Activated coagulation Factor XII (FXIIa) elevates blood pressure (BP) acutely by stimulating adrenomedullary catecholamine (CA) release in Brown Norway (BN) bioassay rats. These effects are absent in kininogen-deficient BN Katholiek (BNK) bioassay rats, indicating that these FXIIa-induced responses require an intact kallikrein-kinin system (KKS). In three hypertensive anephric pediatric patients, ΔFXIIa concentrations tracked peri-dialytic ΔBP. We hypothesized that FXIIa exerts a vasoconstrictor pro-hypertensive action, via the KKS, particularly evident in chronic renal failure (CRF). In CRF patients (n=11) receiving conventional hemodialysis, mean plasma FXIIa concentrations were 3-fold (p<0.05) greater than in healthy controls. Although conversion from conventional to nocturnal hemodialysis did not change mean FXIIa concentrations there was intra-session variation within individuals, such that ΔFXIIa concentrations correlated with changes in mean arterial pressure (MAP, r=0.66, p=0.026) and total peripheral resistance (TPR, r=0.75, p=0.007). In normotensive BN rats, FXIIa infusion (85 ng/min/kg for 60 mins) increased MAP (10±1 mmHg), TPR (0.5±0.1 Units), and CA, whilst left-ventricular end-diastolic volume (LVEDV) and heart rate decreased (all p<0.05). After adrenalectomy, FXIIa infusion decreased MAP (5±1 mmHg), did not raise CA or induce sustained vasoconstriction, and caused a greater fall in LVEDV (all p<0.05). In the 5/6 nephrectomized (NX) rodent CRF model, MAP and TPR were significantly greater in BN NX (n=16) than in BNK NX (n=15) (147±4 vs. 133±2 mmHg, 2.8±0.2 vs. 2.3±0.2 Units; all p<0.05). Plasma FXIIa measured using our semi-quantitive ELISA was 3-fold higher in both BN NX and BNK NX than in controls (p<0.01), but only correlated with MAP (r=0.48, p=0.01) in the BN NX. Plasma CA were elevated in the BN NX (p<0.05) but not in BNK NX. Infusion of a specific FXIIa inhibitor into BN NX decreased MAP (-12 mmHg) and TPR (-0.5 Units) proportionally to baseline FXIIa (ΔMAP: r=-0.72, p=0.002; ΔTPR: r=-0.57, p=0.021), and plasma CA fell by 40-67% (all p<0.05). No such changes occurred in the BNK NX. In summary, a significant component of the hypertension of CRF can be attributed to FXIIa-induced vasoconstriction mediated via the KKS and stimulated CA release. In normal rats, FXIIa appears also to directly or indirectly decrease preload and heart rate.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/29835 |
| Date | 31 August 2011 |
| Creators | Papageorgiou, Peter Christopher |
| Contributors | Floras, John |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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