Epidermal growth factor (EGF) promotes hepatocyte growth and is bound in the liver by specific receptors. We have determined hepatic uptake of EGF in intact rats after an intravenous or intraportal injection of a bolus of "RI-labeled EGF. Ninety-nine percent of the intraportal dose was taken up by the liver in 3 min, whereas only 58% of the intravenous dose appeared in the liver in 10 min. Uptake was inhibited by simultaneous treatment with an excess of unlabeled EGF. At time zero, uptake appeared to be complete. Disappearance from the liver followed first-order kinetics. Within 90 min of an intraportal injection, an average of 19% of the injected radioisotope appeared in bile, of which approximately one-fifth was shown to be immunoprecipitable with a specific anti-EGF antiserum. Light microscopic autoradiography demonstrated a very steep portal-tocentral lobular concentration gradient consistent with a high-capacity uptake system. After intraportal injection or after incubation with cultured hepatocytes, labeled EGF was shown to be bound to its hepatic receptors. The main receptor-ligand complex had a Mr of 160,000-170,000, determined by NaDodSO4/polyacrylamide gel electrophoresis.Epidermal growth factor (EGF), a single-chain polypeptide exhibiting a Mr of 6,045, is found in high concentrations in salivary and Brunner glands of humans and mice and more recently in the pituitary of goats (1-5). Although EGF has been shown to have a growth-promoting capacity in a variety of in vivo and in vitro cell systems (3,(6)(7)(8)(9)(10)(11)(12)(13)(14), its physiologic role and the mechanisms of homeostasis responsible for maintaining its plasma concentration are poorly understood. In adult rat hepatocytes in vivo or in primary culture, EGF stimulates DNA synthesis (15) and has been reported to induce hepatic hypertrophy and hyperplasia (16). In newborn rats, EGF induces thymidine incorporation into developing liver cells and enhances mitosis (15,17). EGF receptors have been found on hepatocyte membranes (18), and an EGF-receptor complex has been isolated from hepatocytes by using a glutaraldehyde/sodium borohydride crosslinking technique (19). In HT-29, A-431, PANC-1, and other cells, EGF has been found to form a spontaneous covalent crosslinkage with its receptor (20-25). Electron microscopic evaluation of isolated hepatocytes in culture demonstrates that hepatocytes have the capacity to take up EGF in vitro (26).We have investigated the role of the intact liver in EGF uptake and processing and have demonstrated: (i) significant hepatic uptake of 1"I-labeled EGF (125I-EGF); (ii) the presence of EGF in bile; (iii) the existence of an EGF-protein complex consistent with an EGF receptor; and (iv) a portal-to-central lobular concentration gradient for 125I-EGF uptake. METHODS Animals. Male Sprague-Dawley rats obtained from Charles River Breeding Laboratories, weighing 300-350 g, were fed standard Purina chow ad lib and maintained on a standard wakesleep cycle.Materials. Mouse EGF was purified from mouse submaxillary...

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Interesting advances occurred recently in nutrient absorption. Kinetics of triacylglycerol appearance in endoplasmic reticulum, Golgi apparatus, and lymph support the hypothesis that endoplasmic reticulum-to-Golgi transport is rate-limiting for lipid absorption. Apolipoprotein B does not appear necessary for initial formation of chylomicron-sized lipid particles in the endoplasmic reticulum, but rather for their movement out of the endoplasmic reticulum and to the Golgi. If peptides are protected from luminal proteolysis by fatty acylation, or if a nonpeptide drug, acyclovir, is esterified with valine to enhance bioavailability, the peptides nevertheless are absorbed by peptide transporters. Experimental conditions needed to use human ileal mucosa for in vitro absorption studies are described. Intestinal mucosa contains leptin receptors, and leptin inhibits galactose absorption, suggesting a new site for leptin's modulation of body mass. The enhancer element for the apoB gene is located much farther from its structural gene in the intestine than in the liver.