Epinephrine-induced cytotoxicity of rat plasma. Its effects on isolated cardiac myocytes.

The plasma from rats injected with epinephrine (5 mg/kg) (epinephrine plasma) was found to be cytotoxic when incubated with isolated heart cells. This cytotoxicity was apparent 60 minutes after the start of the incubation due to the appearance at this time of membrane microblebs and microvilli as seen by scanning electron microscopy and the start of a fall in intracellular concentrations of ATP. The membrane blebs increased in size with time and the cells became contracted. Incubation of the cells for 90 minutes with epinephrine plasma, caused an increase in permeability of plasma membrane to 86Rb+. Incubation with alpha-tocopherol prevent this change. After 180 minutes incubation, these cells no longer retained carboxyfluorescein indicating that extensive membrane damage had occurred. It has been suggested that the presence of membrane blebs are evidence that lipid peroxidation is occurring in the cell membrane. Accordingly, glutathione, which is used by the cell against free radical attack and membrane lipid peroxidation, was measured. Glutathione levels started to fall after 60 minutes incubation, the time when the ultrastructural cell membrane changes started to occur. Pretreatment of cells with 100 microM 1,3-bis(2-chloroethyl)-1-nitrosourea which inhibits glutathione reductase, before the addition of plasma, increased the sensitivity of these cells to the epinephrine plasma, as measured by fall in intracellular ATP. Cells treated with control plasma did not show the changes described above. The nature of the cytotoxic factor in the plasma is still unknown, although the evidence presented suggests that a free radical may be involved.