(1) BP and placebo effect; (2)acute effect of 1,25-D on blood pressure

[Guest guest]

Rodney,

I'm sure you're aware of this, but there is a substantial role of

anxiety and placebo effect in BP readings. There is, for example, the

so-called " white coat effect " , where a patient will get his blood

pressure taken by a pretty young nurse or an intimidating doctor type,

and the BP type is 150/100. Then they go home and it's 120/80.

There's some controversy about whether higher BP readings in the

doctor's office that go down like this mean anything.

Anyway, just something to be aware of in your experiments. I would

take the BP 6 times, throw out the first two values, then throw out

the remaining highest and lowest values, and average the remaining two

readings (I assume it's free, this drugstore machine?).

You may think that you're not suggestible and are " stronger than the

placebo effect " , but this effect of mind over BP needs to be

respected. This is why most research, whenever possible, on BP is

done in a double-blind fashion. Most people will not consider a BP

study as being reliable if it was not done double-blind.

Now, in your defense, however, I did find a paper showing an acute

effect of 1,25 vitamin D (calcitriol) on blood pressure in patients

with essential hypertension, but not in controls. When you take

cholecalciferol, the liver makes it into 25-D, and then either blood

vessels, locally, or the kidneys, hydroxylate it a second time to make

1,25-D. Usually, after taking in low doses of cholecalciferol,

however, (< 1000 IU), the serum level of 1,25-D is unchanged. But...

who knows?

For what it's worth, here's the paper.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=9657624 & query_hl=3 & itool=pubmed_DocSum

Am J Hypertens. 1998 Jun;11(6 Pt 1):659-66.

comment in: Am J Hypertens. 1999 Mar;12(3):332.

Acute cardiovascular effect of 1,25-dihydroxycholecalciferol in

essential hypertension.

Jespersen B, Randlov A, Abrahamsen J, Fogh-Andersen N, Olsen NV,

Kanstrup IL. Department of Medicine, Herlev Hospital, University of

Copenhagen, Denmark.

A role for vitamin D in the pathophysiology of essential hypertension

has frequently been suggested, but acute direct effects on blood

pressure, cardiac output, renal hemodynamics, or hormones have not

previously been demonstrated. The rapid effects of

1,25-dihydroxycholecalciferol (1,25-D) were assessed over 120 min

after a bolus injection (0.02 microg/kg body weight) in eight men with

essential hypertension and in nine healthy men. A placebo group of 10

healthy men was also included. Ionized calcium was monitored closely

during the study, and was kept constant with a clamping technique. In

the hypertensive patients, a transient increase in blood pressure and

a reciprocal fall in cardiac output measured by a CO2 rebreathing

technique (-15%, P < .05) were observed after 1,25-D injection. In the

control group, both blood pressure and cardiac output remained

unchanged. The glomerular filtration rate, effective renal plasma

flow, and urinary sodium and water excretions were unchanged in both

groups. Plasma levels of atrial natriuretic peptide at baseline were

higher in the hypertensive patients than in the control subjects (P <

..02); plasma levels of renin, aldosterone, norepinephrine, endothelin,

and parathyroid hormone(1-84) were similar in the two groups. None of

these hormones was affected during the observation time after the

injection of 1,25-D. In conclusion, acute administration of 1,25-D

caused a fast and likely nongenomic-mediated decrease in cardiac

output in patients with essential hypertension, which together with a

transient BP increase implies a 1,25-D-induced increase in total

peripheral resistance. These data suggest an enhanced cardiovascular

responsiveness to 1,25-D in hypertensive compared to healthy

normotensive subjects.