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Lithium carbonate at the dose level of 1.1 g/kg was administered in diet to normal (18% protein), low-protein- (LP; 8%) and high-protein (HP; 30% diet)-fed rats for a period of 1 mo. The LP diet resulted in a significant decrease in the hepatic levels of zinc, iron, copper, manganese, calcium, and serum levels of calcium and sodium. The HP diet caused a marked decrease in copper and calcium levels in liver, but an increase in potassium levels in serum was observed. Lithium treatment to normal rats led to a significant reduction in the hepatic contents of zinc, copper, potassium, calcium, and serum contents of potassium and sodium, whereas an elevation in serum contents of calcium was noticed. Administration of lithium to protein-deficient rats increased the hepatic concentration of manganese and serum concentration of calcium and the levels almost reached the normal limits. On the other hand, there was a marked depression in potassium contents in the serum of LP- as well as HP-fed rats following lithium treatment when compared to LP and HP groups, respectively.

A close parallelism exists between sialylation and endocytotic activity of the small intestine during postnatal development in rats. Thus, the binding of ¹²⁵I-labelled IgG to microvillus membranes and its relationship to membrane sialic acid has been studied in suckling rat intestine, during (a) postnatal development; (b) cortisone-induced precocious maturation, and (c) after desialylation of brush borders by neuraminidase treatment. Neuraminidase-treated membranes exhibited low (42%, p < 0.001) IgG binding. The observed decrease in IgG binding to desialylated membranes was associated with a decrease in the value of affinity constant, (–Ka = 0.4 × 10⁶ M^–1 in control and 0.23 × 10⁶ M^–1 in desialylated membranes). The number of IgG-binding sites (2.3 nmol/mg protein) was unchanged under these conditions. A similar decrease (50%) in IgG binding to brush borders was also observed in cortisone-injected pups. This was associated with reduced sialic acid (37%) content of the membranes compared to the controls. The value of –Ka was reduced from 0.4 × 10⁶ M^–1 in the control to 0.3 × 10⁶ M^–1 in the hormone-injected pups. The number of binding sites (n) was decreased from 2.2 to 1.4 nmol/mg protein under these conditions. Low concentrations of calcium (0.1–1.6 mM) in the incubation medium enhanced IgG binding (p < 0.001) to brush borders in pups but there was no change in binding of IgG to the membranes at 2 mM Ca²⁺ concentration compared to controls. Addition of Zn²⁺ or Mg²⁺ did not affect IgG binding under these conditions. These findings suggest a functional role of Ca²⁺ and sialic acid residues of the membrane glycans in IgG-receptor interactions in suckling rat intestine.

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SummaryEffect of chronic ethanol administration daily for 40 days together with 30% protein (HP) diet on microvillus membrane (MVM) glycosylation in rat intestine was studied. Ethanol administration to rats on a normal diet enhanced the hexose and sialic acid contents of brush borders but significantly reduced (p <0.05) membrane fucose levels. Feeding of the HP diet induced a generalized increase in MVM glycosylation. Ethanol feeding of rats maintained on the HP diet differently affected membrane glycosylation. Hexosamine content was enhanced, fucose and hexose contents were reduced, and sialic acid levels were unaltered under these conditions. The binding of 125I-wheat-germ agglutinin and 125I-peanut agglutinin to MVM was compatible with the chemical analysis of sugars in the various experimental groups. Incorporation of [14C] mannose or [ 14C ]glucosamine into MVM from different groups of rats revealed an increase in mannosylation but a decrease in glucosamine incorporation into MVM from ethanol-or HP-fed animals. Ethanol feeding along with HP diet enhanced the incorporation of labelled sugars into MVM compared with that of the HP-fed controls. Electrophoretic distribution of radiolabelled membrane glycoproteins from the different groups revealed that glycoproteins of Mr 60,000 were highly labelled. These results suggest that ethanol ingestion along with control or HP diet markedly modifies the intestinal MVM glycosylation but that these effects vary under different dietary regimens.