Angiotensin II stimulates migration of retinal microvascular pericytes: involvement of TGF-beta and PDGF-BB

We studied the promigratory effect of angiotensin II (ANG II) on cultured bovine retinal microvascular pericytes. ANG II stimulated migration of pericytes by 86% at 10(-8) M, but this effect was lost at 10(-4) M. Migratory responses were inhibited by the ANG II type 1 (AT(1)) receptor antagonist losartan but not by PD-123319, an AT(2) antagonist. Addition of PD-123319 to the 10(-4) M ANG II dose restored migratory responses. The promigratory effect of ANG II (10(-7) M) was reduced by 59% in absence of gradient. Although ANG II augmented the latent matrix metalloproteinase-2 (MMP-2) activity of the pericyte by 35%, it also doubled tissue inhibitors of MMPs. ANG II-induced migration was not altered by a broad-spectrum MMP inhibitor (GM6001); it was inhibited by ~50% by antibodies against transforming growth factor (TGF)-beta(1/2/3) and was abolished by antibodies against platelet-derived growth factor (PDGF)-BB. We conclude that ANG II induces chemotactic responses on retinal microvascular pericytes acting through the AT(1) receptor. This effect is opposed by the AT(2) receptor. ANG II-induced chemotaxis is mediated by PDGF-BB and involves TGF-beta, but it is independent of MMP activity. It is also independent of vascular endothelial growth factor (VEGF) because VEGF did not stimulate pericyte migration. ANG II can contribute to the regulation of retinal neovascularization by stimulating pericyte migration.

Cardiac interstitial bradykinin release during ischemia is enhanced by ischemic preconditioning

Ischemic preconditioning is known to protect the myocardium from ischemia-reperfusion injury. We examined the transmural release of bradykinin during myocardial ischemia and the influence of ischemic preconditioning on bradykinin release during subsequent myocardial ischemia. Myocardial ischemia was induced by occlusion of the left anterior descending coronary artery in anesthetized cats. Cardiac microdialysis was performed by implantation and perfusion of dialysis probes in the epicardium and endocardium. In eight animals, bradykinin release was greater in the endocardium than in the epicardium (14.4 +/- 2.8 vs. 7.3 +/- 1.7 ng/ml, P < 0.05) during 30 min of ischemia. In seven animals subjected to preconditioning, myocardial bradykinin release was potentiated significantly from 2.4 +/- 0.6 ng/ml during the control period to 23.1 +/- 2.5 ng/ml during 30 min of myocardial ischemia compared with the non-preconditioning group (from 2.7 +/- 0.6 to 13.4 +/- 1.9 ng/ml, P < 0.05, n = 6). Thus this study provides further evidence that transmural gradients of bradykinin are produced during ischemia. The results also suggest that ischemic preconditioning enhances bradykinin release in the myocardial interstitial fluid during subsequent ischemia, which is likely one of the mechanisms of cardioprotection of ischemic preconditioning.

Role of kinins in chronic heart failure and in the therapeutic effect of ACE inhibitors in kininogen-deficient rats

Using Brown Norway Katholiek (BNK) rats, which are deficient in kininogen (kinin precursor) due to a mutation in the kininogen gene, we examined the role of endogenous kinins in 1) normal cardiac function; 2) myocardial infarction (MI) caused by coronary artery ligation; 3) cardiac remodeling in the development of heart failure (HF) after MI; and 4) the cardioprotective effect of angiotensin-converting enzyme inhibitors (ACEI) on HF after MI. Two months after MI, rats were randomly treated with vehicle or the ACEI ramipril for 2 mo. Brown Norway rats (BN), which have normal kininogen, were used as controls. Left ventricular (LV) end-diastolic volume (EDV), end-systolic volume (ESV), end-diastolic pressure (EDP), and ejection fraction (EF) as well as myocardial infarct size (IS), interstitial collagen fraction (ICF), cardiomyocyte cross-sectional area (MCA), and oxygen diffusion distance (ODD) were measured. We found that 1) cardiac hemodynamics, function, and histology were the same in sham-ligated BN and BNK rats; 2) IS was similar in BN and BNK; 3) in rats with HF treated with vehicle, the decrease in LVEF and the increase in LVEDV, LVESV, LVEDP, ICF, MCA, and ODD did not differ between BNK and BN; and 4) ACEI increased EF, decreased LVEDV and LVESV, and improved cardiac remodeling in BN-HF rats, and these effects were partially blocked by the bradykinin B(2) receptor antagonist icatibant (HOE-140). In BNK-HF rats, ACEI failed to produce these beneficial cardiac effects. We concluded that in rats, lack of kinins does not influence regulation of normal cardiac function, myocardial infarct size, or development of HF; however, kinins appear to play an important role in the cardioprotective effect of ACEI, since 1) this effect was significantly diminished in kininogen-deficient rats and 2) it was blocked by a B(2) kinin receptor antagonist in BN rats.

