?
WHAT IS SYMPATHETIC N.S.
and how brain controls it?
Autonomic - ???
Can you change your heart rate?
Can you change the diameter of the pupil
in your eye?
ANS operates without our conscious command
CNS
Parasympathetic N.S.
Sympathetic N.S.
?
Adrenal
gland
Effector organ
III
VII
ANS anatomy
sympathetic
IX
X
PARASYMP
PARASYMP
Modified from Gannong’s textbook
What do these two systems do?
SYMPATHETIC
PARASYMPATHETIC
“Fight or Flight”
“Rest and digest”
WE
WE ONLY
ONLY DO
DO SYMPATHETIC
SYMPATHETIC in
in class.
class. Please
Please have
have aa look
look at
at
parasympathetic
parasympathetic system
system effects
effects at
at your
your own
own time
time later
later
Fight or Flight
Effects related to cardio-vascular system.
For other effects see handouts.
Heart:
1. Increase in heart rate
2. Increased force of contraction
→ more blood pumped, more oxygen
delivered to the tissues
Blood vessels
Arterioles: re-distribution of blood in
favour of the “critical organs”
Strong constriction
Skin
Abdominal viscera
Kidneys
Relaxation or weak
constriction
Heart
Brain
Lungs
Skeletal muscles
Veins:
in many areas veins also constrict, thus more blood
returns to the heart for faster re-circulation.
1. Cardiac output increase
2. Increased resistance to blood flow
(constriction of arteries)
3. Increased return of venous blood
Systemic blood pressure increases:
Parasympathetic system: dominates at rest and during sleep.
“Night is the realm of vagus” (the main parasympathetic nerve)
“Rest and digest”.
Important effects of
parasympathetic system on the
heart:
1. DEcrease in heart rate
2. DEcrease in force
of contraction
As less oxygen is required
by peripheral tissues
the heart may also
“have a rest”
200
Reflex fall in heart rate triggered by afferent
baroreceptors
Arterial
Pressure
70
80
Heart
Rate
50
An increase in blood pressure →
a) decrease in heart rate b) dilation of blood vessels
Blood Pressure
Decrease
Brain in informed about the blood pressure by peripheral baroreceptors
Brainstem autonomic centres
Afferents
of the ANS
AMPLIFIER
Blood
pressure
mm Hg
100
Carotid
artery
80
50
Activity
of a
baroreceptive
nerve
-50
Time
Data from Dr. H.Waki
Carotid
artery
These sensory nerve
endings get excited
by stretch: the higher
blood pressure the
stronger the signal
Afferents
of the ANS
Sympathetic –
DECREASE
Parasympathetic –
INCREASE
Information processing
by the brain
Effector organ – heart or blood vessel
200
Arterial
Pressure
70
NORMAL
80
Heart
Rate
50
220
Arterial
Pressure
HYPERTENSIVE
90
90
70
Heart
Rate
Is there as abnormality
within the central link in
hypertension?
?
sympathetic
parasympathetic
?
?
?
?
Can you
identify these
structures on
your diagram?
sympathetic
parasympathetic
Is there something wrong going on
here in hypertension ???
End of lecture 1
Lecture 2.
New insights into the central control
of blood pressure
OR: USING VIRAL VECTORS TO STUDY
HYPERTENSION
Dr. Sergey Kasparov
Kasparov
M.D., PhD
Department of Physiology
E9
[email protected]
SK
SK Teaching
Teaching Website:
Website: http://www.bris.ac.uk/Depts/Physiology/Staff/Pysk/Teaching/
The Brainstem
(+)
(+)
Sympathetic
Sympathetic
•Vasoconstriction
•Vasoconstriction
Increase
Increase HR
HR
Cerebellum
Baroreceptors
Baroreceptors
(+)
(+)
(+)
DMN
Spinal cord
NTS
Medulla oblongata
(+) (+)
NA
CVLM
(-)
RVLM
Parasympathetic
Parasympathetic
•Heart
•Heart slows
slows
A hypothesis:
1.In hypertension transmission
of baroreceptor information
is inhibited at the level of
NTS
2.This effect may be due to
the actions of nitric oxide
Some facts about nitric oxide:
1. A gas produced by (mainly) two enzymes, neuronal
nitric oxide synthase and endothelial nitric oxide
synthase (eNOS)
2. Acts on various neurones and can activate
inhibitory synapses in NTS (therefore can inhibit
baroreflex pathway)
