Hypothalamic somatostatin and pituitary and serum growth hormone concentrations during postnatal development in rats exposed chronically to propylthiouracil or a low iodine diet.

The developmental profiles of hypothalamic somatostatin and pituitary and serum growth hormone (GH) concentrations were examined in rats exposed chronically to a low iodine diet or propylthiouracil. Hypothalamic somatostatin and pituitary and serum GH concentrations were similar during development in control and low-iodine-diet animals. Propylthiouracil-induced hypothyroidism, however, was associated with reduced hypothalamic somatostatin and pituitary and serum GH concentrations, the latter being undetectable after 6 days. These data indicate that hypothalamic control of GH secretion is unaltered in low-iodine-diet rats who maintain an euthyroid status by preferential triiodothyronine (T3) production. The marked derangements observed in the hypothyroid animals indicate that thyroid hormones are critical for the postnatal maturation of the GH regulatory mechanism.