RAMIPRILAT ATTENUATES HYPOXIA REOXYGENATION INJURY TO CARDIAC MYOCYTES VIA A BRADYKININ-DEPENDENT MECHANISM/

Isolated rat neonatal cardiac myocytes were subjected to immersion in hypoxic (PO2 < 2 mm Hg), glucose-free Tyrode's solution for 5 h follow ed by concomitant reoxygenation and staining with the membrane-imperme ant fluorophore, propidium iodide, in normoxic (PO2 > 150 mm Hg), seru m-free culture media for 15 min in order to assess sarcolemmal damage indicative of myocyte viability due to hypoxia/reoxygenation injury. P rior to hypoxic exposure, cells were pretreated for 90 min with the an giotensin-converting enzyme inhibitor cyclopenta[b]pyrrole-2-carboxyli c acid, pyl)amino]-1-oxopropyl]octahydro-[2S-[1[R(R*)](2) alpha, 3a b eta,6a beta]] (ramiprilat), concomitantly with ramiprilat and H-D-Arg- Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH (bradykinin B-2 receptor anta gonist HOE 140), the bioactive peptide Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe -Arg (bradykinin) or concomitantly with bradykinin and HOE 140. Hypoxi a/reoxygenation injury to untreated control cardiac myocytes was chara cterized by a significant loss of sarcolemmal integrity measured at 75 +/- 4% of total cell fluorescence (mean +/- S.E., n = 42 cultures). C ompared to propidium iodide staining of the above untreated control my ocytes, those pretreated with 30 or 100 mu M ramiprilat showed a signi ficant reduction of propidium iodide staining to 45 +/- 9% and 40 +/- 8% (n = 9, P < 0.05) of untreated controls, respectively. Pretreatment with the protective concentrations of ramiprilat concomitant with 10 mu M HOE 140 abolished the significant reduction in propidium iodide s taining observed with ramiprilat alone. Similarly, pretreatment with 1 0 or 100 nM bradykinin significantly reduced propidium iodide staining to 35 +/- 5%, and 60 +/- 10% (n = 6, P < 0.05) of the untreated hypox ic controls, respectively. In addition, concomitant pretreatment with protective concentrations of bradykinin and 10 mu M HOE 140 also aboli shed the significant reduction in propidium iodide staining observed w ith bradykinin alone. The results indicate that the angiotensin-conver ting enzyme inhibitor ramiprilat has a protective effect on isolated c ardiac myocytes exposed to hypoxia/reoxygenation and that this effect is most likely related to a local action of bradykinin on the cardiac myocyte via the activation of the kinin B-2 receptor.