Age-related variations in hepatic regeneration and erythropoietin production in the rat

Dietary exposure to perfluorooctanoate or perfluorooctane sulfonate induces hypertrophy in centrilobular hepatocytes and alters the hepatic immune status in mice

It is well established that exposure of mice to perfluorooctanoate (PFOA) or perfluorooctane sulfonate (PFOS) induces hepatomegaly and, concurrently, immunotoxicity. However, the effects of these perfluorochemicals on the histology and immune status of the liver have not been yet investigated and we have examined these issues here. Dietary treatment of male C57BL/6 mice with 0.002% (w/w) PFOA or 0.005% (w/w) PFOS for 10 days resulted in significant reductions in serum levels of cholesterol and triglycerides, a moderate increase in the serum activity of alkaline phosphatase (ALP) and hepatomegaly, without affecting other immune organs. This hepatomegaly was associated with marked hypertrophy of the centrilobular hepatocytes, with elevated numbers of cytoplasmic acidophilic granules and occasional mitosis. Furthermore, dietary exposure to PFOA or PFOS altered the hepatic immune status: whereas exposure to PFOA enhanced the numbers of total, as well as of phenotypically distinct subpopulations of intrahepatic immune cells (IHIC), and in particular the presumptive erythrocyte progenitor cells, treatment with PFOS enhanced only the numbers of hepatic cells that appear immunophenotypically to be erythrocyte progenitors, without affecting other types of IHIC. In addition, exposure to these compounds attenuated hepatic levels of tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ) and interleukin-4 (IL-4). Furthermore, the exposed animals exhibited a significant increase in hepatic levels of erythropoietin, a hormone required for erythropoiesis. Thus, in mice, PFOA- and PFOS-induced hepatomegaly is associated with significant alterations in hepatic histophysiology and immune status, as well as induction of hepatic erythropoiesis.

Hepatic erythropoietin (Ep) production following double partial hepatectomy in the rat

Double partial hepatectomy (hepx) evokes an elevation in serum erythropoietin (Ep) levels in anephric hypoxic animals when compared to non-hypoxic or sham hepx controls. But this Ep response is significantly lower than that found in singly hepx, anephric hypoxic rats. Double hepx also induces numerous cytological changes in the liver. Extravascular accumulation of fat, fibrous scarring, localized necroses, and multiple abscesses, as well as decreased vascularity, occur following the second hepx. A humoral factor was detected in the serum of these animals that is capable of inducing hepatic Ep production when injected into normal rats 18 hours before nephrectomy and hypoxia. This factor, termed hepatopoietin (Hp), was previously demonstrated in the venous serum of singly hepx rats. The serum from animals subjected to double partial hepx is not as potent in inducing Ep production as the serum from singly hepx animals. The discrepancies noted between the single and double hepx groups is attributed to the necrotic cytological changes described above.

Evidence for a sexual variation in production of a hepatic erythropoietic factor by hepatectomized rats

Erythropoietin (Ep) is a glycoprotein hormone that is responsible for mammalian red blood cell production. Adult rat liver regenerating 48-72 h after hepatectomy (hepx) produces elevated levels of Ep in response to hypoxia when compared to sham-operated, anephric hypoxic controls. A factor, termed hepatopoietin (Hp), found in the serum of hepx rats, is capable of stimulating hepatic Ep production when administered to normal rats 18 h prior to hypoxic exposure. Although the hepatic vein is the most potent source of this factor, Hp can also be demonstrated in the systemic arterial circulation. Bilateral nephrectomy (nephrx) of the donor hepx animal 24 h prior to bleeding abolishes this variation, and highest Ep levels are noted when serum from a hepx and nephrx rat is administered to animals immediatley after nephrx and 18 h before hypoxic exposure. Serum derived from hepx male rats displays a greater ability to evoke hepatic Ep production in normal recipients than serum from similarly treated female rats. Regardless of the sex of the hepx donor, Ep elaboration after hypoxia is highest in male recipients. The results indicate that there is a sexual variation in the production of Hp as well as Ep.

The regenerating liver: a site of erythropoiesis in the adult Long-Evans rat

Erythropoiesis, which is primarily hepatic in the rat during fetal and early neonatal life, shifts almost entirely to the bone marrow in the neonatal-adolescent stage of development. In the adult, extramedullary erythropoiesis has been demonstrated in the liver and spleen under certain pathological conditions when bone marrow red cell production is insufficient. In the present study, erythropoietic foci have been found in young-adult rat liver regenerating 24-72 hr after subtotal hepatectomy. This erythropoiesis is both extravascular and sinusoidal, with some erythroblastic islands noted. The centrolobular hepatic area contains the highest concentration of erythroblasts. Peripheral blood reticulocytosis coincides with the appearance of these cells and this is considered as an indicator of effective erythropoiesis. Liver regenerating after partial hepatectomy produces significant quantities of erythropoietin (Ep) in response to hypoxia. Subtotal hepatectomy may confer upon the adult liver the ability to revert to a fetal-like condition both in its ability to produce Ep and to function as a hematopoietic inductive microenvironment for erythropoiesis.

Reticuloendothelial system (RES) hyperfunction and erythropoietin (Ep) production in the regenerating liver

Hepatic cells in rats were evaluated after subtotal hepatectomy using scintillation scanning with technetium sulfur colloid (TSC), autoradiography, and microstereology techniques. The ability of the liver to accumulate TSC increased during the course of the regeneration as did the labeling of Kupffer and parenchymal cells with tritiated thymidine (3H-tdR). Kupffer to parenchymal cell number ratios and Kupffer cell relative areas were also elevated, attaining peak values at 72 hours post-hepatectomy. This period corresponds to the time of peak erythropoietin (Ep) production in rats with regenerating livers after nephrectomy and exposure to hypoxia. These findings suggest that the Kupffer cell may function as a cellular site of Ep formation.