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JEFFERY N. WILKINS, STEVEN E. MAYER, W. P. VANDERLAAN, The Effects of Hypothyroidism and 2,4-Dinitrophenol on Growth Hormone Synthesis, Endocrinology, Volume 95, Issue 5, 1 November 1974, Pages 1259–1267, https://doi.org/10.1210/endo-95-5-1259
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After the administration of several agents which alter thyroid function, storage and synthesis of growth hormone (rGH) and storage of prolactin (rPRL) were studied in the rat pituitary gland. Hormone concentrations in pituitaries were measured by gel electrophoresis; synthesis was measured in pituitary glands incubated in vitro. The pituitary concentration of cyclic adenosine 3′,5′-monophosphate (cyclic AMP) and pituitary adenylate cyclase activity were also determined. In addition, serum thyroxin concentrations and binding of DL-thyroxin-2-14C by pituitary and hypothalamic tissues were measured. We obtained the following results. Hypothyroidism produced by propylthiouracil (PTU) reduced the synthesis of rGH 90-97% and that of rPRL 70-78% and resulted in a fall of 80% in pituitary concentrations of rGH and rPRL. These effects of PTU were reversed by the administration of thyroxin. Dinitrophenol (DNP) reduced serum thyroxin 25% and the concentrations of rGH and rPRL in the pituitary as well as their rates of synthesis in vitro 50%. DNP also reduced uptake of DL-thyroxin-2-14C in pituitary and hypothalamic tissues by 65-85%; in contrast, pro-pylthiouracil increased uptake to 300% of that measured in normal rats. Anterior pituitary cyclic AMP concentration rose following PTU (63%) and DNP(31%), but there was no change in basal or fluoride-stimulated adenylate cyclase activity.
These results suggest that the basis for the previously observed decreased pituitary concentration of rGH and depressed serum rGH in hypothyroidism is due directly to inhibition of the synthesis of the hormone. Depressed pituitary concentration of rPRL in hypothyroidism may be due to a decrease in the rate of synthesis of the hormone—yet further work is required to test this possibility. The decreased pituitary concentration of rGH and rPRL produced by DNP may be due to inhibition of synthesis as the result of displacement of thyroxin from hypothalamic and pituitary binding sites. The increased concentration of cyclic AMP in the interior pituitary of rats treated with PTU or DNP appears to be a response to deficiencies of thyroxin or rGH or both. (Endocrinology95: 1259, 1974)
