Exp. Pathol. 1991 ; 43 : 97 -110 Gustav Fischer Verlag len a Humboldt University, School of Medicine (Charite), Institute of Pathology, Department of Ultrastructural Pathology and Electron Microscopy, Berlin , Germany Ultrastructure of the liver after hypoxia in the postnatal period By H. DAVID, J. ELL ERMANN , M. BIMML ER and D. BEHRISCH With 6 figures Received: January 31, 1990; Accepted: February 16, 1990 Address for correspondence: Prof. Dr. sc. med. H. DAVID, Humboldt-Universitat, Bereich Medizin (Charite), Institut filr Pathologie , SchumannstraBe 20121 , 0 -0 -1040 Berlin , Deutsch- land Key words: hepatocytes; hypoxia. postnatal; liver; cell organelles; morphometry Summary Repeated phases of hypoxia (8 h daily for 2 to 5 days at p02 I 1.33 kPa = 5 .000 m in altitude ) were induced to Sprague-Dawley rats in the postnatal period as well as up to the 64th day of age , and after different recovery phases the ultrastructure of hepatocytes was qualitatively and quantitativel y analysed. Major results were as follows: 1. Increa ses in body and liver weights were delayed but were balanced off after 64 days. 2. Qualitative alterations are reversible spherical transformations of mitochondria, a degradation of lipids and a slight increase in autophagocytosis. 3. The quantitative mitochondri al parameters (volume density, number per unit area, average volume) were not even adjusted to control values after 64 days. Granular endoplasmic reticulum and ribosomes/pol ysomes were insignificantly reduced in comparison to control animal s, structure and arrangement are regular . Lipids and glycogen were differently altered. 4. The finding s ofthe hepatocytes after postnatal hypox ia were rever sible, though the majority of parameters had not yet returned to normal after 2 months. An adaptation to repetitiv e hypoxic conditions is not provable. Introduction Prenatal and postnatal hypoxic conditions are not rare and play a substantive role in human pathology. On the other hand, animal experiments have rarely been conducted on the same subject. We have inve stigated the ultrastru cture of the liver (4,6). Studies into mitochondrial mass and cytochrome concentration were published by KINN ULA and HASSINEN (7). Comparative ultrastructural studies were condu cted into heart under conditions of prenatal hypoxia (3, 5). The investigations of the liver , following repeated , intermittent conditions of hypo xia, present a continuati on of earlier experiments. They were condu cted with the view to find answers to the following questions: 7 Exp. Pathol. 43 (1991) 1- 2 97