Chymase-dependent angiotensin II (Ang II) forming system in humans

AJH-APRIL 1995-VOL.8, NO.4,PART 2

28A ASHABSTRACTS

Saturday,5/20, Trlanc-:,n Ballroom, 3:00 pm-S:OO pm Theme I: Angiotensin-DependentMechanisms in Hypertension

Saturday, 5/20, liianon Ballroom, 3:00 pm-5:00 pm Theme I: Angiotensin-Dependent Mechanisms in Hypertension

ANGIOTENSIN " INFLUENCES ON RENAL FUNCTION IN HYf'lERTENSIVE REN-2TAANSGENIC RATS. K.D. Mitchell and J.J.

Angiotcnsin-(1·7). A Novel Hormone of the RAS. Carlos M. Ferrario, K. Bridget. Brosnihan, E. Ann Tallant and Debra I. Diz. Hypertension Center, Bowman Gray School of Medicine, Winston-Salem, North Carolina.

Mullins. Tulane University School of Medicine, New Orleans. LA 70112, and University Of Edinburgh, Edinburgh, Scotland. The hypertensive rat strain transgenIc for themouse ren·2 renin gene[TGR.: strain name TGR(mRen2)27] represents B genellcally well-defined model of hypertension. However, the mechanIsms responsible for the hypertension thatoccurs as a consequence of expression ofthe ren·2 transgene remain unclear as both plasma

Key Words: Hypertension, an9~:Jensln 11, renal hemodynamics, tubuloglomerular feadback, AT, reteptors, transgenic rat

Angiotenshi-(l-7) [Ang-(l-7)] contributes to the regulation of bloodpressure by opposing the actionsof angiotensin II (Ang' 11). Ang-(1·7) is generated by cleavage of the Pro1_ Phel bond of either Ang I or Ang II by tissue endopeptidases. AlthoughAng-(1-7) is as potent as Ang II in stimulatingthe secretion of vasopressin, it behaves as a vasodilator and natriuretic agent by augmenting prostacydinsecretion. In keeping with this interpretation, Ang-(l-7) lowered the blood pressure of SHR. Further evidence for separate functions of Ang II and Ang-(1-7) were obtainedin cultures of vascular smooth muscle cells. In this preparation, Ang-(l-7) inhibited thymidine incorporation, whereas Ang II had the opposite effect. In transgenic hypertensive rals HmRen·2)27} hypothalami : levels of Ang II and Ang-(1-7) were lO-fold and 6-fohi higher, respecuvely, than in age-matched normotensive SD rats. Increased content of brain angiotensins was associated with central desensitization of angiotensin receptors. In transgenic rats, ICV injection of a specifk , affinity purified Ang-(l-7) antibody caused marked elevations in blood pressure and heart rate, whereas comparable injections of a monoclonal Ang Il antibody produced hypotension and bradycardia. In summary, ....ur data suggest that Ang-(l-7) may act as a negative feedback regulatorofAng IIactivity. Key Words: renin-angiotensin system, blood pressure, transgenic rats, angiotensin

Saturday,5/20, 'Ilianon Ballroom, 3:00 pm-5:00 pm Theme I: Angiotensin-Dependent Mechanisms in Hypertension

Saturday,5/20, Trianon Ballroom, 3:00 pm-5:00 pm Theme I: Angiotensin-Dependent Mechanismsin Hypertension

and kidney renin levels have been shown 10 be suppressed In hypertensive TGR. We recently demonstratad that both whole kidney andsingle nephron hemod}'namlc functIon In 7 to 9 week-

