Jejunal microvilli atrophy and reduced nutrient transport in rats with advanced liver cirrhosis: improvement by Insulin-like Growth Factor I

Abstract

Background: Previous results have shown that in rats with non-ascitic cirrhosis there is an altered transport of sugars and amino acids associated with elongated microvilli. These alterations returned to normal with the administration of Insulin-Like Growth Factor-I (IGF-I). The aims of this study were to explore the evolution of these alterations and analyse the effect of IGF-I in rats with advanced cirrhosis and ascites. Thus, jejunal structure and nutrient transport (D-galactose, L-leucine, L-proline, L-glutamic acid and L-cystine) were studied in rats with ascitic cirrhosis.

Methods: Advanced cirrhosis was induced by CCl4 inhalation and Phenobarbital administration for 30 weeks. Cirrhotic animals were divided into two groups which received IGF-I or saline during two weeks. Control group was studied in parallel. Jejunal microvilli were studied by electron microscopy. Nutrient transport was assessed in brush border membrane vesicles using 14C or 35S-labelled subtracts in the three experimental groups.

Results: Intestinal active Na+-dependent transport was significantly reduced in untreated cirrhotic rats. Kinetic studies showed a decreased Vmax and a reduced affinity for sugar and four amino acids transporters (expressed as an increased Kt) in the brush border membrane vesicles from untreated cirrhotic rats as compared with controls. Both parameters were normalised in the IGF-I-treated cirrhotic group. Electron microscopy showed elongation and fusion of microvilli with degenerative membrane lesions and/or notable atrophy.

Conclusions: The initial microvilli elongation reported in non ascitic cirrhosis develops into atrophy in rats with advanced cirrhosis and nutrient transports (monosaccharides and amino acids) are progressively reduced. Both morphological and functional alterations improved significantly with low doses of IGF-I.

Figure 1

Uptake of D-Galactose into brush border membrane vesicles (BBMVs) (A) Time course of D-galactose. *p < 0.05, **p < 0.01, ***p < 0.001 CO vs othergroups. (B) Kinetic study of the Na+-dependent for D-galactose uptake into BBMVs. Each point represents the mean of initial rate of D-galactose transport (SE was <10%) obtained from three different experiments using a pool of BBMVs from 10 animals from each group.

Figure 2

Kinetic studies of amino acid uptakes into brush border membrane vesicles (BBMVs) (A) Time course of L-leucine (1.0 mM) uptake by brush border membrane vesicles (BBMVs); (B) Time course of L-cysteine (1.0 mM) uptake; (C) Time course of L-glutamic acid (1.0 mM) uptake and (D) Time course of L-proline (1.0 mM) uptake with (in the presence of NaSCN) or without (in the presence of KSCN) sodium-gradient. *p < 0.05, **p < 0.01, ***p < 0.001 vs CO. No differences between groups were found in Na⁺-independent transport for the four amino acids studied.

Figure 3

Alterations of jejunal microvilli Electron microscopy of jejunal mucosa (× 10,000, magnification): (A) Microvilli from healthy controls; (B). Elongated microvilli described in animals with compensated cirrhosis [13,14]; (C). Elongated microvilli with degenerative lesions of membranes from ascitic cirrhotic rats (CI group); (D). Elongation and fusion of microvilli was found in 40% of untreated rats with ascitic cirrhosis (CI); (E) and (F) atrophy of microvilli was found in the remaining 60% of this group (CI). However, atrophy microvilli were not found in CI+IGF group (see (G) and (H)). Effect of IGF-I on microvilli in ascitic cirrhotic rats (CI+IGF group) (× 10,000, magnification): (G), area with mild elongated microvilli, and (H), quite normal epithelium instead of atrophy. Arrows show the increased density in actin microfilaments at the side of connection with the intermediate filaments network in microvilli from treated cirrhotic rats. Thus, the described alterations in untreated rats with ascitic cirrhosis (C, D, E and F) were partially improved by IGF-I treatment (G and H).