Parathyroid function and lipid metabolism in the rat.

The present investigation in experimental animals was designed to obtain further insight into the possible role of parathyroid hormone (PTH) in lipid metabolism. An endogenous hyperparathyroid state was induced in rats by a calcium-poor diet. This type of hyperparathyroidism was associated with a significant increase in serum cholesterol and triglyceride concentrations, a significant decrease in the serum clearance rate of intravenously infused Intralipid and a significant increase in hepatic tissue triglyceride content as compared to the values obtained in control animals. An exogenous type of hyperparathyroidism (parathyroid extract injections) was also accompanied by a slight increase in serum cholesterol and triglyceride concentrations as well as a decrease in plasma postheparin lipolytic activity (PHLA), but the changes did not reach the level of statistical significance. In the aparathyroid state, a significant decrease in serum cholesterol and triglyceride concentrations and a significant increase in plasma PHLA were observed as compared to control rats. In additional studies, it could be demonstrated that the endogenous hyperparathyroid state was not associated with increased intestinal absorption of [3H]triolein as compared to control animals. Furthermore, the hepatic triglyceride secretion rate in these hyperparathyroid rats was significantly lower than in normal rats. In conclusion, hyperparathyroidism induces an increase in serum cholesterol and triglyceride concentrations, the latter being due to decreased peripheral removal. The aparathyroid state induces opposite changes. Thus, normal parathyroid function is required for normal lipid metabolism in the rat.