Abstract
A method of measuring the rate of synthesis of catecholamines in various tissues takes advantage of the steady state relationship in which the rate of catecholamine formation is equal to the rate of efflux. After tyrosine hydroxylase is blocked with α-methyltyrosine, the brain levels of norepinephrine (NE) and dopamine and the NE levels in various peripheral tissues of rats and rabbits decline exponentially. The rate of synthesis of the catecholamines is calculated from the product of the rate constant of amine decline and the normal catecholamine level. The value for heart NE yielded by this method is almost identical with that obtained from the decline in radioactivity after labeling with dl-H3-NE. The application of this method to studies in the rat shows that the turnover time for NE in heart, salivary gland and iris is about 12 hr, compared to 6 hr for brain NE, 3 hr for brain dopamine and 2 hr for NE in the cervical sympathetic ganglia. In the rabbit hypothalamus, NE is formed five times more rapidly than in the midbrain, though the turnover times are almost identical. This suggests that the rate of synthesis might be similar in each adrenergic unit and that variations in rates of synthesis in different brain areas are a function of the number of neurons per gram of tissue.
Footnotes
- Received April 25, 1966.
- Accepted June 21, 1966.
- © 1966 by The Williams & Wilkins Co.
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