33 Atherosclerosis, 32 (1979) 33-42 0 Elsevier/North-Holland Scientific Publishers, Ltd. HYPERLIPOPROTEINEMIA INDUCED BY A TRANSPLANTABLE PITUITARY TUMOR IN THE RAT A. CHRISTINE NESTRUCK, CHRISTINA GIANOULAKIS, JEAN DAVIGNON and MICHEL CHRkTIEN Institut de Recherches Cliniques de Montre’al, 110 avenue des Pins, ouest, Montre’al, P. H2 W 1 R7 (Canada) (Received 8 May, 1978) (Revised, received 6 September, 1978) (Accepted 15 September, 1978) QuB., Summary The MtT-F4 tumor, a transplantable pituitary tumor of rats, induces signifi- cant hyperlipidemia in male Fisher 344 rats. The increasive hypercholesterol- emia was accompanied by hypertriglyceridemia only in the first month of tumor implantation. Clofibrate feeding inhibited the development of hyper- cholesterolemia and maintained normal serum triglyceride levels. In contrast to the changes in lipoprotein cholesterol distribution and profile found in experi- mental hyperlipidemia induced by high fat and cholesterol feeding, the hyper- cholesterolemic tumor-bearing rats showed no accumulation of cholesterol in the very low density and intermediate density lipoproteins, and no appearance of a new class of lipoprotein, B-VLDL. An HDLc-like lipoprotein appeared as hypercholesterolemia developed. Increased amounts of cholesterol were deposited in the aorta. The effects are attributed to the lipolytic hormones secreted by the tumor and antagonism to their action by clofibrate. Key words: Atherogenesis - Clofibrate - HDL, - Hypercholesterolemia Introduction The rat, a widely used model in lipid and lipoprotein metabolic studies, is very resistant to the development of hypercholesterolemia and atherosclerosis. Early studies [ 1,2] demonstrated that hypercholesterolemia sufficient to This work was supported by grants from the Medical Research Council of Canada (MA-6119) and the Quebec Heart Foundation. A.C.N. holds a Research Scholarship from the Cons4 de la Recherche en Sante du Quebec and C.G. is a Medical Research Council of Canada post-doctoral fellow.