Q. How can we test this hypothesis?
A. Use a genetic tool to inhibit NO
production in NTS and measure cardiovascular parameters in a freely moving
animal.
Our tools: replication-deficient viral vectors
VIRUSES AS VECTORS
To make a virus act as vector we need to delete
part of its genome to:
1) Make it unable to replicate and therefore to
cause a disease
2) Clear room to accommodate the expression
cassette, i.e. delete a part of the viral genome
3) Learn how to proliferate the vectors and how
to purify them to high titres
4) Establish efficient transfection protocols
Viral vectors
-
high efficiency of gene delivery in vivo
high levels of transgene expression
stability of expression
Vectors derived from
1) Adenovirus (common cold virus)
2) Lenti/Retrovirus (relatives of HIV)
And several others…
Adenoviral (Ad) vectors
- non-enveloped double stranded DNA virus
associated with mild human infections
fibre
projections
penton
bases
Early ‘E’ genes
E1
0
ITR
E3 E4
E2
20
60
40
L1 L2
L3
80
L4
Late transcription
0
TRANSGENE
ITR
An
100
36 kb genome
ITR
Late ‘L’ genes
L5
Entry of adenoviruses into the cells
Radiotelemetry: Measuring cardiovascular parameters in
conscious freely moving rats
Transmitter
Transmitter
Ambient
Ambient Pressure
Pressure
Reference
Reference
Receiver
Receiver
Calibrated
Calibrated Pressure
Pressure
Output
Output Adapter
Adapter
Automated
Automated analysis
analysis System
System
How to block eNOS?
Inhibition of “endothelial” NOS by expression of its
dominant negative truncation mutant (Lee
(Lee et
et al.
al.
1995).The
1995).The expression
expression was
was driven
driven by
by aa non-selective
non-selective HCMV
HCMV promoter.
promoter.
Functional
homo-dimer
eNOS
Non-functional
dimer
eNOS
eNOS
Native
monomers
Truncated
monomer
The outcome:
Expression of eNOS dominant negative decreases blood pressure
in SHR
EGFP in SHR
Systolic 160
Blood
140
pressure
p<0.05
120
100
eNOSi in SHR
eNOSi in WKY
0
7
14
Waki et al Hypertension 2006
Conclusion:
In this experiment viral gene transfer has been used
to prove a role for the eNOS (endothelial nitric oxide
synthase) in pathological hypertension
Other uses of viral technology:
In experimental medicine
1.
1. To
To increase
increase concentration
concentration of
of aa protein
protein under
under study
study in
in aa cell
cell and
and
study
study its
its function
function
(over-expression)
(over-expression)
2.
2. To
To make
make the
the cell
cell produce
produce aa protein
protein with
with functions
functions which
which are
are not
not yet
yet
understood.
understood. Then
Then -- see
see what
what happens
happens
3.
3. To
To make
make the
the cell
cell produce
produce indicator
indicator proteins
proteins (for
(for example,
example,
fluorescent).
fluorescent). These
These may
may be
be used
used to
to monitor
monitor various
various variables
variables within
within the
the
living
living cells
cells
Other uses of viral technology:
In clinical medicine –
Gene therapy - to deliver therapeutic genes
Examples:
Genes which protect heart from damage
caused by ischemia (during heart attacks)
Genes which improve survival of vascular
grafts used for transplantation
Genes which produce proteins which can
lower blood pressure
WHAT IS WRONG WITH THE
SYMPATHETIC N.S.
In HYPERTENSION?