Angiotensin II is involved in nitric oxide synthase and cyclo-oxygenase inhibition-induced leukocyte-endothelial cell interactions in vivo

Abstract

1. Chronic inhibition of nitric oxide synthase (NOS) provokes a hypertensive state which has been shown to be angiotensin II (Ang-II) dependent. In addition to raising blood pressure, NOS inhibition also causes leukocyte adhesion. The present study was designed to define the role of Ang-II in hypertension and in the leukocyte-endothelial cell interactions induced by acute NOS or cyclo-oxygenase (COX) inhibition using intravital microscopy within the rat mesenteric microcirculation. 2. While pretreatment with an Ang-II AT(1) receptor antagonist (losartan) reversed the prompt increase in mean arterial blood pressure (MABP) caused by indomethacin, it had no effect on the increase evoked by systemic L-NAME administration. 3. Pretreatment with losartan inhibited the leukocyte rolling flux, adhesion and emigration which occurs after 60 min NOS inhibition by 83, 80 and 70% respectively, and returned leukocyte rolling velocity to basal levels. 4. Losartan significantly reduced the leukocyte-endothelial cell interaction elicited by COX inhibition. In contrast, leukocyte recruitment induced by acute mast cell activation was not inhibited by losartan. 5. AT(1) receptor blockade also prevented the drop in haemodynamic parameters such as mean red blood cell velocity (V(mean)) and shear rate caused by NOS and COX inhibition. 6. In this study, we have demonstrated a clear role for Ang-II in the leukocyte-endothelial cell interactions and haemodynamic changes which arise in the absence of NO or prostacyclin (PGI(2)). This is of interest since leukocyte recruitment, which culminates in the vascular lesions that occur in hypertension, atherosclerosis and myocardial ischemia-reperfusion injury, might be prevented using AT(1) Ang-II receptor antagonists.

Figure 1

Effects of losartan (10 mg kg⁻¹, i.v.) on mean arterial blood pressure (MABP) in anaesthetized rats treated with L-NAME (10 mg kg⁻¹, i.v.) (a) or with indomethacin (20 mg kg⁻¹, i.v.) (b). Results are expressed as percentage of basal values. Each point and bar represent the mean±s.e.mean of n=4 – 6 animals per group. ^*P<0.05 or ^**P<0.01 relative to the control value (0 min) in the untreated group. ⁺P<0.05 or ⁺⁺P<0.01 relative to the untreated group.

Figure 2

Effect of losartan pretreatment on L-NAME-induced leukocyte rolling flux (a), leukocyte adhesion (b) and leukocyte emigration (c) in the rat mesenteric postcapillary venules. The mesentery was superfused with bicarbonate-buffered saline. Baseline parameters (0 min) were determined after a 30 min stabilization period. The superfusion buffer was then supplemented with L-NAME (100 μM). Parameters were measured 15, 30 and 60 min after superfusion with L-NAME in animals untreated (n=5) or pretreated with losartan (10 mg kg⁻¹, n=5). Results are presented as mean±s.e.mean. ^*P<0.05 or ^**P<0.01 relative to the control value (0 min) in the untreated group. ⁺P<0.05 or ⁺⁺P<0.01 relative to the untreated group.

Figure 3

Effect of losartan pretreatment on indomethacin-induced leukocyte rolling flux (a), leukocyte adhesion (b) and leukocyte emigration (c) in the rat mesenteric postcapillary venules. Parameters were determined at 0, 15, 30 and 60 min after indomethacin (25 μg ml⁻¹) superfusion in animals untreated (n=5) or pretreated with losartan (10 mg kg⁻¹, i.v., n=5). Results are presented as mean±s.e.mean. ^*P<0.05 or ^**P<0.01 relative to the control value (0 min) in the untreated group. ⁺P<0.05 or ⁺⁺P<0.01 relative to the untreated group.

Figure 4

Effect of losartan treatment on CMP 48/80-induced leukocyte rolling flux (a), leukocyte adhesion (b) and leukocyte emigration (c) in rat mesenteric postcapillary venules. After the 30 min stabilization period, baseline values were determined (0 min). Parameters were measured 15, 30 and 60 min after superfusion with CMP 48/80 (1 μg ml⁻¹) in animals untreated (n=4) or pretreated with losartan (10 mg kg⁻¹ i.v., n=4). Results are represented as mean±s.e.mean. ^*P<0.05 or ^**P<0.01 relative to the control value (0 min) in the untreated group.