Previous evidence has shown that rats with spontaneous hypertension ha
ve on average about twice as many circulating leukocytes in comparison
with their normotensive counterparts, the Wistar-Kyoto rats. Since su
ch high levels of leukocytes may increase the risk for vascular compli
cations for hypertensive animals, it is useful to ascertain whether a
comparable derangement is present in other forms of hypertension. The
present study deals with the properties of the circulating leukocytes
in rats exhibiting another form of experimental hypertension; Dahl sal
t-sensitive (Dahl-S) hypertensive rats were compared with Dahl salt-re
sistant (Dahl-R) control rats. Measurements were performed to determin
e the following: circulating hematocrit levels, leukocyte counts, diff
erential counts, number of activated leukocytes (by means of nitro blu
e tetrazolium [NBT] reduction), leukocyte adhesion in vitro and neutro
phil CD-18 expression, alkaline phosphatase activity in individual neu
trophils and in the plasma, and myeloperoxidase activity in neutrophil
s. The experimental cohort consisted of Dahl-S and Dahl-R rats maintai
ned for a 6-week period on a 6% NaCl diet. The results show a highly s
ignificant elevation in the number of total leukocytes, neutrophil and
monocyte counts, and NBT-positive neutrophils and monocytes in Dahl-S
but not Dahl-R rats. There was a significant loss of alkaline phospha
tase and myeloperoxidase activity in the neutrophils of the salt-treat
ed Dahl-S rats but not in the neutrophils of the untreated Dahl-S or D
ahl-R rats. No significant differences were found in neutrophil adhesi
on under in vitro test conditions between the two strains maintained o
n the salt diet. In salt-treated Dahl-S rats, there was a reduced expr
ession of beta(2) integrins (CD-18) in neutrophils, although a higher
fraction of the circulating neutrophils exhibited above-threshold CD-1
8 expression. These results indicate an increased number of circulatin
g neutrophils and monocytes in Dahl-S rats that are in an activated st
ate and undergo spontaneous degranulation in the circulation without e
xhibiting elevated levels of membrane adhesive properties. Such circul
ating leukocyte kinetics may contribute to a range of vascular complic
ations in the hypertensive rats.