THE RATE OF NOREPINEPHRINE SYNTHESIS MEASURED IN VIVO DURING SHORT INTERVALS; INFLUENCE OF ADRENERGIC NERVE IMPULSE ACTIVITY

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

Tyrosine-C¹⁴ was administrated i.v. at different rates to unanesthetized rats. Accumulation of norepinephrine-C¹⁴ was determined in the heart, brain and submaxillary glands. A technique is described which allows calculation of norepinephrine synthesis rates from the ratio of norepinephrine-C¹⁴ content and mean specific tyrosine activity. Estimated synthesis rates were higher than expected from previous determinations of norepinephrine turnover rates. It is suggested that the turnover rate of norepinephrine may not measure its true synthesis rate. Norepinephrine formation in the submaxillary gland was reduced to insignificant values after sympathetic denervation. The technique was also applied to the estimation of changes in norepinephrine synthesis after alterations of adrenergic nerve impulse activity. Sympathetic decentralization diminished, whereas nerve stimulation accelerated, norepinephrine synthesis in the submaxillary gland of the unanesthetized rat.

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