old hypertensive TGR are wlthfn the normal range, and thatthose rats have an Intact tubuloglomerular feedback mechanIsm. In theseexperiments, Intravenous admInistration of en AT, receptor antagonist (1.-158,809) decraased mean al1erlaJ blJod pressure by more than 50 mmHg. Although glomerular flltratlon rata was reduc~ by 31% following AT, recepto; blockade, renal plasma flow remained unaltered. Systemic adminIstration of L·158,809 also attenuated the magnitude ofthe maxImal stop-llow pressure (SFP) tubuloglomerular feedback response by 84%. In addnronal studies, peritubular capillary Infusion of the AT, receptor anlagonl13t, losartan, at a ratethatdid not aner mean arterial blood pressure, attenuated Ihemagnnude ofthe maximal SFP feedback response by46%. These datademonstrate thataetlvalion ofAT, receptors by ANG Ills largely responsible for the hypertension In TGR, and 'ndicate thatANG II, acting via AT, receptors, elC~rts a pronounced stimulatory Influence on 1ubuloglomerular feedback respontMmes:oln hypertensive TGR. SuchANG lI-dependency of feedback responsiveness mIght cOnlribute to an lnabllity of the kidney to maintain normal rates of sodium excretion at normotensive pressures and thereby to the development and maIntenance of hypertension In this model.

Chymase-Dependent

Angiotens~n

II (Ang II)

Forming System in Humans

Hidenori Urata, Max-Delbruck-Centre for Molecular Medicine (MDC), Berlin-Buch, Germany Recent studies have provided evidence that the human heart contains components of the renin-angiotensin system; renin, angiotensinogen, angiotensin l-converting enzyme (ACE), andAngII receptors, In additionto ACE, a cardiac Ang II forming serine proteinase (human heart chymase) has beenidentified in the human left ventricle. Unlike rat heart, only a minor(10%) component of Ang n forlning activity in the human left ventricle was due to ACE, whereas the majority (80%) of activity was due to ch,mase. Human heart chymase has been purified to homogeneity 'and characterized. Recently, thecDNA and gene for this enzyme have been cloned. Biochemical characterization revealed that heartchymase is the most efficient and specific Ang II forming enzyme described thus far. However, the cellular and regional distribution of ACE andheart chymase seems to bedifferent in heartas well as in systemic organs, implying distinct pathophysiological roles of the two Ang II forming enzymes. Several reports indicate that ACE-independent Ang 11 formation appeared to take place in vivo and is involved in an ischemic damage of cardiovascular organs as well as in neointimal formation after vascular injury. Therefore, it has became quiteimportant to understand the detailed mechanisms of the tissue Ang II formation in humans and its contribution to the pathophysiological changes incardiovascular diseases.

Key Words: cardiac angiotensin IT system, angiotensin I-converting enzyme, human chymase, cardiac function, cardiovascular disease

Mechanisms or Angiotensin 11 Mediated Intracellufar Signaling. K. Bernstein, M. Marrero, B. Schieffer, W. Paxton. Dept. of Pathology, Emory Unlv., Atlanta, GA. 30322 How do seven transmembrane receptors such as the AT, receptor signal? Most scientists would answer this question by evoking thecritical role GTP hinding proteins (G proteins) play in the signalling process. Recently, our laboratory has found that many aspects of intracellular signalling mediated by the AT1 receptor depend on intracellular phosphorylation. We examined the abilily of Ang II 10 regulate theenzymatic activily of phospholipase C (PLC) in rat aortic vascular smooth muscle cells (VSMC). In these cells Ang II stimulated PLC-}'l tyrosine phosphorylation with a maximum increase of 4.5-fold at 0.5 min. This followed thesame time course as the Ang II stimulated increase in inositol l,4,5-trisphosphate (l,4,5-IP~) levels. 1,4,S-IP3 formation was inhibited 75% bythe tyrosine kinase inhibilor genistein. These data show that Ang II stimulates VSMr: phosphoinositide hydrolysis in association with tyrosine phosphorylation of PLC-}'l and support the concept that Ang II stimulated tyrosine phosphorylation is responsible for early signal transduction events. Antibodies to c-src were introduced into VSMC by electropermeabilizatlon, Angiotensin II stimulated tyrosine phosphorylation of phospholipase C-yl was eliminated by the anti-src antibodies but not by control sera. Angiotensin II induces the rapid tyrosine phosphorylation of ppl20, a known c-src kinase substrate. This phosphorylation is also specifically inhibited by anti-c-src antibodies. These dataprovide the first evidence for a direct involvement of c-srckinase in angiotensin II mediated PLe-}'l phosphorylation and activation. Key Words :angiotensin II, phospholipase C, src, smooth muscle cells