CIRCULATING LEUKOCYTE COUNTS, ACTIVATION, AND DEGRANULATION IN DAHL HYPERTENSIVE RATS

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.