Mechanism of avian estrogen-induced hypertriglyceridemia: evidence for overproduction of triglyceride.

Relying on methods other than the determination of turnover rate of triglyceride from the curve of plasma triglyceride radioactivity after administration of labeled precursor, we have confirmed that the endogenous hypertriglyceridemia induced by estrogenization of the chick is accompanied by increased production of triglyceride. Chicks estrogenized with diethylstilbestrol became grossly hypertriglyceridemic and had elevated levels of plasma free fatty acid. Within 5 min of administration of labeled palmitate, estrogenized hypertriglyceridemic birds converted approximately 10 times more plasma free fatty acid to hepatic triglyceride than did controls. In addition, 2 hr after intraperitoneal injection of [14-C]acetate or [U-14-C]glucose, the specific activity of very low density lipoprotein triglyceride (VLDL-TG) of estrogenized birds reached or exceeded that of the untreated controls, and the rapid enrichment of the vastly expanded plasma VLDL-TG pool with labeled triglyceride further indicated that increased production of triglyceride occurs with estrogenization. Furthermore, [14-C]acetate incorporation into VLDL-TG was calculated to be 1.6 and 6.6% of the injected dose in estrogenized birds compared with 0.1 and 0.2% in untreated birds. Increased production of plasma VLDL-TG was confirmed by a kinetic study of VLDL-TG metabolism, employing reinjected, endogenously prepared [14-C]triglyceride-labeled VLDL. The fractional turnover rate of VLDL-TG in estrogenized hypertriglyceridemic birds was substantially less than that in untreated controls (0.32 plus or minus 0.03 vs 0.71 plus or minus 0.03/hr), but the total turnover rate was nearly 50 times greater (244 plus or minus 52 vs. 5 plus or minus 1 mg/hr).