Failure of thyroid hormones to maintain the normal lipoprotein pattern in rats after removal of the pituitary gland

Abstract

Hypophysectomy was found to increase low density lipoprotein (LDL) cholesterol in rats from 0.18 to 1.18 mmol/l in 1 week, while very low density lipoprotein (VLDL) and high density lipoprotein (HDL) cholesterol decreased simultaneously from 0.08 to 0.03 mmol/l and from 2.12 to 1.01 mmol/l, respectively. Serum total cholesterol levels remained unchanged. Thyroid supplementation (T 3 or T 4) with doses causing a euthyroid state did not fully correct the lipoprotein pattern. The increase of LDL caused by hypophysectomy was significantly rectified, but the normal level could not be maintained, whilst the HDL level was not at all affected by thyroid hormones. Serum total cholesterol was markedly reduced in all groups with thyroid supplementation, indicating increased cholesterol catabolism. These results suggest that TSH and peripheral thyroid hormones modulate LDL but no effect on HDL could be detected. Other hormones, notably ACTH, growth hormone, lipotropins and gonadotropins are also involved in the control of lipoproteins at the pituitary level. Their exact impact cannot at present be assessed.