Growth Hormone Metabolism in Essential Fatty Acid-deficient and Pair-fed Nondeficient Chicks

Day-old White Leghorn cockerels were fed a purified essential fatty acid (EFA)-deficient basal diet (0.03% linoleic acid) ad libitum for 1 week. They were then fed one of the following treatments for 7 weeks: 1) basal diet ad libitum, 2) basal +4% corn oil pair-fed to 1, 3) basal +4% corn oil ad libitum, or 4) corn-soybean diet. Chicks fed the deficient diet exhibited marked reductions in weight gain, energy efficiency, and comb and testes weights, increases in liver size, and characteristic changes in tissue fatty acids at 8 weeks of age. Depressions in weight gain, tibial length, epiphyseal plate width, pituitary growth hormone (GH) activity, elevated plasma GH, and a tendency for reduced nitrogen retention, point to an impairment in GH metabolism in EFA-deficient chicks. Results with pair-fed control chicks suggest that smaller tibial length and width, smaller epiphyseal plate width, reduced nitrogen retention, elevated plasma GH and, to a partial extent, reduced body weights, smaller combs and testes, and larger pituitary glands are a result of reduced appetite and food intake rather than a direct biochemical effect of EFA per se. Changes due directly to the EFA deficiency, independent of reduced food intake, were decreased energy efficiency, increased liver weight, elevated trienetetraene fatty acid ratio, and reduced hypophyseal GH. These results demonstrate the importance of equalizing food intake in studies of this nature. Hypophyseal GH content was not affected by treatments in the same fashion as was plasma GH concentration. This indicates that different hypothalamic-hypophyseal mechanisms operate to increase plasma GH in EFA-deficient and pair-fed control chicks.