Role of bradykinin B2-receptor in the sympathoadrenal effects of ???new pressor protein??? related to human blood coagulation factor XII fragment

The effects of two types of renin-angiotensin system inhibitors on the hypertension induced by new pressor protein associated with beta-factor XIIa in rats

Background and purpose:

New pressor protein (NPP) is a human plasma enzyme, which is structurally related to the beta-fragment of activated factor XII. The present study aimed to compare the effects of angiotensin converting enzyme inhibitors (captopril) and angiotensin type 1 receptor blocker (losartan) on the hypertension induced by NPP injection in normal (sham-2NX) and bilaterally nephrectomized rats (2NX).

Experimental approach:

In total, 60 male Wistar rats were sham operated or bilaterally nephrectomized under anesthesia. After 24 h of anesthesia with Inactin® (100 mg/kg), their systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were measured before and after the intravenous administration of captopril, losartan, and NPP.

Findings / Results:

In the sham-2NX group, after NPP injection, changes were observed in SBP (145.99 ± 3.6 mmHg), DBP (93.9 ± 3.87 mmHg), and HR (400.29 ± 12.78 bpm). In the captopril group, SBP and DBP had no significant changes, while HR increased significantly (P = 0.001). In the losartan group, SBP and DBP decreased (P = 0.001 and P = 0.000, respectively), while HR had no significant changes. In the 2NX group, after NPP injection, changes were denoted in SBP (127.89 ± 9.03 mmHg), DBP (65.86 ± 5.69 mmHg), and HR (333.35 ± 11.47 bpm). In addition, captopril injection increased DBP (P = 0.016) and HR (P = 0.036) in response to NPP injection, while losartan injection had no significant effects in this regard.

Conclusion and implications:

It could be concluded that losartan could improve hypertension in normal rats, while captopril deteriorated hypertension in bilaterally nephrectomized rats in this hypertension model.

Activated plasma coagulation β-Factor XII-induced vasoconstriction in rats

By inducing BK (bradykinin)-stimulated adrenomedullary catecholamine release, bolus injection of the β-fragment of activated plasma coagulation Factor XII (β-FXIIa) transiently elevates BP (blood pressure) and HR (heart rate) of anaesthetized, vagotomized, ganglion-blocked, captopril-treated bioassay rats. We hypothesized that intravenous infusion of β-FXIIa into intact untreated rats would elicit a qualitatively similar vasoconstrictor response. BN (Brown Norway) rats received for 60 min either: (i) saline (control; n=10); (ii) β-FXIIa (85 ng/min per kg of body weight; n=9); or (iii) β-FXIIa after 2ADX (bilateral adrenalectomy; n=9). LV (left ventricular) volume and aortic BP were recorded before (30 min baseline), during (60 min) and after (30 min recovery) the infusion. TPR (total peripheral resistance) was derived from MAP (mean arterial pressure), SV (stroke volume) and HR. Saline had no haemodynamic effects. β-FXIIa infusion increased its plasma concentration 3-fold in both groups. In adrenally intact rats, β-FXIIa infusion increased MAP by 6% (5±2 mmHg) and TPR by 45% (0.50±0.12 mmHg/ml per min), despite falls in SV (−38±8 μl) and HR [−18±5 b.p.m. (beats/min)] (all P<0.05). In 2ADX rats, β-FXIIa had no HR effect, but decreased SV (−89±9 μl) and MAP (−4±1 mmHg), and increased TPR by 66% (0.59±0.15 mmHg/ml per min) (all P<0.05). After infusion, adrenally intact rats exhibited persistent vasoconstriction (MAP, 10±1 mmHg; TPR, 0.55±0.07 mmHg/ml per min; both P<0.05), whereas in 2ADX rats, MAP remained 5±1 mmHg below baseline (P<0.05) and TPR returned to baseline. End-study arterial adrenaline (epinephrine) concentrations in the three groups were 1.9±0.6, 9.8±4.1 and 0.6±0.2 nmol/l respectively. Thus, in neurally intact lightly anaesthetized untreated rats, β-FXIIa infusion induces both adrenal catecholamine-mediated and adrenally independent increases in peripheral resistance.

Angiotensin converting enzyme-regulated, noncholinergic sympathoadrenal catecholamine release mediates the cardiovascular actions of human 'new pressor protein' related to coagulation beta-factor XIIa

BACKGROUND

Human 'new pressor protein' (NPP), related to coagulation beta-factor XIIa (beta-FXIIa), potently releases sympathoadrenal catecholamines in bioassay rats, with concurrent elevation of systolic and diastolic blood pressure (SBP/DBP) and heart rate (HR). Elevated plasma NPP/beta-FXIIa levels in hypertensive anephric pediatric patients on hemodialysis associated with fluid status and blood pressure changes were previously reported, suggesting that NPP/beta-FXIIa contributed to their hypertension.

OBJECTIVE

To investigate the mechanism of action of NPP/beta-FXIIa.

METHODS

Hemodynamic and sympathoadrenal responses to NPP (20 microL plasma equivalent/rat) or coagulation beta-FXIIa (300 ng/kg intravenously) were measured in rats treated with pentolinium (ganglion blockade [+GB]) and/or captopril (+CAP; angiotensin converting enzyme [ACE] inhibition).

RESULTS

In controls not receiving GB or CAP (-GB-CAP), NPP/beta-FXIIa raised plasma epinephrine (E) sixfold, SBP/DBP by 14/8 mmHg and HR by 15 beats/min. With blockade of the cholinergic pathway to the sympathoadrenal system (+GB), basal E, norepinephrine (NE), SBP, DBP and HR all dropped. However NPP/beta-FXIIa remained capable of raising E 20-fold, NE fourfold, SBP/DBP by 27/11 mmHg and HR by 20 beats/min, suggesting that it acted through a 'noncholinergic' mechanism. With +CAP alone, NPP/beta-FXIIa raised plasma E 18-fold, NE threefold, SBP/ DBP by 29/8 mmHg and HR by 73 beats/min, implicating an ACE-regulated 'peptidergic' mechanism. Combining +GB with +CAP potentiated NPP/beta-FXIIa actions further by raising E 50-fold, NE sevenfold, SBP/DBP by 55/20 mmHg and HR by 87 beats/min, strengthening the efficacy of this alternate pathway.

CONCLUSIONS

The cardiovascular effects of NPP/beta-FXIIa are considerably mediated by a noncholinergic (peptidergic) ACE-regulated mechanism for sympathoadrenal catecholamine release that is enhanced by +GB and/or +CAP. Under inflammatory procoagulant conditions, endogenously produced NPP/beta-FXIIa may interfere with the antihypertensive effects of ACE inhibition therapy.