Abstract
The tyrosine hydroxylase of adrenal medulla was induced by exposing the rats to 4° for 4 hr. The synthesis rate of normal and induced tyrosine hydroxylase was measured by radiochemical and immunoprecipitation methods. Incorporation of 3H into the enzyme was normal 6 hr after the beginning of the stress but was greater than normal at 10 hr and reached a maximum increase of 65% at 16 hr. Beginning 20 hr after stress application the rate of 3H incorporation declined and approached normal values between 30 and 50 hr. The tyrosine hydroxylase activity was not yet increased 10 hr after the beginning of the stress; however, it was increased at 16 hr and a maximal increment was reached at 24 hr. This new steady state was maintained for the following 24 hr. The enzyme activity then declined, with a half-life of about 3 days. The radioactivity incorporated into tyrosine hydroxylase in glands of normal and stressed rats decayed exponentially, with a half-life of 68 hr. From this first-order rate constant (kd = 0.01) and from the amount of enzyme present the synthesis rate (K[unknown]) of tyrosine hydroxylase was calculated. The synthesis rate was increased in the adrenals of stressed rats. This increase failed to occur if adrenal denervation preceded the stress.
- Copyright ©, 1975, by Academic Press, Inc.
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