Angiotensin II and retinal pericytes migration

Angiotensin II (Ang II) appears to participate in the regulation of neovascularization processes in the retina. Migration of perimural cells such as pericytes plays a key role in regulation of angiogenesis. We hypothesize that Ang II stimulates migration of retina pericytes. For this we studied the effects of Ang II on migration of bovine retinal pericytes using modified Boyden chambers and collagen IV-covered polyester membranes. Ang II stimulated migration of pericytes by 54.8 +/- 9.7% (n = 10, p < 0.001). This effect was blocked by an AT(1) receptor antagonist (Losartan) but not by an AT(2) receptor antagonist (PD123319). We determined using checkerboard assays (n = 3) that Ang II induces migration of pericytes by chemotaxis (gradient-dependent), in opposition to chemokinesis (nondirected). Thus, Ang II via its AT(1) receptor acts as a chemotactic factor and stimulates migration of retina microvascular pericytes. This effect may contribute to Ang II-induced regulation of neovascularization processes in the retina.

Role of kinins in the cardioprotective effect of preconditioning: study of myocardial ischemia/reperfusion injury in B2 kinin receptor knockout mice and kininogen-deficient rats

Kinins acting on the B2 receptor appear to be involved in the cardioprotective effect of preconditioning on myocardial ischemia/reperfusion injury. We tested the hypothesis that in mice lacking the gene encoding for the B2 kinin receptor (B2 knockout mice; B2-KO) as well as in rats deficient in high-molecular-weight (HMW) kininogen (Brown Norway Katholiek rats; BNK), the cardioprotective effect of preconditioning is diminished or abolished. 129SvEvTac (SV129) mice and Brown Norway rats (BN) served as controls. We confirmed that plasma HMW kininogen in BNK rats was 100-fold lower than in BN and 140-fold lower than in Sprague-Dawley rats (33+/-4 versus 1814+/-253 and 2397+/-302 ng/mL, P<.01). Each strain of mice was divided into (1) controls (without preconditioning); (2) one cycle of preconditioning (3 minutes ligation and 5 minutes reperfusion); and (3) three cycles of preconditioning. Each strain of rats was divided into (1) controls; and (2) three cycles of preconditioning. All animals were subjected to 30 minutes of ischemia and 120 minutes of reperfusion. In SV129 controls, the ratio of infarct size to risk area (IS/AR) was 55.6+/-4.6%. One and three cycles of preconditioning reduced IS/AR to 38.6+/-3.2% and 31.1+/-2.3%, respectively (P<.05 and P<.01 versus control). This protective effect was absent in B2-KO mice: IS/AR was 54.8+/-2.9% in controls, 58.5+/-3.6% with one cycle of preconditioning, and 58.5+/-3.4% with three cycles. In BN rats without preconditioning, IS/AR was 84.7+/-3.9%; preconditioning reduced it to 61.6+/-3.4% (P<.01). In BNK rats, IS/AR was 87.1+/-4.8% in controls and 84.3+/-4.1% with preconditioning. Preconditioning also prevented reperfusion arrhythmias in BN but not BNK rats. Within species, risk area, mean blood pressure, and heart rate were similar between strains. We concluded that (1) preconditioning protects the heart against ischemia/reperfusion injury in mice and rats; (2) activation of prekallikrein, which in turn generates kinins from HMW kininogen, may contribute to the effect of preconditioning; and (3) an intact kallikrein-kinin system is necessary for the cardioprotective effect of preconditioning.

Renal effects of Fab fragments of kinin antibodies on deoxycorticosterone acetate-salt-treated rats

The role of the renal kallikrein-kinin system in the regulation of renal function is not completely understood. Intrarenal kinins can influence renal function by acting as paracrine hormones at basolateral, luminal, or both sites in the distal nephron. To examine the role of intrarenal kinins in deoxycorticosterone acetate-salt-treated rats, which have high renal kallikrein, Fab fragments of antibradykinin antibody or DArg[Hyp3Thi5,8DPhe7]bradykinin, a kinin antagonist, were used to block kinins. At the dose used, the antibody (25 mg) and kinin antagonist (10 micrograms/min/rat) inhibited the hypotensive effect of intra-arterially injected bradykinin (100 ng) by 70% and 52%, respectively. The antibody appeared in the urine within 30 minutes after administration. Urinary volume was lowered from 9.4 +/- 0.2 to 6.7 +/- 0.4 microliters/min/g kidney wt (p less than 0.001, paired t test) by the antibody and from 8.5 +/- 0.3 to 6.8 +/- 0.4 microliters/min/g kidney wt (p less than 0.004, paired t test) by the kinin antagonist. The antibody lowered urine sodium excretion from 1.11 +/- 0.04 to 0.88 +/- 0.06 mueq/min/g kidney wt (p less than 0.001, paired t test), whereas the kinin antagonist had no significant effect. Neither altered blood pressure, renal blood flow, or glomerular filtration rate. These data suggest that in deoxycorticosterone acetate-salt-treated rats, excretion of water and sodium is regulated in part by kinins. The antidiuretic effect of the antibody and kinin antagonist might be due to blockade of kinins in the vascular-interstitial space of the kidney, since the kinin antagonist is likely hydrolyzed in the proximal tubule and does not reach the lumen of the distal nephron.(ABSTRACT TRUNCATED AT 250 WORDS)