The effects of complete food removal for 7 days were measured on plasma GH activity, hypothalamic content of growth hormone releasing factor (GH-RF) and pituitary concentration of growth hormone (GH) in male rats. Control male rats were fed ad lib. for 7 days. In another experiment, the starved rats received replacement doses of L-Na-thyroxine (2.5 μg/ 100 g body weight/day) beginning on day 2 starvation. On day 8 all rats were weighed, anesthetized with ether and bled from the abdominal aorta. The pituitaries were removed and individually weighed; the hypothalami were placed in ice cold O.lN HC1 (0.1 ml/hypothalamus). Hypothalamic GH-RF was assayed by an in vitro incubation method. Lyophilized plasma, anterior pituitaries and incubation medium were assayed for GH by the standard tibia test, using a 4-point assay procedure. Statistical analysis of the data showed a significantly lower plasma GH content in starved or thyroxine-treated starved rats (p<0.01). Pituitary GH content and hypothalamic content of GH-RF were also significantly reduced in the starved rats. These results indicate not only that starvation in the rat lowers the levels of GH-RF in the hypothalamus and GH in the pituitary, as shown previously, but that these are reflected in reduced plasma GH activity. (Endocrinology84: 814, 1969)
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Dickerman et al. (1969) studied this question.