Primacy of angiotensin converting enzyme in angiotensin-(1-12) metabolism

Abstract

Angiotensin-(1-12) [ANG-(1-12)], a new member of the renin-angiotensin system, is recognized as a renin independent precursor for ANG II. However, the processing of ANG-(1-12) in the circulation in vivo is not fully established. We examined the effect of angiotensin converting enzyme (ACE) and chymase inhibition on angiotensin peptides formation during an intravenous infusion of ANG-(1-12) in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). WKY and SHR were assigned to a short ANG-(1-12) infusion lasting 5, 15, 30, or 60 min (n = 4-10 each group). In another experiment WKY and SHR were assigned to a continuous 15-min ANG-(1-12) infusion with pretreatment of saline, lisinopril (10 mg/kg), or chymostatin (10 mg/kg) (n = 7-13 each group). Saline or lisinopril were infused intravenously 15 min before the administration of ANG-(1-12) (2 nmol·kg(-1)·min(-1)), whereas chymostatin was given by bolus intraperitoneal injection 30 min before ANG-(1-12). Infusion of ANG-(1-12) increased arterial pressure and plasma ANG-(1-12), ANG I, ANG II, and ANG-(1-7) levels in WKY and SHR. Pretreatment with lisinopril caused increase in ANG-(1-12) and ANG I and large decreases in ANG II compared with the other two groups in both strains. Pretreatment of chymostatin had no effect on ANG-(1-12), ANG I, and ANG II levels in both strains, whereas it increased ANG-(1-7) levels in WKY. We conclude that ACE acts as the primary enzyme for the conversion of ANG-(1-12) to smaller angiotensin peptides in the circulation of WKY and SHR and that chymase may be an ANG-(1-7) degrading enzyme.

Keywords: angiotensin I; angiotensin II; angiotensin converting enzyme; angiotensin-(1–12); angiotensin-(1–7); blood pressure; chymase; hypertension.

Fig. 1.

Peak plasma ANG-(1–12) concentrations produced by intravenous infusion of vehicle (saline) or the dodecapeptide at doses between 0.2 and 200 nmol·kg⁻¹·min⁻¹.

Fig. 2.

Plasma ANG-(1–12), ANG I, ANG II, and ANG-(1–7) levels measured in Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) infused with ANG-(1–12) (2 nmol·kg⁻¹·min⁻¹) at the completion of 0, 5, 15, 30, and 60 min of peptide administration. Values are means ± SE.

Fig. 3.

Top: changes in Δmean arterial pressure (ΔMAP) induced by the continuous infusion of ANG-(1–12) (2 nmol·kg⁻¹·min⁻¹) in WKY (top left) and SHR (top right) pretreated with saline, lisinopril, and chymostatin. Bottom: area under the curve (AUC) of ΔMAP in ANG-(1–12)-infused WKY (bottom left) and SHR (bottom right) pretreated with saline, lisinopril, and chymostatin. Values are means ± SE.

Fig. 4.

Plasma ANG-(1–12), ANG I, ANG II, and ANG-(1–7) levels found at the completion of a 15-min infusion of ANG-(1–12) (2 nmol·kg⁻¹·min⁻¹) in WKY and SHR pretreated with saline, lisinopril, or chymostatin. Values are means ± SE. *P < 0.05 vs. corresponding saline; **P < 0.01 vs. corresponding saline; ***P < 0.001 vs. corresponding saline; †P < 0.05 vs. corresponding lisinopril; ††P < 0.01 vs. corresponding lisinopril; †††P < 0.001 vs. corresponding lisinopril.

Fig. 5.

The ratio of ANG I to ANG-(1–12), ANG II to ANG-(1–12), ANG II to ANG I, and ANG-(1–7) to ANG II found at the completion of a 15-min infusion of ANG-(1–12) (2 nmol·kg⁻¹·min⁻¹) in WKY and SHR pretreated with saline, lisinopril, or chymostatin. Values are means ± SE. **P < 0.01 vs. corresponding saline; ***P < 0.001 vs. corresponding saline; ††P < 0.01 vs. corresponding lisinopril; †††P < 0.001 vs. corresponding lisinopril.