Effects of Hypophysectomy, Thyroidectomy and Thyroid Hormones on Steroid Metabolism in the Rat.

Abstract

Summary Steroid turnover in normal (N), hypophysectornized (H), I¹³¹-thyroidectomized (T), and hypophysectomized-thyroidtreated (HT) rats was investigated. Following injection of dl-mevalonic acid-2-C14, feces were collected for a 14-day period. When compared with normals, cumulative fecal bile acid-C¹⁴ excretion was reduced about 20% in H and T; while in HT, bile acid-C¹⁴ excretion approached normal rate. Cumulative fecal α + β-sterol-C¹⁴ excretion was reduced 28% in T, but was similar to normal in H and HT. Total fecal cholesterol plus coprostanol excretion was reduced in both H (-45%) and T (-25%). Thyroid hormone treatment of hypophysectornized rats resulted in a small increase in fecal sterol excretion, but the daily rate was still below normal (-30%). The total steroid-C¹⁴ synthesized from mevalonic acid-2-C¹⁴ was reduced from normal in both T and H. HT synthesized almost normal amounts of total steroid-C¹⁴. It was concluded that lack of the thyroid hormone in hypophysectomized rats accounts for some of the effects of hypophysectomy on steroid metabolism. However other hormones must also be important, since the effects of thyroidectomy were not the same as those of hypophysectomy and thyroid administration did not restore some aspects of steroid metabolism to normal.