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

Previous evidence has shown that rats with spontaneous hypertension have on average about twice as many circulating leukocytes in comparison with their normotensive counterparts, the Wistar-Kyoto rats. Since such high levels of leukocytes may increase the risk for vascular complications 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 salt-sensitive (Dahl-S) hypertensive rats were compared with Dahl salt-resistant (Dahl-R) control rats. Measurements were performed to determine the following: circulating hematocrit levels, leukocyte counts, differential counts, number of activated leukocytes (by means of nitro blue tetrazolium [NBT] reduction), leukocyte adhesion in vitro and neutrophil CD-18 expression, alkaline phosphatase activity in individual neutrophils and in the plasma, and myeloperoxidase activity in neutrophils. The experimental cohort consisted of Dahl-S and Dahl-R rats maintained for a 6-week period on a 6% NaCl diet. The results show a highly significant 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 phosphatase and myeloperoxidase activity in the neutrophils of the salt-treated Dahl-S rats but not in the neutrophils of the untreated Dahl-S or Dahl-R rats. No significant differences were found in neutrophil adhesion under in vitro test conditions between the two strains maintained on the salt diet. In salt-treated Dahl-S rats, there was a reduced expression of beta(2) integrins (CD-18) in neutrophils, although a higher fraction of the circulating neutrophils exhibited above-threshold CD-18 expression. These results indicate an increased number of circulating neutrophils and monocytes in Dahl-S rats that are in an activated state and undergo spontaneous degranulation in the circulation without exhibiting elevated levels of membrane adhesive properties. Such circulating leukocyte kinetics may contribute to a range of vascular complications in the hypertensive rats.