Quantitative microscopic evaluation of the endoplasmic reticulum in developing human liver.

Quantitative electron microscopic aspects of the liver have not been explored in detail, and the numerical characterization of tissue changes may contribute to the understanding of basic cellular mechanisms in disease processes. Sixteen liver biopsies from children 2 months to 18 years old were analyzed by stereology to study the composition and relative distribution of endoplasmic reticulum membranes within hepatocytes. The histologic aspects of the liver as well as the clinical laboratory data of these patients revealed no abnormalities when being observed for suspected hepatic ailment. Morphometric analysis of four tissue blocks per biopsy was undertaken by means of combined light and electron microscopy, using standard stereologic formulae. The results showed less endoplasmic reticulum in liver cells from children 2 to 9 months old. These low levels were accounted for by reduced surface of smooth membranes. There was a first-order relationship in the growth of smooth endoplasmic reticulum between 2 months and 4 years at a rate of 17.1 sq cm/hr, similar to the membrane accumulation rate in experimental animals. Membrane dimensions from Golgi apparatus and rough endoplasmic reticulum were cell-size dependent, and these organelles matured within 2 months of postnatal life. The significance of these findings resides in the low amounts of smooth endoplasmic reticulum membranes at an early age. This lack of membrane surface agrees with findings in developing liver of various species. Experimental studies showed reduced membrane population and low microsome-bound enzyme activities which, under normal circumstances, allow the hepatocyte to undertake detoxification and drug metabolizing processes. Thus, the reduced membrane availability of the liver in infants may account for their inability to metabolize foreign compounds.