Background There is indirect evidence that nitric oxide (NO) synthesis
in vascular endothelium of patients with hypertension is altered. The
aim of this study was to estimate more directly NO production in pati
ents with untreated essential hypertension by measurement of synthesis
of inorganic nitrate, which is the end product of NO oxidation in hum
ans. Two separate studies were undertaken in patients with hypertensio
n and appropriate healthy controls.(1) Methods In the first study, ten
patients and 13 controls were given a diet containing 82 mu moles nit
rate per day for 2 days, with urinary and plasma nitrate measurement a
nd 24 h ambulatory blood pressure monitoring on the 2nd day. In the se
cond study, 11 patients and 11 controls were studied in the postabsorp
tive state; a bolus of 200 mg L-[N-15](2) arginine was administered in
travenously over 10 min. 24 h ambulatory blood pressure monitoring was
done and complete urine collections were made for the next 36 h. Find
ings In the first study, 24 h urinary nitrate excretion was lower in t
he hypertensive patients than in the control group (mean 450 [SEM 37]
vs 760 mu moles [77] per 24 h; p<0001). There was an inverse correlati
on between average mean daytime ambulatory blood pressure and nitrate
excretion (p=0.007; r(2)=-0.73). In the second study, mean 36 h urinar
y N-15 nitrate excretion was significantly lower in the hypertensive t
han in the control group (1313 [50] vs 2133 [142] pmoles; p<0.001). Th
ere was an inverse correlation also between average mean daytime ambul
atory blood pressure and 24 h urinary N-15 nitrate excretion expressed
per mmole of creatinine (p=0.002, r(2)=-0.59). In addition, total uri
nary N-15 nitrate excretion in the hypertensive group was significantl
y higher in women than in men (285 [16] vs 198 [14] mu g N-15 nitrate
per kg; p=0.026). Interpretation These data suggest that whole-body NO
production in patients with essential hypertension is diminished unde
r basal conditions. The origin of the NO we measured is not known, and
we cannot tell whether the impaired synthesis is primary or secondary
to a rise in blood pressure.