Summary
The acute effects of growth hormone on the oxidation of [1-14C]-pyruvate to 14CO2 were studied in epididymal adipose tissue obtained from hypophysectomized rats. At
concentrations ranging from 10 ng/ml to 1 μg/ml, growth hormone increased the rate
of pyruvate oxidation by 20-60 %. A lag period of up to 30 min was required for the
full effect of the hormone to develop. Addition of fructose to the incubation medium
increased the rate of pyruvate oxidation in response to either growth hormone or insulin.
The effects of 1 μg/ml growth hormone were comparable in magnitude to those of 1 mU/ml
insulin, and pyruvate oxidation in the presence of both agents was no greater than
in the presence of either on its own. The enhancement of pyruvate oxidation by growth
hormone, like that caused by insulin, probably results from activation of pyruvate
dehydrogenase. Increased activity of pyruvate dehydrogenase was found in cell-free
extracts of adipose tissue that had been exposed to either growth hormone or insulin.
The response of tissue segments to growth hormone followed the same pattern as observed
for other acute insulin-like effects of the hormone; it was transient and disappeared
within 3 hours despite continued presence of the hormone. Previous exposure of the
tissues to growth hormone made them refractory to the hormone upon reexposure.
Key-Words:
Pyruvate Dehydrogenase
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Insulin
