Insulin-induced microvascular activity in patients with essential hypertension: a possible role for angiotensin II AT1-receptor blockers-Amendement 26-03-2008.

Title: Insulin-induced microvascular activity in patients with essential
hypertension: a possible role for angiotensin II AT1-receptor blockers.

There is a relation between hypertension and insulin resistance, both
associated with increased cardiovascular risk. Hypertension and insulin
resistance are characterized by dysfunctions in microcirculation, however it is
unclear if microcirculation is the link between these two abnormalities. In
addition to its actions in mediating glucose uptake, insulin knows several
vascular effects. Insulin induces a vasodilatory response by resis-tance
vessels and preterminal arterioles leading to an overall increase in blood flow
(glucose) to the muscles.
The local activity of the vasoconstrictor angiotensin II is elevated in
patients with hypertension. Previous studies show a possible role for
angiotensin II in the hypertensive, insulin resistant phenotype, however a
mechanism remains unexplained. In this study we hypothesize that blocking the
angiotensin II AT1-receptor improves the insulin-induced microvascular
dilatation.

Main study:
1. Does blockade of the angiotensin II AT1-receptor improve the insulin-induced
microvascular effects in hypertensive patients.
2. Does blockade of the angiotensin II AT1-receptor impair the insulin-induced
mi-crovascular effects in normotensive control subjects?

Amendement:
The objective of the amendement is to test the angiotensin II AT1-recptor
blockade with a single oral dose of 600mg irbesartan. Furtheremore, we would
likte to investigate the time-course of this blockade and we would like to
examine if the blood presure drop with this dose of irbesartan is similar to
the blood pressure drop achieved with the ingestion of a single dose of
Felodipien ER (20mg).

Main study:
All subjects will bring 3 visits to the AZM. The following interventions will
be applied:
- hyperinsulinemic euglycemic clamp (HEC) + placebo
- HEC + irbesartan (600 mg)
- HEC + felodipine ER (20 mg)

During all visits 2 catheters will be inserted in the antecubital vein of the
lower arms. On one study day (randomly assigned)
a set of microcirculation measurements will be performed on t=-90 minutes. On
all three study days insulin and glucose will be infused on t=0 min. After 90
minutes of HEC a set microcirculation measurements will be done, and after
these measurements placebo, irbesartan or felodipine will be taken in a single
oral dose. 210 minutes after intake (t=300 min.) another set of
microcirculation measurements will be done. During the study days the heart
rate and blood pressure will be monitored and blood samples will be taken.
The interventions will be randomly assigned. One week is scheduled between each
visit.

Amendement:
All subjects will bring two visits to the AZM.
On the study day with intake of irbesartan the measure and time-course of
angiotensin II AT1-receptor blockade will be measured. Two catheters will be
inserted in the antecubital vein of the lower arms (Venflon; B-D, Helingborg,
Zweden). Three bloodsamples of 5 ml will be taken to measure basal subject
characteristics, the plasma angiotensin II and active plasma renin
concentrations (APRC). After 30 minutes, blood presure and heart rate will be
measured. Next, the dose response-curve to Angiotensin II will be measured.
Angiotensin II will be infused intravenously in increasing dose steps
(angiotensin II is previously incjected intravenously in MEC 06-2-074). Next,
irbesartan will be ingested in a single oral dose of 600 mg. 120 and 180
minutes after ingestion the dose-response curves to Angiotensin II will be
measured again. Blood pressure and heart rate will be measured 30, 60, 90, 120,
150 and 180 minutes after intake of irbesartan. 60, 120 and 180 minutes after
intake 2 bloodsamples of 5 ml will be taken from the katheter in the dominant
arm. The total amount of blood taken is 45 ml. This studyday will take
approximaltely 4,5 hours.

On the studyday with intake of felodipine blood pressure and heart rate will be
measured on the same timepoints as in the studyday with irbesartan (before the
intake of felodipine and 30, 60, 90, 120, 150, and 180 min. after intake). No
dose-response curves will be measured. This study day will take approx. 4
hours.

At least 24 hours will be scheduled these two study days. The intake of
irbesartan and felodipine will be randomised. All subjects fasted from 10pm the
night before each study day.

Main study:
Hypertensive subjects will be asked to discontinue the intake of
antihypertensive medi-cation three weeks before the start of the study. All
subjects will be asked to start a low salt diet (100mmol/day) 7 days prior to
the first study day and to collect urine during 24hrs prior to the first study
day. Microcirculation measurements: 1) perfused capillary density and
functional capillary recruitment in the nailfold, visualized by a capillary
mi-croscope, 2) endothelium- (in)dependent vasodilation of finger skin
microcirculation, evaluated with laser Doppler measurements in combination with
iontophoresis of acetylcholine and sodium nitroprusside, and 3) densities and
diameter of arterioles, capillaries and venules in the bulbar conjunctiva,
measured with conjunctival microscopy. Placebo, irbesartan (600mg) and
felodipine (20mg) will be ingested orally in a single dose. Insulin is infused
in a primed continuous manner at a rate of 50mU·kg-1·hr-1. Euglycemia will be
maintained by adjusting the rate of a 20% D-glucose infusion based on plasma
glucose measurements performed at 5 min intervals. During the visit several
blood samples will be taken, blood pressure and heart rate will be monitored.

Amendement:
Angiotensin II will be intravenously infused to measure the dose-response
curve. During a study day 45 ml of blood will be taken (sampled at 4 timepoints
in the day). Blood pressure and heart rate will be monitored. Irbesartan
(600mg) and felodipine ER (20mg) will be taken orally. All subjects will be
asked to start a low salt diet (100mmol/day) 7 days prior to the first study
day and to collect urine during 24hrs prior to the first study day.

Main Study:
No risks are involved in discontinuing the medication of the hypertensive
subjects. All methods used for measuring
microcirculation are non-invasive. The burden of these measurements is
therefore negligible. Inserting the catheters can be a little bit painful and
after removal sometimes bruises can appear. There is a small chance (<1.0%)
hypoglycemia will occur during the infusion of insulin and glucose. This can
feel slightly unpleasant for the subject, however hypoglycemia is not harmful.
Irbesartan and felodipine will be taken orally in a single dose. The dosages
are not toxic and the expected reduction in blood pressure will not induce
problems concerning hypotension. Due to the intake of a single dose of
irbesartan and felodipine there is only a very small chance for side effects to
occur. The used dose of acetylcholine and sodium nitroprusside is very low and
appeared to have side effects only in very rare cases (for example during an
allergic reaction). The effect is only local in the skin an whenever a side
effect will occur, the study will be immediately stopped. There will be taken
84 ml of blood during one study day. No burden or risk is involved with this
amount. De subject will be sober during the whole study day. Previous studies
showed that this isn't a big burden for a subject.

Amendement:
Inserting the catheters can be a little bit painful and after removal sometimes
bruises can appear. There are no expected risks involved to the infusion of
Angiotnsin II, the blood pressure will be monitored continuously. Irbesartan
and felodipine will be taken orally in a single dose. The dosages are not toxic
and the expected reduction in blood pressure will not induce problems
concerning hypotension. Due to the intake of a single dose of irbesartan and
felodipine there is only a very small chance for side effects to occur. There
will be taken 40 ml of blood during one study day. No burden or risk is
involved with this amount. De subject will be sober during the whole study day.
Previous studies showed that this isn't a big burden for a subject.