Bile secretory apparatus in the newborn dog: relationship between structural and functional immaturities.

In the dog, bile secretion is not fully mature at birth and develops during postnatal life. To try to establish morphologic correlates to the physiologic deficiencies, we examined the ultrastructure of hepatic parenchyma and biliary epithelium in a newborn puppy and in 3 puppies of 1, 3, and 7 days of age. At birth, the hepatocytes contain much glycogen and fat droplets, a small smooth endoplasmic reticulum and Golgi apparatus, rare autophagic vacuoles, and numerous lysosomes. The sinusoidal microvilli are short, and submembrane vesicles are few and small. The bile canaliculus is not dilated, but few and short microvilli and no pericanalicular vesicles are seen. The biliary epithelial cells are normal in size, but the luminal surface of the bile ductule has no microvilli and numerous blebs. These morphologic features change with maturation and, by the first week of life, the fine structure of the hepatocytes, bile ductular cells, and biliary passages resemble that observed in the adult liver. These findings provide morphologic support for the concept that, in the dog, the bile secretory apparatus is immature at birth and develops during postnatal life.