THE UPTAKE AND STORAGE OF H³-NOREPINEPHRINE IN THE RESERPINE-PRETREATED RAT HEART

¹ Laboratory of Clinical Science, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland

The ability to accumulate tracer amounts of H³-norepinephrine in the rat heart returns to almost normal 48 hours after the administration of reserpine. However, at this time the tissue was unable to retain large amounts of exogenous norepinephrine. In the isolated perfused heart the rate of uptake of H³-norepinephrine from the perfusing medium was unaffected at any time after reserpine treatment. In the isolated tissue preparation and in the whole animals the retention of H³-norepinephrine in the heart was severely depressed after reserpine. In reserpine-pretreated hearts H³-norepinephrine was accumulated mainly in the supernatant fraction. Once taken up, the H³-norepinephrine in the reserpine-pretreated heart is rapidly metabolized by monoamine oxidase, presumably because it cannot be protected by binding in nerve storage granules. The accumulation of H³-norepinephrine in the reserpine-pretreated heart can be inhibited by tyramine but not by DMI, and increased by treatment with a monoamine oxidase inhibitor. There is a small store of H³-norepinephrine in the reserpine-pretreated heart which can be partially released by DMPP and reserpine but not by tyramine.

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