Physiological fatty liver and hyperlipemia in the fetal guinea pig: chemical and ultrastructural characterization.

During its prolonged period of gestation, the fetal guinea pig gradually develops a striking hyperlipemia (plasma triglycerides ca. 500-1500 mg/dl) and fatty liver (hepatic triglycerides ca. 25% of wet weight). The parenchymal cells of the liver contain not only many fat droplets in the cytoplasm, but also large numbers of osmiophilic particles, interpreted as precursors of plasma lipoproteins, within profiles of the cisternae and secretory vesicles of the Golgi apparatus. Similar particles are found in intercellular spaces, in the space of Disse, and in the hepatic sinusoids. Near the end of gestation, these particles enlarge to the size range characteristic of chylomicrons secreted from the intestinal mucosa after ingestion of fat. At the same time, the hyperlipemia increases and is characterized by the accumulation of particles resembling chylomicrons morphologically and chemically. The results are interpreted as evidence of intense hepatic synthesis and secretion of very low density lipoproteins which may be related to the extensive transplacental transport of free fatty acids known to occur in this species. After birth, the hyperlipemia subsides rapidly and the hepatic steatosis more gradually. The blood plasma of the guinea pig fetus also contains moderate amounts of low density and high density lipoproteins. The latter decrease to barely detectable levels during the first 2 wk of postnatal life. Comparably low levels of high density lipoproteins are found in nonpregnant and pregnant adults.