An active compound was found by sys-OF ANTIBIOTICS MAY I960 system is thought to be the cause of the hypotensive effect.

The contribution of cytosolic ion and energy milieu changes to ischemia/reperfusion injury was investigated in isolated guinea-pig hearts and mitochondria, with fluorometry and 31P nuclear magnetic resonance (NMR). The fura-2 Ca2+ signal during ischemia in the guinea-pig Langendorff heart changed triphasically (phases I, II, and III) and rapidly returned to the control level after the reperfusion. These triphasic changes during ischemia were affected by various agents that affect the cytosolic ion milieu: the combination of asebotoxin-III and dihydroouabain (which increase intracellular Na+) caused an increase in Ca2+ levels in the final stage (phase III) with a manifestation of contracture after the reperfusion of the heart. Inhibitors of the H+-Na+ exchange such as 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) produced a significant restorative effect on the contractility of the reperfused heart with increased proton and decreased Na+ and Ca2+ in the cytosol. The mitochondrial matrix Ca2+ ([Ca2+]m) preloaded with abnormally high Ca2+ levels was markedly increased by perfusion with either a physiologic concentration of Ca2+ or an acidified perfusate. These [Ca2+]m increases were reduced by the H+-Na+ and H+-K+ exchange inhibitor (EIPA; omeprazole), respectively. These findings will help to explain the Ca paradox at the mitochondria level (i.e., mitochondria for Ca2+ pumping play an essential role in the cellular homeostasis of Ca2+ for the maintenance of cell functions of the heart, acting like a Ca2+ scavenger in the cytosol). Factors that induce Ca2+ overload on mitochondria via sarcolemmal Ca2+ influx and any exchange mechanisms with Na+, K+, Ca2+, and H+ will lead to a loss of contractility, associated with the extremely reduced level of free energy change predicted from the reduced ATP x PCr/Pi ratio by 31P NMR.

The protective effects of Na+ - H+ exchange inhibitors SM-20550 (SM) and 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) against ischemia-reperfusion injury were investigated in guinea pig Langendorff hearts. The changes in intracellular pH (pHi), high-energy phosphates, and biologic intracellular active ions ([Na+]i and [Ca2+]i) were regarded using the 31P-NMR and specific fluorescent signals from the heart tissues together with simultaneous recordings of the left ventricular developed pressure (LVDP). The recovery rate of LVDP from ischemia (40 min) by reperfusion was 36.8% in the control experiments, whereas in the presence of SM 10(-7) M, a gradual increase to 75.9% (55.5% with 10(-8) M), in contrast to EIPA (10(-7) M), 47.5% was observed. SM 10(-7) M restored the ATP level by 70% in 40-min reperfusion, which was already higher than the control in the latter half (20-40 min) of the ischemic period. The recovery rate of phosphocreatine by pretreatment of the heart with SM 10(-7) M was 75% in 40 min reperfusion. The pHi estimated from Pi/phosphocreatine chemical shift became highly acidic in ischemic heart so that SM 10(-7) M caused slight but significant pHi reduction from control pHi of 5.89 to 5.75. The level returned to pHi at around 7.38 during 30-40 min reperfusion, and the recovery was significantly greater than the control pHi of 7.24. The fura-2 Ca2+ or SBFI-Na+ signals during Langendorff ischemia heart increased, and rapidly returned to the control level after the reperfusion. SM suppressed the [Na+]i or [Ca2+]i elevation induced in the late stage during ischemia, resulting in LVDP restoration after reperfusion; Diastolic Ca2+ in the end period of ischemia, SM 10(-7) M 194% versus drug-free 220.7%. Na+: SM 10(-7) M 121.6% versus drug-free 128.0%. The present results suggest that the selective Na+ - H+ exchange inhibitor SM is promising as a potent and specific protective agent against ischemia-reperfusion injuries with Ca2+ overload induced via Na+ - H+, Na+ - Ca2+ exchange.

Plumbagin, an active principle from Plumbaginaceous plants, produced a triphasic inotropic response (first positive, second negative, and third positive phases) in guinea-pig papillary muscle. The inotropic potency of plumbagin at the first positive phase was pD2 6.40, and the methylation of 5-hydroxy group of plumbagin reduced the potency. The triphasic pattern of inotropism of plumbagin was unaffected by reserpine or propranolol treatments. Plumbagin did not produce the positive inotropic effects under anoxic conditions or in the presence of mitochondrial oxidative phosphorylation inhibitors such as 2,4-dinitrophenol and dicumarol.