Angiotensin-(1-12) is an alternate substrate for angiotensin peptide production in the heart

Abstract

Identification of angiotensin-(1-12) as an intermediate precursor derived directly from angiotensinogen led us to explore whether the heart has the capacity to process angiotensin-(1-12) into biologically active angiotensin peptides. The generation of angiotensin I, angiotensin II, and angiotensin-(1-7) from exogenous angiotensin-(1-12) was evaluated in the effluent of isolated perfused hearts mounted on a Langendorff apparatus in three normotensive and two hypertensive strains: Sprague-Dawley, Lewis, congenic mRen2.Lewis, Wistar-Kyoto, and spontaneously hypertensive rats. Hearts were perfused with Krebs solution for 60 min before and after the addition of angiotensin-(1-12) (10 nmol/l). Angiotensin-(1-12) caused the rapid appearance of both angiotensin I and angiotensin II in the perfusate that peaked between 30 and 60 min of recirculation. Production of angiotensin-(1-7) from exogenous angiotensin-(1-12) rose steadily over the course of the 60-min experiment. These data directly demonstrate that angiotensin-(1-12) is a substrate for the formation of angiotensin peptides in cardiac tissue. This finding further suggests that this angiotensinogen-derived product is a previously unrecognized important precursor peptide to the renin-angiotensin system cascade.

Fig. 1.

ANG I, ANG II, and ANG-(1–7) production from exogenous ANG-(1–12) in isolated Sprague-Dawley (SD) rat hearts (n = 6). Both ANG I and ANG II peaked at 30 min of recirculation (ANG I: 191 ± 34 pmol/l and ANG II: 364 ± 81 pmol/l), whereas ANG-(1–7) steadily increased until 60 min of recirculation (97 ± 31 pmol/l). *P = 0.0003 and †P < 0.0001 vs. baseline.

Fig. 2.

ANG I, ANG II, and ANG-(1–7) production from exogenous ANG-(1–12) in isolated Lewis (A; n = 4) and mRen2.Lewis congenic (B; n = 4) rat hearts. ANG I peaked at 30 min of recirculation in both Lewis and congenic rat hearts (489 ± 112 and 625 ± 116 pmol/l, respectively), whereas both ANG II and ANG-(1–7) steadily increased until 60 min of recirculation [ANG II: 493 ± 190 (Lewis) and 628 ± 133 pmol/l (congenic) and ANG-(1–7): 126 ± 39 (Lewis), 96 ± 13 pmol/l (congenic)]. There were no statistical differences in any of the angiotensin peptides between Lewis and congenic rat hearts. *P < 0.01, †P < 0.001, and ‡P < 0.0001 vs. baseline.

Fig. 3.

ANG I (top), ANG II (middle), and ANG-(1–7) (bottom) production from exogenous ANG-(1–12) in isolated Wistar-Kyoto (WKY; left; n = 6) and spontaneously hypertensive rat (SHR; right; n = 6) hearts. ANG I and ANG II both peaked at 30 min of recirculation in both WKY and SHR hearts (ANG I: 676 ± 49 and 644 ± 68 pmol/l, respectively; and ANG II: 620 ± 139 and 808 ± 216 pmol/l, respectively), whereas ANG-(1–7) steadily increased until 60 min of recirculation [228 ± 58 (WKY) and 204 ± 54 pmol/l (SHR)]. There were no statistical differences in any of the angiotensin peptides between WKY and SHR hearts, nor did renin inhibition alter the production of any of the angiotensin peptides measured (represented by open circles and dotted lines). *P < 0.05 and †P < 0.01 vs. baseline.